Pre-war (up to 1942) 1939 LaSalle - Advice on Pinion Seal Replacement

[39LaSalleDriver]

It seems I have developed a drip from the pinion seal on my differential (see photo). I have searched through the forum here and found a variety of information, some of which is irrelevant, some appears a bit contradictory, some is unclear to me based on how things have been phrased (in some cases many different years are intermingled), and much of it is scattered in so many different threads it is difficult to follow.

Bottom line...is this something I can do at home? I primarily ask because I am seeing torque values that I don't know if I can achieve without having the car on a lift (which I don't have).

Since my car is a 1939 (late year model), I likely have the crush sleeve arrangement rather than shims; it will be one of two different types of seal (will have to remove and check before ordering a replacement); and is this seal available through a regular parts house or is Cadillac Parts Ltd. the only known source for it?



In the instructions I've seen posted here that I believe was authored by Brad Ipsen, one thing that really spooks me is the comment "In 1939 Cadillac started to use the collapsible sleeve design...The preload in force is approximately 1200 to 1400 pounds." I presume that is ft. lbs. not in. lbs. Is this a reference to specificially what the factory had to do to "crush" the sleeve and something that I don't need to worry about per se (other than inserting a shim to compensate)? I certainly have no way to generate that kind of ft. poundage while laying under the car.

Later on, the comments state that "Tighten the nut to at least 225 ft-lbs. and measure the inch-lbs drag on the bearings. It should be roughly the same as before disassemble but if 10 inch-lbs are achieved with used bearings and the nut is tightened to at least 225 ft-lbs the job is done."

So if I'm reading this right, I'd need to use either a .005 or .010 inch shim to compensate for the crushed sleeve; tighten the yoke nut to 225 ft. lbs.; check to see if I have approximately 10 in. lbs. of drag on the freely turning axle; and adjust accordingly. Correct?

Where does the pre-load come into play? Some threads say to mark the nut position, tighten to that point and back it off a hair and call it good. Others say if you don't have it set precisely you will destroy your differential (a problem I REALLY don't need).

Any suggestions anyone can offer would be greatly appreciated as I've never touched any differential other than to change/add fluids so I am in new territory here. Could be I am overthinking this whole thing too much.

[The Tassie Devil(le)]

G'day Jon,

There are a couple of things to do when setting up a Pinion.

(1)   The figures mentioned in the Factory Shop Manual are for when installing a new set of bearings, and Crush Sleeve.   The high pressure is for the initial starting of the sleeve compressing, which should neve be done with a Torque Wrench, as the tension to start the compression is REALLY high.   I use a breaker bar, with an extension on the end to make it easier to start the move.   Then as the time gets closer to checking the drag of the bearing, this is still done with the breaker bar, but the drag is measured with the Pinion turning on its' own, with no meshing of the Crown Wheel.

(2)   Once the correct Drag has been reached, no more tightening of the Pinion Nut.

(3)   When re-using an old crush sleeve, I always use at least a .010" shim, so that the Crush Sleeve has to be actually Crushed.

(4)   But, before loosening and removing the Pinion Nut, I will apply a Breaker Bar to physically Break the static Grip of the nut, putting it back into the same place as I found it, then with the Tension Wrench tighten the nut ever so slightly to physically observe just how much pressure there is.   If there is a lot of further tightening of the nut, indicating that the Pinion Bearings are loose (poor drag), then it might mean that further disassembly and parts replacement are necessary.

(5)   If it is just a matter of replacing the seal, and nothing else, I would be wary of tightening the nut up to the 225 Lb.Ft mentioned.   The Pinion Drag should be measured with the pinion free of the Crown Wheel.

Bruce.

PS.   As for doing it at home?   It all depends on your access to the tools, including room to move under the car.   I don't have access to a hoist, but I do have a good workshop where I can work on anything, and a bench capable of holding big stuff.

PPS.   Tools required after you have raised the car, and removed the tail shaft and gained access to the pinion flange:   Large Socket set, Large Breaker Bar, Puller, Tension measuring device for measuring pinion drag, Pinion Flange holder, and the list goes on. 

[Joe G 12138]

    Although I have not specifically worked on a '39, I've done a number of differential seals. I will say that the older shop manuals give some crazy high torque numbers on some pinion nut torques. as I remember it, When I did my '50 Cad the numbers were similar, intimidating, unrealistic, and frankly unmeasurable. Where the heck can you find a 1000-2000 lb torque wrench? And which two guys are going to use it? (one to read it; one across the street pulling on the handle extension). Most dealers didn't even have a full set of 3/4 drive sockets with a ratchet in those days. And if you could get that much torque on it , that 7/8 shaft or threads would give.
    As for doing it without a lift, it can be done but not easily. As Bruce mentioned, you will need a long breaker bar and possibly pipe extension with at least room to swing a 3 ft. handle and pipe wrench or flange holder about the same length. Breaking the pinion flange nut off is harder than installing. In tight spaces (no lift available), many would just use an impact wrench for removal. Personally, On ancient, untouched since factory, or hard to find parts for stuff such as this I prefer to use a breaker bar by hand rather than risk rounding off hex heads, stripping out threads, or other surprises especially when the nut is "down in the pocket" I can almost guarantee that that 80 year old nut will appreciate some preparation. Wire brush as much crap off of the threads and nut and start soaking with pen. oil days or weeks before going at it.
    Anyway, Here's the main points I'd like to pass on if you do proceed. As I said earlier many of the older Shop manuals give confusing or irrelevant information. As an old saying says: "As you go through life my son, no matter what your goal. Keep your eye on the rolling Donut , boy, not the Fxxxing hole!" Your goal is replace a leaking seal. Unless you have a need or reason to mess with that pinion bearing as mentioned in step  3 or 4, don't get confused by the manual wrapping them all together. It's irrelevent if it's a crush sleeve or shimmed pinion bearing. That's a separate task from replacing the seal as shown in later GM shop manuals. If you don't have noises, excessive wobbling, or see signs of bearing issues such as heating, metal shavings, or other issues--leave it alone and fix the seal.
    Next point, no matter what year or make: record where you started before touching anything. Just like a reboot point on a computer. Mark input flange, trans position, u-joints, everything. Some Transmission / Diff. have intentional missing or double splines. I will post a shot of a much newer than 1939 GM reassembly procedure, but very valid. That amounts to them saying pay attention to what you started with. If all you are doing is replacing the seal, and not messing around with spacers, bearings, pre-loads, crush sleeves or other completely unrelated things you should at least be getting everything you touched back to where you found it. Sensible?
    Some GM manuals mention marks, scribes, punches, threadcounts etc. My preference is to cover my butt in several ways. I do the GM thread count method (but make sure before / after start points are the same).I also measure with a scale / square. As an extra triple check I mix and match washers to mark original nut-to shaft dimension. Sometimes I've used PVC pipe scraps cut to match.
    Now that we are back to where we started from without breaking anything, we finish it off. The attached newer manual shot basically says give it a little more; check if it made a difference. (there may be wear involved)  Ok; 3 INCH lbs. more? Let's measure that one depending where you hold the handle!
    Summary: If the pinion seal is all that's bad, fix it. If the expensive, hard to find parts are ok leave 'em alone!  As mentioned earlier, 225 lbs torque is a realistic number.  More on that later...
   
    Attachents : Scribble sheet my measurement notes from a more recent (non-Lasalle) GM pinion seal found left on workbench.  And Differential seal Re-install from a more recent GM shop manual.

     

 

[39LaSalleDriver]

Thanks for your input guys. You're giving me a lot to think on here. I'll try to respond in more detail later today/tonight when I get the time to put together some coherent thoughts and further questions.

Fortunately, this is not something that I am not in a massive hurry to get done today, this week, or perhaps even this month. As a result I have plenty of time to think very carefully about what I'm getting into, or whether I should leave it to a pro.

I'm currently running 90 GL4 Gear Oil in my differential and for a short term fix I think I'm going to step it up to a 140 GL4 to see if that helps me any.

[39LaSalleDriver]

Bruce,

Thanks for your input. I'll address your comments with some follow up questions (highlighted in red).

G'day Jon,

There are a couple of things to do when setting up a Pinion.

(1)  The figures mentioned in the Factory Shop Manual are for when installing a new set of bearings, and Crush Sleeve.  The high pressure is for the initial starting of the sleeve compressing, which should neve be done with a Torque Wrench, as the tension to start the compression is REALLY high. 

Sounds like I don't need to worry about that 12-1400 lb. measurement then...

I use a breaker bar, with an extension on the end to make it easier to start the move.  Then as the time gets closer to checking the drag of the bearing, this is still done with the breaker bar, but the drag is measured with the Pinion turning on its' own, with no meshing of the Crown Wheel.

How is no meshing with the crown wheel/gear achieved? Since the differential on the 39s are a sealed unit that can't be opened, I would presume the gearing can't be separated, or perhaps I'm missing or misunderstanding something (which is entirely possible).

(2)  Once the correct Drag has been reached, no more tightening of the Pinion Nut.

From what is shown in the accompanying illustration from the Factory Assembly Manual, that value is supposed to be 34-40 in. lbs. at 10 rpm. (however that is achieved). I presume this would equate to the 10-20 in. lbs. of drag with the wheels removed that I see referenced by other threads on this forum?

(3)  When re-using an old crush sleeve, I always use at least a .010" shim, so that the Crush Sleeve has to be actually Crushed.

Duly noted.


(4)  But, before loosening and removing the Pinion Nut, I will apply a Breaker Bar to physically Break the static Grip of the nut, putting it back into the same place as I found it, then with the Tension Wrench tighten the nut ever so slightly to physically observe just how much pressure there is. 

In other words, after you break the nut loose, you retighten it with the torque wrench to the marked position to see what that value is?

If there is a lot of further tightening of the nut, indicating that the Pinion Bearings are loose (poor drag), then it might mean that further disassembly and parts replacement are necessary.

I'm thinking if it gets to that point I'm going to have to shop for a whole new differential, which I really don't want to contemplate right now.

(5)  If it is just a matter of replacing the seal, and nothing else, I would be wary of tightening the nut up to the 225 Lb.Ft mentioned.  The Pinion Drag should be measured with the pinion free of the Crown Wheel.

Seems like Joe G. in his post following yours indicates that in his experience the 225 ft. lb. reading is about what is expected. So I don't really know which direction to look. I'm back to your comment about how to measure the drag without the crown gear (or wheel as I presume you're calling it) being engaged. Is it possible you're thinking about another model of differential where the pinion can be separated, because I get the idea that the pinion can't be pulled out of the gearing and measured on these?

Bruce.

PS.  As for doing it at home?  It all depends on your access to the tools, including room to move under the car.  I don't have access to a hoist, but I do have a good workshop where I can work on anything, and a bench capable of holding big stuff.

PPS.  Tools required after you have raised the car, and removed the tail shaft and gained access to the pinion flange:  Large Socket set, Large Breaker Bar, Puller, Tension measuring device for measuring pinion drag, Pinion Flange holder, and the list goes on. 

I'm still working on these aspects and still haven't decided whether I want to tangle with it myself or find a shop to do it for me. The problem is finding a shop that I trust, that can work on these. What few experiences I've had so far with jobbing things out has been disappointing to one degree or another. Invariably they ignore my instructions, don't read the data and documents I provide to them and just go ahead and do the job the way they do it on every other car even though we all know these have some very specific procedures. As such I end up paying too much for work that I have to go back and modify, or I just have to live with my irritation. Yet another reason why I prefer to do as much of my own work as possible, even if I have to take some chances sometimes that it won't work the way I expect.

[39LaSalleDriver]

Although I have not specifically worked on a '39, I've done a number of differential seals. I will say that the older shop manuals give some crazy high torque numbers on some pinion nut torques. as I remember it, When I did my '50 Cad the numbers were similar, intimidating, unrealistic, and frankly unmeasurable. Where the heck can you find a 1000-2000 lb torque wrench? And which two guys are going to use it? (one to read it; one across the street pulling on the handle extension). Most dealers didn't even have a full set of 3/4 drive sockets with a ratchet in those days. And if you could get that much torque on it , that 7/8 shaft or threads would give.

My thoughts exactly. I can get 3/4" drive sockets, breaker bar, torque wrench...but would prefer to borrow them rather than buy because I doubt I would have any further need for them on anything.

    As for doing it without a lift, it can be done but not easily. As Bruce mentioned, you will need a long breaker bar and possibly pipe extension with at least room to swing a 3 ft. handle and pipe wrench or flange holder about the same length.

That swing arc is what is concerning me the most. I use a combination of Race Ramp 12" blocks or jack stands depending on what the job requires. I'm not wild about cranking that much force under a car on jack stands. About the only other solution I can think of is to use the blocks (which are incredibly stable and safe) with the wheels and drums on while breaking loose and torquing back down; and shifting over to the jack stands with the wheels and drums off while fine tuning the drag. Would this sound feasible? And if so, would it eliminate the need for a flange holder of any sort? I would think so since the axles effectively shouldn't be able to move at that point.

Breaking the pinion flange nut off is harder than installing. In tight spaces (no lift available), many would just use an impact wrench for removal. Personally, On ancient, untouched since factory, or hard to find parts for stuff such as this I prefer to use a breaker bar by hand rather than risk rounding off hex heads, stripping out threads, or other surprises especially when the nut is "down in the pocket" I can almost guarantee that that 80 year old nut will appreciate some preparation. Wire brush as much crap off of the threads and nut and start soaking with pen. oil days or weeks before going at it.

I've wondered about that. I do have an impact gun which would probably be able to get the job done handily. Some comments I've read indicated that you should never use and impact gun on that nut for fear of damaging something deeper in the gearing...others say it's probably okay. No doubt I would prep the threads as much as possible beforehand. My first instinct would be to try and break it by hand though.


    Anyway, Here's the main points I'd like to pass on if you do proceed. As I said earlier many of the older Shop manuals give confusing or irrelevant information. As an old saying says: "As you go through life my son, no matter what your goal. Keep your eye on the rolling Donut , boy, not the Fxxxing hole!" Your goal is replace a leaking seal. Unless you have a need or reason to mess with that pinion bearing as mentioned in step  3 or 4, don't get confused by the manual wrapping them all together. It's irrelevent if it's a crush sleeve or shimmed pinion bearing. That's a separate task from replacing the seal as shown in later GM shop manuals. If you don't have noises, excessive wobbling, or see signs of bearing issues such as heating, metal shavings, or other issues--leave it alone and fix the seal.

So far as I can tell, the leak is the only issue that I have. I certainly haven't noticed any other issues...yet anyway.

    Next point, no matter what year or make: record where you started before touching anything. Just like a reboot point on a computer. Mark input flange, trans position, u-joints, everything. Some Transmission / Diff. have intentional missing or double splines. I will post a shot of a much newer than 1939 GM reassembly procedure, but very valid. That amounts to them saying pay attention to what you started with. If all you are doing is replacing the seal, and not messing around with spacers, bearings, pre-loads, crush sleeves or other completely unrelated things you should at least be getting everything you touched back to where you found it. Sensible?

Yes. To my understanding, what I need to do is:

drop the driveshaft after marking it's position;

check drag of pinion with wheels and drums removed (should be approx. 10-20 in. lbs.);

mark the position of the pinion nut, break it loose, retighten and measure the torque to get back to that mark;

remove the seal;

remove the crush sleeve, insert a .010 or .005 shim and reinstall the crush sleeve (or do I just leave the sleeve in place and put the shim in before reinstalling the new seal?);

install new seal;

retighten nut to the mark made (check the torque value which should be in the neighborhood of 225 ft. lbs.), then ever so slightly back it off a smidge;

check drag of pinion with wheels and drums removed (should be approx. 10-20 in. lbs.);

reconnect driveshaft etc.




Does this all sound correct?



    Some GM manuals mention marks, scribes, punches, threadcounts etc. My preference is to cover my butt in several ways. I do the GM thread count method (but make sure before / after start points are the same).I also measure with a scale / square. As an extra triple check I mix and match washers to mark original nut-to shaft dimension. Sometimes I've used PVC pipe scraps cut to match.
    Now that we are back to where we started from without breaking anything, we finish it off. The attached newer manual shot basically says give it a little more; check if it made a difference. (there may be wear involved)  Ok; 3 INCH lbs. more? Let's measure that one depending where you hold the handle!
    Summary: If the pinion seal is all that's bad, fix it. If the expensive, hard to find parts are ok leave 'em alone!  As mentioned earlier, 225 lbs torque is a realistic number.  More on that later...
   
    Attachents : Scribble sheet my measurement notes from a more recent (non-Lasalle) GM pinion seal found left on workbench.  And Differential seal Re-install from a more recent GM shop manual.

     

 

[The Tassie Devil(le)]

G'day Jon,

Firstly, I don't recommend using thicker oil to stop this or any other kind of leak.   The grade of oil recommended by the factory is the grade that is designed for the proper lubrication of the internal parts.   Not to control leaks.   That is why they installed oil seals.

To measure the drag, I use a piece of wood, a string and a spring scale.   The piece of wood is 4" in diameter, with a groove shaped into the outer circumference to hold the string.   The string is wrapped around the disc, and the spring scale attached to the other end of the string.

When I am ready to check the drag, I attach the disc to the pinion flange, and pull on the spring scale, and read the needle on the scale, which in my case is in pounds, and then calculate the pull required to get the needle to the required reading.

When I measure the drag, I get the pinion moving initially, and read the scale whilst pulling the pinion through the length of the string.

Don't forget, that the drag measurement is only on the Pinion, and not also turning the Crown Wheel, axles and diff oil.   These last things do create drag.

The other pictures show the construction of the Pinion Flange holding tool, the Breaker Bar and tube extension, and the various Torque Wrenches that I have in my collection.   The long one is 40", takes a 3/4" Socket, and pulls up to 800 Ft.Lb.

Bruce.  

[Brad Ipsen CLC #737]

The large force of 1200 to 1400-pound force has nothing to do with anything you can measure in the field.  That number comes from the 1940 Manufacturing Information.  This is the instructions from the engineering department to the factory floor on how to put the car together.  They were just discussing the design.  It is not a torque.  It is the force that is on the collapsible sleeve and in turn on the bearings on their tapered shell.  The torque on the nut results in this force on the sleeve.  The sleeve yields (deforms) permanently to result in this force.  From reading the Manufacturing Information Manual Cadillac tested every one of these differentials for noise.  The question addressed was can we reuse the sleeves on another new differential and the answer was yes as long as you make sure on the next one that the sleeve is still long and can be collapsed some more.  In the Cadillac shop manuals this whole question of how to replace this seal was not addressed until the 1949 Shop Manual.  With the introduction in 1939 of the collapsible sleeve I guess they did not recognize that there may be a problem.  With the old design of shims and a thick sleeve there was no problem.  You just tighten it up to torque.  Drag was fixed by the shim pack and thick sleeve.  When they first addressed this in 1949 this statement is made.  "When it is necessary to replace the rear axle pinion oil seal or yoke it is very important that the procedure outlined below is followed to avoid overloading the pinion bearings or collapsing the spacer".  Earlier manuals just say to replace it with no instructions.  I have attached a rewrite of the Cadillac manual adding comments, modern part numbers and adding a shim.  I like that idea especially since Cadillac essentially did that at the factory with new production by reusing sleeves as long as they were long.  I also have copies of the 1940 Manufacturing Information if anyone is interested.  Also have a few seal OD adapters if needed but if you use the method suggested you should be able to get this out without damage.  Also have third members from parting out 39 and 40 cars.

With all of this said in the 80's I installed a new seal in a 1939 Cadillac without knowing anything about this.  I installed like one would install one in a 1938 differential and bad things never happened. 

[39LaSalleDriver]

Thanks for clearing things up Brad. Your post has pushed me towards having confidence to do the job myself. Reading carefully though your instructions I found things starting to finally make sense to me on what needs to be done. In some ways, I think I may have been overthinking it a bit, but I really want to proceed with caution on this project. Already have the shims and seal on order and will update later as I proceed.

[z3skybolt]

Jon,

Where did you purchase the pinion seal?  My 1940 50 series(should be identical to your 39) leaks. I understand there are two different sizes.  Did you measure before ordering?

Thanks,

Bob R.

[39LaSalleDriver]

Jon,

Where did you purchase the pinion seal?  My 1940 50 series(should be identical to your 39) leaks. I understand there are two different sizes.  Did you measure before ordering?

Thanks,

Bob R.

Hey Bob,

Based on the instructions Brad posted, I ordered a National #473179 (NAPA #18671) here: amazon.com/dp/B001OD9BQQ?psc=1&ref=ppx_yo2ov_dt_b_product_details

Since I am a Prime member I have a pretty liberal return policy should I need to do so. I too was aware that it could be another, but figured I have a 50/50 chance this is the correct one. I haven't yet begun attempting a repair, but decided I'd get my ducks somewhat in a row before I started. I also went ahead and ordered a 7/8 14 tap for cleaning up the threads on the pinion nut since I didn't have one of those laying around. Next, I need to find the size and then source an impact socket for said nut. Again, I don't have any larger sockets laying around, but should be able to find something individually rather than buying a whole set. Just don't have enough need for a set that size to justify it.

Probably the biggest issue I have right now is finding or fabbing up something to clamp the pinion as Bruce shows. I unfortunately don't have a torch setup or welder (though I wish I did and could really use them) to do it myself. Going to try and hit up a buddy of mine to see if he can make me something that will work.

[The Tassie Devil(le)]

Jon,

The way mine is set up is so that when using it, the bolts only have to be finger tight, as it is the leverage that holds it in place.

The reason for this is so that it is easy to slip off when I want to turn the pinion, or don't want the tool in the way.

Plus, the tool is made to be multi-adjustable to fit all the diffs that I work on, or have worked on.   When I have the need to use it on a circular pinion flange, I will drill a couple of holes in the welded cross piece to suit the flange bolts.

As you can see, it is only made out of Scrap, but, when needed, it is the most valuable tool for the task.

Bruce.

PS.   One could even use a large pair of Stilsons to hold the pinion flange still, if you are strong enough.

[fishnjim]

My standard for seals is make sure the bearings are OK, before you replace just the seal(any), as it's possible the seal failure is related to too much play in the bearings.  Since it's drive line it could be U-joints too.  Check the run out with an indicator. 
It's also likely true that it's just an old seal that has got brittle and face is worn or cracked, and now leaks and needs replaced.  I'm not sure, I don't do prewar, if it's an old style fiber seal or not.  Maybe has been replaced with a newer version along the parts trail.
Also, if the sealing surface is not flat and true, it'll just leak again with the new seal.   Not uncommon for grooving to occur under the seal surface from dirt etc accumulation which abrades the metal.  That would need to be addressed, or the new seal will just leak all the same.

Worst case, you'll have to take it somewhere to get it right and put a pan under the car in the mean time.
As I said in other posts, these don't seem to ever get the lube oil changed, gunk cleaned out, so may want to address that while you're under there.   Safety: Make sure if you do from the ground that it's well secured, if you're messing around with a large bar, big wrenches, etc. 
ps;I did my share of industrial sealing jobs and applications, much more advanced than an atmospheric pinion, you learn a few things.

[ricardo_padilla]

I had the same oil drip from the differential pinion seal. I used a paint mark before disassembly, removed drive shaft connection, placed another paint mark on pinion nut and threaded pinion (count the threads), with impact tool remove nut and assembly, then you will see the cup and the seal, pushtap the seal in until it hits the bearing (then you will have space for the cup extractor).
A small 3 jaw puller from harbor freight will do (will need to grind the jaws to fit around the pinion and get a good grab on the cup), spray some lubricant and watch the cup slide out, undamaged, then you remove the leaky seal. Get the one caddy daddy sells.
On reassembly, recommend a sealant for seal and cup (shellac will do). use the old seal to install the new one and also a round tube (like the one from a ball joint set from harbor freight). The cup will have to be started with a light hammer tapping all around then use a PVC pipe to tap it hard until it is fully seated (home depot). You will need to clean the nut with a tap  7/8-14 UNF, because there is metal left in there from the pinion having been chiseled on two sides (before you take the nut out, pay close attention). The rest will be in reverse order, following your paint marks.

[z3skybolt]

I had the pinion seal replaced on my 1940 LaSalle three weeks ago. It was leaking a pint every 140 miles. The seal was replaced with a modern one by a professional shop. Total cost $234.00 labor. plus $68.00 for the seal from CADILLAC PARTS LIMITED.  After driving it about 200 miles not a drop has leaked.

Why did I wait 2 1/2 years?

Bob R.

[Chopper1942]

If you are going to only replace the pinion seal, the first thing you need to do is remove the wheels and rear brake drums. Punch mark the pinion flange and driveshaft, so they are reinstalled it the same orientation. Remove the drive shaft from the pinion flange. Use an in/lb torque wrench on the pinion nut and now rotate the pinion using the torque wrench. Record the pinion turning torque. Probably somewhere between 5-15 in.lbs. Now remove the pinion nut and use a puller to remove the pinion flange. DO NOT USE A HAMMER TO BEAT IT OFF. YOU WILL DAMAGE THE REAR PINION BEARINNG. Remove the pinion seal and clean the housing seal bore and pinion splines. Apply either seal grease or rear diff oil to the pinion seal's rubber seal groove. Apply a gasket sealer to the pinion seal's outer diameter and carefully install the seal trying not to damage it. A piece of 1x4 with a hole bored in it larger than the pinion shaft would help to prevent denting or distorting the seal when driving it in.

Clean the spline of the pinion flange and then coat the splines with pipe dope/sealer. Tap the pinion flange on far enough to install the pinion washer and nut. Tighten the pinion nut until there is no slack in the pinion bearings. Now, you want to tighten the pinion nut a little and then check the pinion turning torque with the torque wrench. Keep doing this until the pinion turning torque is the same as when you first measured it. Now, tighten it another 5 in.lbs. Install the driveshaft, drums, and wheels. fill the diff with lube.

[39LaSalleDriver]

I had the pinion seal replaced on my 1940 LaSalle three weeks ago. It was leaking a pint every 140 miles. The seal was replaced with a modern one by a professional shop. Total cost $234.00 labor. plus $68.00 for the seal from CADILLAC PARTS LIMITED.  After driving it about 200 miles not a drop has leaked.

Why did I wait 2 1/2 years?

Bob R.

Wow, this is bringing back a thread from the dead!

Bob, I'd say you got lucky. If I could have found a shop locally that I trusted to do the work and at that price point, I'd have gladly turned it over to them. As it was, the mental anguish I went through worrying that I was going to mess it up would have been worth that much and more.

As it turned out, so far as I can tell, my project was successful. Admittedly, I haven't racked up very many miles on it in the past year and a half since I changed mine, but I would hope the couple of hundred miles I put on it this year would have brought any problems to light. At the very least, I have no further drips.

[Dave Shepherd]

If you are going to only replace the pinion seal, the first thing you need to do is remove the wheels and rear brake drums. Punch mark the pinion flange and driveshaft, so they are reinstalled it the same orientation. Remove the drive shaft from the pinion flange. Use an in/lb torque wrench on the pinion nut and now rotate the pinion using the torque wrench. Record the pinion turning torque. Probably somewhere between 5-15 in.lbs. Now remove the pinion nut and use a puller to remove the pinion flange. DO NOT USE A HAMMER TO BEAT IT OFF. YOU WILL DAMAGE THE REAR PINION BEARINNG. Remove the pinion seal and clean the housing seal bore and pinion splines. Apply either seal grease or rear diff oil to the pinion seal's rubber seal groove. Apply a gasket sealer to the pinion seal's outer diameter and carefully install the seal trying not to damage it. A piece of 1x4 with a hole bored in it larger than the pinion shaft would help to prevent denting or distorting the seal when driving it in.

Clean the spline of the pinion flange and then coat the splines with pipe dope/sealer. Tap the pinion flange on far enough to install the pinion washer and nut. Tighten the pinion nut until there is no slack in the pinion bearings. Now, you want to tighten the pinion nut a little and then check the pinion turning torque with the torque wrench. Keep doing this until the pinion turning torque is the same as when you first measured it. Now, tighten it another 5 in.lbs. Install the driveshaft, drums, and wheels. fill the diff with lube.

Great info, doing it this way for years on many GM rears, in car.