76 Eldorado Transmission Issue

[davidmezz]

The transmission in my 76 Eldorado recently started acting up. The car has 46,000 original miles. The car will no longer move with the shifter in the "drive" position. It revs as if the car is in neutral.  To drive the car I have to be in 2nd gear.  In 2nd gear the transmission does not shift and i can't drive over 35mph due to the high revs. The first test was replacing the transmission filter but that didn't help. The second test was adding a quart of fluid in case of a dipstick issue. That didn't help either.   

Reputable mechanics in my area believe it is a linkage issue that will require a new/rebuilt transmission. The former owner of this car believes it may be a linkage unhook issue and suggested i post in this forum.

Any thoughts or advice would be appreciated. 

David

[Dave Shepherd]

Dave first thing to do is make sure the linkage adjustment is right plus make sure it is adjusted and tight on the transmission, then if all is ok it is an internal issue, is reverse ok

[76eldo]

David,

You should be able to feel if the car is going into gear or not.  ANY competent mechanic can put the car on the lift and look at the linkage to see if it is moving, sloppy, worn, loose etc.  There is nothing mysterious or overly complicated about the linkage.  If you don't have one, get a factory shop manual.  76 was a very popular year, they are plentiful on ebay.

Sounds like you have some internal problems.  If a service did not fix the problem (new filter and fluid) and your vacuum modulator is connected on the side of the trans and it's slipping like that, you have a damaged trans.

Shop around for a mechanic that can assure you that they are familiar with this vintage of trans.  Most towns have an older established trans shop.  Don't shop for lowest price, and i would stay away from the large franchise places unless you know someone that had a good experience there.

It's a blind area, and I hope you can find someone that will take good care of you.

Brian

[Eric DeVirgilis CLC# 8621]

The transmission in my 76 Eldorado recently started acting up. The car has 46,000 original miles. The car will no longer move with the shifter in the "drive" position. It revs as if the car is in neutral.  To drive the car I have to be in 2nd gear.  In 2nd gear the transmission does not shift and i can't drive over 35mph due to the high revs. The first test was replacing the transmission filter but that didn't help. The second test was adding a quart of fluid in case of a dipstick issue. That didn't help either.   

Reputable mechanics in my area believe it is a linkage issue that will require a new/rebuilt transmission. The former owner of this car believes it may be a linkage unhook issue and suggested i post in this forum.

Any thoughts or advice would be appreciated. 

David

David: Excessive linkage play is common in Cadillacs of this generation but that never interfered with proper transmission function once it was engaged. Sometimes it was necessary to move the lever a little further toward N to get it to go into "D2" (which is third). If that doesn't work, I suspect the third gear bands have failed and unfortunately you are going to need a complete trans rebuild.

[TJ Hopland]

Ya my first guess would be linkage too.  Every Eldo from that era I have tangled with has had linkage issues.

If its not linkage then I am with everyone else with guessing that its rebuild time.

The linkage is not too hard to reach from under the hood. If you do mess with the linkage make sure its firmly getting into park.  This usually means the indicator wont line up anymore so you have to count the clicks.  Usually you cant get to 1 anymore either.   THe issue is at one of the pivots in the 'crank' that changes the direction from the vertical from the shifter to horizontal for the transmission.  I had my transmission rebuilt several years ago and had the car roll out of my driveway a few times because it was not going fully into park.  Even at that time I was not able to find new parts.  I ended up just adjusting the linkage so it got into park and then counted the clicks.  You also may have to adjust the park / neutral interlock switch.  I thought I did a write up on fixing these a few years ago when I finally fixed mine but I cant seem to find it anymore.  I did it starting with a universal door hinge bushing kit.  I have a lathe and mill but did it without using those tools because most people dont have those.   

[Glen]

This sounds strange to me because I have over 300,000 miles on my 68 ELDO and I have never had this problem.  It has the same basic THM425 transmission. 

If the problem is linkage I don’t se why it would need a complete rebuild.  90% of the linkage is outside of the transmission.  The part that is inside is accessible when you drop the pan. 

The shop manuals I have shows that drive left and drive right are identical when in first gear as far as clutches and bands applied go.   The manual valve (moved by the shift linkage) when in drive right applies line oil to the intermediate oil line, which is applied to the pressure boost valve increasing line oil pressure to 150 PSI and closing the 2 â€" 3 shift valve preventing the trans from going into third gear. 

What the book does not say is that when in drive right the drive oil is also boosted to 150 PSI and is applied to the forward clutch.  Maybe if drive oil is low in drive left and the clutch slips, the higher pressure in drive right might make it work. 

I would work on the linkage issue first.  It would be cheaper than a rebuild. 

I know, I am rambling. 

[Eric DeVirgilis CLC# 8621]

Very simple test to determine what gear you're in: When you're driving the car downgrade, does it coast easily or does it feel as if the engine is holding the car back as if it never left 2nd? Then when you give it gas, does it have to rev considerably in order to regain engagement? And when it does, can it only accelerate in 2nd as witnessed by excessive RPM?

Another possibility is a bad modulator which will drastically alter shift points- however I doubt it in your case as you make no mention of the car "winding up" before it shifts to second.

[davidmezz]

Thank you everyone for these responses. When the problem started, I would be in regular drive (the first block) and it would rev for a few seconds and then "bang" it would engage hard.  After that the transmission would be fine for the rest of the day.  The next day the same problem would start again while the car was cold.  However, since I had the transmission filter replaced the first block won't engage at all.  The car only revs.  At this point i have to drive the car in the second block.  Unfortunatley in the second block the car seems to drive in one gear and revs high once i get over 35 mph or so.  Reverse is fine and has always been. 

Thanks again,
David

[Eric DeVirgilis CLC# 8621]

Whoa whoa whoa there. Stop the presses.

Transmission "lurching" not disclosed previously.

Proceed to transmission shop. It needs to be rebuilt.

Sorry not to have better news.

[bcroe]

It doesn't matter how low the mileage, a trans that old needs a whole
new set of internal & external rubber seals.  If the job is done soon
enough, the original hard parts may be fine.  Keep trying to drive it,
and more serious damage may be done.  good luck, Bruce Roe

[The Tassie Devil(le)]

Your forward bands are shot.

Bruce.

[Gene Beaird]

If you are certain you reinstalled the filter tube with the o-ring, and the linkage appears to be adjusted properly, I'm with the other posters who indicate you're making a trip to a trans shop.  If the previous two things are good, it sounds like you have a broken, or leaking seal in one, or a couple of places.  It's taking excessive volume from revving the engine to get the transmission to go into a gear.  That indicates to me that you have a leaking seal, probably in one of the clutch packs. 

[TJ Hopland]

Has your timing chain been done?   IF the trans has to be rebuilt this is a good time to do the chain.  The reason doing the timing chain now is good is that to properly do the chain the oil pan has to come off.  In the Eldo's the transmission blocks access to several of the pan bolts.  Pulling the trans without the engine is a pain in the butt compared to other rwd cars of the era but maybe compared to a modern one may not be that bad other than it weighs 2 or 3 times as much as a modern one.   Pulling the engine and trans together is not that big a deal other than the total weight.   You pull em together then separate them and one goes to the trans shop the other gets a good external cleaning then a timing chain set and all the gaskets but the heads.  IF you dont take the heads off you dont run into as many 'might as wells' but you still get a good look at the overall condition of the engine.  Valve guide seals were also plastic and dont do well with age.  They can be replaced without removing the heads.  It goes back together cleaner and less leaky.  Trans gets rebuilt.  Engine compartment can get a good cleaning if desired.   When its done you got a better looking less leaky setup that you know has a great trans and the cam gear is not going to fall apart on and you know that the engine internals looked good so you should not have to worry for a long long time.   

Even with the low miles that cam gear is likely at least badly cracked.  The plastics of that era just were not that great.  Other issue is the plastic bits from the cam gear and the similar plastic bits from the valve guide seals all end up in the pan and oil pickup tube which slows down your oil flow which over time will also take its toll on things.