'71 Eldorado: Exhaust Pipe bolts/nuts

[wbdeford]

Anyone know what size nuts and bolts to use to attach the driver side exhaust pipe to the manifold?  A previous owner rigged it with 5/16" threaded bolts plus 3 washers at each end.  When I removed it to replace the manifold gasket, I discovered the bolt was bent.  The nut wouldn't come off and I had to break it.

The manual specifies 3/8"-24 threads, but that's about it.

[Scot Minesinger]

Yes that is right, fine thread 3/8 studs go into manifold and then two fine thread nuts secures the y pipe flange to the manifold, drawing bell shaped exhaust end of Y pipe against manifold for gas tight seal ideally.  In a way you are lucky, as most of the time the 3/8 nut is frozen on and takes a lot of heat and trouble to remove.  This way you could more easily remove the straight thru 5/16" threaded rod or long bolt by just tightening both ends simultaneously until it failed (or however you did it).

The idea that someone did this to your car makes all previous repairs seem suspect.  I have seen worse.

Have not seen fine thread studs at auto parts stores but they may remain available.  if not you can buy fine thread, threaded rod and cut to length. 

[The Tassie Devil(le)]

Did Cadillac ever use Brass Nuts to secure the pipes to the Manifolds?

I like using Brass Nuts as they don't seize onto the threads.

Bruce.

[beastly beauties]

Bruce,  I remember working on most makes of 1960's and 1970's cars back in the day, and running to the local mom and pop hardware stores to purchase brass nuts for exhaust manifolds. I never could figure out why Detroit couldn't use brass nuts. Don't believe it ever crossed their minds, and of coarse I never bought a used car that had that convenience. I was the one who made it easier for the next owner!     David Symonds 

[The Tassie Devil(le)]

Ford used Brass Nuts.   But maybe that was only Ford Australia.   Never had a problem undoing those.

Bruce.

[Scot Minesinger]

Cadillac never used brass nuts on any exhaust manifold to Y pipe connection that I ever saw from 66 to 1976.

[TJ Hopland]

Parts stores usually have a couple sizes of somewhat universal exhaust studs still.   Its in the 'help' line. 

My guess is that the original stud broke off so they drilled them out.   I would say its a good sign that its a 5/16 because that means there is a chance you could re thread it to the proper size again if you wanted to.  If it was 3/8 with a nut the hole would already be oversized and you may have limited or no options to do it differently.    It could also be that 5/16 was all they had laying around.

[wbdeford]

Should these work, or is the fine threaded side too long?  I don't mind having coarse threads on the nut side.  I just want it to work and to be removable later. 
http://shop.advanceautoparts.com/p/dorman-help-exhaust-stud-kit-3-8-24-x-2-in.-03103/17190185-P

They also broke two of the manifold bolts off in the head (which I am not prepared to deal with at this time), so I know it won't be perfect until that is taken care of anyway.  I am hoping that since they are the 3rd and 6th bolts, that it will at least mostly not leak.  The biggest problem seemed to be they left a lot of old gasket material on the manifold when they installed the new gasket.  On the up side, the remaining 6 bolts were a piece of cake to remove.

[wbdeford]

They definitely drilled them out--into oval shapes.  On one side, I was able to drill out a pretty smooth 25/64" hole for a helicoil.  So, it is ready for a coarse threaded 3/8" stud.  The other side, they drilled at such a bad angle that they missed the edge of the stud.  I may just have to live with a 5/16" bolt on that side. 

[TJ Hopland]

I have had em hold together and not leak for years even with 1/4 bolts and nuts in the rust belt which was why they broke in the first place.   

[Scot Minesinger]

Replacement exhaust manifolds are not too bad to buy used, probably worthwhile in the case where a thru bolt is being used size 5/16 instead of a factory 3/8".  It is understood it may hold, but it is the "may" thing that bugs me.

[wbdeford]

Thanks...will see how it goes with this one.  It was holding with two 5/16" bolts, so hopefully one 3/8" and one 5/16" will work also.

[TJ Hopland]

Changing the manifold the question of how many of those bolts will break comes up and if / when those break they are much harder to deal with.   Often times drilling in the car is not an option so you are now looking at removing the engine or heads.  That is why I often go the route of just making the down pipe connection work since you can usually drill that in the car.   Since I got a oxy acetylene torch its much less of a problem even here in the rust belt.  With the torch its about 98% chance of getting a rusted nut off a stud so now I try and stud as many things as possible if they are in an area likely to rust.

[wbdeford]

It seems like whoever broke the two bolts on mine had so much trouble with that side that they just left the other side alone, even though it had a pretty bad exhaust leak.  I managed to get all the bolts out without breaking any, though one was pretty dicey for a while there, but that side's leak seems to have been taken care of.  I didn't try to disconnect it from the pipe on that side (passenger)

With a new gasket and what seems to be a better connection with one 3/8" and one 5/16" bolt on the driver's side, I'm hopeful there won't be a leak when I next run it.  After putting the exhaust back together, it was back to freeing up the distributor, which was finally successful this afternoon.

[TJ Hopland]

I have been in that situation a few times too so I can understand how it can happen.  Minor leak should be an easy fix, get a set of donuts.  Break down pipe stud or two.  Figure it should be fixed right which requires removing manifold.  Break some of those too now leaks are worse and engine has to come out but the resources to do so just are not available.