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472 Exhaust Pipe toManifold studs

Started by IcebearLars, September 16, 2018, 05:39:51 AM

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IcebearLars

Hi folks,

hope that somebody knows which studs I need to change all four of them connecting the exhaust pipe to the manifold flange where it goes into the exhaust.
I am not speaking about the manifold to head bolts which I found already specified in the shop manual as 3/8-16 x 2 1/8.

These I am searching for are studs and the shop manual only tells the torque specification for "Exhaust Pipe to Manifold Nuts 3/8-24" with 30 foot pounds" - so I guess the upper part of the stud where the nut comes on is a 3/8-24 thread but I am not sure if the lower part thread is the same or another thread since I cant remove them until now (soaking with penetration oil 50/50 acetone/ATF is ongoing but cant break them loose so far).
BTW what tools are you guys using to break studs w/o a head loose?
The studs are 2" long over all.

The studs look like these or these but not sure if they are the right ones.
They have on the one side a 3/8-16 and on the other side a 3/8-24 thread.

Your help is highly appreciated.

Cheers

Lars

Scot Minesinger

I know what you mean, and have replaced all of mine on three 1970 Cadillacs, two in place, and one on the bench.

Generally if you are replacing the exhaust "Y" pipe the replacement flanges with holes that receive the studs on the manifold the studs need to be longer because the flanges are made different.  There is no harm in longer, because you just have to screw the nut on a few more threads.  It is unlikely an authentication deduction would be suffered during GN judging either.

The studs are 3/8" fine thread, which generally keeps the nut on (in lieu of course thread, which will loosen).  The stud part that screws into the manifold is course thread 3/8".  The stud is about 2" long total, not sure.  You will have to have them custom made if you want the fine thread type, as they are not sold.  I just visit the auto parts store and buy a couple of sizes and see what works best, 2.5 or 2.75 inches comes to mind.  The extra studs are handy for water pump alignment, hood hinge to hood install and the like.  These will be all course thread with a brass nut that will never rust and generally stays tight.

Heat is how you remove the stud, lots of heat.  Heat it up real good, and use a sudden jarring blow to break the nut free.  With stud and not hot, wrench is on the nut in a good location that you can smack it with a hammer, rehearse the blow and do not hold back (same if using a socket wrench, or use impact).  If you go with the steady force route the stud will break.  This is same idea behind breaking flare nuts loose on brake and fuel lines.  Sometimes the stud and nut come out as one, and sometimes just the nut.  Then with if stud remains put two nuts on it and repeat. 

I broke one stud, and using progressively larger drill left handed drill bits (e-bay is your friend) was able to get it out by the time I got to size 5/16".  The angle of the stud is such that even in place you can drill them out.

Good luck, this is a thankless by rewarding job.
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

Classic

I have successfully used a Lisle 71200 Stud Remover tool several times (available from Amazon).  Works great.  However, if the stud is badly frozen, Scot's method may work better.

Gene
Gene Menne
CLC #474

IcebearLars

#3
Thanks Gents for your quick reply,

have some questions about the fine/course info Scot shoot over.
Did I understand it correct that the fine 3/8 upper part where the nut screws on is 3/8-24 and the course 3/8 part sitting in the manifold is 3/8-16 as the attached chart I found shows?

As I am a damn German using the damn metic system (which the other 98% of the world is using for screws etc.  >:D) I was interested if there is a metric thread existing which I could use instead getting the studs in UNF/UNC and I found the attached conversion chart.

So if I read both charts right I need a 3/8-24 (M10 x 1.25) 3/8-16 (M10 x 1.5) stud - correct?
Next question is why I have to make them custom buildt? That will be excatly the studs I mentioned in the link above or this Dorman ones should work as well.

Thanks for clarification

Lars

DeVille68

Hi,

I experienced the same as Scot said. The kit I got from USAPartsSupply had both UNC threads.
The studs you reference look good, however I don't know if those are long enough.
I just grabbed my old notes and those are saying that on the manifold side: 3/8'' - 16 ca. 1 cm long and on the heat rise side 3/8'' - 24 ca. 3 cm long. So in total about: 3''
The rest of the length is a smooth middle part.

So I guess those you found are too short.

Best regards,
Nicolas

1968 Cadillac DeVille Convertible (silver pine green)

IcebearLars

#5
Hi Nicholas,

the length you added in cm's is 1,57" and with the middle part it would be close to 2" - right?

Thanks

Lars

DeVille68

yes, about 2 cm sounds right. Then there is the thickness of the gasket, and you need some threads left over. So about 7cm (more or less) would be good.

This is for a 68, maybe yours is different.
If the stud is too long you can cut it or leave it. Too short will obviously be a problem...
1968 Cadillac DeVille Convertible (silver pine green)

IcebearLars

You mean 2" - not 2cm?
Yes it is for a 68 Eldorado.
The original studs are 2" (5,08cm).

Lars

Scot Minesinger

The 68 will be different than the 1970 because of the heat riser in exhaust between manifold and "Y" pipe on passenger side. 
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

DeVille68

Quote from: IcebearLars on September 17, 2018, 03:51:42 PM
You mean 2" - not 2cm?
Yes it is for a 68 Eldorado.
The original studs are 2" (5,08cm).

Lars

Ok, good, when you can take a measurement from the original ones. I don't remember, could also be just 5cm long. I thought they were more like 6cm to 7cm. I can't verify - I am currently not near my car. The heatriser is at most 2cm thick, not more.

Best regards,
Nicolas
1968 Cadillac DeVille Convertible (silver pine green)