Psychovette

I'm changing the stock exhaust system on my '79 to a pre-'75 dual exhaust. Despite using heat and my best efforts, the exhaust pipe mounting studs broke off at the manifold flange. Does anyone know the correct drill and tap size for installing the new studs? I will also be replacing the front exhaust mounting bracket (at the transmission) with the type needed for two pipes. Is there an easy and safe way to change this bracket without damage to my turbo 350 transmission?

Thank You!

joewill

good luck not breaking your exhaust manifold flange too when you drill it out.. I have done it a couple of times.. ruining the manifold.

jnb5101

the cast iron manifolds are much softer metal than are the bolts. unless you have center drills and some experience drilling and tapping the cast iron, i think letting a machine shop handle this job is you best bet.
i don't understand your concern about removing the exhaust hanger. i believe you should be able to remove the bolts attaching the trans bushing and the hanger and jack-up the trans just enough to slide them out.

KapsSA

The manifold studs are 3/8".
I have a set of manifolds from a 78 L48 that I got for free. Two broken studs. Drilled and tapped them but kinda hogged out the holes. If I ever try to use them I think I'll screw the studs in and have the two loose ones brazed in place.

As for the trans mounted exhaust hanger, simply unbolt the trans mount from the trans AND frame, jack up the trans and slip the hanger and mount out together.
BUT...the only dual hanger I've seen that mounts at the trans mount is this homemade looking thing sold by Mid America for like $75!
The available mounts for auto trans applications won't work with the 350 turbo, just the 400.

Lot of guys simply use a pair of universal pipe hangers mounted to the back side of the crossmember.

corvetteload

Take this advice!!!!! Take the manifold to a reputable shop, one that is good at welding, in 5 mins they can have them out. They weld a bolt to it, and it turns right out, has something to do with the heat. I had one done and the guy charged me 15$, well worth it, especially the price to replace or the time you are going to spend drilling......................do a search online for "broken bolt extraction" and you will see what I'm talking about................

Psychovette

Yipes! Thanks for the advice. I didn't know that drilling out the holes and tapping them would be such a touchy project. I think I can save the studs on one manifold. Thanks for the exhaust mount at rear of the transmission info. I already have the correct bracket for the turbo 350.

Thanks for all your help.

mar

If you did it on the drivers side you are in luck- it's the easiest manifold to get out. The drivers side is not bad, but you have to rastle with the a/c compressor. If no A/c you are in luck again.

Take the manifold to a machine shop. Most auto parts stores like NAPA have a dedicated machine shop that does work like that for them. Check with NAPA - they will take care of you and keep in mind that whatever they charge you - it is worth it.

markdtn

Interesting. I have done it many times on various manifolds and never ruined any.

If there is any stud left, heat the whole ear red hot with a torch and grab the stud with vise grips and turn it a little. Re-apply heat and repeat until it comes out.

If no stud left, centerpunch and drill and tap it 3/8.

My .02

bluthundr

If you have access to a stick welder, grab a big electrode, turn the heat way up, and then intentionally stick the rod to the bolt. Release the rod from the stinger and then bend the rod at a right angle and use it to unscrew the stud. The sudden surge of heat will loosen it up as well.

Psychovette

Thanks for all the great advice. Tried heat and vice grips, studs then broke off even with flange. Next I tried drilling and tapping, then the tap broke! Calls to local machine shops convinced me to purchase a replacement since it would be less expensive.