Y Pipe and Catalytic on 1995 GMC Sierra

Hello All. I have a 95 GMC Sierra that needs the y pipe and catalytic replaced on its exhaust system. I am concerned about the bolts at the exhaust manifolds. After 20 years and 215,000 miles, I can imagine that they all break off or strip the flats on the nuts, then I will be stuck! Can anyone explain how they can be removed? Do they drop in or are they threaded into the cast manifold? I have a propane torch and hand tools.

So, before I get started, can I get some recommendations?

What you’re going to want to do is heat up the nuts as much as possible to help in their removal.

The studs are threaded into the manifolds. What I’ve usually found is if the nuts don’t unthread from the studs, the studs unthread out of the manifolds. Then it’s just a matter of replacing the studs and nuts.

And by the way. Use a six point socket to remove the nuts/studs


@Tester … would it be less risky using an impact driver to remove those fasteners?

OP: Be sure to soak the threads in some penetrating oil for a few days first, then thoroughly clean the fasteners so they aren’t slippery.


You can’t feel if the stud is about break off.

If the stud breaks off, then you’ll have to remove the stud with a stud removal tool if enough is sticking out. Or drill out the stud and rethread the manifolds or use a nut and bolt.


Since this is a 95 it’s not OBD2. Cut off the cat with a sawzall and replace with universal cat and be done.

While I usually agree with @Tester, I have to disagree on the impact wrench. I’ve found the hammering of the impact wrench helps break the rust-bond. Soak the stud well with PB Blaster or Liquid Wrench (my preferred) Just be sure to set it below the max so it won’t just immediately snap the buggers off. Keep increasing the setting until they come off.

Alternately, use a Dremel with a metal cutting wheel and split the nut as deep and far down as you can get without damaging the threads. It will “relax” the nut so it will come off.

Of just cut the old cat off and install a universal cat like @pete peters suggested.

Depends on where you live and the environment they have been subjected to. Where I have lived, the manifold bolts rust away where they run exposed to the elements. At least a few of them usually twist off before the nut budges. A buddy of mine lives in a dry, arid area of the country and you can take them off with a crescent wrench…

Propane is nearly useless due to the large mass you’re trying to heat up. Just buy a MAPP canister and use the propane burner. You’ll improve the heating capacity an order of magnitude over propane. And buy a can of B’Laster PB penetrating oil. You won’t regret that purchase.

Not to burst anybody’s bubble . . .

Some 1995 vehicles were actually OBD2 compliant, and the underhood sticker says it

I believe I’ve even run into some 1995 model year GM vehicles which were OBD2 compliant

All manufacturers had to be compliant by 1996 model year. Some were compliant a year or 2 earlier


That was the bastard year for GM vehicles.

Some were fully OBDII compliant, and others were semi-compliant.

The semi-compliant vehicles switched from the ALDL connector where you could jump between the A and B terminals and get engine codes from the flashing Check Engine light, to the OBDII connector we see today.

And unless you had at least a TECH II GM scanner for these vehicles, you couldn’t pull codes.

Thanks GM.


This vehicle is TBI, has one oxygen sensor and it’s not mounted after the cat, so no problem using universal cat.

Thanks all! We put the cat back system on for now. My kid is driving it and talked to the auto shop teacher at his HS. We live in Wisconsin. So it is cold and the truck is pretty rusty so i am expecting the worst. Anyway, we might try fixing it at the auto shop or wait until it gets warmer. Either way we’ll be fighting broke bolts. We’ll use the penetrating oil and lots of heat tips and hope for the best.