C3 - Exhayst/Trans mount bracket

[Jim K.]

I just made a (failed) attempt to adjust my exhaust system so it dosen't rub on the frame (rear outlet, NOT sidepipes). Both sides rub on the bottom two holes in the trans cross member, in fact, are quite tight to the bottom of the two holes. I thought the adjustment would be straight forward but the bracket that holds up the pipes is bolted in between the rear trans mount and the trans; and it seems that to raise that bracket up, I have to change the geometry of the drive train. Furthermore, the exhaust bracket is on the tranny side of the rubber mount (as I type this, that makes sense - to seperate it from the frame, ok). So after looking throught the AIM and not getting an answer...
How do I raise the exhaust pipes to center them through the crossmember holes??? Thanks in advance...
Jim

[Joe L.]

Re: C3 - Exhayst/Trans mount bracket

Jim------

Are you installing new front pipes or are you just re-installing pipes that were previously installed and previously fit ok?

[Jim K.]

Re: C3 - Exhayst/Trans mount bracket

Thanks Joe. Well... niether really. These were on the car when I got it over a year ago, probably only on the car a year before that and they never fit right since I have had the car. last year on th way to Carlisle, i hit an expansion joint on a bridge in NY and broke the pass side manifold; when I had it fixed (in carlisle) I really noticed that both pipes were tight to the bottom of the holes in the xmember. Since I have to replace the non functionong heat riser valve, I figured I would loosten it all up and try to get it right. If the bracket has elongated holes or can be shimmed with out affecting the driveline, I'll try that, otherwise it's bend the tabs and/or get some more bend on the pipes... ?

[Dick W.]

Re: C3 - Exhayst/Trans mount bracket

Jim the best way is to go to a muffler shop and let them put a little more bend in the pipes. If you start shimming, you will change the driveline angles

[Patrick H.]

Re: C3 - Exhayst/Trans mount bracket

Dick's right.

My preference, also is to tighten the connections at the manifolds last, doing the transmission connection (in your case) first. There is a lot more adjustability at the manifold than at the transmission. This sequence has not failed me yet, and I have installed a few sets of the pipes as well as adjusted a few.

Patrick

[Joe L.]

Re: C3 - Exhayst/Trans mount bracket

Jim------

Check the position of the bracket "oxbow" with respect to the hole in the crossmember. Then, if you have a piece of exhaust pipe that's the same OD as your pipes (i.e. either 2" or 2-1/2"), place the pipe through the crossmember hole and so that the upper part of the pipe seats fully against the "oxbow". If the piece of test pipe is pretty well centered in the hole, then the ox-bow bracket is not your problem. If you bend it down the exhaust pipe will not fully seat against it and if you install the forward pipe, while it may now be better "centered" in the crossmember hole, the forward pipe will be angled slightly down. This will cause the rear pipe, once installed, to angle down and it will be too low at the rear of the car.

I suspect that your problem really has to do with the configuration of the front pipe.

[George D.]

Re: C3 - Exhayst/Trans mount bracket

Jim,

I'm making this suggestion from memory, but I had a similar problem. I believe there are 2 different diameter exhaust systems. One at 2" and the other at 2.5 in. There are two different hangers for each size. If you are using the 2" hanger on the 2.5 in pipe it will tend put the pipe lower in the frame holes. I don't know if the part numbers are stamped om the hager, but using the 2.5 in hanger may solve your problem.

George

[Jim K.]

Re: C3 - Exhayst/Trans mount bracket

Hey Joe: Thanks for that advice. i think the issue is a 2" .vs. 2.5" exhaust thing??? What should a 70 350/350 car have? What is on there now is 2.5" and that change to 2" would make it all good. are there two different brackets??? I'd rather make it right than just make it work. Whaddya' think ?

Jim

[Joe L.]

Re: C3 - Exhayst/Trans mount bracket

Jim------

1970 with L-46 originally used 2" exhaust. There are 2 different "ox bow" brackets. One for 2" and one for 2-1/2". Both are GM discontinued but available in reproduction. As a matter of fact, there were even more brackets because automatic trans applications used a different set of brackets.

[Jim K.]

Re: C3 - Exhayst/Trans mount bracket

OK so now I have to decide: do I replace a perfectly good 2.5" exhaust system or get a 2.5" oxbow... I'll have to check prices of the oxbow... Thanks again Joe!!!

[Joe L.]

Re: C3 - Exhayst/Trans mount bracket

Jim-----

The 2-1/2" "ox bow" is not expensive. Dr. Rebuild will even sell you an NOS example with guillotine clamps for $35.