Exhaust Question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

GMCjunkie · 05-29-2003, 07:08 PM

Ill try to make a long story short....

I Just removed headers from my burb and put stock manifolds back on a couple months ago, (my pipes end just before the rear axle). The problem Im having is with my rear ( and only) bracket , mainly the pass. side. It keeps breaking. I drove coast to coast 2 times when I had the headers on there and never broke a bracket. The guy that did the exhaust, welded the new pipe on to fit the manifolds. First problem I was having was the bolts that connect the pipe to the manifolds kept backing off , thus burning out the donut and sounding really loud. I realized after the first time I had to tighten them up,. that If I didnt torque the pipe over WHILE tightening the bolts, the pipe would rub on the frame, you could barely put your finger between them with it tightened up. Now Im being told that the reason the bracket is breaking now, is because when I had the headers on there, the collectors allowed for some play. Now that I have the manifolds its all rigid and when the engine torques or rocks it snaps the bracket.

What do you think??? Are the brackets breaking because you have to torque the pipe over, then tighten the bolts down, or because the manifolds have made the whole thing more rigid??

Sorry if this sounds rattled... Im so frazzled right now.

Any input is greatly appreciated

GMCjunkie · 05-29-2003, 07:10 PM

Oh keep in mind that the drivers side, that does not have to be torqued over, has not broken.

bigvinnie · 05-29-2003, 07:13 PM

sounds like bs, lots of people running stock rams with no problems... are your motor mounts in good shape?

lukecp · 05-29-2003, 09:03 PM

What kind of exhaust brakets do you have? If your bracket is a solid metal piece bolted or welded to the frame, that is your problem. They allow for almost zero flex. If you don't already have them, get some brackets that have the center made of rubber. They will allow the exhaust to flex about 1-1/2" inches without breaking.

**old Rusty C10** · 05-29-2003, 09:44 PM

get the universal mount brackets witht he rubber that allows a little play and the thing wont snap

Longhorn Man · 05-29-2003, 11:28 PM

Yup, I'll second (or third actually) that. You need some flex on the mounting.
Kinda odd that tehy didn't break with the headers...they shouldn't give either.

ddsmith · 05-30-2003, 12:43 PM

Oh boy something I know something about. Is the run of pipe from the manifold to the bracket relatively straight? Headers being tubular will allow some of the flex due to engine torque and road conditions to be absorbed because they are not ridgid. You create a pre-existing stress by torqueing the pipe over to bolt it up then the engine torque and road bumps play havoc on the bracket where the stress is concentrated. The manifold won't flex like the headers did.
I work in a Power Plant and we have thousands of pipes in the plant. I use to believe that the harder you mounted something the less likely a failure was. You know more brackets means less chance to break. Several studies performed showed that the pipes were more likely to fail with solid mounting all over the place because it concentrated stress in a smaller area. A particular joint or weld. They removed many hangers in the plant and the pipes some as big as 36" now move around which prevents concentration of stress. I still don't like watching a 36" pipe carrying 900# of steam moving around especially when I would be turned into a lobster if it did fail.

Woody · 05-30-2003, 01:20 PM

Well I think the other post before this one covered most of it, here is a few other things to check.
First check your motor mounts AND the Tranmission mount. Tranny mounts go bad once they get a little oil on them, not that any of these trucks ever leaked oil! This allows a lot of torquing of the engine. I was cracking manifolds due to a bad tranny mount.

Next try a rubber bracket as suggested before. Also loosen all the brackets (or rehang them) and allow the pipe to not be stressed when you tighten the manifold flange bolts. Then tighten the brackets and be careful not to stress the pipe. This should help things a lot.

Another trick is to use maniflod flange bolts that are spring loaded. (Spring between flange and nut) This allows for some flex at the dounut but it stays tight. I have seen these but can't tell you where, its just been too long ago..........

Good Luck!

05-29-2003, 07:08 PM	#1
GMCjunkie Dude...I'm a CHICK Join Date: Jul 2000 Location: Lakeland Georgia Posts: 6,192	Exhaust Question Ill try to make a long story short.... I Just removed headers from my burb and put stock manifolds back on a couple months ago, (my pipes end just before the rear axle). The problem Im having is with my rear ( and only) bracket , mainly the pass. side. It keeps breaking. I drove coast to coast 2 times when I had the headers on there and never broke a bracket. The guy that did the exhaust, welded the new pipe on to fit the manifolds. First problem I was having was the bolts that connect the pipe to the manifolds kept backing off , thus burning out the donut and sounding really loud. I realized after the first time I had to tighten them up,. that If I didnt torque the pipe over WHILE tightening the bolts, the pipe would rub on the frame, you could barely put your finger between them with it tightened up. Now Im being told that the reason the bracket is breaking now, is because when I had the headers on there, the collectors allowed for some play. Now that I have the manifolds its all rigid and when the engine torques or rocks it snaps the bracket. What do you think??? Are the brackets breaking because you have to torque the pipe over, then tighten the bolts down, or because the manifolds have made the whole thing more rigid?? Sorry if this sounds rattled... Im so frazzled right now. Any input is greatly appreciated __________________ ~~~~~~~~~~~~~* "The unexamined life is not worth living" -Socrates ~~~~~~~~~~~~~* '71 GMC Suburban 4x4

05-29-2003, 07:10 PM	#2
GMCjunkie Dude...I'm a CHICK Join Date: Jul 2000 Location: Lakeland Georgia Posts: 6,192	Oh keep in mind that the drivers side, that does not have to be torqued over, has not broken. __________________ ~~~~~~~~~~~~~* "The unexamined life is not worth living" -Socrates ~~~~~~~~~~~~~* '71 GMC Suburban 4x4

05-29-2003, 07:13 PM	#3
bigvinnie Registered User Join Date: Aug 2001 Location: escondido, ca 92026 Posts: 1,222	sounds like bs, lots of people running stock rams with no problems... are your motor mounts in good shape? __________________ '72 short step, 350, 700R4, tilt, ps, pdb, a/c, lowered coils, etc., other work in progress... San Diego, CA 72 Stepside Project

05-29-2003, 09:03 PM	#4
lukecp Formerly yellow72custom Join Date: May 2001 Location: Austin, TX Posts: 7,531	What kind of exhaust brakets do you have? If your bracket is a solid metal piece bolted or welded to the frame, that is your problem. They allow for almost zero flex. If you don't already have them, get some brackets that have the center made of rubber. They will allow the exhaust to flex about 1-1/2" inches without breaking. __________________ '72 Chevy C10 Mild 350/TH350/3.07. Ochre/White. Old high school ride. '70 GMC C2500 '62 327 4bbl/SM465/4.56-geared Dana 60. White/White. Project or parts truck. '97 Saturn SL DD. 1.9/5-speed. 40+ highway mpg

05-29-2003, 09:44 PM	#5
old Rusty C10 Robert Olson Transport Join Date: Oct 2002 Location: recent transplant to NC USA Posts: 20,345	get the universal mount brackets witht he rubber that allows a little play and the thing wont snap __________________ Bob 1951 International running on a squarebody chassis "If a man's worth is judged by the people he associates himself with, then i am the richest man in the world knowing some of the fine people of this board" http://67-72chevytrucks.com/vboard/a...t.php?f=25&a=9 (you can review the site rules here!) PM Me for your vehicle/parts hauling needs in the North East US or see my Facebook page Robert Olson Transport Live each day to the fullest.. you never know when fate is going to pull the rug out from under you... I hate cancer!!

05-29-2003, 11:28 PM	#6
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Yup, I'll second (or third actually) that. You need some flex on the mounting. Kinda odd that tehy didn't break with the headers...they shouldn't give either.

05-30-2003, 12:43 PM	#7
ddsmith Glowing since 1978 Join Date: Mar 2001 Location: Lusby,MD,USA Posts: 532	Oh boy something I know something about. Is the run of pipe from the manifold to the bracket relatively straight? Headers being tubular will allow some of the flex due to engine torque and road conditions to be absorbed because they are not ridgid. You create a pre-existing stress by torqueing the pipe over to bolt it up then the engine torque and road bumps play havoc on the bracket where the stress is concentrated. The manifold won't flex like the headers did. I work in a Power Plant and we have thousands of pipes in the plant. I use to believe that the harder you mounted something the less likely a failure was. You know more brackets means less chance to break. Several studies performed showed that the pipes were more likely to fail with solid mounting all over the place because it concentrated stress in a smaller area. A particular joint or weld. They removed many hangers in the plant and the pipes some as big as 36" now move around which prevents concentration of stress. I still don't like watching a 36" pipe carrying 900# of steam moving around especially when I would be turned into a lobster if it did fail. __________________ 66 Chevy C30 Stakebody Dump, PS,PB, 327cu in 71 Corvette Coupe 454 4 speed 69 Chevy C20 Custom Camper

05-30-2003, 01:20 PM	#8
Woody Registered User Join Date: Feb 2000 Location: Georgetown, KY, USA Posts: 631	Well I think the other post before this one covered most of it, here is a few other things to check. First check your motor mounts AND the Tranmission mount. Tranny mounts go bad once they get a little oil on them, not that any of these trucks ever leaked oil! This allows a lot of torquing of the engine. I was cracking manifolds due to a bad tranny mount. Next try a rubber bracket as suggested before. Also loosen all the brackets (or rehang them) and allow the pipe to not be stressed when you tighten the manifold flange bolts. Then tighten the brackets and be careful not to stress the pipe. This should help things a lot. Another trick is to use maniflod flange bolts that are spring loaded. (Spring between flange and nut) This allows for some flex at the dounut but it stays tight. I have seen these but can't tell you where, its just been too long ago.......... Good Luck!



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