engine and drivetrain Adjusting Exhaust Downpipe

[gizmosfx]

I'm finishing a rear subframe swap on my 1600. It already had a 5 speed hooked to the original long neck diff. I picked up a 76 rear subframe and an LSD diff from a 320i. I had the driveshaft rebuilt using the already shortened  front half and the rear half from the 76.  The driveshaft guy told me the trans needs to be aligned so the guibo doesn't see any flex. I made an alignment tool. I machined an aluminum adaptor 14mm bore to 1/2. I used a piece of shaft and the adaptor to extend the center shaft from the back of the trans. into a spare center bearing. I had to raise the back of the transmission almost 1/2 an inch and I rebuilt the mount.

 

Now to my problem!

The beautiful stainless Ireland engineering exhaust used to fit perfectly but now since I raised the trans the front muffler (resonator?) is pressed hard against the center bearing. I want to lower it. I have tried pulling down on the head pipe but it seems very resiliant. I dont want to damage it. Is it possible to bend the rear portion of the headpipe down?

I was thinking to put a support under the spot where the welded split is, slip a heavy steel pipe inside the exhaust pipe and bend it down. Will the welds or pipe be damaged?

Also do you guys usually use the bracket from the trans to the downpipe? I have it installed now but it doesn't really seem neccesary.

Thanks

[roadhog0]

Try flipping that resonator section upside down. I had this problem in my 4 speed car. Worth a try at least...

[AceAndrew]

Wait, you had to raise your tranny a half inch?  This doesn't sound right, please post a picture of the cross brace.

 

As for your proposed solution, nobody could say with certainty if the piece would be damaged, its pretty relative.  The tranny to exhuast support bracket is very important.  If you take it off the only thing supporting the exhaust would be the mounting flange on the headers, this is why you sometimes see cracked headers on half-hearted exhaust installs.

 

This might help for the cross-brace ..

http://www.bmw2002faq.com/topic/145774-exhaust-bracket/

[jimk]

Did you allow for the supported weight of the driveshaft on the centerbearing to account for sag in the centerbearing mounting rubber?

Did you rotate the jig/trans output shaft to account for off square in the jig construction while checing for center in the centerbearing?

Edited December 27, 2013 by jimk

[Hans]

I wouldn't go bending the down pipe while its attached to the car. Out of curiosity, why didn't you check the flange alignment using the actual drive shaft?

[M3M3]

 

Wait, you had to raise your tranny a half inch?  This doesn't sound right, please post a picture of the cross brace.

 

As for your proposed solution, nobody could say with certainty if the piece would be damaged, its pretty relative.  The tranny to exhuast support bracket is very important.  If you take it off the only thing supporting the exhaust would be the mounting flange on the headers, this is why you sometimes see cracked headers on half-hearted exhaust installs.

 

This might help for the cross-brace ..

http://www.bmw2002faq.com/topic/145774-exhaust-bracket/

 

 

Did you allow for the supported weight of the driveshaft on the centerbearing to account for sag in the centerbearing mounting rubber?

Did you rotate the jig/trans output shaft to account for off square in the jig construction while checing for center in the centerbearing?

 

 

I wouldn't go bending the down pipe while its attached to the car. Out of curiosity, why didn't you check the flange alignment using the actual drive shaft?

+1 to all of these gentlemen's suggestions/questions.

[gizmosfx]

Thanks for all the responses.

Yes Andrew it sounds like I raised it a lot but the swap was done more than 12 years ago by a previous owner. I think the person doing the swap may have used the stick method to align the front and rear sections. That technique seems to set the trans too low and impart lots of flex to the guibo.

The adaptor I made was not perfect but when I spun the output it stayed centered left to right in the bearing and when I pushed up on it to compensate for the oversize bore I used the center of the vertical travel as my center.

If I watch the guibo and rotate the driveshaft I see no flex. I am fairly certain I have the transmission in the right place.

It seems if I bend the end of the downpipe down about 1/2 an inch it will fit. I am a bit concerned because the pipe is old, rusty and seems brittle from all the heat cycles.

I just checked and it is available as a replacement part. If I totally screw it up I can get another so I guess I should try to carefully bend it a little.

Would heating with an acetylene torch help the bending?

As with eveything else in these cars there always seems to be a little fudge factor involved.

Edited December 27, 2013 by gizmosfx

[schoir]

Judiciously heating it up with an oxyacetyline torch will definitely make it easier to bend and less likely to crack.

 

Regards, Maurice.

[Chamoix]

Gizmo,

I have my old down pipe leaning in a corner in the basement. I won't ever use it. I can send it to you for the cost of mailing. You can use it as a replacement if you trash yours, or try bending mine off the car then install it. Email me an address if you want it. jdaniels @ uga . edu

I'm in Athens, GA (30606) by the way.

[gizmosfx]

Well Then.

The first suggestion of flipping the resonator pipe over seemed the least likely to help when I first read it - - but I tried it and it seems to have worked!

Before flipping and reinstalling the pipe I tried a little pulling action. I slipped a 3 ft piece of 1 1/4 black pipe into the downpipe (perfect fit) and while carefully supporting the welded joint area from below pulled like hell. That pipe is very resiliant and resistant to bending. If it moved it only moved a tiny bit.

 

Thanks to all!

Mission accomplished.

[M3M3]

what it sounds like is the person who installed the 5spd did not install the rear brackets in the right place. they were installed too low if you had to raise the trans that much.  if the brackets were installed in the correct location the down pipe would not hit the tranny support......  

[roadhog0]

I had the same issue when i installed my IE SS exhaust a couple weeks ago. Reason I thought of it Good to hear it helped!

[jgerock]

Sounds similar to my car with relocated brackets. Very close fit between exhaust and modified tranny support bracket.