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5 Speed Crossmember Placement - Question For The Cognoscenti


rms_sandiego

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OK... So I have sourced pretty much everything for a 5 speed install on my '69 2002 and, after stalling for a year or so, have been forced ahead by a guibo that failed catastrophically and took out part of the selector shaft seal on my 4 speed...  

 

I have the old tranny out and have changed the seals on the 5 speed. I shortened the shift platform and shift linkage. I looked at the u-shaped adaptor that mounts on the existing crossmember support brackets and didn't like the design... So I picked up a pair of Lee's stainless brackets from Massive and shortened my cross-member to fit the narrower part of the tunnel....

 

Problem:  There appears to be a few possible approaches to locating the new brackets.

 

1) The centerline of the new brackets has to be 90mm rearward of the old brackets based on the additional tranny length and I have measured and drawn lines the right distance back from the old brackets. The reference guides say the horizontal mounting plane of the new brackets should be exactly 80 mm above bottom of the frame rails. However, the frame rails slope slightly and so figuring out exactly 80mm depends on whether I measure in the centerline or at the front or rear of the new brackets... Depending on how I futz, the bracket height moves up or down a few mm. I would like to be precise.  

 

2) It seems like I ought to be able to take a 4-5 inch length of 1/8th inch steel an inch wide or so, drill holes 90mm apart and bolt one end to the existing bracket and the other to the new bracket and use the plane of the old bracket and the distance to locate the new bracket. Has anyone done it this way?

 

3) Aternatively, I could hold off on placing the brackets until the tranny is in place and then use the tranny and the shortened driveshaft (which I don't have yet) to locate the height of the bracket so as to get the driveshaft etc. aligned.

 

Any advice on which approach to take?

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1- precision in this process is overrated.  See below.

 

2- yes, you could, and it's a good starting place.

 

What you find, though, is getting that sucka to fit in there cleanly is all that matters.

So you end up with it in a 'best compromise' position that puts the least strain on the guibo

for the least amount of hitting the tunnel, exhaust, etc that you can manage.

 

3- which is what you end up doing.  However, if you start at the 'best fit' of 1 and 2, you have

a better chance of reducing strain on the guibo and that buzzing, rattling grinding noise it makes

when the transmission bumps up against the tunnel...

 

Good luck!

 

t

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I guess you're arguing for not finalizing the position of the brackets (which I had intended to weld in place in advance) until getting everthing in and lined up.  Or do you thing it is better to just put the brackets into what looks like the appropriate place and then use washers/shims to move the end of the tranny up and down?

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yup.

 

like toby said..

1 is overrated and will end up with tranny in wrong place or lots of washers needed to get there)

2 is a good start to marking, not drilling holes

3 is what you do. install trans, install support on the trans, support with jack, install driveshaft, align it all the best you can, mark holes for brackets, take it all out, drill, reinstall.  (or if you can do it, drill from inside the car and save the uninstall part)

 

i went through this process putting the massive brackets in my M2 (detailed in build thread).  the final install position was NOT the 90/80 "book" location.

 

do a "this topic" search in my thread for "massive".  bunch of pics.  believe they are around march of 2011.

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option No.2 is the way i've done it, with no issues on two separate 02's. 

bmw factory guys did not always weld original brackets on parrellel to the ground.  mine were way off.  using method two would have resulted in the new bracket being WAY too low.  this was why i had issues using the "U" bracket originally and why i went to the solid mount Massive brackets.

And yes, don't weld it solid until you've tried it.

 

Tack weld, sure.  I used a couple of steel pop rivets, and on the 3rd or 4th try,

when it was as good as it can be, THEN I welded it.  The pop rivets are now part

of the weld...

 

t

no welding for me.  i needed mine removeable.  the tunnel is so narrow and the brackets large enough that i cannot remove the transmission without removing at least one of the brackets.

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Thanks for the tips guys!

 

My existing brackets are tilted downward to the back a bit the way Marshall describes his were in the M2 build. As a recovering engineer (don't ask), I was hoping for more precision and to be able to do more up front, but I think I'll be fitting the tranny in a few more times until i am sure it is correct.

 

I think I'll use approach #2 to temporarily locate the new brackets and tack them in (or maybe I'll drill a single hole for temporary placement. I don't want to drill all the holes for the bolts until I am more confident of the final location.  I don't have my shortened driveshaft yet and will have to wait for that to finalize the placement. I'll make a decision on welding vs bolting when I see if I have the clearance problems Marshall was alluding to that might require removing the brackets to remove the tranny.

 

Marshall: Was it you or someone else that was advocating for using a solid metal disk of the correct thickness as a faux guibo to bolt up the front of the driveshaft to the tranny output and locate the center bearing and tranny height (replacing with the guibo later). It seems like it would guarantee correct alignment and that sounded like a slick approach to someone who hasn't tried this yet... Since I have access to some metal working equipment, creating that kind of a disk would be easier than some other approaches.

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