engine and drivetrain Yet Another 5-Speed & Driveshaft Alignment...

[bnam]

Reinstalling the newly rebuilt/resized driveshaft on my 74Tii.  Centering or even just moving the diff forward has been a real challenge.  I've moved it about 1/3rd of the way and the gap at the guibo was nearly closed.  I've tightened the joint at the guibo. I'm just a bit concerned that I've not moved the diff to the center of the slot and that's putting some tension on the guibo.  Any tips (that don't involve removing the driveshaft)?

 

Getting alignment between gearbox and driveshaft.  It was pretty even side to side, but there was a gap of about 1.5mm opening up on the bottom as I rotated the driveshaft.  Since the gap was at the bottom, lower the center bearing or raising the rear of the gearbox seemed like the options.  I ended up adding another washer to the top of the rear gearbox mount and that closed the gap to under 1mm.  The bluebook says 1mm is max allowable, so I think I am ok. 

 

The engine and gearbox are inclined rear-ward at about 3-5deg.  Since the 5spd is longer by 9mm, the output flange on the 5spd would be abou 5-8mm lower than on 4spd to stay on the same plane as the driveshaft.  However, since the 5spd is typically mounted at the same rear mount ht as the 4spd (with an extension), it should have ended up 5-8mm higher than the 4spd and should have needed to be lowered (or the CSB raised).  

 

But, my 5spd needed to be raised (or CSB lowered -- I think this is what Hack needed to do) -- so I am puzzled as to why...

 

Byas

 

 

[thehackmechanic]

I did it iteratively -- every time I adjusted the gap in the guibo by, say, lowering the CSB, I then loosened the differential, smacked it with a block of wood and a hammer, and retightened it.

 

I would've raised my transmission to close the gap at the bottom of the guibo/flange if I could have, but I couldn't -- when I raised the trani past a certain point, my fan hit my triple-core radiator.

 

As per my blog post, I'm following Marshall's philosophy -- that things like left/right and up/down placement of the trani really don't matter as long as the guibo / flange alignment is good, so quit worrying about them. Unfortunately, that's not quite true, because in my case, when I last drove my car, the trani was occasionally banging against the tab on the left side of the tunnel.

[M3M3]

when I last drove my car, the trani was occasionally banging against the tab on the left side of the tunnel.

 

was that the leftover tab from the original 4spd trans mount?  i cut mine off the car.

[thehackmechanic]

Marshall, I'm using the U-shaped bracket, so it is both the four-speed mount as well as what is being used now.

[M3M3]

Getting alignment between gearbox and driveshaft.  It was pretty even side to side, but there was a gap of about 1.5mm opening up on the bottom as I rotated the driveshaft.  Since the gap was at the bottom, lower the center bearing or raising the rear of the gearbox seemed like the options.  I ended up adding another washer to the top of the rear gearbox mount and that closed the gap to under 1mm.  The bluebook says 1mm is max allowable, so I think I am ok. 

 

i leave no gap.  

 

The engine and gearbox are inclined rear-ward at about 3-5deg.  Since the 5spd is longer by 9mm, the output flange on the 5spd would be abou 5-8mm lower than on 4spd to stay on the same plane as the driveshaft.  However, since the 5spd is typically mounted at the same rear mount ht as the 4spd (with an extension), it should have ended up 5-8mm higher than the 4spd and should have needed to be lowered (or the CSB raised).     But, my 5spd needed to be raised (or CSB lowered -- I think this is what Hack needed to do) -- so I am puzzled as to why...  

 

you math is not making sense...to me at least.  the tail of the 5spd ends up needing a mount almost a cm higher than the 4spd mount.  at least it did on my car.  i installed engine, trans, driveshaft, csb and diff without a tranny mount.  just a jack under trans.  aligned whole thing, then marked where the trans mount brackets needed to be.  removed everything, installed brackets on tunnel.  in reality the 5spd hits the top of the tranny tunnel before getting to the height needed so the csb has to be lowered to align. 

Marshall, I'm using the U-shaped bracket, so it is both the four-speed mount as well as what is being used now.

ahhh..probably should not cut the mount tabs off then......

[M3M3]

for reference, here is the difference in where my mounts needed to be (before i cut the old ones off.).  the new one is level.  the factory one was not installed correctly at the factory, which was a major issue when i used the U bracket for conversion originally.

[bnam]

 

you math is not making sense...to me at least.  the tail of the 5spd ends up needing a mount almost a cm higher than the 4spd mount.  at least it did on my car.  i installed engine, trans, driveshaft, csb and diff without a tranny mount.  just a jack under trans.  aligned whole thing, then marked where the trans mount brackets needed to be.  removed everything, installed brackets on tunnel.  in reality the 5spd hits the top of the tranny tunnel before getting to the height needed so the csb has to be lowered to align. 

 

Here's how I envision it --

 

 

The 5-speed is longer, and assuming that the output shaft is still located on the same axis as on the 4 spd, the rear mount (red) should be lower on the 5-speed so that the output is line with the driveshaft.

 

However, using the U-bracket, the rear mount is at the same height as the 4-speed, so if this diagram and assumptions are valid, the rear of the 5-speed when mounted with a U-bracket should be lowered (perhaps with a thinner rear mount) in order to keep it inline with the driveshaft.

 

However, in practice, on my car (and it appears on yours and Hack's as well), the rear of the 5-speed had to be raised in order to remain in line with the driveshaft axis.  So, puzzled as to why?

 

BTW, after I reinstalled the drive shaft I took the car for a drive -- to pick up my son from day-care.  As I drove I heard rubbing sound (similar to putting a card into the spokes of a bicycle wheel).  I began to think of all the things that I may have done wrong.  When I got to the day-care, drove one side of the car up a handicapped space parking ramp (lot was deserted) and looked underneath.  I had forgotten to take the bubble wrap around the center u joint and it was flapping (and melting) against the exhuast -- duh(!) but relieved.

Edited January 22, 2014 by bnam

[bnam]

Any thoughts on why typical experience -- needing to raise the 5-speed rear to get alignment -- is opposite of what my diagram would suggest is needed?

Byas

[rms_sandiego]

I think the biggest problem with the diagram is that it assumes the mounts are parallel with the axis of the driveline and that there is no sag inherent in the U-bracket. When I had my tranny out, it was pretty obvious that the two sides weren't even parallel with each other much less with the driveline axis. I think this is an area where there was not the kind of quality control you might see on a modern car.