RT Diff Mount install question

[ihiryu]

Okay, I've had my diff mount for some time, and I was looking to do it.  I searched around but could not find on how to do it.  

 

I've seen pictures of it post installation, but how hard is it to do the install?  

 

I'm assuming I'll have to drop the diff (so removing the axles and straps) is that it?

 

[RebekahsZ]

Yeah, drop the whole setup. The fit is really tight. Be prepared to hammer and pry a lot to get it lined up. Second install is easier. Now that I have the RT mount in place, I now leave it up there and just unscrew the two bolts in the diff to remove the diff. But the first time I recommend bolting the mount to the diff and jacking, hammering and prying the diff into place. Lining up the four bolts that connect the mount to the tunnel is the hard part. Dead low hammer and courage are what you need.

[billseph]

^Exactly what I'd recommend too. I just did this a few weeks back, and after several attempts and different orders of operations for installation later, I found that bolting the RT mount to the diff and jacking it up as a unit was best...I did mine along with an R200 swap into an early 240Z as well FUN TIMES!!!!!

 

[bigbore468]

I have a 1976 S30 coupe and installed an RT style mount from Technoversoins last week.  I also got the urethane trans mount that bolts to the diff.

All I had to remove was the front diff mount crossmember and exhaust to install.

One tip is after you remove the two stock diff strap brackets; this is where the RT mount will bolt onto, clean/scrape all the undercoating and dirt from the frame walls.  It will make the installation of the RT mount way easier.

If you have the Technoversions mount, the hardest part was tightning the bolts for the top and diff mounts.  I used a stubby open end to hold the nuts while hitting the bolts with the gun.

Also made spacers instead of shaving down the urethane mount, which dropped the front of the diff slightly more than my last set up; so I had to cut the front diff crossmember for clearance.

There is a thread about this issue in this forum.

Good luck.

Edited February 21, 2013 by bigbore468

[duragg]

It all caused me wicked vibration due to the lower nose of the diff and higher ratio of my rear end.

Still finalizing my angles to this day.

[scott]

I was lucky and did not have to hammer my RT mount into place. It lined up with the differential strap mount holes and I was able to install the bolts. Watch out for your fuel lines and any other wiring or lines that run through the tunnel to make sure they are up and out of the way.

 

If you use the polyurethane transmission mount recommended for mounting the front of the differential, the nose of the differential will be lower than the stock position. This works well for most V8 engine swaps like mine which position the transmission output shaft lower. The lower differential pinion angle aligns the drive shaft u-joint angles and also reduces the overall drive shaft angle. This takes out the vibration caused by out of phase drive shaft u-joints.

 

If you are installing the stock front differential cross-member (which I did), you will need to make a few notches where the heads of the differential mounting bolts interfere with the crossmember

 

If you have a motor and transmission located in the stock position and need the differential front located in same position, then you will need to cut/grind down the polyurethane mount to allow nose of differential to align with stock position (I've tried this on an earlier install and it works to get differential aligned to stock position).

 

With the differential mounted with nose the stock up position, it is possible to install front crossmember without notching it.

[ihiryu]

Thanks for the help, seems a little more complicated than I expected.

 

Car is at the body shop as of now, once I get it back (before paint) the TTT arms and diff mount are going on.  

 

My question is, is there any down sides of leaving it at an angle.  I'm currently running a RB20 swap, and everything stays at stock angles.  If I don't modify the mount what will happen?  Just a bunch of noise I assume?

 

And could you go over how it needs to be modified?

 

Thanks guys!

[scott]

If you want to keep the differential at the stock angle, you should reduce the height of the polyurethane mount. One way to reduce the height is to grind down center part of the mount (a kind of half round notch) so that the mount fits down over the rounded portion of the differential nose. Check the angle of the differential after installing it with the mount and RT bracket and compare to angle of transmission tail shaft. They should be within about 1 degree of each other.

 

You can get a simple angle measuring tool that has a magnet built into it so it can easily attach it to the drive shaft flange on differential and on tailshaft of transmission to measure angles.

 

If the drive shaft u-joints are not at the same angle, you can have a vibration, usually more noticeable at higher speed. I have had this happen. No noise, but the vibration shakes car at speed and it is annoying. It's eventually hard on the u-joints and can be hard on transmission tailshaft seal because it causes the drive shaft to wobble.

 

It's not too hard to grind down the polyurethane mount. I was able to do it with some simple hand tools (hacksaw, files, rasps). Once I got the angles matched, the vibration went away.

[cheesepocket]

I'm still chasing my vibration issues.  I found some pretty good stuff online regarding getting the angles right, here's one

http://www.hotrodhotline.com/md/html/drive_shaft_harmonics.php

though every article I've found assumes a live rear axle whose pinion angle naturally changes as a reaction to the tire torque.  We can set our angles exactly as our diffs shouldn't rotate upward under torque like a live axle would.

Some sites are adamant about measuring the angle directly at the U-joint caps to get a consistent machined surface, this can be done using the right size socket as a spacer.

 

I found some slop in the front u-joints of my nearly new driveshaft, and also discovered the bolt head clearance notches in the forward diff crossmember were not made big enough so the bolt heads were directly transmitting noise to the crossmember.  I'm really hoping these two things are my answer,and then the only other issue is excessive lash through the R200 and/or halfshafts.

 

I'm also going back to factory style rubber mounts for the mustache bar and am testing a factory Camaro rubber mount for the front of the diff.  MIne's a street car and the diff howling is maddening.  I'll document here if this quiets things down well.