Installing my new Diff

Aloha,

I'm finally to the point of installing the new diff in my 89 TR and I'm setting it up to test the preload. Just to get a starting point, I installed a shim behind the LHS cover bearing cup that was the same size as the one that came out. I also used the same shim under the RHS cover. The crown gear is not installed.

I have 3/16" play! That's huge! This diff is flopping around in there with that much side to side movement.

I thought I might have to re shim this whole thing but that's a lot of room to make up.

Has anyone else had this experience when replacing the LHS cover and installing a new diff?

I know I'm not missing any parts so I assume either this side cover is much shorter or the diff is.

 

I can not say something about this cover.

but the diff may have NO play. it must have a little bias. not as much as F says. a little less would be better ( my own experience ) because then there is less stress on both side covers

 

When Rob in Australia replaced his side cover he had a very similar problem.
In the end he had shim thicknesses on the limit. I suggest you drop him a line to see what he did. (uzz32soarer).


P

 

I sent him a PM but haven't heard back from him yet. In the meantime, I SCORED!! I went to a local repair shop that specializes in Chrysler differentials. The owner opened a drawer on his toolbox and there were all the shims I could possibly need and they were the right size. Exactly the same as the F shims! I should have my preload finished today!!!

 

Scott, check your email.

Rob.

 

Aloha and happy Saturday!

OK, after getting the correct bearings I'm almost there. However, I have a couple questions about setting this up. First, here's where I'm at:

When measuring preload using the hand scale tied around the axle flange, and the ring gear installed, I get between 38 and 40 lbs to rotate. Is that a good number? I used the original shim thicknesses before I installed the ring gear and it felt perfect. After installing the ring gear, things were bound up with those shims so I added .75mm to both shims and I'm currently getting about .010" backlash. I know that's too much but it's close. I'm using 3 stacks of feeler gauges under the right side cover because I don't have those shims yet.

Question 1. How important is it to have both side covers and the ring gear bolted down to torque spec using all nuts and bolts while taking measurements? Can I just install a few and torque them close? Obviously I am measuring, and measuring, and measuring. So the closer I get to "correct" the more nuts and bolts and torque spec I will use. Is this going to mess with me in the end or should I be OK? That backlash measurement is just so darn small...

Question 2. How much will lubed bearings make for the preload? Should I just lightly coat them with gear lube? Obviously dry bearings will cause resistance but is it enough to be relevant?

I will post a pic of my gear marking compound swipes after I get some good answers here. SteveM, Newman, Aussie Rob, PhilW, all you experts please chime in!

Thanks!

 

sorry please that I answer and not yet one of those you asked

1st question: to measure it rough it is ok only 4 nuts to get an idea how much shims you need. but when you are coming to finish the adjustment you need all nuts

2nd question: just put a little gearoil to the bearings

 

Hi Scott ... GOOD LUCK !

And we would (already NOW) some pics please ...

Will you also "Blue" the C&P when installed ?

 

Got it. Thanks for answering. There are a lot who've done this job so I'd like to hear from anyone willing to share their experience.

One thing that was mentioned was to heat up everything with a heat gun to simulate running conditions when taking the final measurement. Opinions on that? Fmanual doesn't say anything about temp when measuring.

It's been a long hard week and I'm just getting back to this so if I'm redundant, I apologize.

 

Here's where it is at the moment. I'm going to reassemble shortly and do some "painting".

More to come.
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I would not heat something because the numbers F gave is for normal room temperature.

the only part I always warm are the bearings for the diff before I replace them.

about those 38 to 40 lbs I´m not sure but will have a look tomorrow

 

Here we go. Let me know what you think.

I have .004-.005" of backlash.
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Lots of things to discuss here.

First, oil it all up. Get oil into those bearings.

All bolts need to be done up to torque to get FINAL numbers.

If you are close and everything is nice and tight the way the manual says, then heat up your casing with a heat gun to 75 deg C. You will be amazed at the changes, it will become as loose as loose.

I don't care what the factory manual says, the only way to do this properly and maintain nice tight specs when the car is at operational temperatures is to make right when the case is heated up a bit.

If not, you may feel the backlash in the diff as you come on and off the throttle when the system is at operating temps.

There is a certain 'feel' to setting one up. Put two CV joint bolts into the flange and try and turn by hand. With the case warmed and everything done up tight, you should be able to turn that diff using the two CV bolts. It should be loose enough that you can turn it with one hand, but you should not be able to 'flick' the diff.

Hard to describe, but there must be constant resistance so no matter how hard you try to flick spin the diff, it has too much resistance to do that. ie: no inertia on it's own. But it can't be too tight that you can't turn it with one hand.

When you think you have it right with a cold housing, then heat it up and you will flick spin the diff pretty easy. Way too loose at this point.

 

Rob, What did you base this statement on?

Please read the last post with the pics of the marking paint. It's much tighter now and I want to know what you think of those pics.

I started with original shims 2.7mm left and 1.7mm right. This gave me a perfect preload.

After installing the crown gear, I had to add .65mm to both which gave me a .127mm backlash. That's within spec and it feels good.

 

You don't want a diff that will loosen up too much as the case expands. The heat soak is amazing. You have an engine sitting on top of the gearbox and a set of headers running a few inches past the entire length of the casing. It's going to get hot and really quickly. Basically, if you do a proper warmup before driving then your case has already started to expand.

You will feel backlash as you come on and off the throttle if it's too loose. And that will drive you insane.

 

Fchat seems awfully quiet today....

Would some others please post their experience setting up the diff? Specifically what shims did you end up with. My concern is I'm so far out of spec compared to everyone else, I'm not doing something right.

My original shims before diff went nuclear: 2.7mm Left 1.7mm Right (Currently this gives me perfect preload without crown installed)

With crown installed 3.35 mm Left 2.35mm Right. This maintains the preload and gives me .127mm backlash. (.005") That is within spec but seems excessive on the shims.

Aussie Rob provided me with these shim measurements for 3 cars he's done:
Car One: Inner - 2.45mm Outer - 1.50mm
Car Two: Inner - 2.58mm Outer - 1.33mm
Car Three Inner - 2.65mm Outer - 1.60mm

Also, I was concerned about case stretch but after Romano in Germany confirmed that a case he had was exactly the same width as mine, that theory is out.

All things being equal, I should end up with the exact same shims, or close, as what was removed. Since the original shims give me a perfect preload, the only explanation, unless I'm doing it wrong, is that the new diff mounting surface for the crown is about .65mm "thicker" to the left. Has anyone else had that experience with a Forza Components diff?

Hey Rob, I'll heat it all up after I'm comfortable with the answer to these questions.

 

The specs any factory give you is with a cold unit on the bench. They have calculate the heat up in their design. I wouldn't heat up, I never did on anything unless they told you to do it. I've never done a TR diff but the tooth pattern look a bit on the toe. With a little more backlash it would center a little more.
JMO. Wait for the TR experts to answer.

 

the yellow color seems much better than the blue and pink I have here.
but the footprint of the gears are really not ok. as I see it the pinion has to move in driving direction more to the front of the car. where the footprint are just now is too much to the center of the diff

look at the pics how it has to be

on your pictures there are not all nuts at the side cover on! so you will not get right marks of the gears

also I still wonder about those 38 to 40 lbs??? only lbs is no torque, only weight.
in the WSM there stands 3,1 to 3,3 Nm, those 40 lbs then are about 4,5 Nm, so too much.

AFAIK: 8,8508 in.lbs = 1 Nm - right???
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You may find this helpful... lots to confirm prior to the marking paint.
Rgds,
Vincenzo
[ame=http://http://www.youtube.com/watch?v=dAqAqODmcj4]Differential Ring and Pinion Gear Setup[/ame]

 

this may help....
Rgds,
Vincenzo
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Remember you are also using an aftermarket carrier and just a light difference in the bearing height will make a massive difference.

Also, my car had 2.65 / 1.60 with the stock diff and carrier and ended up with 3.43 / 2.45 with the Forza Diff and Capristo carrier.

I measured the Forza diff to be 100% exact as a Ferrari M diff that I also have here, and put mine down to the bearing height in the aftermarket carrier and maybe a slight expansion of the casing.

 

Funny, I watched that video quite a while back. Although informative, it doesn't really apply to the TR. Concept is always the same but the application is quite different.

Thanks though.

 

Now I'm feeling a lot better about where I'm at. I read those original number to be your final numbers. Now that I see you had to shim even more than I will in the end, and the fact the we are using the same brand diff and cover, I think I'm on the right track.

 

Thanks for all who had input today. It was all helpful. I'll try again tomorrow to get a little closer and be more accurate.

More to come.

Scott

 

Correct Robert: also my new (exellent) FORZA diff had exact the same dimensions as the OEM ...