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true trac writeup

124K views 259 replies 66 participants last post by  Funkycheeze 
#1 · (Edited)
True Trac part number
911A342

Toyota part numbers
90366-35023-77 Inner pinion bearing
90366-30022-77 Outer Pinion Bearing
90368-50006 Carrier bearing (2 required)
90311-38010 Pinion seal
90311-38011 Side seals (2 required)
41182-22011 Cover gasket
41231-22010 Crush sleeve
90179-18001 Pinion nut

Solid pinion spacer if you opt for this instead of the crush sleeve.
https://www.justdifferentials.com/SKCST7-5-p/skcst7.5.htm



First off, you need to make sure you have all the parts necessary to do the conversion. Second, make sure you have a differential with a good ring and pinion. You will need a large bench vise to make this easier.

First drain the fluid from the differential, then clamp the nose of the diff in the bench vise, and remove the nut that is on the nose of the diff. You'll have to use a small punch or screw driver and a hammer to bend the notch out so it will unthread.

Once that is out, slide a long punch/prybar between the differential case and the side output shaft. then smack the punch/prybar with a hammer to pop the output shaft out of the differential. Do this for each side.

Next, remove the 8 bolts holding the cover in place and remove the cover. Now remove the 4 bolts that are holding the center section in place. You'll have to use a long breaker bar or an impact gun as they are tight.

Once they are out, remove the caps, but mark them so you will remember which side they belong to. Also, when pulling the center section out, there is a shim on each side. KEEP THESE!!!! You will need these and may need an assortment of them to get it adjusted right after assembly. Most 4x4 shops can get you a shim pack for a decent price.

Now that the carrier is out, remove the pinion bearing. Remember how everything went together! Take pictures if possible. The outer pinion bearing will slide out from the nose. Now, if replacing the inner pinion bearing, you will want to use a punch and a hammer from the front of the diff and drive the race for the pinion bearing out. If replacing the outer pinion bearing, you will use a punch to push the race out from inside the case.

Next, the differential case needs to be cleaned. You can have it hot tanked at a machine shop, or, do what I did. I put it in a 5 gallon bucket and then poured purple stuff engine degreaser in till it was completely submerged. i let it sit for over an hour then scrubbed it with a stiff bristled brush. there is a black coating on the inside of the diff that will probably not come off. Do not worry about this. After I took it out of the bucket, I then scrubbed it with soap and water to get the degreaser residue off, and to prep it for paint. then i put the ring and pinion gears in to let them soak as well. When painting, make sure to block all the holes for the bolts and also make sure no paint will get inside the diff case.








Now, if you do not have a shop press, you will need to take the True Trac and the carrier bearings to a machine shop to have them pressed onto it. Also take the pinion gear with you to have the old bearing pressed off and the new one on if replacing it. Make sure the shim is left on the pinion gear when they press the new bearing on if these gears came out of the case you are using and you are not changing them. If you are changing gears, you will need a pinion depth shim kit, which can be purchased at most 4x4 shops for Toyota 7.5in differentials. Setting the pinion depth is critical! Once all that is done your almost ready to assemble.






Dave soaked all the bolts and whatnot in carburetor parts cleaner for several minuets to remove all the gunk that was on them. I have found that a sonic cleaner with HOT water and a little bit of Purple Power, or dawn will work as well. Next, you will need a seal/race install kit(Brass punch in a pinch) to drive the new pinion bearing race/s into the diff case. Make sure you do this carefully as it must be perfectly straight, and you do not want to damage the surface that the bearing contacts. .



Once they are in, slide the pinion gear in, then put the new pinion seal in and make sure you slide the parts back onto the pinion shaft in the correct order(remember the pics I said to take?), and make sure you put the new crush sleeve/solid pinion spacer in there and not the old one. Be sure to use the new nut use a new nut. If using a solid pinion spacer, you should be able to measure the length of the OLD crush sleeve to get a starting point for the shims that come with it. You likely will need to add a small amount on top of this thickness to account for wear and tear on the original crush sleeve. Adjust until the preload on the pinion bearings are correct.

Once together, you need to very very slowly tq the nut (if using crush sleeve) until it takes ~3.5-5.2inch lbs for a used bearing or 10.4-16.5inch/lbs for new bearings to turn the pinion gear. If you tq it too much you must pull the nut back off and get a new crush sleeve so be very careful. Too much preload on the pinion bearings will destroy them very quickly! If using the solid spacer setup, once the bolt is tq'ed, check the preload. If it is too low, add another shim. if it is too much, remove a shim. Repeat until it is correct!

For he solid pinion spacer, Marlin Crawler says to hit the nut with the impact. Yotatech says about 90lbs. For Ford 7.5, 8.8, 9in diffs, the tq spec is 125ft/lbs. Your call.

http://www.ratechmfg.com/fordspbs.htm

Next, you will have to use a small flat head screw driver and a punch to bend the little tabs back that lock the bolts that hold the ring gear to the center section. then use an impact gun to remove these bolts. Then you need to use new tabs when bolting the ring gear to the True Trac. The bolts need to be tq'ed to 71ft/lbs, then push the locking tabs up against the nuts as they were before.

Next, insert the True Trac in with the races on each bearing and for starters use the shims you had removed before. The shims are used to adjust end play and the preload on the carrier bearings. The preload should be ~3.5-5.2inch lbs as should the total preload. The backlash should be 0.0051"-0.0071". You may need to install different thickness shims to ge the preload right, and adjust them to move the carrier from left to right or vice versa to make sure the "wipe" pattern is correct. Once the right end play and preload is set install the caps and tq them to 58ft/lbs and recheck that the preload and backlash are still within spec.










Use a new diff cover gasket and coat it lightly with ultra gray rtv sealant. It is best to rub a lil on your fingers and then smear it on the gasket so that there will be no excess to squish out. Then install the diff cover and tq the bolts to 16ft/lbs. Reinstall the axle stubs, and then fill the diff with the proper amount of fluid, and its ready to be installed.

I used standard 75-w90 for the initial break in then switched to Amsoil Extreme duty 75-90 synthetic after maybe 1,000 miles.





Here is a very helpful link.

http://www.cygnusx1.net/supra/library/TSRM_MKII/ra/RA_018.html

http://new.photos.yahoo.com/williamb82/album/576460762348387882

This is why I needed the True Trac.







 
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#209 ·
Update for those who care...

Even with the new bearings, I'm going to have to make thicker shims (~.030in now) to get the backlash correct. It appears Seamus' issue is not an isolated event and the new 342/644 is NOT a direct replacement for the old 342. Lastly, $50 for shims was a drop in the bucket for this project.
 
#210 ·
Yup. Most everyone will need new shims if you've changed ring and pinion or if you install a new lsd case that varies in thickness at all from stock. You technically don't need thicker shims, you need to slide the carrier assembly left or right to set the backlash correctly, so one thicker, one thinner. The issue with the 644 trutrak is they shortened the damn case. Toyota didn't make shims thick enough to compensate for the difference, I seriously doubt the Yukon shims are any thicker then the thickest Toyota ones, and even if they were you need a lot more then a couple sizes up. Custom shims from a machine shop, cha ching!
 
#212 ·
Ah. That almost would have worked for us. The thickest Toyota one in the book is .127. We needed something about .132-0.136. With our stock shims, we were short .032 too.

And for anyone thinking they can run 2 thinned down shims per side, good luck with that. You would be hard pressed to find a machinist who can machine something down that thin. Their tooling has to have a way to clamp onto the part. Not saying its impossible, but for most it will be easier to just make a new shim like our guy did.
 
#216 ·
So I have a question about the carrier bearings. I'm getting ready to re do my 4:30 diff as it's out. I'm going to do the solid spacer and weir maxgrip kit. Just wanting to get things straight before I order all the bearings needed

the part # listed is 90368-50006

Everything I've looked up has # 90368-45002
Has 45002 been discontinued and 50006 what's being used as a replacement?

Also would it be a good idea to go ahead and replace the rear pinion (outer) bearing while I'm in there? 90366-30078-77
 
#218 ·
I checked a few online toyota parts dealers. The part # I kept getting online was 90368-45002 for the carrier bearings

The one listed in the guide on page one is 90368-50006. Just trying to make sure which one it is before I order everything
 
#220 ·
The carrier bearing part numbers listed in this thread are NOT for the stock LSD. They are for the truetrack, which has a larger inner diameter for the carrier bearings.
 
#222 ·
My delimna is the ring and pinion. I have been through 2 roaring/whining diffs and don't want to waste money on another one. My opinion is that they will last if you drive them on the street but if you take them to the dragstrip they just won't hold 400 hp after 5 to 10 runs. I have followed several posts and most of them are complaints about theirs whining also. My second one came from someone on these forums everyone raves about but it roared the day I put it in and after making a few runs at the dragstrip it started roaring so bad I was embarrassed to drive it through my neighborhood.

If I do decide to go back with the same thing (which I don't want to do), do we have a Toyota online guy we can buy the parts wholesale from?
 
#223 ·
My used 3.73s have been super quiet behind 550+ horsepower even after track days etc. It is all in the setup, and I use a 80W140 gear oil due to the extra heat.
 
#226 ·
I don't do drag racing much - more roadcourse lapping. Years ago I ran a 12.1xx at around 125 mph. If your replacement ring and pinion that 'roared' right after installation didn't have severe preexisting damage, then the set-up was not correct.
 
#227 ·
Who set it up? There are a million DIY diff rebuild vids on Youtube, but you can not learn all of the ins and outs just from watching a vid. I do everything myself, except diff setup. I take mine to a buddy who is a Toyota tech and does these at work all day. I've done enough with him to be comfortable doing them on my own now, but when I have one that really needs to hold a lot of power, I'll be going back to him.
 
#228 ·
Pinion preload is key to a quiet diff. Get it wrong, and it will howl like crazy! Carrier preload is important too, but most howling is due to the pinion.
 
#229 ·
And contact pattern, especially if you are swapping different gears into your housing. I have found to get a good pattern on used gears you often end up with backlash on the high end of the spec, which is fine.

Pattern on both drive (especially drive) and coast should be as good as you can get it, and pinion preload needs to be accurate (recommend a solid spacer here). Side shim preload should be set so that the second 'washer' shim you install can go in about halfway by hand and tapped in the rest of the way with a brass drift and hammer. Backlash spec is .003 to .007 but I find used gears usually end up in the .005 to .010 range when the pattern is perfect. Any adjustment in backlash affects the pattern as well. Spec for the truck 7.5" diffs is .003 to .010

3.73s in my Supra ended up at .009 backlash with a perfect pattern both sides and are whisper quiet even with all the poly in my car and minimal sound deadening. Many track miles on that diff too - again I use an 80W140 oil and 'bellows' style sealed diff breather due to all the heat in a diff that only holds around 1 liter of lubricant.
 
#230 · (Edited)
Update:

For those who have issues with the truetrac case being too 'short' and not a thick enough side washer being available from Toyota, you can put a shim under the side carrier bearing (between the bearing and truetrac before you press the bearing on). You would put it on the side closest to the ring gear if your backlash was still way out of spec, or on the other side if the backlash is in spec but you can't get a washer thick enough to get the proper carrier bearing preload.

Here are the shims I used (.010 thick ones are also available, I chose .020 to put me into the middle of the available washer thickness ranges when close to the correct backlash setting, based on how much backlash it had with a thick washer):

https://www.amazon.com/gp/product/B003A03P9A/

And here are some pics of where to put the shim. A good bearing puller is needed to remove a carrier bearing, and you need to make sure the bearing seating surfaces and both sides of the shim are very clean before pressing the bearing back on.

https://drive.google.com/open?id=16aAfzWBDmzJ1g0k_I5H1ssTRf9FYIfbn
https://drive.google.com/open?id=1S7-EZW4S5hNuWpHjbmi8KeR_100gDKq9
 
#232 ·
Yep his diff is all within spec now. As shown though, I had to shim under the bearing .020" to then use factory size spacer washers when fitting the center section into the housing.
 
#235 ·
So after Ryan (funkycheeze) was able to bestow his magic upon my differential, I discovered an interesting situation which I have not previously seen brought up before in this thread.

The stub shafts do not go far enough into the truetrac receiving gear for the clips to snap into place. Put another way, the stub splines are not long enough. What this means is that I am able to pull out the stub axles with medium effort as they are not locked into the differential housing.

A dude called Dustin did have this issue a couple years ago with a different differential:
http://www.celicasupra.com/forums/s...lips-needed!!!&p=850643&viewfull=1#post850643

He discovered that LSD and non-LSD differentials have different length stub axles. The wording in that thread is a bit backwards - it's not 100% clear which of the stub axles is shorter - LSD or non-LSD. My differential was originally an LSD, and at least conceptually it makes sense that LSD stubs might be shorter due to the larger LSD centre section inside the carrier.

So off I go onto the internet and I verify that yes indeed, there are two stub axle part numbers:
https://www.toyodiy.com/parts/p_U_1985_TOYOTA_CELICA_MA61L-BLPQFA_4101.html
41334 SHAFT, REAR DIFFERENTIAL SIDE GEAR
41309-14010 W/LSD 2 $275.14
41309-22012 2 $262.05

I tried to find pictures on the internet of these parts with no success. But... check this out:
http://trdparts.jp/english/parts_lsd_mechanical.html
take a look at CELICAXX
"For vehicle with optional L.S.D., Exclusive side gear shaft required. (*4)"
and... *4 41309-22012 2 Toyota Genuine Part "0"

This looks to me like the TRD LSD requires open-diff stub axles! This would correlate with my suspicion that the LSD stubs are shorter.

So... does anyone have any open-diff stub axles they can compare with LSD stub axles? measurements of overall shaft and spline lengths to compare will be valuable.

I've been running my diff in this manner for two years with no issues, however I'd like to understand what options are out there.
 
#236 ·
Makes sense. The diff I installed the true trac in was a 3.727 non-lsd from a Cressida. Mine locked into place without issue. The snap in place sound was clear as day when we installed the stub axles.
 
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