Differential Rebuild - Truetrac, 1310 U-ioints

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  1. #1
    CelicaSupra.com Member Tire Shredder's Avatar
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    Differential Rebuild - Truetrac, 1310 U-ioints

    Hi Everyone,

    My supra's differential had become worn out in recent years, with my major complaint being LSD performance. I've been avoiding it due to cost, and suggest you be prepapred before taking on this project. I was fortunate enough to receive a bonus from work which eased the pain, so I decided to pull the trigger on a differential rebuild with the best parts I could find that would suit a turbo build in the future. Little did I know the 7MGE would soon die, so I have yet to use it yet.

    When I looked at the tools required, and my inexperience in reading a gear pattern, I decided to have a pro do the work. I enlisted Ken Francisco in Arizona (www.gearinstalls.com), somebody I had found when doing research on the truetrac and how to adapt the FWD version for use in a RWD vehicle. I was very impressed with his write-ups, attention to detail and general attitude displayed on his website. He had a great reputation on toyota 4x4 forums and thought it was worth a shot.

    As per usual with modifying old cars, things don't always goes as planned, including learning new 4.10 and lower gearsets are discontinued, despite what online vendors may have you believe. This snag drove me to purchase 3 different gearsets (that didn't exist) requiring lots of communication with Ken, and a good deal of patience on his behalf to sort out, of which I can give nothing but praise. All told I think 50 emails were exchanged, including regular picture progress updates - just excellent! Ken was able to quickly locate a good used gearset locally, and it all worked out in the end. Quality of work appears to be great and his price was reasonable. With the exchange rate and shipping, the bill was significant, but these parts are too expensive to risk on poor workmanship and I consider it cheap insurance.

    He recently provided a write up that would be useful to the community, including directions on how to flip truetrac gears. This post is intended to capture what Ken didn't. YOU CAN FIND IT HERE. I have also saved a copy locally, so if you are reading this post years after I posted it and Ken's site is down, shoot me a PM and I can send you a copy, or potentially re-host it.

    The diff is equipped with a solid spacer from Weir, flipped truetrac and a NEW flange to accept a spicer 1310 joint. I found it difficult to track down all the parts info including specs on the driveshaft interface, so hopefully this is useful for somebody else:

    Parts List
    BRAND DESCRIPTION PART NUMBER QTY
    TOYOTA Inner Pinion Bearing 90366-35023-77 1
    TOYOTA Outer Pinion Bearing 90366-30078 1
    WEIR Solid Pinion Spacer T7.5SPS 1
    TOYOTA Pinion Staked Nut 90179-18001 1
    TOYOTA Carrier Bearing 90368-50006 2
    TOYOTA Pinion Seal 90311-38010 1
    TOYOTA Side Seals 90311-38011 2
    EATON Detroit Truetrac 911A342 1
    YUKON GEAR Pinion flange ***optional YY T35050 1

    The Gears
    I wanted quality new gears to reduce the chance of noise. 4.10 was the tallest ratio listed for most manufacturers but should have given good performance around the city. My preference was as follows:
    1. G2
    2. Nitro
    3. Yukon
    4. Motive

    At one point in time I had paid for one of each brand from various suppliers. What I learned is that there are only 2-3 gear distributors that all these online vendors use to warehouse parts. Despite what their websites say, they were not available. The Nitro gear distributor told me that modifying toyotas is becoming less popular, and those that are, install larger tires and need shorter gears. In order to re-stock, they would need to complete another production run, which requires a vendor to place an order of a minimum of 100 units...(so don't hold your breath). Ken was able to locate a used set of good condition 3.73s from www.justdifferentials.com - They upgrade trucks frequently, and give customers credits for their used gearsets and may be worth checking out. In a nutshell, it's used gearsets for us from here on out. Things may change in the future but do your own due diligence before handing out any cash.

    The LSD
    Some of the part numbers floating around in the sticky thread are a bit outdated and the combination of bearings required is also confusing. The parts list above is the current state of required parts. When you order a 911A342 diff, you actually get a 911A644 as was engraved on my diff. Curiously, most vendors show the 911A644 as unavailable. These parts are apparently interchangeable. I have not had both in my hand at the same time, so I can't say if there is a difference, if any.

    Diff Lubricant
    There's mixed information regarding this floating around online, and even conflicting information published by Eaton themselves. While older documentation states that synthetic lubricants are to be avoided, newer documentation and videos acknowledge the use of synthetic lubricants to be acceptable. I believe this older documentation assumes that all synthetic lubricants contain friction modifiers. Although this is a common and reasonable assumption several do not. If you do desire synthetic lubricant, you must be careful which one you select. Regardless, GL-5 compliant fluid is a must. The Differential Manual addresses some of these concerns.

    The FAQ section appears to be copy and pasted from older documentation:
    "Truetrac units perform best when using GL5 mineral / petroleum based gear oil. Synthetic lubes are discouraged. Do NOT use friction modifier additives or lubes formulated with friction modifiers. See the “Lubrication” section of this product manual for further details and specifications."

    And yet, within this very same manual, in the lubrication section, you'll find that synthetics can be acceptable:


    "High quality mineral or synthetic gear lubes are required for use in Detroit Truetrac differentials.Regardless of the lube type, always use a GL5 rated lube with the least amount of friction modifier. Mineral lubes lacking friction modifiers (limited-slip additives) were historically recommended for all Truetrac applications because friction modifiers can slightly reduce the bias ratio (limited-slip aggressiveness) of Truetrac differentials. However, to address the continually increasing power outputs of modern powertrains, many vehicle manufacturers have switched to synthetic lubricants as a counter measure for increased axle temperatures and prolonged service intervals. In general, consult the vehicle owner's manual for the manufacturer's recommendations for lubrication type, weight and fill volume. This will ensure lube compatibility with the seal materials and bearings used in the axle. Eaton Performance technical support is available for any concerns in lube selection"



    While this video with an Eaton representative states fluid flexibility as a selling feature and excellent performance with either synthetic or petroleum based lubricant.

    I've chosen to go with a synthetic GL-5 oil that does not include friction modifier, Redline 75w90 NS (it's the NS that's important!) time will tell if this was a good decision, but I'm feeling pretty lucky.


    The Input Flange / Driveshaft
    If you intend to run over 400hp, tribal knowledge on the forum is that you should upgrade the size of your driveshaft's U-joints. With that, typically goes an R154 transmission and a custom length (or mk3 hybrid) driveshaft.

    The driveshaft Flange-Yoke typically used with the popular Spicer 1310 is Spicer 2-2-1679

    This flange has a bolt circle diameter of 3.344" and bolt diameter of 0.406" ...commonly referred to as a 60mmx60mm pattern common on many Toyotas. There are a few ways to get this bolted up to your MK2 diff:

    1) Re-Drill the flange via machine shop. I've heard it's been successful but looks sketchy to me (and I'm an Engineer!)
    2) Used Toyota 2WD Flange. Usually referred to in only that much detail. Really, you want an input flange from a 1988 to 1994 2WD Toyota Pickup - they have 7.5" differentials as well.
    3) DriftMotion Adapter - I believe this also has the 60x60 pattern but worth double checking. This adapter would be useful if you've already built a differential and don't want to lose your carefully set pinion bearing preload.
    4)New Yukon Gear Input flange P/N: YY T35050 To my knowledge, I am the first in the mk2 community to try this. I decided on this option to avoid junkyard hunting. There is no data or images of this part posted online and Yukon's customer service was no help. I took a gamble and it paid off. It fits perfect on our diffs and should fit up nicely to the spicer flange yoke. Flange length is the same as the stock mk2, but facilitates the spicer flange yoke with no modifications.

    Side Note: R154 slipe yokes for the transmission side are commonly available from Dana/Spicer. Your driveshaft supplier should need no more info than that to get you setup. I'll be purchasing from Shaftmasters.comas a complete unit but Driftmotion also carries a standalone part

    I will update this post with more driveshaft data once I measure and receive mine

    Pinion Flange Bolts
    The truck/1310 flange requires larger bolts than the stock Mk2. I recommend ordering genuine Toyota fasteners. They are high grade, the correct length and include careful design consideration for the bolted joint - the flange bores are exposed only to unthreaded bolt shank to improve shear strength.

    BRAND DESCRIPTION PART NUMBER QTY
    TOYOTA Pinion Flange Bolt 90080-10294 4
    TOYOTA Lock Washer 90560-10H00 1 (package of 4)
    TOYOTA Flange Nut 90080-17239 4
    Last edited by Tire Shredder; 12-14-2016 at 01:21 AM.
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  3. #2
    CelicaSupra.com Member drjim's Avatar
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    Great information.

    - Jim
    1985 5-speed "Ms. Swan"

    OH, What A Feeling!

  4. #3
    Whistles racerxj220's Avatar
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    Several V8 guys have said GL-4 works fine running 9's or better. Even with synthetic.

    I had GL-5 in mine last time, and I did see some very fine residue on the drain plug.

    I've got some Brad Penn GL4 classic in it now for my high HP build.

    If it blows it blows. Not really a lot in the oils that's going to make or break them, IMO.


    I always thought the "new" flange was from a MK3 supra. I probably keep remembering incorrectly. Jawsgear built my truetrac and my driveshaft about ten years ago.

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  6. #4
    CelicaSupra.com Member Jazzyfizzle's Avatar
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    Very nice info here! I will be Pm'ing you when i rebuild mine.

  7. #5
    CelicaSupra.com Member Don L.'s Avatar
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    Awesome write up! Great info and should be retained by all. Thank you!

    Don L.

  8. #6
    CelicaSupra.com Member SupraFiend's Avatar
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    Nice post, that Trutrac thread is horrendous to use these days.

    There were different TruTracs available to us over the years, we even had one built for rwd use at one point. The 644 was listed as the best one to order at one point. Maybe they only make the 342 now and you just got some old stock? I'm not sure, but the one we did a few years ago was a 644 as well.

    Pretty sure others have run that new flange, Ryan should see this post soon and clarify.
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  9. #7
    Member rycrok8's Avatar
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    I bought a truck flange from low range off road and drilled it to fit a Dana Spicer 2-2-349 DODGE Flange Yoke.
    "1 TDT-TDFTC Triple Drilled Flange W/Dust Shield for Tcase "
    Haven't installed yet, but here's to hoping.
    drilled out to larger bolts, 7/16" , and will be using high grade.
    Making a custom 3" driveshaft with 1310's all around for my higher HP so it'll be all sized correctly.
    Saving now for my tru-trac... looks like summit has the better pricing.
    Now to get rid of that wheel hop.

  10. #8
    CelicaSupra.com Member Funkycheeze's Avatar
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    Yeah I use a flange for a 1310 joint. You can get it from quite a few Toyotas, 2WD truck rears that are 7.5", and any 7.5" front (normal or reverse rotation). I got a flange with bolts from a yard for like 20 bucks.

    Also those old 2WD trucks are a good source for tall gears - most are 3.73 or 3.52 and have minimal wear due to the low power output of the 22R.

    For diff lubricant I definitely noticed the difference between oil with a slip additive and without - much better lockup without it. I use a 75W140NS as the diff gets hot on the roadcourse, and it keeps it quieter on the street, too.

    One side note - I have not bothered to flip the gears in my truetrac but it seems to be working just fine even after over 60,000 km of use - plenty of lockup and no strange wear on the unit when I had the diff apart a couple months ago to replace a pinion bearing. How important is this?
    Last edited by Funkycheeze; 12-16-2016 at 05:06 PM.
    '84 P-type, 5spd, torrid red, black/grey leather
    Built 7MGTE (JE's, ARP studs, MHG), BOSS STG4 60mm, AEM standalone, R154, 2 1/2" IC and 3" turbo back - the works
    Coilovers, ROH wheels, 4 corner BBK, Konis, ADDCO bars, PST bushings etc. etc.

  11. #9
    Boosting Mod SilverMk2's Avatar
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    Marlin makes a pretty inexpensive flange that has both bolt patterns on it. Also I'm pretty sure the flange new from Toyota is cheaper than that Yukon flange FWIW.

  12. #10
    CelicaSupra.com Member Funkycheeze's Avatar
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    Toyota PN for the flange is 41204-35050

    Might be a bit less, but still probably around $100. As a side note, some people have been reporting that the truetrac is a bit 'short' now, necessitating a carrier bearing shim on the ring gear side larger than any available from Toyota (in most cases around .020 to .030 thicker than the largest available). My recommendation in this case is to use a 50mm ID shim, 1mm thick behind the carrier bearing on the ring gear side of the truetrac. This will reduce the shim thickness needed by .039 so you can still use Toyota shims to get a good set-up.

    I have found when using old gears that getting a good contact pattern is most important. Often you will end up on the high end for backlash (.006 to .010) with a perfect pattern, and this is fine as long as you really need to force the second side shim in - lots of carrier bearing preload is also important. I can usually get the side shim about 1/3 to 1/2 of the way in by hand, then the rest with a brass drift and hammer. Keeps the ring gear from tilting away from the pinion under load and changing the contact pattern.
    '84 P-type, 5spd, torrid red, black/grey leather
    Built 7MGTE (JE's, ARP studs, MHG), BOSS STG4 60mm, AEM standalone, R154, 2 1/2" IC and 3" turbo back - the works
    Coilovers, ROH wheels, 4 corner BBK, Konis, ADDCO bars, PST bushings etc. etc.

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