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Thread: MS85 Diff upgrade

  1. #1
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    Default MS85 Diff upgrade

    Hi boys and girls!

    i'm new here - have been searching for answers for a while but no luck, so I'll just put it out there!

    I own an 1975 ms85 toyota crown, beautifully ugly, and very slow. but, like a walrus, you want to get out of the way when it comes charging towards you!

    I want to get a bit longer legs out of her, as the 3 speed auto does it's job, but does rev pretty hard on the highway.

    I was wondering if anyone could recomend a straightforward diff conversion. the current engine bay sticker says trans/axle - A30 F082

    So I figure I have the F series diff which is a 4.1. what vehicles should I be looking at salvaging a better diff from (for highway cruises?) ?

    I don't mind not having any acceleration - It's a very torquey motor so i figure it'd be able to handle an upgrade.

    Thanks In advance,
    Rainman

  2. #2
    Junior Member Conversion King TheStitt's Avatar
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    Default Re: MS85 Diff upgrade

    Lowest factory ratio for the F series is the 3.55 from a Ra65 manual, you can also get 3.7 and 3.9 I'm pretty sure.
    You can also get aftermarket ratios for them ebay should sort that, though I persoanlly havn't used an after market gear set.

    Your plan would be to wrecker hunt check diff codes and pull a F series from another car IRS or Live axle, take both centres to a diff shop and get the required crown wheel pinion combo to your centre.

    I also assume you still have the M motor in the front your not after a strength increase just a ratio change.....
    ST177 UZS131 Crown Royal 'G' the pimping limo like daily 1UZFE 144rwkw

    DST17T MS53 68 Crown Custom Wagon 7MGTE 266rwkw

  3. #3
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    Default Re: MS85 Diff upgrade

    Thanks for that, TheStitt!

    yes the motor is the original 4M, I want to keep mods pretty stock. I'm not bothered if it's slow!

  4. #4
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    Default Re: MS85 Diff upgrade

    Another alternative is to keep the diff and move to a 3 speed auto with overdrive from a later model Crown. This was the setup in my step-dad's MS83 wagon. I think highway cruising was 1800 revs at 100km/h. On the 110 series Crowns that came with said gearbox it is designed to work with the higher ratio diff (4.1 from memory), so should have taller gearing to boot - but I could be wrong.

    I think ClassiCrown used to list information like gear ratios before Microsoft kind of turned everything on it's head with "Multiply".

    Cheers,
    Brendon

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    Default Re: MS85 Diff upgrade

    Thats interesting, MS112.
    Does it bolt right in? I wish I had known before the car got stolen and when recovered, the gear box was blown up and I had a bitch of a time trying to find an original A30 gearbox... other than that it was ok, just smelled funny :-)
    R

  6. #6
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    Default Re: MS85 Diff upgrade

    I have not done the swap myself, but I can say a few things:
    • The bellhousing bolt pattern will be the same.
    • There is a very good chance the gearbox crossmember will be the same.
    • In fact, the 3 speed (with overdrive) gearbox that was swapped into the MS83 was then used to replace the failed gearbox in my MS112, so definitely interchangeable.


    On that last point I also tried to use the tailshaft from said MS83 in my MS112 but it was incompatable. I think the tailshaft-diff bolt pattern was wrong. But the gearbox worked with either vehicle with no modifications*.

    *The MS83 of course needed to have the overdrive wired up for it to work - it's a solenoid on the side of the gearbox which controls it.

    Edit #1: I will of course check with my step-dad to make sure the above is all correct and that no physical modifications such as changing the tailshaft length were needed.

  7. #7
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    Default Re: MS85 Diff upgrade

    Interchangeability of gearboxes confirmed.

    Gear ratios of A43D from MS112 can be found here: http://personal.utulsa.edu/~nathan-b.../1descript.pdf

    Unfortunately I cannot find the gear ratios for the A30 gearbox you mentioned.

    Cheers,
    Brendon

  8. #8
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    Default Re: MS85 Diff upgrade

    All you need for the conversion will come from an MS112. The box and torque converter bolts up to the engine. (may need to use the MS112 flex plate) Use the MS112 rear cross member as the 4sp auto is longer. Use the MS112 tail shaft and change the flange on the diff to suit. (or swap diff centres over) Use the oil cooler lines from the MS112. Your T-bar shift will bolt straight up. There will be wiring changes needed to connect the neutral start switch and reverse lights. Also the overdrive will need to be wired up.

    Sounds like a bit, but its all pretty easy work and you will love the result when you are cruising on the highway at a reasonable rev.

  9. #9
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    Default Re: MS85 Diff upgrade

    Quote Originally Posted by crownv8 View Post
    All you need for the conversion will come from an MS112. The box and torque converter bolts up to the engine. (may need to use the MS112 flex plate) Use the MS112 rear cross member as the 4sp auto is longer. Use the MS112 tail shaft and change the flange on the diff to suit. (or swap diff centres over) Use the oil cooler lines from the MS112. Your T-bar shift will bolt straight up. There will be wiring changes needed to connect the neutral start switch and reverse lights. Also the overdrive will need to be wired up.

    Sounds like a bit, but its all pretty easy work and you will love the result when you are cruising on the highway at a reasonable rev.
    That is interesting, it never occurred to me that the rear crossmember was also from a newer series, however in my case I was under the impression that the original tailshaft was used without issue in the MS83. I still have the original tailshaft, I will have to go have a look to see if it was not shortened account of the longer gearbox.

    I apologise for possibly posting conflicting information here.

    Cheers,
    Brendon

  10. #10
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    Default Re: MS85 Diff upgrade

    The original ms83 cross member is relatively straight. The ms112 one is bent like a banana. Probably so they didn't have to change the chassis to fit the longer box. Its not much about 75mm from memory. Hence the shorter tail shaft is required and there are a couple of different diff flanges. Depending on year it may bolt straight up, or it may be different.

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