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Taller gears

3467 Views 26 Replies 15 Participants Last post by  AJ
I'll be looking for a 3.90 or maybe a 3.73 rear end for the Blupra, with matching speedo gears...yes I did a forum search using the terms "3.73" and "3.90" and (surprisingly) didn't find any similar posts. Any feedback on which diff would be best with a moderately modded 7M-GTE would be appreciated.

Anyone have a source on these?

TIA -- Bob
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Whelp...... Even though they are somewhat large :piggy:

MA70 7M-GTE's have the 3.73's.... :D
i always thought a lower gear was better for a turbo car... helped build load, which builds boost.

and of course, the lower your gears (to an extent) the higher your top end, and the more fuel efficient your car can be.

if i recall, i think most people have recommended 3.73s, in the posts ive read on here.
You have it backwards! Lower gears (eg 4.3:1) give you more acceleration and less top end. Higher gears (eg 3.5:1) are good for relaxed highway cruising at the expense of low-speed pickup.

FWIW I just finished putting 3.5:1 gears in my Supra which originally had 4.1:1 gears. I've found it suits the power delivery of a 2JZ-GTE much better, and I think you'll find a 7M-GTE will be much the same. It still gets out of the hole plenty quick, and at highway speeds it sits on a nice relaxed 2400rpm instead of 3000. I'm loving it! :)
Thanks, guys...much appreciated! Now...will a MkIII 3.73 diff fit in a MkII without mods?

The car definitely jumps out of the hole quickly with the 4.3 diff (fun!) but I'd like the better top end and gas mileage. Unfortunately, my lead foot has only gotten a bit *worse* since the conversion!!

You might want to ask Don C./Shawn (Nix 99. 1-800-782-0682) or Ophir (PacNW) as they both have 3.42's in their 7M-GTE's.

Consider calling River City Differentials (916 852-7109, Sacramento area) and talk to Sean about his building up a tru-trak posi. He uses 7.5 inch toyota truck diffs for the larger selection of ratios. I bought one with 3.90's to replace my 4.30 howler.

As far as the speedo gears there is a thread on the yahoogroups site trying to put the Toyota part #/diff. gear info together. Don't know if there is a clear picture for this yet.

BTW How did you like the map light?
Speedo gears

Hi there. Most of the recent research on speedo gears lately has been me. I have a thread in here in the driveline forum called "Changing the rear..!?"
It documents what I know so far.
I started on a thread called "Part numbers from Jeff Watson" or some such, but I jumped threads.
Hope it helps.
'83 Ltype with a howling rear and a wobbly shaft (no innuendo meant ;-)
'85 Ptype
and I have a shop for you Bob when you're ready to do it! He rebuilt mine with new ring/pinion and knows his toyota rearends. Can drop a locker in it like others have done too, or rebuild the l/s like he did w/mine.
It's on Sepulveda, btw...
Don C. has 3.73's i his now.Ophir has 3.42's.

Bob we have gears from toy trucks,need to be installed in your housing.Price depends on ratio and miles 8)
i've got the 3.91 gears and it seems to be a good mixture of highway cruising and get-n-go! highway at 85 i hit about 3k. could you imagine the 5.125 in the 1g series cars on the supra lol! out of first at like 20 mph
Malibyte said:
Thanks, guys...much appreciated! Now...will a MkIII 3.73 diff fit in a MkII without mods?
No. The MkIII diff is completely different and much larger. It's possible to do it but you'd have to modify the rear subframe and tailshaft, and you'd need custom half-shafts. I think it would end up being pretty expensive too.
Fitting a MK3 diff into a MK2

While working on my MK2 and dreaming about some mods to it (make a removeable middle plate for the crossmember to allow a 1-piece with no sweat), this has crossed my mind. I'd really like to get a 7.5" and a 8" diff side-by-side to see what's involved in this/how different they are. Seems to me...

Hafta get the right flange on the drifeshaft. Is the MK3 diff longer than the MK2's?

Change the mounting scheme to accomodate the different way of mounting

Custom halfshaft...would it be possible to take a MK3 and a MK2 halfshaft, chop them in half, and weld the MK3 inboard half to the MK2 outboard shaft? Can custom driveshaft shops do things like that?

Sounds like one of the hardest parts would be getting the halfshafts coming out at a nominal 90 degree angle when the vehicle was sitting on the ground. Don't want them deflecting too much in normal operation. Shorten the lifespan of the CV joints.

This could apply to nearly any custom rear diff come to think of it.
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The Mk3 diff is slightly bigger in all 3 directions just eyeballing it. The driveshaft is the easy part. Technically speaking you could probably weld the 2 shaft ends together. I'd highly not recommend it though. I think you'd have a hard time getting 100% weld penetration on the shaft. Plus you'd have issue with straighness most likely. Not even sure what alloy Toyota used for the shaft (I'd assume a 4000 series steel), so you could have welding problems doing it. Generally speaking welds are bad for strength. IMHO not very many people are pushing the power needed that a factory MkII carrier with upgraded LSD can handle. Heck, the 2 fastest MkIIs around run the factory carrier with TRD LSD.
Thanks again guys...will follow-up on these and find out which is the best way to go from a price and performance POV and go from there - probably won't get a chance to do any of this until after the holidays....!

-- Bob --
Yep, my 2JZ is running 18psi and my 20 year old stock diff never broke even after some fairly "spirited" driving! Sure it was getting noisy but that started before the 2JZ conversion; it was just old, 250,000km on the dial.

Anyway, the point is F series diffs are plenty strong and you'd have to be doing something fairly silly to break one!
like drag race it? Yes you've done that with yours too, but many others haven't been so lucky. Ask William82 how many hes gone through
Killing diff's

But William82 was also running a 7MGTE with a 4.30 rear! That explains the broken gears.
norbie was running a 2jzgte. btw, i didnt break any gears. i broke the lsd's. after effortlesly breaking 2 in a row on 2 launch attempts, i figured id wait for the true trac before draging it again. then i started snapping w58's on the street with street tires.
btw, i have a car to put the 7mgte, r154, and true trac with 3.727 r&p in so hopefully ill have some time slips after the holidays when i can get to the swap.
Go with the 3.73s. They just feel right for the 7mgte MKII, IMHO. To keep things from being laggy on the low end besure to get a good 3" 02 elbow/exhaust.
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