Supra gearbox or M21??

[HK1837]

If anyone is interested i'll do a spreadsheet file showing how much sense an M20 with 2.6:1 diff makes for a weekend cruiser that has to see highway use.

[wbute]

Yeah I would be interested in that.

[agr071]

Will it be a pig to get moving from a standing start Byron.
If not, i'd be interested in the spreadsheet as well.

--- Updated ---

My only concern is that i once blew up a M21 behind a worked 308, and all i did was change back from 4th to 3rd doing 40km/h.
I was easy on my ute as it had a 6cyl banjo diff in it and i never even damaged an axle or diff gears. So i'm easy on vehicles.

[the ski man]

to check out my ratio combos i use this nifty program:

http://www.locost7.info/gearcalc.php


allows you to input everything as its designed for clubman kit car builders.

i've run some numbers and the 2.7 with 4 speed looks great, the lingering question is how tough the combo will be in a higher power combination.

i had previously had 2.79 rear with the m21 but kept snapping teeth on first and second. i ended up getting rid of the tall diff and i hadnt had an issue since.

--- update ---

im also really grateful for your input Byron, and like the suggestion, it means keeping some sense of originality about the car but making it user friendly.

[HK1837]

Here you go guys. I put the 4 x most common aussie 4spd ratio sets in plus the 2 x common Supra boxes.
The lines below show each diff ratio, line next to the diff ratio is 1st, line below is top (4th or 5th).
So looking at the 3.36 diff with M21 (which is standard for 308 Sandman) 1st geat is 8.53:1, top is 3.36. By putting an M20 box in it and a 2.78:1 diff, 1st gear is all but the same and top gear becomes 2.78:1. This is basically the same top gear as fitting a W55 or W57 into the same vehicle leaving the 3.36:1. By using an M22 with a 2.6:1 you get a 1st gear slightly lower than an M20 with a 3.08 diff (standard behind 253 in HQ-HJ) but top gear at 2.6 is the same as putting a 5spd with the 3.08 diff.

M21 M20 M22 XU-1 W55 W57
1st 2.54 3.05 3.74 2.54 3.566 3.285
2nd 1.83 2.19 2.68 1.83 2.056 1.894
3rd 1.38 1.51 1.68 1.25 1.384 1.275
4th 1 1 1 1 1 1
5th 0.85 0.861

3.55 9.017 10.8275 13.277 9.017 12.6593 11.66175 1st
3.55 3.55 3.55 3.55 3.0175 3.05655 top
3.36 8.5344 10.248 12.5664 8.5344 11.98176 11.0376
3.36 3.36 3.36 3.36 2.856 2.89296
3.08 7.8232 9.394 11.5192 7.8232 10.98328 10.1178
3.08 3.08 3.08 3.08 2.618 2.65188
2.78 7.0612 8.479 10.3972 7.0612 9.91348 9.1323
2.78 2.78 2.78 2.78 2.363 2.39358
2.6 6.604 7.93 9.724 6.604 9.2716 8.541
2.6 2.6 2.6 2.6 2.21 2.2386


I'm not suggesting this is an ideal setup, especially lugging around town in 4th gear at 50kM/h. But what it is good for is for a weekend cruiser style van, taken to car shows etc but not driven much otherwise. Especially for a stock 308. Aussie 4spds are not super strong and can be broken. But if they do break under normal use it is usually because they are worn, not because they are weak. When these things were/are new they will handle decent power. All new bits can be bought for them now.

Bugger, doesn't post properly. How do attach a file?

[mcdvi]

I used to do lots of hi way driving in my old van, I went through this exercise about 15 years ago.
Removed my M21 & fitted a Supra 5 speed behind the 308 with a 3.08 diff, 2k dollars later had myself a real hy way cruiser.
12 months & about 80,000 ks later it tore the cluster gear clean out of it. (about 400k north of mt isa near the Barkley homestead) In the middle of nowhere.
Got a replacement box $1200 sent to Isa from Townsville fitted it myself 7 continued home to the Gold Coast. All good mate. 12 months or another 80 odd thousand k's later,
Exactly the same thing happened.
You would not give me one of those boxes now, I hate them. My car was never used to do burnouts or crap & it has always been well maintained, I needed it to be reliable.
After much thought & advice we ended up putting a turbo 700 in it, (the first auto i ever owned) At the time the transmission was worth more than the car,lol. But i never had a problem again. (100k/r 1300 rpm) converter locked up.
Now the old girl sits in the shed, with the 3rd motor in it, waiting to get taken back to Mandarine Red & get an m21 back into her.
Just my 2 cents worth,
Cheers Vic.

[RAEME]

G'day Guys
I hope you dont mind another input. If your keen to do a conversion i would (and have done) convert a T5. They are about the same price and remember supras havn't been made for a long time with those boxs, T5 are a lot newer and are put behind 5lt from factory they are an easy convert and parts are every where.
Regards Chris

[adam perth]

IMHO, i wouldn't build a car ground up with a 5 sp., but if there is one already in it like HZSANDMAN says, you really enjoy them more than an aussie box.

the problem with the Toyota stuff is that you can't get a decent sized clutch to run on the toyota spline to take the torque of a V8.

[HK1837]

Attachment tag has appeared!

Here is the file.

[YELLOW]

Been interesting reading this...

After having heard people raving on about Supra 5-speeds behind Holden motors for years I thought they must be 'the juice` so that`s the way I went...

Stock 308, 3.08 diff, and yeah the gear shift is perfect, 2 clutch failures (disentergration) later with not alot of K`s on the clock and I`m ready to go to a T350 next time (but oh how I hate driving autos`) and yeah, I`ve changed my driving style for this latest clutch!