m20 4 speed to a t5 5 speed conversion? - Chevelle Tech
Transmission & Driveline Transmissions and Differentials

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  • 1 Post By 136379G
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post #1 of 9 (permalink) Old Dec 2nd, 19, 10:01 PM Thread Starter
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m20 4 speed to a t5 5 speed conversion?

I have a 72 ss 350 / 383 stroker Chevelle

I had a 700r4 single wire overdrive worked great on the RPMs

I switched to a m20 4 speed but did not take into account the RPM issues

I have a m20 4 speed with 373:1 posi rear

When i run the car up to 70 mph the rpms are screaming

I want to switch to a T5 five speed

Has anyone done this b4 on this site

I dont want to spend the money for a T56

I am going to sell my trans set up on E Bay to offset the cost of the T5 setup
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post #2 of 9 (permalink) Old Dec 4th, 19, 11:42 AM
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m20 4 speed to a t5 5 speed conversion?

Without significant mods, I believe the T5 is a pretty weak tranny. If on a budget and looking to go 5 speed, you may try looking for a McLeod muscle car 5 speed or a Richmond super street ? Either way, they will cost a fair bit more than the T5, but should hold much more power and abuse. With any of those 5 speeds though you’ll be looking at bellhousing, clutch, driveline, shifter, maybe pedal linkage and crossmember mods. Maybe a rear gear change is a better option?
Not trying to deter you from a 5 speed, just maybe from that 5 speed.
Also, what rpms is it running at 70?
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post #3 of 9 (permalink) Old Dec 4th, 19, 12:37 PM
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McLeod 5 speed is pretty much a bolt in deal. From what I have read the T5 might as well be made of glass.

1974 chevelle with 73 laguna nose sbc 357 Brodix IK180 heads Comp Cams XE274H Edelbrock RPM airgap 650 AED double pumper, M20 muncie, Truetrac with 3.73s
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post #4 of 9 (permalink) Old Dec 4th, 19, 11:25 PM
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Re: m20 4 speed to a t5 5 speed conversion?

The T5 is less than ideal.

One minor issue is finding one, those trannies aren't just laying around all over the place in every shop's scrap bin anymore, the newest V8 T5 hasn't been made for 27+ years now. If you do find one, it probably won't be as cheap as it should be considering it's drawbacks. If it is cheap, plan on rebuilding the thing.

The biggest problem with them is the case design, they are inherently weak. They're nice trannies, very smooth, good quality build, but they don't hold up to any kind of power. The case is too weak to hold the clutch gear and the counter gear together, so they spread and the gears fail.

Instead of putting yourself through a fruitless endeavor with new problems cropping up every time you turn around, just get an aftermarket 5-speed or a T56.
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post #5 of 9 (permalink) Old Dec 4th, 19, 11:31 PM
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Re: m20 4 speed to a t5 5 speed conversion?

I would consider that if I were in your shoes. However:

I wouldn't run anything but a 2.95 first gear GM V8 T5. Any other stock T5 gear set else is a gearing mismatch for a healthy small block. Especially for 3.73s. So if you want it to drive like it should, do that. I prefer the 0.63 5th gear.

The front of the case expands slowly over thousands of miles. The countershaft bearing race hole in the case goes from a circle to an oval. While a Muncie pattern G-force case is readily available (they make it, and a Ford pattern case,) they will do the same thing in 150,000 miles.

The 88-92 F-body V8 trans. has cable speedo drive, a canted transmission mount, and longer total length. The 88-up has multi-surface blocker ring surfaces vs. the earlier design. It will take some work to fit it.

I could go on and on. But a fresh, proper operating condition GM V8 T5 would be an enjoyable driver. If you're going to pluck an S10 box with granny ratios, early synchro design, and VSS-only tail, then you may be disappointed in everything but the shifter position.

If this is a car you intend to keep, do it right the first time so you can enjoy it as much as possible. That may mean saving up for a new T56 Magnum, which is often a really good option, when it comes to finding a core, doing fab work, working with shifter position, etc. on the older production stuff.
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post #6 of 9 (permalink) Old Dec 5th, 19, 1:28 AM
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Re: m20 4 speed to a t5 5 speed conversion?

i would look into a tremec 5-speed trans
a .68 or .80 overdrive is nice

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post #7 of 9 (permalink) Old Dec 6th, 19, 12:23 PM
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Why not just leave the M20 and change the rear to 3:08???
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post #8 of 9 (permalink) Old Dec 7th, 19, 12:31 PM
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Originally Posted by 136379G
Why not just leave the M20 and change the rear to 3:08???
He outlined it pretty well in post #1. 3.73 may be an ideal gear ratio for his engine, other than highway. Why should he cut off his car's legs?

OD transmission demand will continue to outpace 4 speeds and 3spd autos in the aftermarket.

If you enjoy a car, and you built it so it can be a DD and fast, you're leaving a lot on the table by gearing compromise. A 3.08 rear is exactly that. An S10 T5 is that. A 4 speed is that.
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post #9 of 9 (permalink) Old Dec 9th, 19, 1:10 PM
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Re: m20 4 speed to a t5 5 speed conversion?

My 2 cents would be to with the Richmond super street. Everything from the Super Street crosses over to the Muncie except the clutch disc and the yoke for front of driveshaft. The Richmond trans is rated for 600 lbs torque, so if more engine power is produced no trans worries. Super Streets are a little harder to come by but have been around for many years so they are available. Also no tunnel mods with the Richmond.
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