The Quest For Overdrive . . .

[Ricko1966]

Look at your gear ratios. M21 would be downgrade for a truck that has to tow occasionally. A 700r 4 would make the truck tow better and have overdrive.A granny 1st 4speed and a steeper rear gear would cut your rpms and make it tow better. M21 will just be harder to take off and extra shifting. You need to widen the gear spread,not bring it closer together.

 

[Rusty Nail]

The T5 is not nearly as durable as the NV3500, or even the HM290 predecessor. Many have been broken behing a very mild small block in the 3rd gen F-body.

*and 3rd gen F bodies were FAST AF!
the most brutal 180hp u ever saw
yep
uh huh

y dont u just put a glasspack on it or a Magnaflow?
or! Corvettes had that kewl DougNash box on the back of em
might as well get a thousand singles from the bank and take em to the t itty bar, you'd have more fun....lol

i'm rollin with the "leave it alone" posse

xc_hide_links_from_guests_guests_error_hide_media

 

[Old Guy Bill]

Yep, the original GM combo isn't going to be cheap or easy to improve in my opinion... a 700R automatic is the only thing I'd personally even consider..

 

[77Dmax]

An nv3500 or 4500 would be my choice. They are out there for cheap if you look hard enough.

 

[jjester6000]

An nv3500 or 4500 would be my choice. They are out there for cheap if you look hard enough.

With the NV3500, I'd have to convert over to a hydraulic clutch which I really don't want to do. NV4500's on the other hand are pretty damn expensive at least around where I live ($1500-$2000).

 

[jjester6000]

Owned: Saginaw 4 speed, Muncie 4 speed, Saginaw 3 speed, Saginaw 3 speed with borg Warner overdrive, sm420, sm465, np435, subaru 5 speed 5mt.

Driven all of the above plus dump trucks with whatever transmission they had, jeep xj 5 speeds, so yeah, heavy duty stuff so I know nothing sporty.

As mentioned in the very first post on this thread, I know of a Saginaw 3 speed Overdrive transmission for sale that I could buy.

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I also have a Saginaw 4 speed 2 groove (I think 3.25:1 first gear) so concievably I could combine them both into one transmission (I've heard of people doing it). Or I could just use it as is since Saginaw 4 speed's (as I learned the hard way) don't really hold up well in trucks.

I also know of a Clark 5 speed that I could buy instead (I don't know if this one specifically has OD or not).

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It seems to be mated to what I assume is a 366 big block, so if it shouldn't be too difficult to make it bolt up to the 250 (Don't they have a larger diameter input shaft and 12 inch clutch?).

 

[DoubleDingo]

I'm pretty sure that Clark will be more truck-like in shifting than any sm420 or sm465.

The borg Warner overdrive transmission needs 4.57 gears. In overdrive the final drive is 3.19. 4.57x0.70=3.19. You're not towing using overdrive with that setup, and it may not hold up either.

 

[Grit dog]

The T5 is not nearly as durable as the NV3500, or even the HM290 predecessor. Many have been broken behing a very mild small block in the 3rd gen F-body.

My point was I always thought a NV3500 was pretty durable light duty trans. Idk how you’d bust one behind a V6 without really trying hard to. Isn’t the HM290 the same but just a vehicle mfg designation?

 

[jjester6000]

I'm pretty sure that Clark will be more truck-like in shifting than any sm420 or sm465.

The borg Warner overdrive transmission needs 4.57 gears. In overdrive the final drive is 3.19. 4.57x0.70=3.19. You're not towing using overdrive with that setup, and it may not hold up either.

Yeah, the Clark would not really be viable unless I regeared.

If I can talk the guy with the Saginaw down, I might pick it up (Even though it's rare, I think I could get it cheaper).

 

[Ricko1966]

With the NV3500, I'd have to convert over to a hydraulic clutch which I really don't want to do. NV4500's on the other hand are pretty damn expensive at least around where I live ($1500-$2000).

You are aware you can keep your pedals add a master to the firewall and make a pushrod to go hydraulic?

 

[Frankenchevy]

As mentioned in the very first post on this thread, I know of a Saginaw 3 speed Overdrive transmission for sale that I could buy.

You must be registered for see images attach

I also have a Saginaw 4 speed 2 groove (I think 3.25:1 first gear) so concievably I could combine them both into one transmission (I've heard of people doing it). Or I could just use it as is since Saginaw 4 speed's (as I learned the hard way) don't really hold up well in trucks.

I also know of a Clark 5 speed that I could buy instead (I don't know if this one specifically has OD or not).

You must be registered for see images attach

It seems to be mated to what I assume is a 366 big block, so if it shouldn't be too difficult to make it bolt up to the 250 (Don't they have a larger diameter input shaft and 12 inch clutch?).

In the context of manuals (specifically excluding automatics with OD, as they generally lockup providing additional
benefits) OD probably won’t matter as much as a useable gear spread and appropriate final drive ratio for reasonable freeway speeds.

I still think if your trans needs to be replaced with another manual, a 465 will be a cost effective route. Those 3.55s should be a good blend of freeway and surface street. I had 33” tires, 3.73s and a th400 (1:1 with average converter slip) in my truck previously, and it was fine on the freeway.

 

[ChuckN]

I don't think 1st gear is deep enough for your application in the M21

Came here to say this. Or at least, in some iterations, the M21 has a really tall first gear. Seems like the clutch would really suffer. Let alone take off power.

 

[77Dmax]

M21/22s have a 2.20 first, which would be awful for towing. Autogear can update the ratios, but that would soak up the 1k budget though

 

[bucket]

My point was I always thought a NV3500 was pretty durable light duty trans. Idk how you’d bust one behind a V6 without really trying hard to. Isn’t the HM290 the same but just a vehicle mfg designation?

Right, my point was just expanding on your point. The nv3500 is definitely more stout than a T5, but you can still break one in a full size, V6 truck. Therefore, a T5 would be ridiculously fragile.

Yeah, my son broke his nv3500 in his '93 C1500 W/T. It lost 2nd, 4th and reverse. It saw lots of hard (but not abusive) use since he had been driving it. But no towing or load carrying.

I believe '93 was the first year for the nv3500 in a GM truck? The HM290 was the predecessor and looked extremely similar, but there were different internals.

 

[DoubleDingo]

Yeah, the Clark would not really be viable unless I regeared.

If I can talk the guy with the Saginaw down, I might pick it up (Even though it's rare, I think I could get it cheaper).

Dude, if you get anything but an sm420 or sm465 you're regearing the diff and your 1k is shot. You have the bellhousing right now that an sm420 mates to. Trans and mild trans to center bearing driveshaft mod, and it will be a fun agile truck within budget. Sm465, I think uses a different bellhousing, but similar driveshaft mods, so a little more coin but still might be in budget. Your other ideas, 1k is shot quickly