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Old 02-29-2012, 02:57 PM
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4 Speed Transmission for '76 GMC Sierra

I recently purchased a '76 GMC Sierra with the stock 3 speed moved from the column to the floor. I'd like to put a 4 speed in it, and I know little to none about transmissions. Does anyone have any suggestions? The truck has a 355sbc with the factory rear end. I'll do the work myself, but want to stay under $1,000 on parts if possible.

Any suggestions, tips, etc, would be greatly appreciated.

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Old 03-01-2012, 08:43 AM
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You could use a 4 speed Saginaw, a GM Super T10 or a GM Muncie car transmission. The real trick to your budget is identifying what you have and selecting a suitable replacement.

So identify which 3 speed is in there now (if its a saginaw, you can simply replace it with the appropriate 4 speed saginaw and be done with it). Also get us an approximation of your engines output, the rear gear ratio, and what you realistically want to do with this truck.
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Old 03-01-2012, 09:10 AM
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Transmission is Muncie M15 I think (its supposedly original), but will double check. Don't know what the engine output is, and haven't found anywhere local to get some numbers. The truck has 4.11 gears. As far as what I realistically want to do with it...I'm happy with the current setup, and don't have any plans to boost power except for maybe a cam change.

Thanks for the reply and will do some research on your suggestions.
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Old 03-01-2012, 09:07 PM
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The M20 4 speed was used in these trucks, but it has a granny 1st gear that would be unusable in normal driving. There was also a 4 speed with overdrive used in these trucks in the 80's and it had the RPO code of MM7, but I don't have any other info on that transmission. I think this overdrive transmission was the NP A833, but I can't verify.
This link has some info you might find useful.
http://www.classicjunkyard.com/new_process_a833.htm

Bruce
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Old 03-02-2012, 05:04 AM
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The big truck Muncie (granny low) will require a different trans crossmember
and floor modifications. You would also need to find the trans cover
for the floor in a junkyard----I have not seen all that many.

And yes--the overdrive 4-speed is a New Process A833.
Essentially the same trans in the older Dodge trucks
and 60s-70 performance cars.

It does have some internal modifications for the GM applications tho.

I have this 4-spd in my old D-150, suitable for running around, but I do not think it can do any serious truck work. I do like it tho.
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Old 03-02-2012, 05:07 AM
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pretty sure the bolt on cover is available aftermarket, but the SM-420/465 probably isn't what he is looking for, given there 3spd ratios 2nd-4th. only good thing is there dirt cheap
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Old 03-02-2012, 08:41 AM
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The M20 car 4spd doesn't have a granny 1st. Its 2.5x:1, Which is still higher than most transmissions sold today (take a look at your friends TKO with its 3.27:1 1st gear) A car M20 with a set of 3.73s in the back has the same mechanical advantage as a set of 4.11s with an M21 or M22 rockcrusher 2.20 1st

To the OP: Are you looking to do real 'truck work' with this, or are you looking to build a 'truck rod' to cruise around in? I bet a 2.85 1st Saginaw would get the job done nicely and you could gear the trucks axle down to a 3.42 or lower numerically and still have plenty of pep in 1st gear, and decent economy in 4th.
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Old 03-02-2012, 11:35 AM
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Quote:
Originally Posted by AutoGear
The M20 car 4spd doesn't have a granny 1st. Its 2.5x:1, Which is still higher than most transmissions sold today (take a look at your friends TKO with its 3.27:1 1st gear) A car M20 with a set of 3.73s in the back has the same mechanical advantage as a set of 4.11s with an M21 or M22 rockcrusher 2.20 1st

To the OP: Are you looking to do real 'truck work' with this, or are you looking to build a 'truck rod' to cruise around in? I bet a 2.85 1st Saginaw would get the job done nicely and you could gear the trucks axle down to a 3.42 or lower numerically and still have plenty of pep in 1st gear, and decent economy in 4th.
Not looking to do any real "truck work" with it...and its never going to be a "truck rod" either. Basically just want to have a nice clean truck that can run a little. I've actually had my eye on the A833, as it seems to be what I'm looking for. From what I've read, it has a pretty short gear pattern (its currently a pretty long throw up to second) and will handle more than what the truck will ever put out.
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Old 03-02-2012, 12:47 PM
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The A-833 Trans in a truck will have avery long throw.

Since this is the same trans that was used in Chrysler's cars for years and years, it has a much longer shifter.

Granted on the Dodge pickups, the shifter itself is mounted a couple of inches higher than on the cars, but yoou still end up with a pretty long shift handle and throw.

1st to second in my Dodge is almost 12" if not a bit more.
I'll go measure it this afternoon and give youo a length.

Using a Muncie or Saginaw 4-spd with the shifter mounted to the trans, you will have a real long throw
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Old 03-02-2012, 07:49 PM
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If I had a daily driver with 4.11 gears I'd want a tranny with overdrive.
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