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- - OD trans (https://67-72chevytrucks.com/vboard/showthread.php?t=552241)

Was there ever some sort of manual OD trans available? either 3sp with OD or 4speed with OD?
Either in the 60-66 model years or something later.
Thanks Mike

Yep, I have one and it's great. Kinda sought after too. Try the search feature on this site for posts on 3 spd O.D. transmissions .

Does the dual range 4 speed in my 65 4x4 count as OD? Hi range 4th gear?

George

There's two 3speed with overdrives. The first one was used from the 50's through 1965 and had a four bolt side cover with an unsynchronized first gear like this one:

http://www.ebay.com/itm/1958-1959-19...0e3a8e&vxp=mtr

The second one was used in the late 60's and had a seven bolt side cover and a synchro first gear (ie. mine). Search function on here should get a bit of posts on them.

Here's some literature if you want to read up on them. They are distinctive if you look in wrecking yards because they have an electric solenoid hanging out of the left side and a governor switch hanging out of the right side.

http://www.speedprint.com/deves50/overdriveindex.php

Hope this helps.
Regards,
Steve
New Orleans

Steve

Thanks for the info. I will know one if I see one now. I have a 65 4x4 with a dual range 4 speed. I was wondering if that was what you were talking about. I see it isn't.

George

Thanks for this. I am learning a lot on this forum.

George

I have one as well in my 60. it helps especially when i have 4.56 gears.

Hawks,

Do you know how I can find out what the gear ratio is in my rear differential short of taking it apart and counting?

Do you have a PTO transmission, too?

George

Mid-to-late '80s Chevy trucks had a 4spd manual OD available. It's a Chrysler/GM hybrid trans. 4th gear is .73:1 (or .72, depending on sources). 1st and 2nd gears are roughly the same as a TH350, 3rd is 1:1, 4th is OD.
Some of them use a standard Chevy bellhousing mount (I have one of those in my '61 Suburban), and some cases had a Mopar mount and require a specific bellhousing.
The maincase and guts of the trans are the same as the Mopar A-833 4spd OD, but the tailshaft is unique for the Chevy units, and uses a TH350 speedo drive gear set and rear seal.
The shifter was Hurst, and there are two versions available, and they are both unique to the Chevy trans only. The Mopar unit will NOT work, because of the dimensions of the GM tailshaft housing.
Input shaft for the GM trans is standard GM length, spline-count and bushing/nose diameter.

The cases are usually aluminum, but I heard that some were also steel, and finally found one that is steel a few months ago. My preference would be for a steel one, as in the Mopar world, the aluminum 4spd OD cases are known to eventually fail behind lots of power. The problem is the second shaft registers directly in the case, without a bushing or bearing. Eventually, the hole in the case starts to wallow out, and the more it wallows out, the more the gears try to separate while in action, which causes the hole to wallow out more, etc.
The fix is to bore the case to have a bushing or bearing.
Originally, big block Mopar trans cases were cast iron, which made them bulletproof. The Direct Connect Super Stock race case was aluminum, and had a big steel insert bushing in the front of it, for the shaft to ride in. (got one of those in the shop here, too)
-Brad

Brad,

I was wondering about the rear differential, but thanks.

George

your truck performs like this now with stock tires: 4:56 rear ratio

2000rpm 3000rpm 4000rpm
31mph 47mph 63mph
torque 884ft/lbs

change to 30" tires:
2000 3000 4000
39mph 59mph 78mph
torque 707 ft lbs

change tires & transmission (t5)

2000 3000 40000
49mph 73.4mph 98mph
torque 556 ft lbs

with this engine and this rear axle you will never be able to get any fuel mileage (lower engine rpm) .

You could change to a 700r4 with stock tires and this is how it would perform:

2000rpm 3000rpm 4000rpm
43mph 64.35mph 86mph
torque 646 ft lbs

PM me to discuss farther Kieth my truck with a 200hp tbi 350, 700r4, 30" tires, and a 700r4 runs 65mph at 2000rpm and has 477 ft/lbs to the ground but it is no race truck and it runs out of steam at75mph with a 30mph headwind....

Quote:

Originally Posted by gfatula (Post 5712341)

Hawks,

Do you know how I can find out what the gear ratio is in my rear differential short of taking it apart and counting?

Do you have a PTO transmission, too?

George

The best way to find out is to just take the rear cover off the diff. just count the teeth on the ring and pinion and divide. the pinion gear will be a little hard to see but it can be done. also i don't have a PTO just the older style 3 speed OD. I hope that helps