Re: Overdrive Transmission Swap Info for GM units

by driveit Tue Apr 22, 2014 2:09 pm

I am going more for gas saving than anything right now.

Good news. Think I found a 700R4 yesterday. Guy has one that was pulled out of an 82 Pontiac. The motor ran great, but he didn't need the transmission. 150.00 I hope it all works. I am going to call him tonight to find out when I can go look at it.
Anything to look for as far as checking it out?

by pila Tue Apr 22, 2014 2:46 pm

The early 700R4 transmissions were not as durable as the '87/'88 years. The 3.73 rear gears are popular with that OD transmission, but 3.43 etc would likely be a good compromise for mileage and some decent zip too.

The last Caddy my wife had ( it was totalled in summer of '12 ) was a Fleetwood, which was an over-dressed Chevy Caprice. It had a good 350 SBC engine and the 700R4, with 3.73 rear gears ( trailer package ) and for a big car, it was a zippy combination.

Those 882 heads were the most produced of the Chevy SB heads from what I discovered. OK for mild builds, but not a neck-snapper for performance, and like mentioned, lots of better heads out there for reasonable bucks these days.

by driveit Tue Apr 22, 2014 5:26 pm

Thanks for the advice, but I was really just trying to find out what to look for on the transmission. Any indication of it being good or not?

by driveit Tue Apr 22, 2014 11:35 pm

Deal fell through on the tranny. Back to square one...

by pila Wed Apr 23, 2014 1:00 am

If you have any auto salvage yards in your area, you might check for a late 80s GMC or Chevy van, with a 700R4. They were very durable.
Hard to say about how to determine if a trans is OK. Removing the oil pan may show if it's not very good, with a lot of debris in it etc.....

by driveit Wed Apr 23, 2014 9:08 am

I have been checking for a month now. I found one, but it has the electronic speedometer. Don't know how to switch it out. It was in a Camaro.

by driveit Wed Apr 23, 2014 2:36 pm

Gonna wait on the tranny for now. Unless it is an unbelievable deal. Maybe I can still make it to the knoxville show with my TH350. I am guessing and hoping that it will be less that 150$ for gas. Heres to hopin!

I think now since I am not on a time crunch just to get another gear I will start looking for a 5 or 6 speed. That is really what I wanted anyway.

by thatfnthing Thu Apr 24, 2014 10:33 am

IIRC in most 5 or 6 speed transmissions, 4th gear is 1:1 and 5 and 6 are both OD. So you are still facing the same issue with the rear gearing.

If gas mileage is your overriding concern right now and you indeed have a 3.08 rear gear, you are better off swapping the rear gear to 2.73 and leave your TH350 alone right now (assuming it runs well). It will be cheaper and more cost-effective.

by driveit Thu Apr 24, 2014 11:41 am

I have a 2:73 in it right now, but I have a 3:08 in the shed at my mom's place.

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