Chevy & GMC Vans

I thought it was a turbo 350 but its not... it's either a turbo 250C or turbo 350C

I found these numbers on it:

BOP31D
M on the bellhousing
OFM3640852
GM17

I can't find squat for info on this thing.

It has a 1 wire hookup on it which I thought was for revese lights but seemingly a real turbo 350 has NO wires on it.

Please help identify this thing...

350 metric?

Hmmm...I found this "The THM200 and the THM250 have pans shaped like a THM350, HOWEVER, the THM200 will have the words HYDRAMATIC DIV. and METRIC stamped into the pan."
at this site
http://www.nastyz28.com/chevy-transmiss ... cation.php

Ya I found out it's a THM-250 C

It's a very weak V6 type trans with an electric lockup giving it 3.5 gears.

I'm trading it to a guy for a 700r4 and purchased a 1979 THM-350 with a stage 2 shift kit already installed.

Thanks for your help so far.

Here's a pic of my progress and what the trans is going into... 1989 Mazda B2200... gonna have a 250hp chevy 267 cu/in motor and a turbo 350 trans.

That THM250 may have been a better choice for your mini truck, as the trans body is much smaller in diameter, and would fit in the trans tunnel with less modification. Strength won't be an issue, as these trannies came behind 305 and 265 chevy V8's, as well as the 200 and 229 V6. You don't need the super low 1st gear of the 700R in a light weight mini, but you would have to count the shift detent stops on the linkage to see whether it is an overdrive unit or not.

Same basic transmission that was installed in the Buick Turbo Coupe, and the successor, the Grand National. Hardly a weak design in my book.

I'm not using a 700r4 for the truck... i'm using a turbo 350 with a stage 2 shift kit.

The T-350 will actually bolt directly to the stock mazda trans crossmember.

I'll resell the 700r4 and make some money to put back into my truck...mainly a custom driveshaft. Have to marry a chevy driveshaft to a mazda diff.

Marrying a chevy/spicer shaft to your Mazda shaft will be quite easy. Mazda has a flat flange, and spicer and neapco make 1310 U-joint flanges. Beat one of the flanges off of your Mazda driveshaft, and take it with you to your local driveline shop. If they can't find a perfect match, the holes can be drilled in the axle flange to match. Be sure that the snout that centers the shaft flange to the diff flange is perfect. If need be you can buzz the diff flange off, and have a machine shop open/match the pair before installation.

The shaft on this mazda is a split shaft with a hanger bearing... would it be ok to use a 1 piece solid shaft instead?

yes, but be sure to keep your pinion angle and transmission angles within a degree or two, or you may find some teeth chattering vibrations.

*edit*
I assume you are lowering the truck anyhow, so some diff rotating is in your future anyways...?

I'm wondering if the stock mazda driveshaft will take 250hp... if it will then i can simply chop the snout off the chevy and weld it to the mazda.

The chevy is aluminum while the mazda is steel.

The driveshaft will hold up fine. I would hold off on chopping the Mazda end off of the shaft. Most likely it will have to be shortened, and you can simply buy a weld yoke that fits your driveshaft tube. Being Mazda and Ford shared that truck platform, chances are good that it will have 2 inch tubing, which is very available. Then your toughest problem would be pounding in a new u-joint.

I'm very lucky that I have 2 mazda shafts and 2 chevy shafts as well as a friend with a machine shop so it shouldn't be too costly to do this.

Do they make such a thing as multi size U-joints?

If they do that would be simple.

As for length the T350 trans will sit in the same spot with the same amount of tail shaft length so the shaft should be perfect... hopefully lol

yep, there are a whole bunch of what the industry refer to as "bastard" joints, with one size on one side of the cross, and another size on the other. I have joints in my Suzuki Samurai that are 1310 spicer on one side, and Toyota Land Cruiser on the other. You should be in luck.

Sweet

Make sure your buddy has driveline experience. Improper phasing of the ujoints will cause vibrations like no other. Phasing is the alignment of the yoke placement. Look at your shaft as it is, you will see that the U-joint yokes are all installed in the same direction, to cancel out harmonics of turning in a concentric circle. Pretty darn close is good enough, because a degree or two will not affect things. If its just welded on wherever, you will have nothing but trouble. If you need more of an explanation, I have a buddy that put together a video on phasing, so you can see what I mean. Let me know if you need to see it.