Hi,

A topic best discussed on a Saturday with beer...

I was talking with Tom Langdon about transmissions and potential upgrades. Of course a Turbo-350C is an easy bolt-on swap to get 3-speeds. He mentioned that with an overdrive transmission, 200/700-4R, I'd be disappointed with the performance when in OD. He stated that it would shift in/out of OD pretty quickly.

So I whipped out my excel spreadsheet and see yes indeed, the RPMs with my stock 3.08 differential would be about 1600 at 60MPH. Too low.

The TH350C looks right for this differential, but I could also go with a 200 or 700 and run it in 3rd gear if I planned to eventually bump up the differential. I wouldn't get the benefits of the locking torque convertor in that case.

What are your experiences with the different transmissions?
Is upgrading ring & pinion on a 10-bolt to 3.73 something I could do? I'd replace bearings too. The repair manual doesn't make it look easy with special tools.

Thanks,
Mark

Here's a snapshot of the spreadsheet...

What RPM are you looking for at what MPH?

I like to aim at 70MPH and 2100-2200 RPM.

1900 at 60 ain't bad either.

For this the 700R4 and 3.73 would be about the best fit.

Now for the gear change. I would not recommend this as a first time to do job. Those tools in the manual are not used by me to do gear work. Take it to a shop. Well worth the 200 if you take it out and have it all cleaned out.

Thanks Tom, I didn't really know where to aim for RPMs. Part of me says stick with TH350C because the car will run 20MPH slower. I seem to have this thing about limiting the trouble my soon to be teenagers can get in, IF I ever let them drive this car.

BTW I'm getting just plain tired about all the performance issues (backfiring, etc). I'm starting to do more research now because I think i'll start buying parts in Sept instead of later. But I've got to get my act together and fix the windshield leaks and perhaps put in shoulder belts first.

Mark

Regarding the gear change..
I knew I could do it... Why not? Until I started. Long story short I didn't have a good way to hold the axle still enough to get the needed preload,,,Didn't have the necessary tools to first find the actual center of the axles and therefore could not find the true pinion height... and on and on. There were two possibilities. It would not be done correctly, (almost certain) and/or I would almost surely hurt myself in the process. (Hi Doc...Me again) I eventually took it to an axle shop and happily paid them to do it for me.

Regards:
Paul

I still like the 200R4 gear spacing over a 700R4.

Especially if your engine is not a torque monster of an engine like a 292 or a turbocharged 250.

Even if you do not use 4th gear on a 200 or 700 R4, 2nd 3rd will still lock up the torque converter, it does not need to be in 4th to achieve lock-up.

You may not like the performance in 4th gear with 3:08 gears, but everywhere else you will like the performance gain.

3:73's will be great with a 200R4 also.
Plus you do not need to have your driveshaft changed as you would with a 700R4

You can run a 200R4 trans & not change your gear set at the same time, it is not necessary, but you would not need to go into overdrive until about 80+ or so MPH.

I have a 700R4 trans in my Syclone 4.3 V-6
It runs fine in that combo, but I am also pushing 550 ft lbs of torque.
If it was a naturally aspirated 4.3 V-6 I would rather have a 200R4 in it.
In a 700R4 the gear drop from first to 2nd gear is horrendous, unless you have a lot of torque or a turbo to overcome this massive RPM drop I would not recommend a 700R4.

MBHD

Thanks Xerxes for that ... premonition of my future ... I'll take it to a shop to change.

MBHD - good point especially about not having to change the driveshaft with the 200R4. I'm looking for the closest thing to bolt-on that I can get. When I pull the engine & transmission out, I'll put in the new transmission and say bye to the power glide.

I was looking at the old steel hammer I welded up in high school shop class. Tons of pits and defects. You really don't want me to be near cutters and welders.

Mark