Haggisbash

I was looking at gear vendors under/overdrive transmissions, has one ever been fitted to a C3?

tektrans

I was actually thinking about it maybe down the road.
The tunnel where the driveshaft sits is VERY narrow on our cars-it wil DEFINITALY need to be cut/clearanced for the GV to fit.

7T1vette

Yes, it has. I remember at least two threads on installing a GV unit in a C3. I believe that there is some modification of the floorpan in order to get the larger unit to fit.

But, I really don't see the wisdom of installing an add-on unit to get an overdrive gear, when it costs as much (or more) than installing a complete beefed-up overdrive transmission that will easily install in the C3 structure.

AGVI

It doesn't make sense.

Shark Racer

In some instances, it makes sense. The C3 is not one of those instances.

I think a GV costs about double what a typical automatic overdrive install will cost.

On my 83 F250 I was very much considering a GV - 4-speed manual with very wide gears. Having a split between 2 and 3 and 3 and 4 would have been a boon, as well as 4th OD.

That said, the GV was worth more than the truck.

Doug Kraft

Maybe a retired truck driver with a manual trans would like one because he misses all the gear changes he has had to do.

iokepakai

Got a Richmond 6 spd trans in my Vette....Best upgrade on the car..Money well spent....
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7T1vette

Lots of 5 or 6-speed choices....new or used....that will easily fit in a C3. Gear Vendors unit is an 'albatross' for the C3 application.

timgman

My neighbor has that unit in his van.. while cool for tjhat I'd recommend going for the 6 speed / 5 speed option..

tektrans

There are a few reasons actually that favor a GV unit.
1-Next to zero HP loss-I beleive you lose 1 hp per 100 hp going through it.
2-Besides a 4L80-which is huge and expensive there is no other transmission that is as cost effective and stronger that a th400. Even a stock th400 can be much stronger than a built 700r4 and much cheaper to replace.
3-You dont have to remove your present transmission to install a GV unit.
4-Many may not realize this but the re-sale value on GV units is outstanding.
5-If you decide to sell your car you can just transfer your GV piece to your new ride-if different trans then just purchase new adapter.

7T1vette

A THM-400, while very stout, is a power sucker. So, putting a GV behind it will NOT make that combo more efficient than a 4L80E [or similar modern O/D trans].

tektrans

A 4L80 is a power sucker as well as a wallet sucker for a well built piece.

7T1vette

It's a simple matter of relative efficiency between the auto tranny designs. The THM-400 was never designed to be efficient; it was designed to function well and had a large safety-factor for accepting input torque. The 700R4/4L80 design was created to be more fuel efficient and lighter...meaning it can't handle the same amount of input torque without having problems.

Both are good transmissions. And each can be built to handle significantly increased torque requirements. But a 700R can't be built as stout as a THM-400 can be, and the 400 can never be as efficient as the 700R.

Shark Racer

FWIW, so there isn't any confusion, the 700R4 is the same trans as the 4L60, and the electronic variant thereof is the 4L60E. There are also the 4L65E and 4L70E which are heavier duty versions of the 4L60E and function identically.

The 4L80E is a much larger transmission than the 4L60E and was used in heavy duty truck applications where a THM400 would have been used in previous years. It was also used in a handful of ultra luxury and grand touring cars, like Rolls Royces and Aston Martins. The gear ratios of a 4L80E are identical to a THM400, except with the addition of a 4th gear overdrive.

7T1vette

You are correct. The 700R is kin to the 4L60 unit.

Haggisbash

Hmm, so the easiest course of action for me would be to change the TH400 for a 200R4, I want the O.D because fuel has now hit NZ$2.30 (US$1.78) per litre here. That's US$8.69/gal
Seems the 200R4 is the easiest way to a four speed? From what I can see the biggest change is the TV cable and the torque converter?

DC3

I haven't made the swap yet, but I've come to the same decision for my '73.

While researching, I came across an article I can no longer find but it basically said the 200-4R consumed less HP than the 700R4 and a lot less than the TH400 I'll be replacing. Unfortunately, the article didn't give any specifics about HP loss for any of the transmissions. It did mention the 200-4R had less rotating mass and weighed less than the other choices.

DC

Shark Racer

Basically, yes. If you want to be able to manually select first you'll have to get a new shift plate or grind a little extra room into the stock plate.

7T1vette

The 200-4R is a good choice. Just make certain that it has been rebuilt for the power you intend to put through it and that the configuration is right for the C3. Other than adding the TV cable and having a differently positioned dipstick tube, it's pretty much a direct swap.

[Oh, the cable mounting brackets on the left side of the oil pan need to be correct for the 200-4R or modified to be correctly positioned. The bolt pattern on the 200 is different from that of the 400, so you can't just swap over those brackets.]

Haggisbash

Does anyone make a kit for this swap? I will be struggling to lift the car high enough to get the trans out in my basement garage (it was made for hobbits like me) so may have to farm out the actual trans swap. The rest I'm pretty sure I can handle, I've never swapped out an auto trans and the last time I did a manual trans was about thirty years ago.