[1971455HO]

I hate to even ask this question, but I don't have access to my car right now. How long is the tailshaft housing on a 70 -73 th400 transmission. I want to say it is 4". but I'm not positive. I'm adding a GEAR VENDOR overdrive and need to order it soon, so I have it when. Also, if anybody else has done this what length drive shaft did you end up with (center-center U-bolt measurement? Don't want to cut my original. Thanks.

[Sirrotica]

Summit has pictures with dimensions here:

https://help.summitracing.com/app/an...ion-dimensions

Just curiosity, a 4L80E fits much better than a GV and a T400, any reason not to use a 4L80E?

I can't help with any dimensions on a GV unit, but here's a picture of one coupled together with a T 400:



A 4L80E is 3 7/8 inches longer than a stock 73 T/A, T 400.

[1971455HO]

Thanks, the gear vendor just seems easier. I don't know all the moves for installing a 4L80e. I think it takes a lock up converter, a change on the shifter detent to shift correctly, a control box to make it work along with fabbing up a new crossmember and maybe some other things I don't even know about. I'm not against doing it if it is a better way to go, but it seems like a lot more work. The aux. overdrive is pretty straight forward, just needing a couple wires ran to control it. Both options require a shorter driveshaft. I do have a concern about drive shaft angle with the gear vendor overdrive though.

Thanks for your suggestion though. Who sells 4L80E transmissions with the Pontiac bolt pattern? Also, what is the best converter to run with one of these. I don't need a high stall, I have 3.08 gears and changing cam back to common sense lift & duration.

[69 Limelight]

Pretty sure TH 400"s were produced with several different tailshaft housing lengths depending on vehicle they were installed in. Unless you're absolutely sure your transmission is original to car and transmission that it was supposed to be built with wasn't deviated from at production, I don't think I'd be wanting to order a GV unit with specific length adapter housing without first measing yours. Those adapter housings are expensive and pretty sure once you hit "submit order" housing is yours and probably can't be exchanged for different length. Good luck.

[kingbuzzo]

I'm interested in this GV product - keep us updated on your adventure...

[1971455HO]

Yeah, my TH400 is the original VIN matching PQ code. Keeping the trans...just making it more road worthy. My 3.08:1 gear changes to 2.40 with the Gear Vendor.

3.08:1 @ 70mph= 2750 rpm (w/26.27" tall Goodyear Polyglas GT F60 - 15)

2.40:1 @ 70mph= 2150 rpm

[1971455HO]

Thinking about what sirotica said though about the 4L80E. That just might be the better route. Don't know yet. Still thinking about it.

[AG]

Short tail TH400 rear extension is 4" and long tail (big car TH400) is 9.5". I'm putting 2.78 gears in my '72 LeMans to get to 2170 rpm at 65 mph with a 28" tire since I don't race it.

[Sirrotica]

In case you didn't know, The 4L80E is a T 400 with a factory OD unit. About 75% of the internals are interchangeable between the transmissions.

Main difference is a T 400 is fully mechanical, the 4L80E is is electronically controlled, requiring a stand alone controller to be used. That controller also allows the 4L80E to be adjusted with a twist of the knob, instead of tearing into the governor, valve body, modulator, etc, and physically modifying the shift characteristics.

After much study on the subject, plus owning 2 chevy trucks equipped with the 4L80E, I know my next project car will also have a 4L80E in it. Tough as nails.

Of course it's your car, and it's your choice to which way you go.....

FWIW, My 4X4 93 diesel dually at 270,000 miles just had the original 4L80E transmission finally give up about a month ago, The other truck, 95 2wd dually straight truck, also a diesel, only has 250,000 on it, still going strong.

Below is a picture of a T 400 and a 4L80E side by side, as I previously said just 3 7/8 inches difference in length. The 4L80E fits in almost any GM muscle car with no floorpan modification. Don't let anyone else tell you, that you need to butcher up the floorpan to use a 4L80E, it's not true. It's a common falsehood that you'll have to forever change the floorpan to accomodate the 4L80E. The truth is, you will have to modify the floor slightly to accommodate a GV unit, easily seen from the pictures I've posted.

[giles]

Steve T (455hota) on here installed a gear vendors unit behind a THM 400 20 years ago on a 71 TA he had at the time. I was interested but decided against it for my car when I saw how much he had to “massage” the floor pan for clearance. Based on this I’d go with a 2004R. Same length as THM 400, same crossmember mount, non electronic versions and they can be built to withstand the abuse of 9 sec turbo Buicks so I think they can live behind a 455. You do have to add a throttle valve cable to the throttle lever as the only mod.

[Formulabruce]

While Brad makes great points, and is a great 4L80E supporter. ( I own 2 and love them) I will tell you a stage 2 th2004r will slide in with much less money, effort IMHO.
1. Th2004r uses the th400 cross member, AND mount.
2. Th2004r uses 1 wire for Lock up, I use the th400 kick down wire.
3. Th2004r doesn't need any adapters.
4. Th2004r uses a th350 drive shaft that are so plentiful.
5. Yes you can use a detent upgrade in shifter, but Do not have to, works fine with stock detents.
The th2004r will shift on its own once built, NO " box" needed. ( a 4L80 will do if built with manual valve body)
Then its a 4L80, with no " E" .
So for around 3k, you can get a stage 2 th200r4 built well, and have .67 OD.
One sits behind my HO. I do run an an additional tranny cooler up front.

[1971455HO]

Thanks tons gentlemen for all your great advice. I've mulled it over in my head head a lot and did a good bit of asking around for who could hook me up with various configurations. I finally decided on using the 4L80E. Bought a built for my car 4L80E direct from Hughes Performance. They were totally knowledgeable about what my car needed. Spent the extra money and had them machine the tail-shaft for using the factory speedometer cable. Didn't want to start digging my factory gauges out of the dash. Bought the trans, converter, adapter plate (Chevy trans to BOP engine), shift controller, trans mount, etc. etc.
Didn't stop there. Bought all the stuff to convert to fuel injection (tank, in tank pump, supply & return from Tanks Inc. Bought Holley Sniper Quadrajet EFI, harness and distributor that controls timing with the Sniper EFI.

Keeping my original carb, mechanical fuel pump, original trans, original cross member, original driveshaft for preservation. I hired all this out to a reputable speed shop close to me. I'm getting too old to wrestle engines and trans out of cars. Now days, I can back-hand a balloon and it bruises me for a month (LOL). Plus the young boys jump on this stuff like its childsplay. I thank all of you again for all your advice and comments. Cant wait to get it back and drive it on the Interstate @ 75 and only be running around 1800-2000 rpm. Thanks Sirrotica for pointing me toward the 4L80E. I think it will be just what I need.

[Formulabruce]

You figured out Reverse lights?
Using your back drive at all?
Your column has to be Fully clocked counter clockwise
To get your key out, and your reverse lights come on in that position..
Hope it all goes well and you enjoy it!

[Sirrotica]

Originally Posted by 1971455HO

Thanks tons gentlemen for all your great advice. I've mulled it over in my head head a lot and did a good bit of asking around for who could hook me up with various configurations. I finally decided on using the 4L80E. Bought a built for my car 4L80E direct from Hughes Performance. They were totally knowledgeable about what my car needed. Spent the extra money and had them machine the tail-shaft for using the factory speedometer cable. Didn't want to start digging my factory gauges out of the dash. Bought the trans, converter, adapter plate (Chevy trans to BOP engine), shift controller, trans mount, etc. etc.
Didn't stop there. Bought all the stuff to convert to fuel injection (tank, in tank pump, supply & return from Tanks Inc. Bought Holley Sniper Quadrajet EFI, harness and distributor that controls timing with the Sniper EFI.

Keeping my original carb, mechanical fuel pump, original trans, original cross member, original driveshaft for preservation. I hired all this out to a reputable speed shop close to me. I'm getting too old to wrestle engines and trans out of cars. Now days, I can back-hand a balloon and it bruises me for a month (LOL). Plus the young boys jump on this stuff like its childsplay. I thank all of you again for all your advice and comments. Cant wait to get it back and drive it on the Interstate @ 75 and only be running around 1800-2000 rpm. Thanks Sirrotica for pointing me toward the 4L80E. I think it will be just what I need.

You're welcome, I spent a lot of time weighing out every option there is for converting an older muscle car to OD, I even have a 200 4r core transmission sitting in the shed I could have used. The 4L80E has the tried and true T400 innards, with GM engineered OD. It won't need any parts to make it strong, it already is as strong as most people on this board will ever need. Plus any halfway decent transmission shop can rebuild it properly for under a grand, local guy gave me a price of $800 to do mine.

The thing that absolutely made up my mind is owning 3 chevy trucks with the 4L80E, all of them made it over 250,000 miles. Two of the trucks were company trucks, so I know they weren't babied, and were more than likely abused.

As I posted previously at 270,000 miles the K3500 dually turbo diesel 4L80E finally gave up without any warning, lost OD, then 3rd, and I made it back home in 2nd gear.

I bought another K3500 454 gas engine to replace it, because it is badly rusted, and I just didn't want to dump another $800 into it to get the transmission rebuilt, plus the transfer case needs a chain and bearings too.. The truck is a 93, so it has lived a long life, owes me nothing over the last 12 years I've owned it.

Good luck with the conversion.........

[Formulajones]

Generally what I do on the 4L80E conversions with floor shifters and back up lights, is move the neutral safety switch down to the shifter, which was a factory setup anyway on many types of cars.

I then either make my own harness or buy a repop harness if it's available. From there it's as simple as unplugging the wires at the neutral safety on the column, running the new wires under the carpet and down to the new neutral safety switch on the shifter. Then you have a neutral safety that works as it should with functional back up lights.

The backdrive portion likely won't be able to be reused with the 4L80E. The problem you run into is the shift lever on the 4L80 is moved back about 2 or 3 inches from the 400 turbo location, so the linkage will no longer line up with the frame bracket mechanism that pivots the rod. Even if you are able to relocate the frame bracket, then the rod becomes too short and it starts a domino affect.
The problem with moving the frame bracket back, is that on many cars, it also moves it down on some applications as you move further away from the curvature of the frame. It ends up back so far that the rod that has to go up to the column now doesn't clear the floor pan either where it transitions upward to the toe board.
Just some things you run into.....

FYI Shift Works makes the conversion shifter pieces to work with the 4L80E to keep your factory shifter. They also sell at least one version I'm aware of, of a shifter mounted neutral safety switch.

[turbo69bird]

Originally Posted by giles

Steve T (455hota) on here installed a gear vendors unit behind a THM 400 20 years ago on a 71 TA he had at the time. I was interested but decided against it for my car when I saw how much he had to “massage” the floor pan for clearance. Based on this I’d go with a 2004R. Same length as THM 400, same crossmember mount, non electronic versions and they can be built to withstand the abuse of 9 sec turbo Buicks so I think they can live behind a 455. You do have to add a throttle valve cable to the throttle lever as the only mod.

My buddy Brian out of new Britain CT builds these units for all the gran national guys if you need his info just PM me he build a very strong 200r4

[Formulabruce]

One Can get a 4L80 E built with a hydraulic shifted / maual valve body so it works like a TH400. This would be a 4L80.
NO controller.
I have a stage 3 th2004R and love it. 1 wire.
That said, I saw a 4L80 case recently that is BOPC. Haven't seen one built though.
I recently sold a BOPC 200 4R. Trans for a chevy camaro.

[Formulajones]

I'm not sure why you would want to??

The electronic control is what makes this trans a beauty to tune and drive. The electronic control of the converter lockup alone is worth the price of admission.

It's great behind even the rowdiest street cars as I can control when the converter locks up, how it locks up, how fast or hard it locks up, and the same is true with how it unlocks, making converter lockup with any camshaft and rearend ratio a non issue. All done from sitting in the car. Completely eliminates all the complaints you hear about the TV cable and vacuum switch style lockup converters behind even mild camshaft setups, which is why so many are building that style trans without a lockup, and missing all the benefits of a good lockup converter.

Not to mention the ease of tuning shift points with a few key strokes, how firm you want things and at what throttle angle. I can even do things like command the converter to lockup at full throttle anywhere from 2nd gear onward, if you do a converter capable of holding the power.

There's much more but would take too long to list. I understand it's the cost that people really struggle with though.

[Formulabruce]

Formulajones, I agree with you, I have a 4L80E Tuner myself and mostly use it for fuel economy with 4.11 gears.
My point was merely to show that the trans can be taken off the controller, like my 2004R was. Has a TV cable though and 1 wire lock up which can be adjusted as well.
Most of the manual 4L80s I have seen are in off road trucks.
Just pointing out the options...

[Formulajones]

Originally Posted by Formulabruce

Formulajones, I agree with you, I have a 4L80E Tuner myself and mostly use it for fuel economy with 4.11 gears.
My point was merely to show that the trans can be taken off the controller, like my 2004R was. Has a TV cable though and 1 wire lock up which can be adjusted as well.
Most of the manual 4L80s I have seen are in off road trucks.
Just pointing out the options...

I'd have to check but I thought it still had the ability to accept a vacuum modulator?? Or maybe a simple full manual valve body conversion would accomplish it.