# Upgrading TH400 to 4speed with overdrive - Gear Vendors?



## IceBolt (Jul 28, 2020)

So my '67 400ci/TH400 is my daily driver and love it. I do drive on the highway quite a bit and at 75mph, I'm turning @ 3200RPM; PHS says I have a 3:36 rear but I have not confirmed this. Considering switching to a 700R4 to something similar. Did find "Gear Vendors" that offers a bolt-on adaptor to a TH400 to add the 4th gear. Any experience with this approach?









GM 4-Speed Auto - Gearvendors


GM 4-Speed Automatics 700R4/4L60E/4L80E There are two basic GM 4-Speed automatics: The light duty 700R4/4L60E found mainly in half ton and car applications, and the heavy duty 4L80E in the heavier applications. 700R4/4L60E’s have a low 3.06 first gear which is good for initial take off but this...




www.gearvendors.com


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## Mine'sa66 (Oct 30, 2019)

The gear vendors product is a good one. Works as intended.


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## NOS Only (Nov 14, 2017)

GV is a good piece but you'll have a lot hanging off the back of the tranny and it will cost you a good buck. The 700R4 and 4L60 are the same tranny as is the 4L60e but the 4L60e uses a little electronics but nothing to get panties in a bunch. Cheapest OD bang for your buck (depending on your HP) would be a mild build 700R4/4L60. I get them done at local tranny shops for $700.00.

Keep in mind you'll need an adaptor plate, TV cable geometry correcting carb bracket and a shorter driveshaft.


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## IceBolt (Jul 28, 2020)

I'm only at about 350HP; might but a little more aggressive cam but that's all. $700.....is that for a rebuilt transmission? I'm in CA, hourly mechanic rates are rarely under $150 per hour!


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## NOS Only (Nov 14, 2017)

I'm in NY and my guy recently went from $650 to $700. CA with all their B.S. is most likely a bit higher.

A post 1986 700R4/4L60 with an "MD8" or "K" case, red discs and Corvette modulator will live a happy life behind a 450 horse or less engine.


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## Lemans guy (Oct 14, 2014)

I have the gear vendors and love it. It is behind my Beefed up TH350, with dual gate shifter. Gear vendors gives some pretty good info on their web. It is a cool unit. It basically puts an overdrive behind each gear you have. So I have six gears, 1st, 1st over, 2nd, 2nd over, 3rd 3rd over.. with my dual gate I can use the gear vendors as automatic or stick and it works great in both. It is very strong.

you will likely need a new driveshaft or have yours cut. I had the driveshaft shop make me a new one, it was around $200. I have had 700R4’s they are OK, in a lot of pickup trucks too.

I had Performance Torque Converter PTC put a ratchet diode in my Coan TH350 they said it would take 1000 ft lbs of torque, and they use TH350’s in drag cars with great success. The Th400 is beefy off the shelf.

Gear vendors is more money, but more unique and cool as well. And you can turn it on and off with a button on the shift ball. You will have to bang up some sheet metal on the trans tunnel and I also used an aftermarket frame cross member made especially for Gear vendors in A-Bodies from G-Force. A real stout product.

There are more economical ways than Gearvendors. But I love mine.


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## Lemans guy (Oct 14, 2014)

Oh and at 75MPH I will turn about 2500 RPM’s with a 308 rear end


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## IceBolt (Jul 28, 2020)

Thanks Lemans Guy! All options i'm considering require a new or shorten driveshaft. My brother has a shop in Colorado with a lift, can weld, and make side panels. I do like all the services/details that Gear Vendors have on their website. I'll check out 700R4 prices here and Colorado then make a decision. First, time to fix my Vintage Air system....starting to warm up even in CA. Cheers, Carl


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## NOS Only (Nov 14, 2017)

Also, look into the 4L80e as another option. A bit of overkill with 350 horse, but something else to consider.

F.Y.I.: 700's are basically a Turbo 350 with an O.D.. The 80's are basically a Turbo 400 with an O.D..


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## IceBolt (Jul 28, 2020)

NOS Only said:


> Also, look into the 4L80e as another option. A bit of overkill with 350 horse, but something else to consider.
> 
> F.Y.I.: 700's are basically a Turbo 350 with an O.D.. The 80's are basically a Turbo 400 with an O.D..


Thanks NOS Only; if I were to buy a new one - what companies do you suggest? I know Monster and


700R4 Master Conversion Package


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## NOS Only (Nov 14, 2017)

Save your $$$ and put it elsewhere in the car. No need to buy new. Any competent tranny shop that knows their O.D.'s can build you what you need.


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## IceBolt (Jul 28, 2020)

I live in the Bay Area in CA; does anyone have any good tranny shops to recommend?


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## NOS Only (Nov 14, 2017)

I only know of 2 CA tranny shops. Both are good.... damn good, and they charge for it.

One is Mike's.... A friend of mine has one of Mike's Powerglides in his '33 Willys. It cost him 5 grand.

Another is Art Carr aka: California Performance Transmissions. Art has been around since the horse & buggy.

Like I mentioned, seek out a local tranny shop that knows their chit.


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## IceBolt (Jul 28, 2020)

NOS Only said:


> I only know of 2 CA tranny shops. Both are good.... damn good, and they charge for it.
> 
> One is Mike's.... A friend of mine has one of Mike's Powerglides in his '33 Willys. It cost him 5 grand.
> 
> ...


Thanks, will ask around.


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## ylwgto (Oct 27, 2009)

IceBolt said:


> I live in the Bay Area in CA; does anyone have any good tranny shops to recommend?


My dad and I have been taking our old cars to Brian (owner) at John Wise Transmission in Belmont for about 15 years. Highly recommended. He does everything, but specialized in transmissions. One of the last shops that works on muscle cars on the Peninsula...old school knowledge. He recently did a super t10 5 speed conversion on my dad's '69 Cougar.

I also had my Th400 rebuilt at Watsonville Transmissions a LONG time ago. They did a good job, but not even sure that shop is there anymore.


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## IceBolt (Jul 28, 2020)

ylwgto said:


> My dad and I have been taking our old cars to Brian (owner) at John Wise Transmission in Belmont for about 15 years. Highly recommended. He does everything, but specialized in transmissions. One of the last shops that works on muscle cars on the Peninsula...old school knowledge. He recently did a super t10 5 speed conversion on my dad's '69 Cougar.
> 
> I also had my Th400 rebuilt at Watsonville Transmissions a LONG time ago. They did a good job, but not even sure that shop is there anymore.


Thanks ylqto! Local recommendations


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## IceBolt (Jul 28, 2020)

ylwgto said:


> My dad and I have been taking our old cars to Brian (owner) at John Wise Transmission in Belmont for about 15 years. Highly recommended. He does everything, but specialized in transmissions. One of the last shops that works on muscle cars on the Peninsula...old school knowledge. He recently did a super t10 5 speed conversion on my dad's '69 Cougar.
> 
> I also had my Th400 rebuilt at Watsonville Transmissions a LONG time ago. They did a good job, but not even sure that shop is there anymore.


Went to see Brian at Wise Transmission; very knowledgeable and discussed several approaches. Will probably go with a 700R4 Level 2 from BowTie Overdrive; they are working up a quote for me.


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## NOS Only (Nov 14, 2017)

If they can't build their own.... Move on.

GM overdrives for competent tranny shops is not rocket science.

Find someone that knows what they're doing. If there is ever an issue they'll turn their backs on you and tell you to deal with the company and Bowtie Overdrive has issues.


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## BearGFR (Aug 25, 2008)

Lemans guy said:


> I have the gear vendors and love it. It is behind my Beefed up TH350, with dual gate shifter. Gear vendors gives some pretty good info on their web. It is a cool unit. It basically puts an overdrive behind each gear you have. So I have six gears, 1st, 1st over, 2nd, 2nd over, 3rd 3rd over.. with my dual gate I can use the gear vendors as automatic or stick and it works great in both. It is very strong.
> 
> you will likely need a new driveshaft or have yours cut. I had the driveshaft shop make me a new one, it was around $200. I have had 700R4’s they are OK, in a lot of pickup trucks too.
> 
> ...


I'd really like to know more about your GV installation.

I know they can take the torque because that's what the majority, and maybe all, of the heavy hitters who participate in Hot Rod's Drag Week use - and they're running 6-7 second quarter mile ET's.

With a GV I could keep the same shifter, console, trans cable, etc. and not have to modify anything inside the cabin.

My concerns are fitment on my '69, and also transmission heat. With the converter I have it's right on the edge of "slip range" at 3200 RPM. If I put a GV in the car, then at highway cruise it's going to always be slipping a little so I'm concerned about that. My TH400 is not a switch pitch unit so it doesn't have the valving or passages to enable using a switch pitch converter.

Bear


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## Lemans guy (Oct 14, 2014)

Bear, I love my GV. Like you I wanted to keep what I had a Coan Racing Th350 trans, shift kit, dual gate shifter with a B&M ratchet shifter. Kept Original Console etc and had the Th350 beefed up with a ratchet diode to take 1000 ft lbs of torque.

I put that GV in myself. I have A 12 bolt posi rear out of A 67 Chevelle.

So GV, wow really well made piece. Bolts right on the back of the 350 or 400.

I used a G-Force aftermarket cross member as you need the drop in the mount to keep your pinion angle right and to fit the gear vendors in. G- Force makes one especially for the GV. I would recommend this as it wmaybe doable without it but much harder to get right or even fit.

Next you will have to bang some sheet metal on the trans tunnel up just a bit to fit the GV. This sounds more daunting than it really is. Remove the carpet dry fit it in andmark the area, pound it up with a 3lb sledge. A little effort but it will work.

Of course the driveshaft will need to change. I had the Driveshaft shop in Chattanooga, Tn jus build me a new one. And as I recall they had a recommendation different than GV manual to make the length Evan a 1/4 shorter than GV said to, Because they had done a lot of shafts for GV install.

I went with Rex and boy were they right. I have some notes on that, so if you decide to do it. I will dig them out for you. They had great prices and sure they would ship, but I am sure you have driveshaft shops in Texas to do it. I used to live in Dallas.

with GV you put a little electric box real small under dash, mine is under headlight switc, and a button on console that changes from auto to manual shifting for the GV and a button on the shift ball, where you can go in and out of the GV anytime you like. It basically splits all three gears to have an overdrive, so you will have 6 forward gears. My second over is 1.13 and 3rd is 1:1 of course and 3rd OD I think is .78.....so you can decide which one at any time. Just don’t bang it in too hard as normal.

My converter is a Coan with 2500 stall, actually, 2400 to 2600 and 3rd OD at 75MPH is 2400 or 2500 RPM’s. I am not sure the slippage will hurt that much, maybe lose some gas mileage, but give cooler cruising etc.

I cruise a lot on 4 lanes in 3rd over, you know with grass median not interstate at 50 or 55MPH at 2000 RPM and no problem with the converter.

They are deifinetley cool and very strong units.


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## Lemans guy (Oct 14, 2014)

Bear, I love my GV. Like you I wanted to keep what I had a Coan Racing Th350 trans, shift kit, dual gate shifter with a B&M ratchet shifter. Kept Original Console etc and had the Th350 beefed up with a ratchet diode to take 1000 ft lbs of torque.

I put that GV in myself. I have A 12 bolt posi rear out of A 67 Chevelle.

So GV, wow really well made piece. Bolts right on the back of the 350 or 400.

I used a G-Force aftermarket cross member as you need the drop in the mount to keep your pinion angle right and to fit the gear vendors in. G- Force makes one especially for the GV. I would recommend this as it wmaybe doable without it but much harder to get right or even fit.

Next you will have to bang some sheet metal on the trans tunnel up just a bit to fit the GV. This sounds more daunting than it really is. Remove the carpet dry fit it in andmark the area, pound it up with a 3lb sledge. A little effort but it will work.

Of course the driveshaft will need to change. I had the Driveshaft shop in Chattanooga, Tn jus build me a new one. And as I recall they had a recommendation different than GV manual to make the length Evan a 1/4 shorter than GV said to, Because they had done a lot of shafts for GV install.

I went with Rex and boy were they right. I have some notes on that, so if you decide to do it. I will dig them out for you. They had great prices and sure they would ship, but I am sure you have driveshaft shops in Texas to do it. I used to live in Dallas.

with GV you put a little electric box real small under dash, mine is under headli


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## IceBolt (Jul 28, 2020)

Lemans guy said:


> Bear, I love my GV. Like you I wanted to keep what I had a Coan Racing Th350 trans, shift kit, dual gate shifter with a B&M ratchet shifter. Kept Original Console etc and had the Th350 beefed up with a ratchet diode to take 1000 ft lbs of torque.
> 
> I put that GV in myself. I have A 12 bolt posi rear out of A 67 Chevelle.
> 
> ...


Great info @ Lemansguy, I have a 3 lbs hammer and not afraid to bang a few things! My main concern is to get the correct length on new drive shaft. I'm assuming they will provide guidance to measure....or know what I'll need based on TH400, 400ci original engine, and 3:36 rear end? I have no idea what the tolerance would need to be except to make sure the car is sitting on wheels when measuring.


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## NOS Only (Nov 14, 2017)

I do 2600 - 2800 RPM at 75 MPH with 4:30 gears with my 700R4


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## Lemans guy (Oct 14, 2014)

That is real good NOS, nice cruising speed. Yes I also used an air chisel with a blunt hammer bit that punched thee sheet metal up a bit.

As for the drive shaft length GV gives very good instructions to measure it exactly, but the driveshaft shop recommended cutting it a tad shorter, maybe a 1/4 inch. They said they had done a lot of GV shafts and you needed that room to bolt it up easy and boy were they right. If you start to do it let me know and I will double check my notes on it to make sure what that size was 1/4 I think. But would have to refresh.


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