83 Turbo 700R4 Fluid Leak?

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83 Turbo 700R4 Fluid Leak?

Post by Ken0069 » Mon Aug 25, 2014 9:38 am

I've got one of these transmissions in an 83 Chevy half ton pickup and it's been leaking for years. Looks like it comes from the speedometer housing but I took all that out a week ago and replaced all the seals and it's still leaking?

But here's the weird part, it ONLY LEAKS AFTER IT'S BEEN SITTING FOR 2 OR MORE DAYS? There is NO evidence under the truck that it leaks while it's being driven as all the under side of the truck is dry as a bone?

Another thing, after the truck has sat for that period of time it's slow going in any gear? If I let it run for a minute or two before I put it in gear it does fine, or, if I drive it every day it works fine also but leave it sit long enough for it to start leaking fluid out and it's also slow going in gear.

Having said all that I'm wondering if this transmission has a torque converter anti-drainback valve that's bad? If the converter is actually draining back into the pan then that would explain both the leak and the slow going in gear part as the pump will have to put the fluid back in the converter before it will work.

So do any of you transmission experts know if there's a converter anti-drainback valve in these TH700 transmissions?
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Re: 83 Turbo 700R4 Fluid Leak?

Post by TexasT » Mon Aug 25, 2014 12:59 pm

Check the tv cable seal, dipstick seal and the shift shaft seal.
As the torque converter drains back the fluid in the pan rises and uou are getting a leak. I'd clean those areas up and hit em with some baby powder and watch where the wet turns up.
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Re: 83 Turbo 700R4 Fluid Leak?

Post by Ken0069 » Tue Aug 26, 2014 11:26 am

Ok so no one knows anything about an anti-drainback valve in this transmission then?? :?:
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Re: 83 Turbo 700R4 Fluid Leak?

Post by TexasT » Fri Aug 29, 2014 9:10 pm

I'm not aware of an anti drainback valve in a 700.
My 2004r had a leak from the tv cable because I squished the tophat grommet. Once I replaced it the leak stopped.
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Re: 83 Turbo 700R4 Fluid Leak?

Post by Ken0069 » Sun Jul 08, 2018 5:33 pm

Ok, I resurrected this old post because I'm still driving this same truck, that's still doing the same thing it was doing back in 2014?? I did figure out that if I left the transmission fluid level in the pan 2 quarts low it doesn't leak, BUT, just like before, if I let it sit for a couple of days it's slow going in gear and I have to run it for a minute or so before it will pull off in either low or reverse?

The two quarts low isn't necessarily a problem per se because it's got a deep pan on it from when I used to tow a 20ft enclosed car trailer with it so running it that low doesn't seem to hurt it because it's still got the normal amount of fluid in the pan that a stock depth pan would hold.

But again, I'm convinced that there is a check valve somewhere in that thing that's suppose to keep the torque converter from draining back into the pan over time.

Since it's been a while, I was wondering if some new guys in here may have had some dealings with one of these things that could tell me how to fix it.

Anyone have any info on fixing this potential check valve problem?
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Re: 83 Turbo 700R4 Fluid Leak?

Post by af2 » Sun Jul 08, 2018 5:43 pm

Ken0069 wrote:
Sun Jul 08, 2018 5:33 pm


But again, I'm convinced that there is a check valve somewhere in that thing that's suppose to keep the torque converter from draining back into the pan over time.

Anyone have any info on fixing this potential check valve problem?
No check valve. The converter should fill when started. If not then look elsewhere.
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Re: 83 Turbo 700R4 Fluid Leak?

Post by woody b » Sun Jul 08, 2018 8:09 pm

Like AF2 said, no check valve. A leak at the speedo gear is common on those. A new gear if you can find one might help or the housing could be worn some. The shaft on the plastic gear is kinda threaded to direct fluid back into the transmission while running. When it's not spinning fluid just sits against the seal. (or leaks) It takes a few days due to the fluid level to get up to the gear to leak. The pump is probably a little weak, causing the delay going into gear after it sits for a while. The pumps were problematic on those. I'm not (usually) a snake oil fan but a bottle of Lube Guard sometimes works wonders on 700R4's. The early ones had plenty of problems. We used to have to push them in the shop and fix them before they could go out on the lot for sale. (New trucks, GMC dealer)
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Re: 83 Turbo 700R4 Fluid Leak?

Post by Alan Roehrich » Sun Jul 08, 2018 8:57 pm

Stator bushings and sealing rings on the input shaft, both worn. That allows the torque converter to drain back more than usual,it actually siphons.

Those were the absolute worst of the 700 R4 transmissions, the 86 was much better, and they got better from there.

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Re: 83 Turbo 700R4 Fluid Leak?

Post by Ken0069 » Mon Jul 09, 2018 4:44 pm

Alan Roehrich wrote:
Sun Jul 08, 2018 8:57 pm
Stator bushings and sealing rings on the input shaft, both worn. That allows the torque converter to drain back more than usual,it actually siphons.

Those were the absolute worst of the 700 R4 transmissions, the 86 was much better, and they got better from there.
Thanks all for the comments/suggestions.

Actually this transmission is a newer model from a Camaro that I bought locally but I can't remember what year car that it came out of. I do know it's a newer transmission than 1983. I had a guy overhaul this one using B&M stuff along with a shift kit to try to "firm up the shifts" when I was pulling the Studebaker and trailer with it. There was a NEW front pump put in it when it was overhauled along with a rebuilt torque converter when it went in the truck

The leak seems to be from the spedo housing and I've replaced the seals and stuff in that once before back when this first manifest itself. It didn't stop the leak though.

Will look into the Lube Guard thingie and may try a bottle of that.
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Re: 83 Turbo 700R4 Fluid Leak?

Post by TrOll » Wed Jul 11, 2018 10:31 am

Since your original post was back in 2014 and you are still driving it, it doesn't seem to be a major problem at this point. :wink:
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Re: 83 Turbo 700R4 Fluid Leak?

Post by midnightbluS10 » Thu Jul 12, 2018 3:57 am

woody b wrote:
Sun Jul 08, 2018 8:09 pm
Like AF2 said, no check valve. A leak at the speedo gear is common on those. A new gear if you can find one might help or the housing could be worn some. The shaft on the plastic gear is kinda threaded to direct fluid back into the transmission while running. When it's not spinning fluid just sits against the seal. (or leaks) It takes a few days due to the fluid level to get up to the gear to leak. The pump is probably a little weak, causing the delay going into gear after it sits for a while. The pumps were problematic on those. I'm not (usually) a snake oil fan but a bottle of Lube Guard sometimes works wonders on 700R4's. The early ones had plenty of problems. We used to have to push them in the shop and fix them before they could go out on the lot for sale. (New trucks, GMC dealer)
Lubeguard isn't snake oil luckily. It's recommended by multiple OEM's as a fix for torque converter shudder as well as different TSB's. It works or they wouldn't call for it to be used.

It's not slick 50 or prolong any of that other junk you'll never see an oem recommend for service on their vehicles.

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