TH400 leaking worse than ever... - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**COBALT** · 05-20-2002, 11:34 AM

So I'm going to drop it out and replace the front/rear main seals + drain fluid and replace filter and pan gasket. My question is what do I do about the converter?

I know the real leaking problem is coming from the front somewhere, but blow-back is covering the tranny with fluid every time I drive it, so I can only guess it's the front main seal.

The only way the converter could leak is if there was either a hole in the side of the converter, or where the main shaft from the tranny goes into the converter by the main seal, right?

How should I inspect the converter?

------------------
'69 3/4 ton C20 2wd w/ 350ci/400THM and a wood bed!
'69 3/4 ton Custom 20 2wd w/ ORIGINAL 350ci/4sp Manual and a wood bed (parts beast).
Seattle, WA.

*See pics of my trucks and project at www.webshots.com!

Chevyc10! · 05-20-2002, 11:37 AM

If your dropping the tranny then you will be able to give it a good look. But if the input isn't messed up then that really all you can check, besides looking for holes. Sounds like the front seal is FUBAR. I've never had a converter leak on me...

------------------
68 SWB
The Surgeon General doesn't say anything about smoking a Ford!!!
Would rather be ran over repeatedly by a Chevy than drive a Ford!!!

Paralyzed from the neck up and confined to a hat!

71GMC_3/4T · 05-20-2002, 02:33 PM

I have a similar problem with mine. So far, I've replaced the seals on both the speedo and kickdown switch. I plan to try the dipstick tube seal next.
Mine doesn't drip out of the little hole at the bottom of the inspection cover like I would expect if the torque converter or front pump seals were bad. I got to thinking that the seal for the dipstick tube could have been damaged by the previous owner when he had the engine out. I'm pretty sure it isn't the pan gasket but the fluid drips off the ridge of the pan.
Let me know what you find, new69...

**COBALT** · 05-20-2002, 02:43 PM

I will. Thanks for the replies.

It's funny you mentioned the hole in the converter cover, and the dipstick tube. Ever since I bought the truck I've had this slick film of tranny fluid all over the cover, the tranny pan, and as far back as the X-member. It does look like it's coming out of the hole in the converter cover, but the amount of fluid has never been very much on the ground! It's just all over the damn tranny.

A couple of weeks ago I got under there with some cleaner and a few rags, and cleaned it up, and went driving for 5 minutes or so. I had it covered with fluid again! It must be coming out of the front pump seal, the pan, and the dipstick tube all at the same time.

By the time I get done with it it shouldn't leak at all...

------------------
'69 3/4 ton C20 2wd w/ 350ci/400THM and a wood bed!
'69 3/4 ton Custom 20 2wd w/ ORIGINAL 350ci/4sp Manual and a wood bed (parts beast).
Seattle, WA.

*See pics of my trucks and project at www.webshots.com!

bouncytruck · 05-20-2002, 03:29 PM

One of the rebuild books I have shows how to drain the converter by drilling a small hole in it and then plugging it with a rivet. Is it possible that someone could have done this in a previous rebuild and now it is leaking? You may also have a crack in the TC. If you drop the tranny, you'll be able to inspect the TC for crack, balloning, etc.

------------------
'69 K-5 Blazer - 350/TH350, 6" lift, 35" tires
Bothell, WA

**COBALT** · 05-20-2002, 03:34 PM

bouncytruck: that's exactly what I was thinking. I've heard of that technique to drain the converter while the tranny is still in the truck. I also know if you use the wrong kind of rivet you could ruin the converter (it will always leak and NEVER be right again).

Considering what I find I may want to see if I can pick up a used torque converter just to have around. I have another TH400 that needs rebuilding and doesn't have a TC anyway, so...

Thanks for reminding me.

------------------
'69 3/4 ton C20 2wd w/ 350ci/400THM and a wood bed!
'69 3/4 ton Custom 20 2wd w/ ORIGINAL 350ci/4sp Manual and a wood bed (parts beast).
Seattle, WA.

*See pics of my trucks and project at www.webshots.com!

Gordo · 05-20-2002, 04:03 PM

I have sen the "neck" of the converter (the part that inserts into the front pump) crack and it will be noticable when you inspect it. I also have seen the converter drilled, tapped and plugged with a 1/8 pipe plug for draining. My trans shop does this and haven't seen one leak yet.

------------------
1971 C10 swb stepside 350/700R4/3.73posi
Killingworth, Connecticut

bouncytruck · 05-20-2002, 04:08 PM

new69, I have a book that explains how to drain the TC and how to check it for Ballooning, etc. Your welcome to borrow it over the long weekend but you'll have to come over to Bellevue to pick it up.

------------------
'69 K-5 Blazer - 350/TH350, 6" lift, 35" tires
Bothell, WA

**COBALT** · 05-20-2002, 04:27 PM

Let me guess:

"How to Work With and Modify the Turbo Hydra-Matic 400 Transmission", by Ron Sessions, Motorbooks International, 1996.

Now you're going to ask "Wow! How did he know that!", and I'm going to respond "...because I'm psychic."

lol

Yeah...you're just trying to lure me to Bellevue! Maybe I'll come out and let my tranny leak all over your driveway.

Seriously, is that the book you meant, bouncytruck?

Gordo: I like the tapping idea. Do they tap it as a pressure fitting?

------------------
'69 3/4 ton C20 2wd w/ 350ci/400THM and a wood bed!
'69 3/4 ton Custom 20 2wd w/ ORIGINAL 350ci/4sp Manual and a wood bed (parts beast).
Seattle, WA.

*See pics of my trucks and project at www.webshots.com!

[This message has been edited by new69owner (edited May 20, 2002).]

*Zkast* · 05-20-2002, 07:07 PM

If you guys are having trouble sealing the front pump/torque convertor area of GM transmissions, Don't just replace the seal.

If the trans has a few miles on it and the there is a good sized leak coming from teh bell housing area, there are 3 things that make it leak.
1. Seal rubber hardens, shrinks and cracks.
2. torque convertor bushing inside the pump (just behind the seal). Causes the TC to move more than the seal can handle.
3. pump to body gasket. This is a tough one to find, it will act similar to a front pump seal/bushing.

When we have a leak on a known good transmission, it is recommend the customer have the Seal, bushing and front pump gasket replaced. Also through a shift shaft seal in for good measure

If your not comfortable pulling the pump out of the transmission its best to let the pro's do it. It only takes one wrong move and cut a teflon seal.. then the fun begins.

------------------
Pictures and more...
piston@zkast.com
'71 LWB
350/350T, PS/PB
Special options? Yes, RUST... Need some?
------------------------------------------
Webmaster/Team owner
www.zkast.com
Garrett - Olathe, Kansas

[This message has been edited by Zkast (edited May 20, 2002).]

Gordo · 05-20-2002, 07:47 PM

The tap would be a 1/8 pipe thread along with a 1/8 pipe plug. I have also seen the bolts with gasket washers holding the front pump in place loosen up and leak.

------------------
1971 C10 swb stepside 350/700R4/3.73posi
Killingworth, Connecticut

bouncytruck · 05-21-2002, 11:02 AM

New69, Yeah, that's the book I have. You must have ESP or something. By the way, my truck does a fine job of leaking all over the driveway, but thanks for the offer.

Hope you get it fixed.

------------------
'69 K-5 Blazer - 350/TH350, 6" lift, 35" tires
Bothell, WA

05-20-2002, 11:34 AM	#1
COBALT Senior Member Join Date: Sep 2001 Location: Seattle, WA, USA Posts: 5,817	TH400 leaking worse than ever... So I'm going to drop it out and replace the front/rear main seals + drain fluid and replace filter and pan gasket. My question is what do I do about the converter? I know the real leaking problem is coming from the front somewhere, but blow-back is covering the tranny with fluid every time I drive it, so I can only guess it's the front main seal. The only way the converter could leak is if there was either a hole in the side of the converter, or where the main shaft from the tranny goes into the converter by the main seal, right? How should I inspect the converter? ------------------ '69 3/4 ton C20 2wd w/ 350ci/400THM and a wood bed! '69 3/4 ton Custom 20 2wd w/ ORIGINAL 350ci/4sp Manual and a wood bed (parts beast). Seattle, WA. *See pics of my trucks and project at www.webshots.com! __________________ '69 3/4 ton C20 2wd-350ci/TH400 '69 3/4 ton Custom 20 2wd-350ci/4sp Manual '99 2wd 5.7 Chevy Tahoe Seattle, WA.

05-20-2002, 11:37 AM	#2
Chevyc10! Registered User Join Date: Dec 2000 Location: Centerville Ga. USA Posts: 804	If your dropping the tranny then you will be able to give it a good look. But if the input isn't messed up then that really all you can check, besides looking for holes. Sounds like the front seal is FUBAR. I've never had a converter leak on me... ------------------ 68 SWB The Surgeon General doesn't say anything about smoking a Ford!!! Would rather be ran over repeatedly by a Chevy than drive a Ford!!! Paralyzed from the neck up and confined to a hat! __________________ 68 SWB The Surgeon General doesn't say anything about smoking a Ford!!! Would rather be ran over repeatedly by a Chevy than drive a Ford!!! Paralyzed from the neck up and confined to a hat! Kathleen, Georgia USA

05-20-2002, 02:33 PM	#3
71GMC_3/4T Weapons Of Construction Join Date: Apr 2000 Location: Colorado, USA Posts: 1,095	I have a similar problem with mine. So far, I've replaced the seals on both the speedo and kickdown switch. I plan to try the dipstick tube seal next. Mine doesn't drip out of the little hole at the bottom of the inspection cover like I would expect if the torque converter or front pump seals were bad. I got to thinking that the seal for the dipstick tube could have been damaged by the previous owner when he had the engine out. I'm pretty sure it isn't the pan gasket but the fluid drips off the ridge of the pan. Let me know what you find, new69... __________________ 1971 GMC 2500, 402/TH400 4.10 Daily Driver Lafayette, CO

05-20-2002, 02:43 PM	#4
COBALT Senior Member Join Date: Sep 2001 Location: Seattle, WA, USA Posts: 5,817	I will. Thanks for the replies. It's funny you mentioned the hole in the converter cover, and the dipstick tube. Ever since I bought the truck I've had this slick film of tranny fluid all over the cover, the tranny pan, and as far back as the X-member. It does look like it's coming out of the hole in the converter cover, but the amount of fluid has never been very much on the ground! It's just all over the damn tranny. A couple of weeks ago I got under there with some cleaner and a few rags, and cleaned it up, and went driving for 5 minutes or so. I had it covered with fluid again! It must be coming out of the front pump seal, the pan, and the dipstick tube all at the same time. By the time I get done with it it shouldn't leak at all... ------------------ '69 3/4 ton C20 2wd w/ 350ci/400THM and a wood bed! '69 3/4 ton Custom 20 2wd w/ ORIGINAL 350ci/4sp Manual and a wood bed (parts beast). Seattle, WA. *See pics of my trucks and project at www.webshots.com! __________________ '69 3/4 ton C20 2wd-350ci/TH400 '69 3/4 ton Custom 20 2wd-350ci/4sp Manual '99 2wd 5.7 Chevy Tahoe Seattle, WA.

05-20-2002, 03:29 PM	#5
bouncytruck SKINNY TIRES RULE! Join Date: Sep 2001 Location: Bothell, WA Posts: 11,038	One of the rebuild books I have shows how to drain the converter by drilling a small hole in it and then plugging it with a rivet. Is it possible that someone could have done this in a previous rebuild and now it is leaking? You may also have a crack in the TC. If you drop the tranny, you'll be able to inspect the TC for crack, balloning, etc. ------------------ '69 K-5 Blazer - 350/TH350, 6" lift, 35" tires Bothell, WA __________________ bouncytruck 1972 K5 The Hauler 1994 K1500 Suburban The Daily2010 Kia Soul Wife's Ride2014 Fiat 500L

05-20-2002, 03:34 PM	#6
COBALT Senior Member Join Date: Sep 2001 Location: Seattle, WA, USA Posts: 5,817	bouncytruck: that's exactly what I was thinking. I've heard of that technique to drain the converter while the tranny is still in the truck. I also know if you use the wrong kind of rivet you could ruin the converter (it will always leak and NEVER be right again). Considering what I find I may want to see if I can pick up a used torque converter just to have around. I have another TH400 that needs rebuilding and doesn't have a TC anyway, so... Thanks for reminding me. ------------------ '69 3/4 ton C20 2wd w/ 350ci/400THM and a wood bed! '69 3/4 ton Custom 20 2wd w/ ORIGINAL 350ci/4sp Manual and a wood bed (parts beast). Seattle, WA. *See pics of my trucks and project at www.webshots.com! __________________ '69 3/4 ton C20 2wd-350ci/TH400 '69 3/4 ton Custom 20 2wd-350ci/4sp Manual '99 2wd 5.7 Chevy Tahoe Seattle, WA.

05-20-2002, 04:03 PM	#7
Gordo Registered User Join Date: Jan 2001 Location: Killingworth, CT. USA Posts: 3,378	I have sen the "neck" of the converter (the part that inserts into the front pump) crack and it will be noticable when you inspect it. I also have seen the converter drilled, tapped and plugged with a 1/8 pipe plug for draining. My trans shop does this and haven't seen one leak yet. ------------------ 1971 C10 swb stepside 350/700R4/3.73posi Killingworth, Connecticut __________________ 1971 C10 swb stepside 350/700R4/3.73posi (retired as of 4/22/03) 1998 S10 short bed 2002 S10 Blazer 1942 Oldsmobile 1958 Massey Harris Pony 1951 Wife Killingworth, Connecticut May those who love us, love us, any of those who do not love us, may God turn their hearts. And if God is unable to turn their hearts, may he turn their ankles so we may know them by their limping. A man who works with his hands is a laborer; a man who works with his hands and his brain is a craftsman; but a man who works with his hands and his brain and his heart is an artist.

05-20-2002, 04:08 PM	#8
bouncytruck SKINNY TIRES RULE! Join Date: Sep 2001 Location: Bothell, WA Posts: 11,038	new69, I have a book that explains how to drain the TC and how to check it for Ballooning, etc. Your welcome to borrow it over the long weekend but you'll have to come over to Bellevue to pick it up. ------------------ '69 K-5 Blazer - 350/TH350, 6" lift, 35" tires Bothell, WA __________________ bouncytruck 1972 K5 The Hauler 1994 K1500 Suburban The Daily2010 Kia Soul Wife's Ride2014 Fiat 500L

05-20-2002, 04:27 PM	#9
COBALT Senior Member Join Date: Sep 2001 Location: Seattle, WA, USA Posts: 5,817	Let me guess: "How to Work With and Modify the Turbo Hydra-Matic 400 Transmission", by Ron Sessions, Motorbooks International, 1996. Now you're going to ask "Wow! How did he know that!", and I'm going to respond "...because I'm psychic." lol Yeah...you're just trying to lure me to Bellevue! Maybe I'll come out and let my tranny leak all over your driveway. Seriously, is that the book you meant, bouncytruck? Gordo: I like the tapping idea. Do they tap it as a pressure fitting? ------------------ '69 3/4 ton C20 2wd w/ 350ci/400THM and a wood bed! '69 3/4 ton Custom 20 2wd w/ ORIGINAL 350ci/4sp Manual and a wood bed (parts beast). Seattle, WA. *See pics of my trucks and project at www.webshots.com! [This message has been edited by new69owner (edited May 20, 2002).] __________________ '69 3/4 ton C20 2wd-350ci/TH400 '69 3/4 ton Custom 20 2wd-350ci/4sp Manual '99 2wd 5.7 Chevy Tahoe Seattle, WA.

05-20-2002, 07:07 PM	#10
Zkast Account Suspended Join Date: May 2002 Location: Olathe, Kansas Posts: 929	If you guys are having trouble sealing the front pump/torque convertor area of GM transmissions, Don't just replace the seal. If the trans has a few miles on it and the there is a good sized leak coming from teh bell housing area, there are 3 things that make it leak. 1. Seal rubber hardens, shrinks and cracks. 2. torque convertor bushing inside the pump (just behind the seal). Causes the TC to move more than the seal can handle. 3. pump to body gasket. This is a tough one to find, it will act similar to a front pump seal/bushing. When we have a leak on a known good transmission, it is recommend the customer have the Seal, bushing and front pump gasket replaced. Also through a shift shaft seal in for good measure If your not comfortable pulling the pump out of the transmission its best to let the pro's do it. It only takes one wrong move and cut a teflon seal.. then the fun begins. ------------------ Pictures and more... piston@zkast.com '71 LWB 350/350T, PS/PB Special options? Yes, RUST... Need some? ------------------------------------------ Webmaster/Team owner www.zkast.com Garrett - Olathe, Kansas [This message has been edited by Zkast (edited May 20, 2002).]

05-20-2002, 07:47 PM	#11
Gordo Registered User Join Date: Jan 2001 Location: Killingworth, CT. USA Posts: 3,378	The tap would be a 1/8 pipe thread along with a 1/8 pipe plug. I have also seen the bolts with gasket washers holding the front pump in place loosen up and leak. ------------------ 1971 C10 swb stepside 350/700R4/3.73posi Killingworth, Connecticut __________________ 1971 C10 swb stepside 350/700R4/3.73posi (retired as of 4/22/03) 1998 S10 short bed 2002 S10 Blazer 1942 Oldsmobile 1958 Massey Harris Pony 1951 Wife Killingworth, Connecticut May those who love us, love us, any of those who do not love us, may God turn their hearts. And if God is unable to turn their hearts, may he turn their ankles so we may know them by their limping. A man who works with his hands is a laborer; a man who works with his hands and his brain is a craftsman; but a man who works with his hands and his brain and his heart is an artist.

05-21-2002, 11:02 AM	#12
bouncytruck SKINNY TIRES RULE! Join Date: Sep 2001 Location: Bothell, WA Posts: 11,038	New69, Yeah, that's the book I have. You must have ESP or something. By the way, my truck does a fine job of leaking all over the driveway, but thanks for the offer. Hope you get it fixed. ------------------ '69 K-5 Blazer - 350/TH350, 6" lift, 35" tires Bothell, WA __________________ bouncytruck 1972 K5 The Hauler 1994 K1500 Suburban The Daily2010 Kia Soul Wife's Ride2014 Fiat 500L



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