TH350 is bleeding! - The 1947 - Present Chevrolet & GMC Truck Message Board Network

383drvr · 10-15-2003, 12:09 AM

The 350 transmission in my 83 is leaking from the tailshaft area. But it only leaks intermitantly. Not necessarily when its on a hill, it leaks sometimes when the truck is perfectly level in my backyard. It will go weeks and months sometimes before "purging" almost a quart onto my drive

So, Do you think its a rear seal even though it leaks on and off? I've had this truck for a few months now, and the previous owner (mechanic), said he just replaced it...

If it is the rear seal, is it something I can fix myself in a few hours or over the weekend? Its my only driver.... What is the process in replacing this part?

Thanks!

Frank-id · 10-15-2003, 12:28 AM

Repairing a rear trans leak is not difficult,........... with some good parts and tools. The repair is pretty straight forward. Remove the driveline out of truck, place drain pan under rear of trans, and remove tail housing from trans. Go to a good parts house and buy a few quarts of ATF , a rear seal and rear bushing. The seal usually only leaks when the rear bushing is all worn big. Take bushing and seal to local trans shop and pay to have same installed. The trans shop will have correct tools and experience as to fit. Go to truck and reinstall all parts removed earlier. If extension housing gasket is not broken, reinstall with a dab of silicone. Fill ATF to full after short warm up.

gchemist · 10-15-2003, 02:56 AM

You have a problem with the output shaft o-ring.
Read this http://www.73-87.com/garage/yokeleak.htm

383drvr · 10-15-2003, 11:25 AM

Cool. Only problem is I dont have a ride to the trans shop... Is it possible for me to do it? Or does it require presses and specialty tools that I wont have?

Also, I need a new speedo gear, Where are they available? (please dont say trans shop) :p

Slonaker · 10-15-2003, 08:35 PM

I replaced the o-ring in my th-350 like was suggested on Swervin's site in gchemist's post. I had an intermittent leak, and that fixed it. I did not need any special tools. I got the parts at the dealer for less than $10 because the guys at the local parts stores kept guessing which o-rings I needed, and selling me the wrong parts. The dealer got it right the first time and did noit charge much more.

I got my new speedo gear from, you guessed it, a tranny shop. There is a place here in town where the tranny shops buy their parts. I got a new gear there for two or three dolllars, I think. Go ahead and get a new "bullet" and seal while you are at it. Ther whole set with new seal and o-ring was under $10 at the shop here.

Slonaker

79 stepside · 10-23-2003, 04:54 PM

I crawled out from under my p/u, cleaned off my hands, hopped on the internet, found your site, registered, typed in my search, and found an EXACT picture of my problem with the instructions on how to do it. First thread I looked at too! I'm impressed and also grateful! Too late to go to the parts store today, but will do the dis-assembly today and get the parts in the morning. I can see the fluid oozzing out of the weephole. I'm going to look for a thread on driveshaft removal, and hope for the same luck.
Thank yall!
JL

Thanks for the welcome below. I've bookmarked the site, and WILL spend much time here I'm sure. Bought my truck brand new in '79, and will have it forever. Lots of sentimental value, as I basically grew up in it.

gchemist · 10-23-2003, 06:29 PM

79 stepside,
Welcome to the site.
By the way, a small dab of BJ welds works too.

**swervin ervin** · 10-23-2003, 08:17 PM

You don't want to cover up the hole in the yoke. It was put there for a purpose. The purpose is to help relieve the pressure that the yoke causes as it moves in and out. This is on trucks because they have more bounce and up and down motion. If this pressure isn't relieved, it causes other blown seals. Now, this is theory and a good one if you ask me. Plug it if you want to. But for me, I prefer to do it the right way. I don't think GM went to all this trouble for nothing, do you?

79 stepside · 10-27-2003, 12:45 AM

Thanks for the original question and for the help given as it fixed my problem also. Had to go to a couple of Chevy houses to get all the orings and seals, but the work was easy. Getting the driveshaft back in was the hardest part. The oring in the cup took care of the oozzing out of the weep hole, and I replaced the rear seal and the oring around the speedo gear assy also. Now maybe I can drive this thing a little more often.
Thank yall a bunch...
Jimmy

84Stepper · 10-28-2003, 12:11 AM

I replaced the O-ring in my leaky truck, I just followed swervins advice on his website. Real easy. Got the o-ring at the chevy parts store at the dealer. Thanks again Swervin for all you have done to help me.

10-15-2003, 12:09 AM	#1
383drvr Registered User Join Date: Oct 2003 Location: Dallas, Tx. Posts: 308	TH350 is bleeding! The 350 transmission in my 83 is leaking from the tailshaft area. But it only leaks intermitantly. Not necessarily when its on a hill, it leaks sometimes when the truck is perfectly level in my backyard. It will go weeks and months sometimes before "purging" almost a quart onto my drive So, Do you think its a rear seal even though it leaks on and off? I've had this truck for a few months now, and the previous owner (mechanic), said he just replaced it... If it is the rear seal, is it something I can fix myself in a few hours or over the weekend? Its my only driver.... What is the process in replacing this part? Thanks!

10-15-2003, 12:28 AM	#2
Frank-id Registered User Join Date: Sep 2003 Location: Twin Falls, Idaho Posts: 73	The turbo 350 trans an easy keeper Repairing a rear trans leak is not difficult,........... with some good parts and tools. The repair is pretty straight forward. Remove the driveline out of truck, place drain pan under rear of trans, and remove tail housing from trans. Go to a good parts house and buy a few quarts of ATF , a rear seal and rear bushing. The seal usually only leaks when the rear bushing is all worn big. Take bushing and seal to local trans shop and pay to have same installed. The trans shop will have correct tools and experience as to fit. Go to truck and reinstall all parts removed earlier. If extension housing gasket is not broken, reinstall with a dab of silicone. Fill ATF to full after short warm up. __________________ Chevy stepper 400sb 350 turbo

10-15-2003, 02:56 AM	#3
gchemist BAD BOW-Silverado XST Join Date: May 2000 Location: Senior Member from Austin, TX Posts: 6,431	You have a problem with the output shaft o-ring. Read this http://www.73-87.com/garage/yokeleak.htm __________________ Gerardo a.k.a. Mad Chemist Silverado XST videos

10-15-2003, 08:35 PM	#5
Slonaker Insert Witty Text Here Join Date: Oct 2002 Location: San Antonio, TX Posts: 3,415	I replaced the o-ring in my th-350 like was suggested on Swervin's site in gchemist's post. I had an intermittent leak, and that fixed it. I did not need any special tools. I got the parts at the dealer for less than $10 because the guys at the local parts stores kept guessing which o-rings I needed, and selling me the wrong parts. The dealer got it right the first time and did noit charge much more. I got my new speedo gear from, you guessed it, a tranny shop. There is a place here in town where the tranny shops buy their parts. I got a new gear there for two or three dolllars, I think. Go ahead and get a new "bullet" and seal while you are at it. Ther whole set with new seal and o-ring was under $10 at the shop here. Slonaker __________________ '86 Chevy C10 (Sold 04/19/13 ) Stock '01 Silverado Last edited by Slonaker; 10-15-2003 at 08:38 PM.

10-23-2003, 04:54 PM	#6
79 stepside Registered User Join Date: Oct 2003 Location: Sunnyvale, Texas Posts: 11	First time visit, my exact problem I crawled out from under my p/u, cleaned off my hands, hopped on the internet, found your site, registered, typed in my search, and found an EXACT picture of my problem with the instructions on how to do it. First thread I looked at too! I'm impressed and also grateful! Too late to go to the parts store today, but will do the dis-assembly today and get the parts in the morning. I can see the fluid oozzing out of the weephole. I'm going to look for a thread on driveshaft removal, and hope for the same luck. Thank yall! JL Thanks for the welcome below. I've bookmarked the site, and WILL spend much time here I'm sure. Bought my truck brand new in '79, and will have it forever. Lots of sentimental value, as I basically grew up in it. Last edited by 79 stepside; 10-23-2003 at 11:21 PM.

10-15-2003, 11:25 AM	#4
383drvr Registered User Join Date: Oct 2003 Location: Dallas, Tx. Posts: 308	Cool. Only problem is I dont have a ride to the trans shop... Is it possible for me to do it? Or does it require presses and specialty tools that I wont have? Also, I need a new speedo gear, Where are they available? (please dont say trans shop) :p

10-23-2003, 06:29 PM	#7
gchemist BAD BOW-Silverado XST Join Date: May 2000 Location: Senior Member from Austin, TX Posts: 6,431	79 stepside, Welcome to the site. By the way, a small dab of BJ welds works too. __________________ Gerardo a.k.a. Mad Chemist Silverado XST videos

10-23-2003, 08:17 PM	#8
swervin ervin You get what you pay for Join Date: Dec 1999 Location: Cherryville, NC Posts: 4,798	You don't want to cover up the hole in the yoke. It was put there for a purpose. The purpose is to help relieve the pressure that the yoke causes as it moves in and out. This is on trucks because they have more bounce and up and down motion. If this pressure isn't relieved, it causes other blown seals. Now, this is theory and a good one if you ask me. Plug it if you want to. But for me, I prefer to do it the right way. I don't think GM went to all this trouble for nothing, do you? __________________ Mike 1985 Chevy C-10

10-27-2003, 12:45 AM	#9
79 stepside Registered User Join Date: Oct 2003 Location: Sunnyvale, Texas Posts: 11	Tranny bleeding stopped Thanks for the original question and for the help given as it fixed my problem also. Had to go to a couple of Chevy houses to get all the orings and seals, but the work was easy. Getting the driveshaft back in was the hardest part. The oring in the cup took care of the oozzing out of the weep hole, and I replaced the rear seal and the oring around the speedo gear assy also. Now maybe I can drive this thing a little more often. Thank yall a bunch... Jimmy Attached Images __________________ Jimmy '79 Chevy Stepside (purchased new in '79) '67 Camaro '97 Ford F-150 Diesels: '80 Mercedes 300TD '85 Mercedes 300TD '77 Mercedes 300D (parts car)

10-28-2003, 12:11 AM	#10
84Stepper Registered User Join Date: Feb 2003 Location: Edmond, Oklahoma Posts: 425	I replaced the O-ring in my leaky truck, I just followed swervins advice on his website. Real easy. Got the o-ring at the chevy parts store at the dealer. Thanks again Swervin for all you have done to help me. __________________ 84 Chevy Stepside, 350, TH350, 268h Comp cam, Hooker headers, MSD Pro Billet, Edelbrock Performer manifold and 1604 carb, 40 Series Flowmasters dumped, and Western Chassis 3/5 drop w/ c notch. New 3:73 Eaton Posi



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