Leaky 3speed AT - The 1947 - Present Chevrolet & GMC Truck Message Board Network

bmartin9122 · 06-05-2006, 07:09 PM

Hey guys,

I had my tranny rebuilt in January, and a big concern at the time was the significant transmission fluid leak. I know a small leak comes with the territory, but this was enough to cause me some real concern.

Anyways, the shop who did the rebuild has had a devil of a time stopping the leak(s?)!!! First, they replaced the pan gasket. Then, they thought the pan had been over-torqued damaging the new gasket. Next, they figured the orignal pan was warped and replaced it with a new, aluminum deep-sump pan. Later, it was thought the mating surface on the old tranny was warped, so they ground it flush. After some more research, they discovered a hairline fracture in the housing and welded it closed. The last word was they thought the mating surface was still slightly warped and needed some more grinding.

I've seen some ideas like a possible leak from a kick-down cable or overflow from the fill tube itself. Are their any other ideas as to where the gremlin may be hiding???

Thanks!!!

-Bryan

Slonaker · 06-05-2006, 07:56 PM

My TH350 leaked from the seals at the kickdown, dipstick tube, and speedo bullet. They are all easy fixes. The total for all these parts was about $20.

Mine also leaked from the hole in the center of the yoke. There is a fix for that on 73-87.com (same fro 700R4 and TH350).

Later it developed a leak at the pump on the front. It looked like the fluid was coming from the pan, but it was not. A mechanic friend figured that one out for me. I pulled it and paid to have that fixed.

What finally did mine in was the bushing/seal around the converter. It started leaking badly. I finally pulled it and had the whole thing rebuilt after 4years of chasing leaks and spreading kitty litter on the driveway. It doesn't leak a drop now.

Good luck,

Slonaker

**oldgold70c10** · 06-05-2006, 08:21 PM

The old transmission that was in my truck leaked from the front too (near the pump). The torque converter would sling the oil all over and make it look like it was comming from the front of the pan and the converter itself. transmission in there now hasn't leaked since it was installed in January, so leakage is not normal.

**VetteVet** · 06-07-2006, 01:28 PM

There's a seal on the shifter shaft that commonly leaks after many miles, and the vent tube will leak if the tranny is overfull.

06-05-2006, 07:09 PM	#1
bmartin9122 Registered User Join Date: Jan 2006 Location: Texas Coastal Bend Posts: 169	Leaky 3speed AT Hey guys, I had my tranny rebuilt in January, and a big concern at the time was the significant transmission fluid leak. I know a small leak comes with the territory, but this was enough to cause me some real concern. Anyways, the shop who did the rebuild has had a devil of a time stopping the leak(s?)!!! First, they replaced the pan gasket. Then, they thought the pan had been over-torqued damaging the new gasket. Next, they figured the orignal pan was warped and replaced it with a new, aluminum deep-sump pan. Later, it was thought the mating surface on the old tranny was warped, so they ground it flush. After some more research, they discovered a hairline fracture in the housing and welded it closed. The last word was they thought the mating surface was still slightly warped and needed some more grinding. I've seen some ideas like a possible leak from a kick-down cable or overflow from the fill tube itself. Are their any other ideas as to where the gremlin may be hiding??? Thanks!!! -Bryan __________________ 79 GMC Sierra Grande K15 --PPG paint code 62608 Sunburst Orange Metallic (WA802K) --Gentex auto-dimming rearview mirror model K31 --Carriage Works billet grille model 40071 --Go Industries 2.5" tubular stainless headache rack --Sylvania Silverstar sealed headlights model H6024ST --Texas Saddlebags center console model 101 --Brown's Welding class IV V-5 pipe bumper --Ramsey RE8000 winch --33" tires Last edited by bmartin9122; 06-05-2006 at 07:10 PM.

06-05-2006, 07:56 PM	#2
Slonaker Insert Witty Text Here Join Date: Oct 2002 Location: San Antonio, TX Posts: 3,415	Re: Leaky 3-speed A/T My TH350 leaked from the seals at the kickdown, dipstick tube, and speedo bullet. They are all easy fixes. The total for all these parts was about $20. Mine also leaked from the hole in the center of the yoke. There is a fix for that on 73-87.com (same fro 700R4 and TH350). Later it developed a leak at the pump on the front. It looked like the fluid was coming from the pan, but it was not. A mechanic friend figured that one out for me. I pulled it and paid to have that fixed. What finally did mine in was the bushing/seal around the converter. It started leaking badly. I finally pulled it and had the whole thing rebuilt after 4years of chasing leaks and spreading kitty litter on the driveway. It doesn't leak a drop now. Good luck, Slonaker __________________ '86 Chevy C10 (Sold 04/19/13 ) Stock '01 Silverado

06-05-2006, 08:21 PM	#3
oldgold70c10 Who's got steelies? Join Date: Feb 2006 Location: Morrison, Oklahoma Posts: 1,025	Re: Leaky 3speed AT The old transmission that was in my truck leaked from the front too (near the pump). The torque converter would sling the oil all over and make it look like it was comming from the front of the pan and the converter itself. transmission in there now hasn't leaked since it was installed in January, so leakage is not normal. __________________ 1969 C10 LWB W/ 250 I6 & 3spd 1970 C10 with '67 small window cab, 68 front end, blue; 305/TH350, 3.08 limited slip rear end, manual brakes, power steering; & 4-wheel drums-My daily driver. 1975 Chevelle Malibu Classic Coupe 350/th350 mint green 1970 C20 Suburban 350/700R4 4.10 gearing green & white 1978 Big 10 Silverado 350/th350, working ac, 2 tone blue-My summer daily driver 1983 GMC 1500 Sierra 305/SM465 2.73 rear end How to add a trip odometer to your 67-72 stock speedometer How to rebuild your Q-Jet My Truck Page My Youtube Channel

06-07-2006, 01:28 PM	#4
VetteVet Msgt USAF Ret Join Date: Jan 2005 Location: Kalamazoo, Michigan Posts: 8,719	Re: Leaky 3speed AT There's a seal on the shifter shaft that commonly leaks after many miles, and the vent tube will leak if the tranny is overfull. __________________ VetteVet metallic green 67 stepside 74 corvette convertible 1965 Harley sportster 1995 Harley wide glide Growing old is hell, but it beats the alternative.



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