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#1057299 - 05/15/18 04:10 AM Leaking Transmission Pan Gasket  
Joined: Jun 2016
Posts: 267
ChasUno Offline
ChasUno  Offline

Joined: Jun 2016
Posts: 267
Bradenton, FL
Last week I got round to dropping my transmission pan to change out a leaking gasket. The old gasket was in a terrible state and literally fell apart when the pan was removed. It was brittle and hard, and appeared to be cork/ fiber based. Now, the transmission pan had been leaking ever since I got the car on the road in the Spring of 2017, not so bad that it needed urgent attention, just bad enough to leave plenty of drips wherever the car was parked. It was on my "to do" list for ages, and finally I got round to sorting it.

Getting everything apart wasn't too much of an issue, and thanks to the purchase of an XL kitty litter tray that I had under the transmission, dropping the pan with fluid in it turned out to not be such a bad job after all. There was relatively little in the way of spills thanks to the kitty litter tray catching most of the stray fluid. I left the trans to drain overnight to get out the majority of the fluid, and then made sure all the old gasket material was removed and that the mating surfaces were as clean as possible. I did this by using Scotch pads and brake cleaner, and the pictures below show how clean everything was. I also inspected the sump pan edges for warping, and there wasn't any that was noticeable, and no noticeable distortion around the bolt holes either.

[Linked Image]

[Linked Image]

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[Linked Image]

I fitted the new trans filter to the transmission, and then installed the sump pan and gasket. The gasket is the rubber type, and the holes are slightly smaller than the bolts, which helpfully holds the bolts in place while raising the sump into position. Once in position I tightened all the bolts by hand until they just started to nip the gasket. Then, as per instructions, I continued to tighten the bolts by hand in a crisscross pattern, starting in the center and working outwards. I then used my torque wrench at just below 10 lbs/ ft (the manual says 8 lbs/ ft, though 10 lbs/ ft is the lowest my wrench will go to), and then repeated the crisscross pattern as previously until all the bolts were at the correct torque.

Filled it up with trans fluid and took it for a test run, came back and checked for leaks. It was leaking noticeable out of the front edge, behind the torque converter, more so on the drivers side corner, so I torqued the bolts some more, this time about 1/4 of a turn. There was an improvement, though there was still some leaking, so I tried another 1/4 of a turn. Again, an improvement but still an ooze. Finally I decided to up the torque to 12 lbs/ ft, and this seemed to improve matters.

At this point I was working on replacing the speedometer cable and had the car jacked up on the drivers side. This showed up another "ooze" from the rear passenger side of the trans sump (the angle of the car on stands pushed the fluid to this area). I tried increasing the torque again, this time to 15 lbs/ ft. The leak now appeared to have gone, but if left over night it still managed some small drips. Eventually I had the speedo cable fitted and put the car on the level, and that was a lot better. However, the fluid was low (I lost some when I removed the speedometer drive gear) after checking the dipstick, so I topped up by a quart. Now it started dripping from the front of the pan again, around the area of the two front bolts. Note that these last leaks occurred after I topped up the fluid and hadn't actually driven the car, therefore they are directly linked to the fluid level in the trans sump pan.

I've researched online and it seems to be a common issue of people not being able to stop TH200-4R trans pans from leaking, even after new fitting a new gasket and correctly torquing the pan. Much of what else I've read also says not to use any sealant, which I didn't. I'm not sure what else I can do? Is it possible that the new Duralast gasket isn't capable of sealing properly? Should I use a different make of gasket? Any suggestions/ tips as to how I can get a leak free trans sump will be gratefully received.

1986 Monte Carlo SS

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#1057302 - 05/15/18 01:53 PM Re: Leaking Transmission Pan Gasket [Re: ChasUno]  
Joined: Mar 2000
Posts: 5,241
upflying Offline
15+ Year
upflying  Offline
15+ Year

Joined: Mar 2000
Posts: 5,241
Reno, NV
Mine didn't leak when I had a 200R4. I'd remove the pan again and place the pan upside down on a perfectly flat surface with a flashlight inside. Check around the sealing edge for light leaking out, pan could have been previously over tightened and distorted. Lightly hammer the pan sealing surface level so no light from your flashlight leaks out.
I'd go back to using cork since I think that is OEM style sealing..or use the black silicone gasket maker.
Don't overtightened bolts to stop the drips, you can and will strip the threads.
Let us know how it works out.

86 MCSS Notchback coupe, LS3, 4L65E, QP 9", Eaton Truetrac, 4 wheel disc, column shift, Dakota Digital, silver with maroon bench interior

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#1057332 - 05/18/18 11:35 PM Re: Leaking Transmission Pan Gasket [Re: ChasUno]  
Joined: Jun 2006
Posts: 1,513
thepezking639 Offline
10+ Year
thepezking639  Offline
10+ Year

Joined: Jun 2006
Posts: 1,513
Livonia, MI
Stamped pans kind of suck, I'd upgrade to a hughes deep pan made of cast aluminum

extra capacity, better filter, and seals better for sure.

86 SS 6.0L LQ4, TBSS GEN IV intake, 92mm TB, 30lb injectors, LS3 cam and valvesprings, stainless long tube headers, Microsquirt ECU, Built 200-4R, B&M Megashifter, Torsen LSD, QA1 Lvl 3 Suspension Kit, UMI Front & Rear Braces. Check out my build thread:
#1057334 - 05/19/18 02:35 AM Re: Leaking Transmission Pan Gasket [Re: ChasUno]  
Joined: Dec 1999
Posts: 11,262
86ttop Offline
15+ Year
86ttop  Offline
15+ Year

Joined: Dec 1999
Posts: 11,262
Brooksville, Fl
I am pretty sure the OEM pan gasket is/was paper/cardboard, it usually does the job. I think the filter kit comes with one. good luck!

Leo Paugh
It's not an attitude, it's just the way I am.
You are not forgotten
If things improve with age, I must be approaching magnificent. thumbs
#1057335 - 05/19/18 05:30 AM Re: Leaking Transmission Pan Gasket [Re: ChasUno]  
Joined: Apr 2008
Posts: 382
GNX89 Offline
GNX89  Offline

Joined: Apr 2008
Posts: 382
Los Angeles, Ca
I've used the autozone gaskets and had good luck with them. I usually clean all the old gasket off both sides then spray some brake clean on a towel and go over the surfaces with that. Then I use some of that Indian headgasket shellac on the pan side and then the gasket on. I've done my car twice and my brother's car and I have had no leaks. I just hand tighten.

#1057340 - 05/19/18 11:37 PM Re: Leaking Transmission Pan Gasket [Re: ChasUno]  
Joined: Jan 2008
Posts: 1,106
FinallySS Offline
FinallySS  Offline

Joined: Jan 2008
Posts: 1,106
Nice Sunny Hawaii
Why, oh why you didn't install the drain plug! J/K..................

Damn! the pan look so good. I cleaned mine, but no where near you pan. Trans look good too! Did you rebuild the trans recently?

1986 Silver MCSS - Poly bushing and Hotchkis spring w/Bilstein, Posi w/3.73, MSD 6-AL, E-Brock 600cfm, Aluminum 2-row radiator.
1986 Black MCSS - R.I.P............Finally.

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