What sealant do you use on the TH400 with pan gasket? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

HeavyHauler · 03-20-2026, 06:45 PM

I am getting ready to reinstall the trransmission pan on my TH400 in my 1968 Chevy C10 shortbed fleetside.

I have a stock TH400 pan gasket with a cork gasket. Do you guys use some type of sealant with the gasket or do you just use the gasket and nothing else?

The last time I installed it a few months ago it leaked with this same trans pan and some type of composite rubber/cork gasket and a sealant that I used which seemed to take a long time to cure.

I appreciate any input.

**leddzepp** · 03-20-2026, 07:29 PM

I use an FIPG on all gaskets. It’s more expensive than other sealants, but it works like it’s supposed to and is used in OEM applications by Honda, Toyota, etc.

HO455 · 03-20-2026, 09:35 PM

I've used CAT blue anaerobic sealant along with a gasket with good results in the past. I generally use anaerobic sealants on gaskets. Although last summer I used the Felpro sealant below on my T350 with a gasket. No leaks so far.

https://www.summitracing.com/parts/p...SABEgI1IPD_BwE

HO455 · 03-20-2026, 11:18 PM

Double post.

HeavyHauler · 03-21-2026, 08:45 AM

I am going to use Permatex Ultra Black with that cork gasket. I hope it seals Wish me luck!

Joyridin · 03-21-2026, 09:34 AM

I use interior spray trim adhesive on the pan. Wait about 5 minutes, then put on the gasket. Flip it over on a flat surface and put some pressure on the pa for a few minutes. Install form there.

I have never had a leak.

72c20customcamper · 03-21-2026, 09:42 AM

Moroso silicon gasket no sealant last year so far no leaks

**kwmech** · 03-21-2026, 12:30 PM

Only thing I use is gaska-cinch on the pan itself to hold the gasket in place. Other than that.....nothing. Use a quality cork gasket, make sure the pan is flat and the area around the bolts is not coned out and torque the bolts to 100 INCH pounds

HeavyHauler · 03-21-2026, 02:17 PM

Well I got it installed and the Permatex Ultra black sealant says to tighten up the bolts snugly. Wait 1 hour then tighten to spec. Then wait 24hrs to cure.

I am just going to snug down the bolts lightly with 1/4 ratchet using light pressure after 1 hr and then wait until tomorrow to fill the trans with fluid.

I dont trust using my torque wrench for the 12ft lbs as it seemed to squeeze out the gasket and sealant too much the last time I did that.

I will just snug the bolts again and then wait for it to cure as I have had better luck in the past doing that.

Grounded63 · 03-21-2026, 02:34 PM

Straight cork gasket, no sealant.

Those are pretty much the instructions for not using a gasket at all. Like sealing a differential cover or T-case. On something like a AT pan gasket that shouldn't need a sealant to seal. There really shouldn't be enough sealant on there to squeeze out. It just makes the gasket slick. That's why it won't stay in place.

HeavyHauler · 03-21-2026, 03:00 PM

Quote:

Originally Posted by Grounded63

Straight cork gasket, no sealant.

Those are pretty much the instructions for not using a gasket at all. Like sealing a differential cover or T-case. On something like a AT pan gasket that shouldn't need a sealant to seal. There really shouldn't be enough sealant on there to squeeze out. It just makes the gasket slick. That's why it won't stay in place.

We will see. It will either leak like a faucet like you say or not.

**70STOVEBOLT** · 03-21-2026, 03:17 PM

I may have missed it, but what kind of pan are you using? If it’s the stock pan it may have been distorted by a PO due to over tightening. Valve covers and steel trans pans only require minimal torque to seal, it a lot easier f people will crank the bolts down tight and bend the metal. It doesn’t take much. If it’s a chrome pan, those are difficult to get to seal up.

**57taskforce** · 03-21-2026, 03:45 PM

Permatex the right stuff has never failed me, I prefer molded silicone gaskets with a steel core where possible over cork or regular rubber.

Grounded63 · 03-21-2026, 05:50 PM

Quote:

Originally Posted by HeavyHauler

We will see. It will either leak like a faucet like you say or not.

I never said it will leak like a faucet . . .

**mr48chev** · 03-21-2026, 07:52 PM

When I was putting my 71 back together with the turbo 400 I stopped at a long time friend's transmission shop to pick up a speedometer drive and then bought one of the cork gaskets as if it is good enough for him it is good enough for me.

HeavyHauler · 03-21-2026, 08:34 PM

Quote:

Originally Posted by Grounded63

I never said it will leak like a faucet . . .

Sorry! I got your post confused with another on a different site. Hopefully it seals!

**71CHEVYSHORTBED402** · 03-21-2026, 10:54 PM

Quote:

Originally Posted by HeavyHauler

I am getting ready to reinstall the trransmission pan on my TH400 in my 1968 Chevy C10 shortbed fleetside.

I have a stock TH400 pan gasket with a cork gasket. Do you guys use some type of sealant with the gasket or do you just use the gasket and nothing else?

The last time I installed it a few months ago it leaked with this same trans pan and some type of composite rubber/cork gasket and a sealant that I used which seemed to take a long time to cure.

I appreciate any input.

FWW, I skipped the cork - and common rubber (junk) favoring a Moroso gasket #93103, with ARP bolts #651-0750 for my 400Th pan. No sealant and no leaks.

HeavyHauler · 03-22-2026, 10:55 PM

It sealed with no problems.

ullose272 · 03-23-2026, 03:28 PM

i used a lube locker gasket with nothing on it and its sealed up nice. i do have a deep aluminum pan however with a machined surface.

03-20-2026, 06:45 PM	#1
HeavyHauler Registered User Join Date: Nov 2011 Location: USA Posts: 534	What sealant do you use on the TH400 with pan gasket? I am getting ready to reinstall the trransmission pan on my TH400 in my 1968 Chevy C10 shortbed fleetside. I have a stock TH400 pan gasket with a cork gasket. Do you guys use some type of sealant with the gasket or do you just use the gasket and nothing else? The last time I installed it a few months ago it leaked with this same trans pan and some type of composite rubber/cork gasket and a sealant that I used which seemed to take a long time to cure. I appreciate any input.

03-20-2026, 07:29 PM	#2
leddzepp Moderator Join Date: May 2007 Location: Southern Cal Posts: 20,237	Re: What sealant do you use on the TH400 with pan gasket? I use an FIPG on all gaskets. It’s more expensive than other sealants, but it works like it’s supposed to and is used in OEM applications by Honda, Toyota, etc. __________________ 1972 C/10 Cheyenne Super SWB. Restored, loaded, slammed. 1968 C/10 50th Anniversary LWB. Unrestored, stock, daily driver/work truck. RIP ElJay RIP 67ChevyRedneck RIP Grumpy Old Man RIP FleetsidePaul

03-20-2026, 09:35 PM	#3
HO455 Registered User Join Date: Feb 2016 Location: Portland Oregon Posts: 12,406	Re: What sealant do you use on the TH400 with pan gasket? I've used CAT blue anaerobic sealant along with a gasket with good results in the past. I generally use anaerobic sealants on gaskets. Although last summer I used the Felpro sealant below on my T350 with a gasket. No leaks so far. https://www.summitracing.com/parts/p...SABEgI1IPD_BwE __________________ Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. RIP Bob Parks. 1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377

03-20-2026, 11:18 PM	#4
HO455 Registered User Join Date: Feb 2016 Location: Portland Oregon Posts: 12,406	Re: What sealant do you use on the TH400 with pan gasket? Double post. __________________ Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. RIP Bob Parks. 1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377 Last edited by HO455; 03-20-2026 at 11:20 PM. Reason: Double post.

03-21-2026, 08:45 AM	#5
HeavyHauler Registered User Join Date: Nov 2011 Location: USA Posts: 534	Re: What sealant do you use on the TH400 with pan gasket? I am going to use Permatex Ultra Black with that cork gasket. I hope it seals Wish me luck!

03-21-2026, 09:34 AM	#6
Joyridin Registered User Join Date: Sep 2020 Location: Cleveland, Ohio Posts: 703	Re: What sealant do you use on the TH400 with pan gasket? I use interior spray trim adhesive on the pan. Wait about 5 minutes, then put on the gasket. Flip it over on a flat surface and put some pressure on the pa for a few minutes. Install form there. I have never had a leak.

03-21-2026, 09:42 AM	#7
72c20customcamper Registered User Join Date: Jul 2018 Location: Catskill Mountains,NY Posts: 9,479	Re: What sealant do you use on the TH400 with pan gasket? Moroso silicon gasket no sealant last year so far no leaks __________________ Mark 72 c20 custom camper Husky edition, 66 SS396 Chevelle 1964 Hawk, 63 Avanti,62 lark 1969 AMX , 1968 c20 stepside ,85 K20 1977 Suburban sold 68 anniversary.

03-21-2026, 12:30 PM	#8
kwmech Senior Member Join Date: Mar 2003 Location: Colfax-California Posts: 8,941	Re: What sealant do you use on the TH400 with pan gasket? Only thing I use is gaska-cinch on the pan itself to hold the gasket in place. Other than that.....nothing. Use a quality cork gasket, make sure the pan is flat and the area around the bolts is not coned out and torque the bolts to 100 INCH pounds

03-21-2026, 02:17 PM	#9
HeavyHauler Registered User Join Date: Nov 2011 Location: USA Posts: 534	Re: What sealant do you use on the TH400 with pan gasket? Well I got it installed and the Permatex Ultra black sealant says to tighten up the bolts snugly. Wait 1 hour then tighten to spec. Then wait 24hrs to cure. I am just going to snug down the bolts lightly with 1/4 ratchet using light pressure after 1 hr and then wait until tomorrow to fill the trans with fluid. I dont trust using my torque wrench for the 12ft lbs as it seemed to squeeze out the gasket and sealant too much the last time I did that. I will just snug the bolts again and then wait for it to cure as I have had better luck in the past doing that.

03-21-2026, 02:34 PM	#10
Grounded63 Registered User Join Date: Dec 2016 Location: Canon City, Colorado Posts: 265	Re: What sealant do you use on the TH400 with pan gasket? Straight cork gasket, no sealant. Those are pretty much the instructions for not using a gasket at all. Like sealing a differential cover or T-case. On something like a AT pan gasket that shouldn't need a sealant to seal. There really shouldn't be enough sealant on there to squeeze out. It just makes the gasket slick. That's why it won't stay in place.

03-21-2026, 03:17 PM	#12
70STOVEBOLT Senior Member Join Date: Jun 2005 Location: Winona Lake, IN Posts: 7,062	Re: What sealant do you use on the TH400 with pan gasket? I may have missed it, but what kind of pan are you using? If it’s the stock pan it may have been distorted by a PO due to over tightening. Valve covers and steel trans pans only require minimal torque to seal, it a lot easier f people will crank the bolts down tight and bend the metal. It doesn’t take much. If it’s a chrome pan, those are difficult to get to seal up. __________________ 70 C/10 SWB 402/TH400/3.73 "The Needy Beast" 200,000 Mile Club Disc Brake Club Owner installed options: Front Sway Bar Power Steering Power Brakes Cigar Lighter Courtesy Lights Deluxe Side Markers Wiper Delay Sliding Rear Window Power Windows Power Locks Sniper EFI 2015 Silverado 1500 LS 4.3/6L80/3.23 lowered 2" front & rear

03-21-2026, 03:45 PM	#13
57taskforce All about them K’s Join Date: Jun 2014 Location: Land of Entrapment Posts: 6,975	Re: What sealant do you use on the TH400 with pan gasket? Permatex the right stuff has never failed me, I prefer molded silicone gaskets with a steel core where possible over cork or regular rubber. __________________ Tyler '57 3100 http://67-72chevytrucks.com/vboard/s...d.php?t=813888 '72 K20 Cheyenne: 5” lift, 35’s, front dana 60 blah blah blah… http://67-72chevytrucks.com/vboard/s...d.php?t=662879 ‘69 K10 SWB: 4” lift 33”s… in a million pieces http://67-72chevytrucks.com/vboard/s...d.php?t=805206 '98 Silverado LT K2500HD ECLB Vortec 454/4l80E: 6" lift 35x12.5x20’s

03-21-2026, 07:52 PM	#15
mr48chev Registered User Join Date: Jul 2007 Location: Toppenish, WA Posts: 16,391	Re: What sealant do you use on the TH400 with pan gasket? When I was putting my 71 back together with the turbo 400 I stopped at a long time friend's transmission shop to pick up a speedometer drive and then bought one of the cork gaskets as if it is good enough for him it is good enough for me. __________________ Founding member of the too many projects, too little time and money club. My ongoing truck projects: 48 Chev 3100 that will run a 292 Six. 71 GMC 2500 that is getting a Cad 500 transplant. 77 C 30 dualie, 454, 4 speed with a 10 foot flatbed and hoist. It does the heavy work and hauls the projects around.

03-22-2026, 10:55 PM	#18
HeavyHauler Registered User Join Date: Nov 2011 Location: USA Posts: 534	Re: What sealant do you use on the TH400 with pan gasket? It sealed with no problems.

03-23-2026, 03:28 PM	#19
ullose272 Registered User Join Date: May 2011 Location: Boise, ID Posts: 95	Re: What sealant do you use on the TH400 with pan gasket? i used a lube locker gasket with nothing on it and its sealed up nice. i do have a deep aluminum pan however with a machined surface.



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