TH400 Pan Recommendations

88 XJS

I’d like to replace my original rusted steel TH400 pan with a cast aluminum pan that comes with drain plug. I noticed there are a lot of choices. I need to measure mine to see if I have deep or not. I’m hoping to find one that doesn’t need any mods for the trans mount or pick up tube or dipstick.

Any brands that worked well?

Or is painted steel still the way to go?


My car had a deep pan, which surprised me. The are apparently used on trucks and other heavy-duty applications. I guess I expected a shallow pan in a car this low.
B&M is a good choice, they set the standard for auto trans parts for many years, especially TH350 and TH400.
You’ll have to spend an hour or so grinding on the pan to clearance it for the mount. You need a decent hand grinder and a cutter that won’t load up with the aluminum chips. Details on my cast pan are about halfway down on this page.

I think the cast pan is the way to go and is worth the effort.

Having said that there are a million steel pans out there that work just fine.


An hour or so??? That’s a lot of grinding! Is it just to remove the outer cooling fins? I was hoping to find one that fits without modification. I know B&M are high quality, but there must be many others out there. The cooling fins are really not necessary, IMO.

Yup. Lots of options. Good luck!

Bob Brackney

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Just working from memory here. IIRC, a shallow pan will not fit – but I’m not sure why not, I guess the filter sits too low. A deep pan will fit, but it leaves the filter and pickup sitting some distance above the bottom, meaning you’ve got some fluid in there that the pickup can’t reach. The OEM pan in the Jag is somewhere between a shallow and a deep pan. Perhaps any pan can be used if the filter attachment scheme is altered accordingly, I dunno.

There’s also supposedly a difference in the outline shape of the pan for a GM400 after some date, and the Jag requires the earlier shape.

The tranny mount, of course, is a PITA.

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Shallow pan will not fit due to factory “deep” pickup. A decent aftermarket pan will come with the correct length pickup tube to put the filter in the bottom of that pan. That’s because it’s a common mod to go from shallow to deep. So if you are going to an aftermarket deep pan you are giving up maybe 1/2" of clearance under the pan. Which you need to be aware of since it’s near the middle of the car and thus not the ideal place to lose clearance. I’ve never had a problem with it.

Dunno about the shape of the pan. B&M only sells one TH400 pan, FWW. I do know that B&M (in terms of shift kits) refers to the trans in my 89 as a “pre 87” style. There was a change to the valve body post-87.


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Greg, as I put my 400 trans back under the car yesterday, I thought that before I installed the exhaust system (This morning) I would take a few photos.
When I first got my car I wanted to change all fluids and filters. The transmission mount removal to do a oil and filter change did not make me happy.
I made a simple mod using a welder so that I could use a mount commonly used on full-size GM cars. You can change the height by shimming. Drain plug came next.
I am happy with the OE pan, BTW.
Car sits close enough to the ground already!
The trans. overhaul has stopped my car from “Moaning” on first start-up, too!

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Nice! No whine, but I get a bit of a rattle from the trans/torque converter area on cold startup at idle. Is that normal?

Did you put in an aluminum accumulator piston? Or just flip it upside down without the spring?

Thanks for the advice, I’ve decided to stick with a steel pan. GM TH400’s have been fine for decades without cast aluminum, I’ll save a good $100, and if anything hits it, I’d rather have a dent than a crack.

I’ll just have to make sure to torque the pan back on evenly and perfectly to prevent leaks.

B&M Chrome 20289 look good. Oh, and the weight savings will keep my XJS fast :wink:

There are racetrack-shaped washers that could help evenly distribute the bolt torque along the flange, if you can find (or make) some.

is there a special torque sequence like putting on a head/head gasket?

Just in general: snug all down, then torque to spec in an X pattern.

Yes, but what is the secret of a leak free GM400 transmission pan gasket? I replaced the one in my wife’s 1990 XJ-S convertible and a shop replaced the one in my 1990 V12 Vanden Plas, and they both leak. I have drip pans beneath both cars and I am forever cleaning the drip pans and adding a cup or two of DEXRON fluid to the transmissions.


Welll… my go-to sealant is a thin stripe of RTV around the inner periphery of the bolt path: I’d install and just hand tighten the nuts enough to squish it up a bit, then let it sit for 24-36 hours.

Tighten fully, and… no leaks!

Let the silicone howls of protest begin!!!

What do they do from the factory? I don’t think my pan has ever come off my 88 XJS (50k miles) and it’s leak free (although fluid is pink so it must have?)

Perhaps when lowering it full of fluid, a steel pan may bend a bit? Most people who switch to cast aluminum say no more leaks.

My new steel one with drain plug, I’ll be able to empty the fluid weight out first before dropping the pan next time.

There are reports that shops don’t even bother removing the mount. They just remove all the other bolts and bend the pan down around the end of the flange. Then bend it right back to close it back up. I presume that means reusing the old gasket.

I hate trying to seal up cheap-@$$ stamped sheet steel flanges. The best method I have found is to set the pan down on a flat surface, set the ball end of a ball pein hammer in one of the bolt holes, and whack it with another hammer. Done right, the area surrounding the hole is dished downward toward the bolt head. Repeat all the way around. When the bolts are tightened down, they spread the load around to the outer edge of that dishing.

Big thick smoooshy gaskets are essential. In this day and age, I’d think that means silicone. Cork strikes me as old tech.

Yup. done that on valve covers and oil pans to flatten the bulge around the bolt holes.

Dave’ s revised trans mount makes so much sense!!!

It looks like the "adapter’ that came with my “swap” kit…

I used an alloy pan on my Corvair van’s engine. sealed a h… of a lot better…

Aye, I suspect a deeper trans pan would need a pickup change…

I think the alloy pans are pretty stout and it would take a big hit to crack one…



I have bought deep aluminium pan from Summit Racing:

I haven’t installed it yet, but from what I see it looks like that I might need to do some milling to aluminium pan to make it fit at the end where mounting plate is sharing same bolts with oil pan.
I’ll report how it goes when I get to it and that might take a while as it is not my first priority now :slight_smile:

The TH400 pan & rad trans cooler were probably the first things to be replaced on my 91. I went with a Hughes aluminum pan from Summit. Holds one more quart than stock so it wasn’t to low, I believe the pan came with a longer tube. I also installed the mild B&M shift kit while the pan was down.