BW35 Sump gasket sealing problems

[Robmsharp]

This will be my fourth attempt at trying to stop the ATF from leaking out of this gasket and before I go ahead I thought I'd ask the SOC collective for their suggestions, here's a history of what I've tried for each of the three sealing attempts so far.
Its worth noting that each time I've used a new gasket from different reputable Stag suppliers (LD, Rimmers & Paddocks) and in each attempt I've thoroughly cleaned all sealant residue before fitting the new gasket.
1. This attempt was using Hylomar Blue both sides of the gasket and using thread sealing compound on the bolts before tightening them up.
2. This attempt used silicone sealant both sides of the gasket.
3. This attempt used flange gasket sealant both sides of the gasket.

For this 4th attempt so far I've removed the sump and cleaned up both metal mating surfaces. I've checked the flatness of the sump faces using a steel rule and shining a light from behind which showed very little warp (if any) between any of the surfaces. Checking the flatness of the gearbox mating surface isn't so easy but I have rubbed over the surafces with 1500 wet and dry which revealed that a few of the threaded holes seem to have raised themselves proud of the surface - almost as if when the bolts were tightened that the thread had started to distort - none of these raised areas were what I would have thought were significant enough to cause the leak.

Once again I have a new cork gasket ready to fit and I happen to have a tube of Wellseal in the toolbox. I've never used this stuff before and I was wondering what you guys would think if I tried to use this for this attempt.
All suggestions for how I try and make this 4th attempt successful would be most welcome.

[sujitroy]

I'm in USA and picked up a non cork gasket for my BW35. I was surprised it was less than $2 at the time. I swapped out my steal pan for the later aluminum one. I didn't use any gasket sealer but should have as it seeps very little.

[DJT]

Russ used to warn against using any sealant on this gasket as any excess that ends up inside the ‘box can wreak havoc in the small galleries. He recommended grease.

Having said that, I used Wellseal SPARINGLY on both faces and had no leaks from my BW35. It was still oil tight when it was fitted to another local member’s Stag after I swapped to a ZF.

[marshman]

As DJT says you shouldn't use any sealant on that gasket. It is not necessary. As long as you have checked the mating faces are flat and free of burrs it will seal with a decent cork gasket.

Are you 100% sure it is the gasket that is leaking? The BW35 box is notorious for dumping ATF, especially if left to stand for a week or two. The non-return valve from the torque converter is usually blamed. Fluid leaking back into the box raises the level.

There are various theories as to where the fluid actually exits the box but my favourite is that it comes out of the top of the dipstick filler tube and runs down and then around the outside of the sump making it look like the gasket is leaking. The reason I believe (insert your own theory here) the fluid exits via the dipstick/filler tube is that overnight the temperature drops and the air and fluid in the box cools and contracts. Then during the day it warms a few degrees and the fluid expands as does the air and the excess fluid gets forced up the tube. Not much gets pushed out each time but over the course of a week or so it mounts up.

Roger

[Robmsharp]

Thanks for your replies, I'm absolutely certain its leaking from this gasket as theres evidence of the ATF on the sump bolts and pan. Under normal cicustances I would agree with Russ re sealant on this gasket and its only desperation and frustration that led me to try the silicone ang flange sealants and I certainly wouldn't use them again. This time around I'm inclined to try the Wellseal and hope that does the trick, but does anyone have any opinions on the raised areas around the threaded holes I've seen? And can anyone suggest how best I get these areas flat? (assuming its these raaised areas where the fluid is leaking from).

[PhilB]

Have you got a pyramid shaped hole cutter that you can use by hand to clean up the thread hole edges. Hold a magnet up to the hole after clean up to get the swarf dust etc
Don't forget the eye protection

[Robmsharp]

I have a chamfer drill bit that would do the job but the gear box material looks to be aluminium so a magnet won't help. Hopefully if I use it and because I'll be using it vertically any swarf will drop down to the floor. but to be on the safe side I'll use masking tape to catch any material coming off.

[Alacrity]

OK, as a auto transmission rebuilder since 1979, I think we can safely say your transmission is NOT leaking from the pan gasket. The tin sumped BW35 could leak from the pan if over tightened but it is very rare for the Ali sump to leak. Just think, what is the lowest point on the transmission, & where is the oil going to drip from? That right, the lowest point. ALWAYS look above the point it is dripping from to find your leak. The most common leak point by far & away is the selector shaft seals, simple to change but be very careful not to scratch the shaft or the bore when getting the old ones out. You can also get leaks from the inhibitor switch, kickdown cable, filler tube & park mechanism shaft on the rear of the main case. The latter is not a nice job & often requires the transmission to be removed. All these will drip off the sump bolts.You need to wash it all down so it is clean & dry around all the places mentioned then get it hot & check again, but look above the sump pan joint.

[Mark S]

Th BW35 originally fitted to my car had a Belzona repair at the back, no doubt due to one of the longer bolts being fitted in the wrong place previously which had bottomed out and cracked the case.

[Robmsharp]

Thanks for all your replies I'll be sure to carefully go through the checks .

[Robmsharp]

Alacrity, is it possible to change the selector shaft oil seal in situ? If yes, how do you advise to remove and replace the seal?

[Alacrity]

Yes, they are simple to lever out with a pick or small screwdriver - but make sure whatever you use isn't sharp. As I said above, you need to be careful not scratch the Ali case seal recess & especially the selector shaft itself. Some folk have managed to fit double seals (1 on top of the other). Good luck!