Transmission case leak

[Spittybug]

A few years ago I had the pleasure of the dreaded secondary shaft nut working its way out of the back of my transmission. I took that opportunity to open it up and replace the #2 roll pin with a beefier one and to generally inspect everything. When it came time to put it all back together, I remember a debate as to the best product to use to seal the two halves together. I believe I went with the Permatex anearobic (since I still have the tube). I also spray painted the case an off white color to dress it up and to make any future leaks more obvious on inspection. The spray job hasn't held up to well under there however...

Fast forward to today. I've noticed a few drops of gear oil every now and then collecting on the floor and it seems to be slowly getting more pronounced. I've been under there to check the source. It would certainly appear to be weeping from the case joint somewhere. It isn't engine oil from the rear seal, of that I'm sure. The speedy sleeves and the stub axles are clean. The drip that forms on the case is on the lowest point on the seam. I'm pretty confident it isn't from the fill or drain plug.

I'm going to assume that either my mating surfaces weren't 100% flat and clean or that the sealer didn't get everywhere it needed to. If I go with the former assumption, what's the best way to true up the surfaces? Or should I find a different sealer that might fill in any imperfections?

Secondly, if I'm going to go through the trouble of dropping it out again and cracking it, I'll get it powder coated. I found a guy just down the street that I never knew existed and it would be quick and easy. Anyone done that? Any problem with it being aluminum? He's an ex-technician and knows to protect mating surfaces and screw holes so that they don't need work after the coating.

[WelmoedJ]

To be able to exactly pinpoint the spot of the leak, you want to put a piece of newspaper on the floor under the gearbox.
If you mark the paper's location in regard to that of the gearbox you most likely will find the location.
Mind that if it's leaking somewhere from the side, it will follow Newton's law ;)

I've been around your "location" (DMCH) and know how it feels outside.
You enjoy the benefits of a working A/C system, I'm sure of.

[Bitsyncmaster]

I would suggest you fine where it leaks for sure. Any leak will always show up at that low point. My drivers side axel has a slow leak but the drip on the floor is at that center low point.

When I want a perfect surface, I use 220 grit wet/dry paper wrapped around an anluminum sanding block (machined bar stock for my sanding block).

[Delorean Industries]

I would highly suggest not powder coating the case halves. Sealing issues will be a definite problem along with the races for the differential falling out from the heat. The end result will not be a simple reassembly and will require setting the final drive clearance. The risk alone of the case halves warping is the biggest issue though.

Best thing to do is carefully tape off all machined surfaces, blast the unit and then coat in POR 15 reduced and shot via a paint gun. Just my advice after trying multiple approaches to this.

[Spittybug]

Thanks for all the advice. The issue of minor but perceptible warpage causing additional leaking issues is enough to prevent me from doing it. Josh's advice of POR15 makes great sense to me since I have good experience with it. As far as pinpointing the source of the leak, I may try taping a long thin strip of paper towel or diaper material along the length of the seam and see where is gets wet. Searching for the drip on the floor serves only to find the lowest point on the transmission.

So is the consensus that the Permatex anaerobic is indeed the correct product to use? I presume that a gasket isn't used because it is constantly wet along the lower half of the case? Still, I would have thought that a good rubber gasket would work....

[DMCMW Dave]

So is the consensus that the Permatex anaerobic is indeed the correct product to use? I presume that a gasket isn't used because it is constantly wet along the lower half of the case? Still, I would have thought that a good rubber gasket would work....

You can't have a gasket between halves in this kind of gearbox as the tolerances are too important to trust to a piece of paper/cork/rubber. If the gasket was too thick or thin the differential gears could mesh wrong. I suspect if this transmission was designed now there would be a groove and a rubber seal (like a straight o-ring) in the groove but the case halves must ultimately be metal to metal.

[David T]

You have to use the correct sealer. I used to use Hylomar (the recommended sealer, I found a tube at a Jaguar dealer) but the case leaked. I now reseal with any good silicone gasket sealer and the seam stays dry. Tolerances are VERY important which is why there is no gasket to interfere. Making a leakfree seal starts with flat, smooth surfaces properly prepared with the correct finish and primed. You may also have a case porosity where the oil is soaking through a sandhole. The fix is to seal it inside or outside with the appropriate sealer. Clean the case off and watch for where it begins to get moist. Always look towards the front and up, leaks travel down and to the rear of the car (usually). Do not overfill, it just makes leaks bigger.

Question: How do you know when to check the oil on a British Car?
Answer: When it stops leaking!

Question: How do you fix oil leaks?
Answer: With $100 dollar bills!

David Teitelbaum

[tgraham]

So is the consensus that the Permatex anaerobic is indeed the correct product to use?

That's what I've used on mine. Zero leaks. I used the "gasket maker" variety of anaerobic sealant - there are a couple... not sure if it matters.

Travis

[jawn101]

I still haven't gotten up the time/courage/tools/help to drop my transmission and do some maintenance on it (though I do have the parts now) and I've been reading every transmission thread I can with great interest. I'm actually losing sleep over this project because I know how important it is for everything to be perfect and how hard it is to drop the thing again if there's something to correct.

Personally I've never worked on a transmission of any kind before, but I have a reliable and experienced owner friend who has; but I don't believe he's ever cracked a D tranny.

So now I've learned about the need for perfect mating surfaces between the halves due to the lack of a gasket channel. Are there any other pitfalls specific to this trans to look out for? Anyone who's already done theirs want to come over and do mine? :)

[David T]

The transmission in the Delorean (a Renault UN-1) is really a pretty easy and simple transaxle to work on. The Workshop Manual is pretty good and you don't need a lot of special tools to work on it. You DO need a clutch alignment tool if you replace the clutch. You should also do the "Differential carrier bearing preload" as described on F:06:03. As intimidating as it sounds all you need is a piece of string and a small spring scale.You should not have to disassemble the primary shaft, the secondary shaft, or the differential assembly. DO NOT FOLLOW THE PICTURES IN THE WORKSHOP MANUAL. If you do you will have 5 speeds in reverse!
David Teitelbaum

[jawn101]

The transmission in the Delorean (a Renault UN-1) is really a pretty easy and simple transaxle to work on. The Workshop Manual is pretty good and you don't need a lot of special tools to work on it. You DO need a clutch alignment tool if you replace the clutch. You should also do the "Differential carrier bearing preload" as described on F:06:03. As intimidating as it sounds all you need is a piece of string and a small spring scale.You should not have to disassemble the primary shaft, the secondary shaft, or the differential assembly. DO NOT FOLLOW THE PICTURES IN THE WORKSHOP MANUAL. If you do you will have 5 speeds in reverse!
David Teitelbaum

Got it. One other question and then I'll be done threadjacking.. the workshop manual says in F:06:01 to remove and discard the shaft end nuts. The primary shaft nut (103101) isn't available, and the secondary (103076) is 25 bucks.. for a nut. I'm assuming these don't *need* to be replaced just because they're removed, right?

[DMC5180]

They are designed to be one-time use because you stake them to lock in place. Reuse the Old (Unavailable) Nut using 271 RED loc-tite (both nuts) I would replace the other nut if available but that's just me.


As for finding the source of the oil leak, I would spray the area down with Starting fluid in well ventilated area . It is an excellent oil/grease remover and will flash dry quickly. (Just don't light a match!) Then try dusting the the area with baby powder. The oil should wet the powder and make the source more visible.