D18 Transfer Case Leak

Lookout Ranch

Well Oiled
All-Star
May 9, 2015
9,828
Sierra Foothills
First Name
Kurt
Willys Model
  1. Wagon
Willys Year:
  1. 1957
As mentioned in my trip report, I've got a fairly robust leak from the transfer case. It's always hard to tell with these things, and I need to remove the parking brake to get a good look, but after wiping the transmission and TC with a rag and watching closely, the leak appears to originate from the area of the shims -- between the body of the TC and the rear bearing retainer for the output shaft.

I'd appreciate any thoughts on how to diagnose and fix it.

Background

I rebuilt the TC and transmission recently, and after installation it didn't leak at all when resting. After driving it a bit, including a 100-mile day trip to the mountains, it appeared to leak only a little from the top, out of the ports for the shifter rails at the back of the transmission cover. No big deal.

After another day trip to the mountains, which included about 45 minutes of low intensity 4WD, this other fairly serious leak developed, enough to create a puddle the size of a saucer over the course of a gas stop. It leaks faster when the transmission is hot and the the gear oil is more runny. And it drips after being wiped down, whether the vehicle is running or not, suggesting it is gravity-fed and originating below the level of the gear oil.

I'm pretty certain it isn't coming from the speedometer cable connection. I've got a neoprene washer as a gasket there, and I can't see leakage in that area, though it is hard to see with the parking brake still installed.

When the shims and rear bearing retainer were installed, I put a little Hylomar Blue on the TC and the bearing retainer faces but didn't coat the shims. I also coated the threads for the bolts that hold the bearing retainer and shims in place.

Should the shims have been coated before final installation? In looking around the web, it seems that some do coat the shims (with copper spay, for example) and some do not.

In any case, I've got to get it sorted out. It leaks just a little to much to be treated as a petty annoyance.
 
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Carter,

One other place where a leak can occur is along the splines of the rear yoke. In my case, this allowed oil to destroy the brake shoe lining on the parking brake (attached to the back of the T-case). I'm hoping I sealed this leak well enough the last time I had the T-case apart - time will tell.
From what I've read over the years, Willys oil leaks are similar to Land Rover leaks, but, perhaps not as bad...
 
Thanks Pavel, I'm pretty sure it isn't leaking via the splines (sealed with black RTV) or the output shaft seal. The area around the parking brake drum remains dry. The wetness is around the shim area and the lower part of the pan.

It's conceivable that it is leaking via the pan gasket. It's just so hard to sell where leaks are given the way the oil can migrate hidden in seams and then appear elsewhere, at a low spot.

Currently my suspicion continues to be directed at the shims or possibly one of the threads around one of the bearing cap bolts, but perhaps I should try removing and reinstalling the pan first, to eliminate it as a possible source, given how notorious they are for leaks.
 
Carter,

I spray the shims with copper sealant. At work and brainfarting on the brand and name. It comes in a rattle can. First I get them all cleaned and dailed in for tollerances regarding endplay. I set them up on the tight side. Then disassemble and spray both sides of the shims with the sealant as well as the case and output housing, assemble using ample sealant on the yoke splines as pavel mentioned.

If you are replacing seals, personally, I omit the felt soaker and run 2 seals. It puts the seal contact in a different place on the yoke, instead of in the wear groove.

The last case I did for my daughter's rig, I used a yoke seal for a 1970's jeep Quadratrac case stacked with the standard seal for the Dana Spicer 18. They came up just flush with the casting on the output housing. It works with 2 regular seals, but they stack up about 1/16" proud of the output casting.

Best of luck,

Duane

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Just read your last post. Dad taught me a few tricks on getting them not to leak. Then when they didn't leak, he would have my brother and I checking fluid levels because he assumed they were empty. LOL

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It's also possible to have a porous housing. I remember a Dynahoe trans housing, which was a Warner T98. I hope it isn't, but...?
diggerG
 
My thoughts after 40+ years of trying (and successful) to get a leak free Willys. It is VERY difficult to get a D18 leak/seep free. First, I machine/stone all mating surfaces and only use either military seals and gaskets or ones that I have made on a CNC machine. The military seals are double lipped to keep oil in and water out. I use Permatex 518 anaerobic sealer on all of the gaskets and mating surfaces. I coat the shims with 518 sealer as well. I hard chrome and regrind the output yolks to a few thousandths oversize for a tighter fit in those seals and do put a bit of silicone on the splines upon assembly. A common issue that is overlooked is the breather. I extend the breather via fittings and hose to a mini air cleaner high on the firewall. You would be surprised how the oil will go up the hose. Good luck.
 
I'm not even trying for a leak-free T90 and D18. I'm just hoping to get to the point where it only needs to be topped up every few days when I'm traveling, not every few hours.
 
I'm not even trying for a leak-free T90 and D18. I'm just hoping to get to the point where it only needs to be topped up every few days when I'm traveling, not every few hours.

No problem. I don't even like an oil film on the case. Check the breather first.
 
I am running a Dana 20 transfer case, and it recently did the same thing as you describe. I found three issues that could have caused the leak. I fixed all of them at the same time, so I do
not know which was the culprit. I know that you have a Dana 18, but the case castings are very similar. 1. There are five bolts that join the transfer case to the transmission adapter. Make certain
that you have tightened all five. Depending on your setup, one or two of the five will likely be hidden from view. 2. There was a machined hole at the top of my transfer case casting that was not covered by the transfer case to transmission adapter gasket. That left a portion of the hole exposed to the outside. I looked at another transfer case, and the machined hole was present, but plugged. It was apparently machined into the case to allow a tool bit to pass through during the manufacture of the case. The fix was to cut a thread in the hole, and run a bolt into it. The outside end of the bolt was trimmed flush so that the gasket would have a surface to seal against. 3. A portion of the gasket that went between the transfer case and the transmission adapter had broken off between two adjacent bolt holes, and was totally missing.
 
I'll be interested to hear if you stopped the shim leak. I've had my TC out 4 or 5 times trying to fix leaks and no luck so far. It's rather embarrassing to carry a drip pan to put under it when I stop by a friends house and have to park in his driveway.
 
A mechanic I know uses ..... Now remember you don't want to goop anything on the shims that might make them thicker ..... he uses thread sealant on his shims. it's thin, doesn't "glue" the shims together and is oil resistant. You want to stop capillary action between the shims. just a VERY thin coating will get the job done.
 
Maybe, I think it is. This should be in the tool box of everyone that works on engines and transmissions. It is like pipe dope for water pipes, but made for engines or things that have oil and heat. It is thinner than pipe dope though. It should be used on most every nut and bolt in an engine. Well on the exterior where oil might follow a thread and ooze out.
 
Lots of different brands of thread sealant. Kinda liquid teflon. I usually use it and teflon tape on any fastener that goes directly into fluid. I still like the 518 sealant I mentioned earlier. You can apply a very thin coating. I set the end play on that bearing at virtually zero initially. Twice around the block and you have your .004" -.006".
 
I've heard bad things about using tape so I stick with Automotive thread sealant. What I heard about the tape might be wrong, but why tempt the engine gods when the liquid stuff works.
 
I've heard bad things about using tape so I stick with Automotive thread sealant. What I heard about the tape might be wrong, but why tempt the engine gods when the liquid stuff works.

I agree, I work on air leak testers and using the tape is a no-no. It can shred off during install and get caught in the pneumatic valves. Only good for water pipes IMO.
 
It's too soon to report results. It's mostly back together but I won't be able to finish and fill it until next weekend. It's just as well, this will give the Permatex #2 a chance to firm up a bit.

Here are a couple of observations from the teardown.

The pan had a mix of 3/4" and 5/8" bolts. It looks like a couple of the 3/4" bolts bottomed out, leaving the pan without a tight seal on the gasket in a couple of places.

I removed the rear bearing cap and thoroughly cleaned the shims, applied copper spray and put it back together with one less shim. The preload movement ended up at about 0.002, which is the low end of what Novak recommends. Applied Permatex #2 to the threads for the final torque.

The output shaft seal hadn't leaked at all.

I retorqued all the bolts on the TC and the attachments to the transmission. Several had loosened up a little since the rebuild and turned a little before arriving at the correct torque.

Next weekend I should be able to get it all back together, refill it, and see if it holds gear oil. I'll be happy if there's only an occasional drip.
 
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