The Secret to a Leak Free D18

Okay, I know that's a pretty bold statement, and I know I'm going to catch a lot of flak for this thread, and I'm sure somebody(ies) will raise the B.S. flag, but I'm making it anyway. I have a leak free D18. I fought this issue for so long, many nights under there changing output shaft seals, trying different felts, gaskets, RTV, helicoils, praying, cussing, variations of the above, etc. Here is the 99% solution: Replace the bolts with studs.

Your t-case is a huge chunk of cast iron that is held onto a cast iron adapter with steel bolts. The problem is that when you are bouncing the JEEP around on trails or just down a rough road, there is a lot of force trying to pry those bolts out of the adapter. When that happens, even the slightest stretching of the threads will allow seepage. This is the same problem we face with our D27 knuckles, and the solution is similar; we put button head bolts into the knuckle to create a steel stud to keep the wheel from falling off, and it works the same way to use a stud on the adapter. Here is the process:

1) Remove the t-case.

2) Chase all the adapter threads with a tap.

3) Inspect the threads. If any are even the slightest boogered up, carefully drill and tap one size bigger.

4) Install studs with loctite onto the adapter.

5) Coat one side of a t-case gasket with gray RTV. Let sit until tacky. Install RTV face against adapter.

6) Coat the other side of the gasket (now stuck on the adapter) with gray RTV. Let sit until tacky.

7) Heave the t-case into place and wrench down with grade 5 nuts and lock washers.

8) Start planning that nice epoxy floor you've always wanted but never could pull the trigger on because of all the oil stains.

 

bolts and THE RIGHT STUFF
no leaks

 

My leak always came from the stamped steel TC pan. Fixed that with the Novak billet pan. No adapter between t14 and d18.

 

You could always leave out the oil. Then there would be no leaks.

 

That's how I used to know when it was out of oil: it quit leaking.

 

Fought leaks on mine for year. I found out that it will quit leaking (well, almost) if I stop overfilling it

 

Mine has leaked persistently from the speedometer cable connection. The best I have been able to do to stop that leak was fill the threaded collar with Ultrablack, but it still leaks some. There appears to be no seal in there to stop oil from coming out.

Don

 

Yep....any D18 can leak from any number of locations. Not every one leaks the same. I'm not sure what adapter you are talking about. The stock setup bolts directly to the back of the tranny and i havent seen one leak there as noticable as other places.

IMO, the top 2 leaks in all the D18 setups ive seen from MB/GPW's to CJ5's are from the pan and the other being from the rear seal. The pans ive fixed with a good seal gooped with that black RTV stuff, new lock washers and the bolts gooped with RTV. There are 2 of the pan bolt holes that tap all the way into the case. Even if you seal up the pan, gear oil will run down the threads and leak.

The other comes from the rear seal. I changed the seal 4 times and I was told that unless the surface on that rear yoke is all but brand new, it will leak. They were right. If you buy a new seal, buy a new yoke. No leak

 

They make sleeves to fix the groove in the yoke. I have one and it works great and I still have my original yoke. I've heard replacements can introduce a vibration.

 

Another trick is to use the "flanged" bolts from a 30 or 44 diff cover. They distribute the load over the pan rail and help reduce leaks. Another trick if you can find one is many military transfer case pans had a second support around the pan rail to distribute the load also. These don't dimple the way the civi models do. Whenever I find one I snap it up and use it on mine. The aftermaket aluminum pans work well for this and can actually strengthen the case slightly too.
A little sealer on all the bolt threads goes a long ways as does tapping/cleaning the bolt holes first and cleaning them out with spray brake cleaner. The yoke has to be pit and groove free on the seal surface. Some sealer on the splines of the yoke makes a huge difference too. I put it on the inside end of the yoke splines (end towards the transfer case) so when I install the yoke it "smears" the sealer in the splines and creates a better seal. RTV Ultra Black or "The Right Stuff" both work great.
Also, some seals do not come with the green or red or orange sealer on the outside. If just metal I put a very light coat on the outside of the seal before installation. If the seal bore is scarred at all I put a dab where the scarring is. This really helps.
Another oft overlooked item is the vent. These often plug up and force oil past the seals as the oil heats up and the air expands. I always remove them during a rebuild and thoroughly clean them out so air can flow freely.

 

Vibrations how?...Unless the machining is wrong and it spins off balance, but even then, it just rides on that rubber seal. Even If that is the case, it would do more than cause "vibrations". It would shake the bearing and gears apart in the transfer case. Ive Never heard of that and even if there was a manuf at one time making some like that, it would be like making oval ball bearing that were supposed to be spheres....how long would that last? Every single customer would be calling the retailer mad because it blew up.

I bought my yoke from Brent Mullins jeep parts. He has them made and they are only like $30. He is very reputable and has many jeep parts made that several other suppliers buy from. He had all those new repo cj2a radiators made everyone sells.

When you spend the time and money rebuilding the transfer case and you are at your end trying to fix that leak, just go on and buy a new yoke.... I mean you probably already replaced the seals and bearing...whats a $30 yoke?

Besides, what is the thickness of that sleeve? It could wear out that seal as the standard seal ID is designed to fit the OD of the stock yoke....unless the sleeve comes with its own seal.

 

Saw a good one on one of these forum's. "It's not leaking, it's marking it's territory!"

 

Thanks to jayhawkclint for posting.

I've been pretty unsuccessful at getting mine to quit leaking. So much so that I gave up and just made a sheetmetal drip pan to catch the leaks.

Someone mentioned over filling. I think I've had this problem but not sure. Is there a better fill to point other then the top plug?

Speedo - I put an o-ring on mine and it helped. If you take off the parking brake stuff it's much easier to get to the speedo cable attachment.

If I take mine apart again I will be replacing the yoke.

 

Me too, if I take mine apart again to redo the rear seal, will swap to a new yoke. Along these lines, since mine leaks at the rear seal, could this cause dirt & grime to stick to the emergency brake parts and pads, creating the awful brake squeaking noise? Would a routing hosing with brake cleaner be acceptable? Thanks

 

Yup. Speedi sleeves have been used for many, many years on yokes, harmonic balancers, etc. The list is endless. The seal should have enough give to allow for the slight extra thickness. Make sure you fill the groove before installation. I think the instructions mention this. Epoxy, even body filler works well for this. Fill the groove, sand it smoothe and install per instructions.


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Thank you for the Info. My e-brake was next on list full of oil of course. To bad they don't make a offset seal Like Mercedes does for the crankshaft that would be easier yet. Speedisleves sounds good.