SM420/D18/OD install

I've read most (if not all) of the posts on this. I've read our tech page and I've read the AA and Novak web pages on this. I still have questions though. I'm assembling these components for my '55 CJ5. I purchased the Advanced Adapter spud kit from Herm since that is the one he highly recommended.



Question #1 is about the overdrive. Herm's instructions say that the measurement from the face of the transfercase to the planetary hub should be .677", Does this have to be exact or just no further than that? Without the gasket between the transfercase and the adapter, mine is 5/8" or .625". The gasket will make it even less. The only thing I could think to do would be to move the clamp ring on the output of the transmission, but then I run the risk of the transmission output shaft moving too much.



Question #2 is about the front driveshaft clearance on the SM420. Since I have a later model SM420 with ribs, I knew that I would have to grind on them some. This however looks to be like a lot of grinding. It is more than I expected and it has me concerned.

When I first checked it everything looked like it was just a little bit of grinding needed.


Then I rotated the yolk the other direction and started to get a little worried.


After test fitting the drive shaft I am definitely worried. Granted that the drive shaft angle is all wrong here, but the U-joint wont clear the case.


I'm going to ask Herm as well, but I thought that I would see if you guys had any ideas or could offer any advice. Pics would be great.
Thanks

 

I'd ask Herm about the overdrive measurement issue.

Regarding grinding on the ribs, grind away what you need! As long as you don't get into the case you should be fine. Remember, these tranny's were used in the 1 ton, and IIRC up to 1 1/2 ton trucks and the ribs were to keep case flex to a minimum. With a 1/4 ton rated Jeep you should be fine. Just grind enough for clearance though with a little extra, don't go nuts.

 

When I put a SM420 in my Jeep I was lucky enough to talk to Tom Woods driveshafts. He asked if I would install a prototype yoke on my transfercase. It is a large u-joint flange that he modified to clear the SM420 trans. It fit without grinding although I have a case with no ribs on it.
I have never seen an advertisement for this drive flange but I think he would make one on request.
I have been running the yoke for at least 7 years, probably much more. Still on the same u joint.
You might give him a call and see if he will make you one.

 

Thanks. I will start grinding tomorrow to at least get the yolk to clear. Calling Tom Woods is a good idea too. Hopefully Herm responds to my email.

 

Well Herm was helpful. As I daydreamed on my way to work today I started wondering if I could install shims between the lock collar and the spud shaft. Here is Herm's answer;

He mentioned the V6 yolk and drive shaft as well. I am going to grind off enough to at least get the current yolk to clear anyways. I'll decide on the drive shaft after it is all installed in the Jeep.

 

Don't worry about grinding on the transmission case, these things are pretty thick. You'd have to go crazy with the grinder to cut a hole in it.

 

Well I'm glad that I did a test fit on everything first. I got to thinking "what holds this spud shaft in place if I didn't have an overdrive behind it". So I got to looking closer and realized that I had overlooked that I needed to use a T90 bearing and bearing retainer. I can purchase these from AA but they want $38.33 for the bearing. I know I can get it for half that from my local bearing dealer. Anybody know what size it is? It is AA part number 716302.

 

Well Herm came through for me. He is mailing me the bearing and retainer at a MUCH better price. I ground down the rib on the transmission case so that the yoke clears. However I don't think that the 4 cyl. u-joint would ever work with the SM420. It looks like I would just about have to cut a hole in the case for it to clear. Either that or the case is REALLY thick.

 

Well I got the bearing and the bearing retainer in the mail, but now I have another problem. The bearing retainer fits in the adapter just fine unless the spud shaft is installed. Once the spud shaft is installed, the bearing retainer hits the ridges on the spud shaft. I almost think that the spud shaft was not machined down all the way. I guess that it is time to call Herm again.

Here is the spud shaft installed without the bearing retainer in place.


Here you can see the ridges on the shoulder of the spud shaft. I think that theses need to get machined off.


This is as far as the retainer will go in with the spud shaft in. When I remove the spud shaft, the retainer sits flush with the face of the adapter.

 

Well Herm said that he has seen this before, but only with Novak adapters. He was surprised to run into this with the AA kit. He said it is an easy fix though and the bearing retainer just needs to have the ID opened up a bit on a lathe. He popped one in the mail and I should get it tomorrow. I'll let you know if it fixes the issue or not.

 

The machined bearing retainer way the key. It all went together well after that. The measurement from the back of the transfer case to the overdrive bowl gear is much better now as well. It came out to 0.670. Everything shifts and spins the correct way and ratio. I put the transmission in 4th and the transfer case in high range. I put tape on the clutch plate and on the brake drum. Turning the clutch by hand I could watch the brake drum and count the rotations. I checked all the gears and neutrals. The transmission shift cane still needs to be bent and painted, but I will do that later. Does the oil trough just sit loosely in the overdrive though? I looks like it may rattle.

I bet Coleman didn't know that they made bearing heaters.