HELP Herms 30% OD I'm at my wits end with this thing

Mark W.

Mark W.

Well Oiled
Dec 6, 2014
1,059
Silverton Oregon
First Name
Mark
Willys Model
  1. CJ
Willys Year:
  1. 1948
OK I bought one of Herms 30% OD units It currently has 15,000 miles on it. And from day one it has never stayed in Direct Drive unless I hold the shift cane in Direct. Its been back to Herm once about 4000,00 miles ago his son Adam rebuilt it and declared it ready to go. I installed it with .090" of shim per his suggestion and that made it better but still not great. Now its worse and I just added another .010" for a total of .100" of shim and taking it out for a slow run around the Block its still climbing right out of Direct. Has anyone here got one of these things to work right and if so clue me in please as to how.
 
Mark W. said:
OK I bought one of Herms 30% OD units It currently has 15,000 miles on it. And from day one it has never stayed in Direct Drive unless I hold the shift cane in Direct. Its been back to Herm once about 4000,00 miles ago his son Adam rebuilt it and declared it ready to go. I installed it with .090" of shim per his suggestion and that made it better but still not great. Now its worse and I just added another .010" for a total of .100" of shim and taking it out for a slow run around the Block its still climbing right out of Direct. Has anyone here got one of these things to work right and if so clue me in please as to how.
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Mark, since you do not live obscenely away from Herm, have you considered driving up there?
 
You might be able to reach out to Sal at Vintage Jeeper.

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I talk with Sal every now and then. The thing is he has never even seen one of the 30% units (not that I even know if this is part of the problem). I'm most likely going to talk to him. I am also going to see what I would have to do to buy a 25% Unit.

It will end up running the engine 190rpm more to see the same 60mph (my freeway travel speed) Not a huge difference. And I guess I will be able to get up a hill in OD a little farther before down shifting as I'll have about 2 more HP at the higher rpm according to my dyno chart.
 
Never heard of a lube slinger. Are you talking about the oil scoop? As to the .667 measurement I was and have been told by Adam Telford that the 30% units have a much different cone dimension.
 
KLankford said:
My 25% drive kicked out a lot and they sent me an adjustable poppet for the lever shaft, not an issue now unless I guess I really hot rodded it. It was shimmed as well. He didn't have a vendor for the 30% during the covid era.
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Are you talking about the detente ball and spring? this is the next place I am going to try to correct this.
 
I know a mechanic in Creswell that deals in Willys. If you’d like I could have him talk to you, perhaps. Wondering whether the gear mesh is tossing it out or if the top dana18 gear needs shimmed. (I’ve never worked on one, just thinking)
 
I drove up to Herm's this morning. I had an appointment with Adam his son to finally figure out WHY this thing (my 30% ATV OD) has never worked correctly) A little less then a 2 hour drive.

Adam tore right into the thing and in short order determined the Shift rail was the problem. In a nut shell the detente notch for the direct drive position is in the wrong place. This results in the Syncro collar not moving forward enough to completely engage the Gear on the Planetary. He said he had just learned of this being a problem on a unit he worked on just a couple weeks ago.

When working on one unit you would never notice that was a problem because there is nothing to compare to. He happened to work on 4) units at one time for a customer and when he put the four shift rails on a pin through the shift fork holes he noticed one of them the notch was not in the same place (this unit had been having the same problem staying in gear). So investigated more and sure enough that was causing the problem.

So once he knew where the problem could be coming from he then figured out where and how to measure the Collar in both Direct and Over to be able to tell if the notch was in the proper place.

SO a New Shift rail and fork corrected the position problem. While he was in it already I had him go ahead and replace a couple parts that showed some wear after the 10,000+ miles since the last time he had it in hand in Aug of 2024. New Blocking rings and a Triple check of the collars position in Direct and $100.00 and I was headed home 2.5 hours later with basically a rebuilt OD unit that should now work as designed. He said he was surprised at how little wear there was on most of the Unit which we agreed was due to my obsession with the oil level.

I'll get it installed some time this week (a number of Doctors appointments to deal with) And report on the results.

So no amount of shimming would have ever made it better. He said to run the same amount of shims I had in it and all should be good LOL.
 
Mark W. said:
I drove up to Herm's this morning. I had an appointment with Adam his son to finally figure out WHY this thing (my 30% ATV OD) has never worked correctly) A little less then a 2 hour drive.

Adam tore right into the thing and in short order determined the Shift rail was the problem. In a nut shell the detente notch for the direct drive position is in the wrong place. This results in the Syncro collar not moving forward enough to completely engage the Gear on the Planetary. He said he had just learned of this being a problem on a unit he worked on just a couple weeks ago.

When working on one unit you would never notice that was a problem because there is nothing to compare to. He happened to work on 4) units at one time for a customer and when he put the four shift rails on a pin through the shift fork holes he noticed one of them the notch was not in the same place (this unit had been having the same problem staying in gear). So investigated more and sure enough that was causing the problem.

So once he knew where the problem could be coming from he then figured out where and how to measure the Collar in both Direct and Over to be able to tell if the notch was in the proper place.

SO a New Shift rail and fork corrected the position problem. While he was in it already I had him go ahead and replace a couple parts that showed some wear after the 10,000+ miles since the last time he had it in hand in Aug of 2024. New Blocking rings and a Triple check of the collars position in Direct and $100.00 and I was headed home 2.5 hours later with basically a rebuilt OD unit that should now work as designed. He said he was surprised at how little wear there was on most of the Unit which we agreed was due to my obsession with the oil level.

I'll get it installed some time this week (a number of Doctors appointments to deal with) And report on the results.

So no amount of shimming would have ever made it better. He said to run the same amount of shims I had in it and all should be good LOL.
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Great outcome. That sort of problem can be almost impossible to solve without diligent effort, careful observation and a bit of luck. Like you said, looking at one, with nothing to compare it with, you’d never know that a key component was a little off spec. Glad he worked it out.
 
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Well I finally had time to get CHUG down off the ramps and to run it around the block and it would appear the OD no longer pops out of Direct. In first gear Direct I can even bounce the throttle and it remains solidly in Direct with no indication of popping out.
I have the trans cover (the one on the floor) removed and a couple of times I heard something that sounds almost like something touching a drive flange or the rear drive shaft. So I'll crawl under one more time and see if I can figure that out.
It is noticeably harder to shift out of Direct not sure if that is just because I am so used to it not really being in Direct or if its due to the increase in Detente spring pressure. I don't know if Adam left in my spacer or not. Either way in a couple hundred miles I am sure my muscle memory will conform.
Now to reassemble the Floor cover and get the controls attached to the trans shift cane put back in place. Then a longer test drive most likely ending up at the local car wash for a long over due wash. CHUG has been filthy since we got home from the RUN OF THE HILLS in Ashland in June. I hope I can get it clean again LOL.
I'm happy its finally working as it should be.
 
Took CHUG to the store on the way home the two piece OD shift cane I made broke in half shifting to OD. It just like fell apart lol. I have come up with a much improved geometry and a new cane for it that is much easier removed when needed. And it has a much reduced travel now. Think I'm going to like it.
 
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