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Herms 30% OD unit I'm at my wits end.

C

CHUGALUG

Member
Joined
May 11, 2019
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.
 
I have an ATV/herm od I bought used from a member here.

I installed it and it works fine, although for a time it would not shift unless stopped. This has since corrected itself without any input from me.

The shifter it came with was an amazingly horrid POS that was purportedly supplied by Herm. I threw it away because it was for a t-14 I believe and not something I would pass along to anyone.
 
Well I have 15,000+ miles on mine. I built my own shift linkage which works quite well. What doesn't work is it staying in Direct drive in 1st under any kind of a load. I can feel it climbing out of gear when I hold my hand light enough on the stick when its coming out of gear.

I was hoping for some help I know others have had trouble. I also know others that have had no trouble. Or at least none they mention.

I guess the next thing to try is to ramp up the pressure on the detente ball. At least I don't have to pull it to do that.
 
Not directly related, but a suggestion...

I once had a similar situation with a CJ5 4-speed. Long story short, the "climbing out of gear" eventually turned out to be the bell housing assembly was out of concentricity with the engine and transmission.

After months of frustration, the problem was cured with a dial indicator, and a beer-can shim.
 
I don’t know anything about the Herm 30% unit. May be totally different. I have experienced the same issue with my Saturn unit. When I pulled it, I found that the spiral snap ring had come out of place.
1786360147777.jpeg
I then pulled the bowl gear assy to look for a reason why. I found the 2 little screws missing that holds it together.
1786360301677.jpeg
No problems since then.
Good luck to ya
 
Just thinking out loud here. Is the detent ball and spring in good condition? Also the grooved area where the ball rests in the direct position. Do some serious measurements concerning engagement depth also.
 
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CHUGALUG 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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I had the same problem with one of his 30% OD units about 9 years ago.
It would not stay in direct and I was forced to drive in OD all of the time.
I went round and round with Herm via email/phone and I/my equipment was always the problem.
Finally I took the OD unit to his house and he tore it down to measure the housing. He admitted that the run of 30% housings were manufactured .060 out of spec.
I would be willing to bet that you have one of those units.
You are going to have to take the unit to his house and meet with him face to face if you want it made right.
 
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Never owned an overdrive. But. All this talk of detents makes me squirm. The gear should not need any force from the detent or shift parts to stay engaged. That is not their function, IMHO.
 
CHUGALUG said:
Oh thats easy to answer. because this is a 30% unit and not the 25% unit AA sells. They are different with reguards to how far the Planetary hub should protrude.

which by the way for the 25% unit Herm has the same instructions.
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I understand but if the machining is consistent it should easily be determined what the proper protrusion vs shimming should be. Personal experience has shown differences with regard to D18 cases and measurements to the output gear from cover face.
Sounds like "one size fits most"
 
Norcal69 said:
I had the same problem with one of his 30% OD units about 9 years ago.
It would not stay in direct and I was forced to drive in OD all of the time.
I went round and round with Herm via email/phone and I/my equipment was always the problem.
Finally I took the OD unit to his house and he tore it down to measure the housing. He admitted that the run of 30% housings were manufactured .060 out of spec.
I would be willing to bet that you have one of those units.
You are going to have to take the unit to his house and meet with him face to face if you want it made right.
Click to expand...
How were you made right? was it a matter of more shims? was it a refund? Did Herm bang on it with a hammer until it worked? I am currently at .100" of shim. That should sure make up for the .060" out.
 
How much "stick out" did it measure with the .100" of shims?

Should be .667″ from the case to the outward edge of the bowl gear. If the gear is .060" out of spec that accounts for more than half of your shims.

I know you recently rebuilt the transmission, I think it might be good to re-measure end play on the main shaft, which could have changed with the miles put on it after re-build. If endplay on the transmission main shaft is excessive this will negate what you are trying to do with the shims.
 
PeteL said:
Never owned an overdrive. But. All this talk of detents makes me squirm. The gear should not need any force from the detent or shift parts to stay engaged. That is not their function, IMHO.
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Perhaps there are a few problems with both Herms and AA's current offerings, but the Warn units pretty much run forever if you keep the lube at the proper level. I installed the one in my CJ 5 in 1970 and it's never been out of there. The unit in my 3B was installed in 74 and I rebuilt it once in the intervening 52 years, all behind several different sbc's, at least one of which bested 400 ft-lbs. Their utility with either 134 (at least in stock form) is somewhat limited but with the optional 4.88 CJ gears and a 225, absolutely perfect in a CJ 5. And with V8 power, a they work great with a lot higher speed gears, limited only by what you want for a CR.
 
I made some other measurements to send to Adam (never heard back from him) But I don't remember getting an accurate T case mounting surface to The top of the Cone. I guess I will hopefully tomorrow when I can get it apart. As to the end play I will do that if necessary but I would prefer not to have to remove the top of the trans again.


I wrote this yesterday the 12th planning on working on it today. BUT the wife woke me up and said get dressed your taking me back up to the hospital SO I spent today in a room with weird and sick people hoping the wife didn't catch anything waiting for a couple tests and for her to get some IV fluids and a couple more prescriptions. Home at 6:30 totally wiped out. BUT the new shims (I bought 10) .005" shims from McMaster Carr Shipping cost $2.00 more then the shims. SO If I am not so occupied tomorrow the 14th I'll crawl under the jeep get some measurements and see where I am headed.
 
Ok I got the OD out and I measured the Top of the Syncro cone to the edge of the Trans case. And best as I can estimate I am getting right around .632-.637 Its really hard under CHUG to make sure the calipers are at exactly 90°. I have .030" of shim here and will try installing that to see about bringing it up to .637 or very close to that. It was a real PITA to pull the back section of the OD off. I guess it will hold in Direct when it wants to LOL.

Had to stop work for a while and clean up the other side of the carport/garage as we are getting 2 ton of Wood pellets tomorrow. The majority of our Winter heat. The local Farm store puts them on sale in JULY and I always put off the delivery as late as possible This year a couple weeks was all I could talk them into.

I should have it back together tomorrow and try another test drive. I might even be able to save the gasket.
 
I am not sure what you mean by "Syncro cone". If you are talking about the "Synchro Hub" you are not measuring the right thing. I suspect you are talking about the bowl gear, or planetary case as it is sometimes called, if so I think you are on the right track, but also think you may need even more shims.

Norcal69 said "He admitted that the run of 30% housings were manufactured .060 out of spec.". If you are measuring right, you have close to the stick out required for a case that is NOT out of spec. I am thinking you may need to add more than .030 of shims, may need to add .060 to make up for the error in the hosing.

The measurement is made from the mounting surface of the transfer case to the edge of the bowl gear for the overdrive. When I I have installed an overdrive I measure this with a stack of feeler gauges, I haven't tried using a caliper for it.

From Herm's instructions;"
  1. Before assembly, you must verify the proper location of the gear assembly. This measurement of .667″ is taken from the case to the top of the planetary.
 
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OK I am measuring from the top of the cone shaped protrusion ( the part shown sticking the farthest out of the back of the transfer case) to the gasket surface on the Transfer case. currently at .632-.637 depending on how I hold the Calipers. I'm thinking about making a go no go gauge on the lathe. A round section of shaft that is exactly .667"

OD cone.jpg
 
The .667 is a max measurement correct? At .667 or less, the Saturn needs no shims. That is for the Saturn anyway. Slightly less than that would be correct, if I understand right.
At .637 the Saturn would be happy.
Since this is a different type unit, maybe the same doesn't apply. I'll go back to my corner now.
 
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