Transmission ok in reverse, bad in forward

fulvio · June 05, 2016, 09:30:31 AM

I know there are a ton of posts in this forum about transmission problems, but I was not able to find one that exactly fits my situation.

1989 C34, #929 here. Universal M25XP, Hurth transmission.

As the title says, my transmission works just fine in reverse. However, in forward the shaft spins quite slowly (definitely less than 10 revolutions per second), regardless of engine RPM, and so it gives almost no thrust. As for noises: I get the usual, satisfying "clunk" when shifting to reverse, but no sound at all shifting to forward. Other than that, no unusual noises.
I went so far as disconnecting the control cable, to make sure the shifter lever on the transmission block is moving the full range, but that is not the issue.
Admittedly, when I checked the fluid level it was pretty low - just to the tip of the dipstick. So I got my hopes up that adding fluid the problem would go away, but no. I added 100 ml of transmission oil (which I believe is 33% of the 0.3 L capacity according to the manual) and it seems to cover the line in the dipstick now.

Probably unrelated: This started happening not long after I replaced my prop with a new Bruntons AutoProp (and added a vetus bullflex flexible shaft coupling), so at first I thought something was wrong with the prop. But then I had divers go down and replace the zincs and they said the prop is fine (with video to prove it). I wouldn't exclude that there might be an engine alignment issue, since I also did a bunch of engine work, and that could have caused problems with the transmission. The low fluid level could be a symptom of that.

Any suggestions before buckling down and taking the transmission out? I know that means lifting the engine up, removing the bell housing, etc, etc, and I am not looking forward to it.

Thanks!

Ken Juul · June 06, 2016, 08:04:03 AM

disconnect the shifting cable at the transmission. Then manually shift the transmission. Make sure it is going all the way into forward. May just be a cable adjustment.

fulvio · June 06, 2016, 10:13:05 AM

Thanks for the reply!

I did that. It's definitely not a cable adjustment issue.
(In fact, I took the opportunity to replace both control cables. I should have done that long ago.)

ron deru · June 08, 2018, 08:46:22 AM

I'm two years behind on this one. But what you described is my exact situation. Can you tell me what was the final solution and were you happy with it?

KWKloeber · June 08, 2018, 11:17:27 AM

I just had a new C30 owner who JUST had the issue, it turned out that there was no way to adjust it out. There was just not enough travel in one direction and too much in the other. He modified the bracket and remounted the cable end in a different location and all is well now.

Basically, he put an extension on the bracket so he could clamp the cable a little bit further aft than OEM. Shifts smoothly now. I didn't have eyes on, so I don't know if it was due to cable stretch? or something else?

Whether this is your issue or not......?

-k

Paulus · June 08, 2018, 12:13:21 PM

I posted the same problem in 2014. Great in reverse but no power in forward. Had the transmission rebuilt. Ken Juul gave me the same advice, there was nothing wrong with the linkage. The transmission was rebuild at Torresen.
Pleased with the with the rebuild. Also, the $$ pain has gone away.
Paul

lazybone · June 09, 2018, 11:57:34 AM

It has been a few years since I've seen the insides of one but I think that that hurth has separate clutch packs for forward and reverse. They are consumables.

Stu Jackson · June 09, 2018, 12:19:32 PM

Quote from: lazybone on June 09, 2018, 11:57:34 AM
It has been a few years since I've seen the insides of one but I think that that hurth has separate clutch packs for forward and reverse. They are consumables.

The tech wiki has the Hurth manual so you can look inside without using a wrench.

Ron Hill · June 11, 2018, 02:37:57 PM

Guys : One of the biggest problems that MK1 owners have with the Xmission not doing well in FWD is because of a bad adjustment at the transmission!!

Previous owners have changed from the "Rubber Ducky" transmission Edson shifter (which tended to break off!!) to the SS Edson shifter. The SS Edson shifter (really made for the MKII pedistal) will hit the MK1 steering pedistal guard in FWD at the steering wheel on the MK1, but not be all the way in FWD at the transmission itself. This will cause the inside clutch plates (my term) to somewhat slip because they are not fully engaged.
I wrote this up in the Mainsheet tech notes years ago.

When I change engines to an M25XPB I took my SS shifter handle and with the help of a hydraulic press, bent it (to a more straightened position)!! Also wrote that up in the Mainsheet tech notes.

Great Info in those old Tech Notes!! A MUST READ !!

A few thoughts

KWKloeber · June 11, 2018, 02:45:01 PM

MMD are very professional (and one of my vendors/distributors) if you need a rebuild

-k

Bill Shreeves · June 11, 2018, 07:12:52 PM

I too had the same experience and verified the slippage didn't improve even when shifting manually without the linkage attached and therefore no travel limitation. I installed a ZF10 to replace the ZF5 that I didn't want to have rebuilt. It was a shame. The ZF5 was only 500 hours old but, the PO never replaced or checked the fluid which ruined it.