Transmission Gear Ratio

Sue Clancy · June 13, 2016, 06:58:48 AM

On our 1987 MK1 boat we have the original (we believe) Hurth HWB 50 transmission which seems to be failing in forward. We had all the seals replaced 2 years ago after some leaking but now the boat will not hold the forward gear. We have gone through the diagnosis of the issue by removing the cables and shifting manually but to no avail. At this point we are ready to invest in a new transmission. My husband spoke to someone at Foley Engines who indicated that we needed to know the gear ratio off the plate on the transmission. There is no visible plate with any info we can see/get to. We don't have the original manual that might have contained this info. either though our research suggests it is 2:1.

Can anyone confirm this before we go ahead and try to order this today in hopes of getting off the dock this summer.

Ken Juul · June 13, 2016, 07:20:45 AM

there is a hurth transmission manual in the "manuals" section of the tech wiki.

prh77 · June 13, 2016, 07:26:48 AM

A couple of guys in out club got their Hurth boxes rebuilt in the NY area for under $800. No problems since. Not fun to remove as the bell housing has to come off.

Sue Clancy · June 13, 2016, 07:32:48 AM

Yes, we saw that manual however not knowing the source of that or whether it applies to every boat, we were hesitant to trust the info.

In that manual it shows A=2.05 B=1.86 however it was unclear whether that was true for all the HWB50s installed on all the Catalinas.

Hesitant to do another rebuild at this point. Thought it could be quicker to just get a new one. We are well aware of the pain of getting this thing off as we just did it 2 years ago. My husband is still recovering both mentally and physical from that one.

Also we prefer not to get the new model if possible because of the issues with it being longer - Installed a new coupling last time and would prefer not to deal with removing that and cutting the shaft to accommodate that. Boat is in the water at this point.

Stu Jackson · June 13, 2016, 10:39:48 AM

It could be just the damper plate. For some unusual reason, the C36 guys seems have had the most issues with their transmissions, even though their boats are the same as ours with the same engines. While many of their plate issues were with the M35s, you might want to noodle around their forum and see what you can find. IIRC, there are two different makes of plates and one is superior to the other.

This: ... There have been a number of reported failures of the R&D damper plates. Replace it with the Sachs damper plate and you'll be fine... ...

I did a search there on "damper+plates": https://www.catalina36.org/search/node/%22damper%2Bplate%22

Might want to try one on M25 damper plates.

I agree with your concerns about the implications of the newer longer transmissions, which make them less than a "slap in" replacement. But once you're in there, if it's only a plate, then you don't have to deal with the implications.

Good luck.

Ron Hill · June 13, 2016, 02:29:13 PM

Sue : The original Hurth 50 transmissions were the 1:18 ratio and most of the newer ones were the 1:2 ratio.

The new ZF 10s I believe are 1:2 ratio? The ZF 10 is about one inch longer than the old HB 50 and will bolt on to the M25/XP bell housing.

The damper plate primarily acts as a "cushion" between the transmission and the engine while shifting. The usual symptom for replacement is when you hear the damper plate springs rattling. I don't know of a case where it had caused "slipping out of gear".

A few thoughts

Indian Falls · June 23, 2016, 08:27:08 PM

The manual I have shows clutch packs for reverse and clutch packs for forward. If you can turn your prop shaft by hand while in gear that's a good indication the pack is done for.
I would look into finding someone to rebuild the unit if it were me. If you do replace the transmission please let us know on this forum... I would love to have a whole unit to rebuild and have as a spare and even offer it to sailors in the middle of the season for a swap, should anyone have a breakdown at an inopportune time.

Sue Clancy · June 24, 2016, 06:31:38 AM

We are going ahead with a transmission replacement with a new ZF-10. We had previously had the seals all replaced 2 years ago because we could not get a new transmission at the time. We have the transmission in hand and my husband will be working on this with a friend over the weekend. In terms of the old transmission, we has arranges a credit with the company we got it from to do a swap. If anyone is willing to pay more than $150 plus shipping we can see if we can change that.

Will update after the project is done on how things went.

Momentum · June 26, 2016, 08:39:33 PM

Guys I had a major problem last Thurday with my transmission. I pulled out of our finger (in reverse) and when I was ready to move to forward I had no response.
I quickly dropped the ancor in the marina and was able to control the stern from hitting other boats. With the help of our friends I was pulled into another slip. Checked the cable and the oïl of the tranny and all was OK. Then with a dinghy I was pushed back into my regular slip.

With my friend we took the tranny out...the input shaft was damaged and the damper plate was completely gone. Tons of steel was in the bell housing.

We were bearly able to take the transmission out and when I do get my new damper plate I believe that the only way its going to go back in is by lifting the rear of the motor the clear the shaft/coupling.

Now the boat is 12yo with about 1300 hrs on the engine. The boat is in the water about 4mo/yr so it's like 3yo!!!.

My damper plate has NO springs. My engine is a universal/westebeke 35B.

As I can see it's seems to be a no so rare problem. I'm replacing the damper plate only (280$Us). I was told that the imput shaft is still usable but next Fall I'll remove again and get it replace. Two pros that I trust believe that I'm still good for many years with it but none the less will change it in a couple of months.

Momentum · June 26, 2016, 08:50:37 PM

Pictures of the input shaft

Momentum · June 26, 2016, 08:52:26 PM

Pictures of the tranny and the plate with ratio

Momentum · June 26, 2016, 08:55:02 PM

More pics

Momentum · June 26, 2016, 08:57:08 PM

Did I do something wrong?

Stu Jackson · July 01, 2016, 04:43:18 PM

Sue, there was a good transmission discussion more recently, here:

http://c34.org/bbs/index.php/topic,8610.0.html

It includes a less expensive source for damper plates and a replacement transmission. Don't know if you've seen it, with a link to the C36 site with a post by Maine Sail.

https://www.catalina36.org/forum/technical-discussion/transmission-slippage

Sue Clancy · July 01, 2016, 06:19:01 PM

Thanks Stu for that link. Some interesting thoughts on maintaining the ZF10. At this point we successfully installed the new ZF10 and have the engine back and running and shifting well. A few things to tidy up tomorrow and then hopefully a test sail.

We probably paid a bit more for it but it came quickly and it's done. Unlike many we track maintenance items in our log but not cost. It's too depressing.

Sue