Wet clutch slipping

[Guest Al Brass]

Hi guys,

I have a '14 Hup Model 32 HA that has a wet (engine oil) multi-disc (9x steel plates) clutch. The clutch has slipped since the car went back on the road in '97 but I have managed 13,000 miles even so. If I get on the gas too quickly after a shift, it slips for miles, unless I lift the gas pedal and let it bite. Once it has bitten, it seldom breaks loose again but if it does, it is almost always in second.

Recently, I decided to take a look and found a few things wrong. The most significant fault was wear ridges on the internal drive faces and the outer drive pins that the plates bear against. I fell the plates were perhaps catching on these and not dropping hard home until I backed off on the gas. I also found a very loose flywheel spigot bearing and some excessive crankshaft end float, both could have contributed I think. Lastly, the plates were quite shiny, a result of the slipping I suppose.

One thing that I don't know is how good this style of clutch was originally. I would be most interested to hear from anyone with a similar clutch to learn what I can expect in the way of performance. In my mind, I keep thinking there may well have been a problem that saw other types of clutches being more widely used and I may be expecting the impossible. What do you think?

Regards

Al

Edited July 27, 2011 by Al Brass
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[Rusty_OToole]

I think your diagnosis is right about the plates hanging up on the pins. New pins of very hard steel might be in order.

The clutch was probably satisfactory in its day. The main trouble was the clutch sticking together and not releasing when cold. That, plus the complexity and expense doomed this style of clutch as soon as the asbestos lined, dry plate clutch got invented.

Hudson was about the only company that stuck with the oil bath clutch but their later models had a single friction plate and were lined with cork.

I think if you rebuilt your clutch with new pins and file the worn surfaces on the dogs smooth it would be fine. You might also want to check the springs to see that they still have enough tension. One way to do this is line them up and lay a straight edge on top. Any that are bent or shortened will show up, if they are all uniform they should be OK.

This is just a story, so take it for what it is worth. A true story.

I knew an Indian motorcycle expert named Charlie Mahoney. He had a mid 3Os Indian 4 with a multi plate wet clutch. Originally it had alternating brass and steel plates.

Some time in the fifties he rebuilt the clutch using plates he cut from Masonite to replace the brass ones. He told me he tested the Masonite first by leaving a piece to soak in oil for a few months. It did not dissolve or change, the oil seemed to make it stronger.

Because the Masonite was thicker than the brass he had to omit some plates but the clutch worked better than ever.

Another thing he did was put springs in the plates to push them apart. This was to prevent them sticking together when cold.

To do this he drilled small holes in the outer tabs of every second driven plate. In these holes he put the springs. The springs consisted of small pieces of Neoprene O rings.

Im not suggesting you do the same just telling the tale.

[Guest Al Brass]

The big problem with experimenting with this clutch is the necessity to pull the engine, strip the mainshaft from the gearbox and remove the crankshaft to get to the clutch !! It has never dragged more than just a little when cold and a strong foot on the clutch brake stops the clutch immediately. You will see in my photo of the plates they have small sprung feet around the perimeter of the larger discs, I think this must work well. According to the Hupmobile literature, the discs are made from sawblade steel and I can vouch that they are very hard.

After I got the car going, I wondered if the springs were weak so I had some more made, a set of the same spec and a set of heavier ones. I ended up with the heavy ones fitted and that improved the slipping problem but I ended up with a shaking leg if I tried to hold the clutch in for any period of time !! I have managed with it though but I have fitted the new set of standard ones I had made and will try them again with the rebuilt clutch. Thanks for your vote of confidence, I'm really hoping I don't need to strip it again.

Regards

Al

[Rusty_OToole]

What kind of oil are you using. If you have STP or synthetic or some oil in there that is slipperier than what they had in 1911 it could be a problem.

If it is possible to isolate the clutch from the engine, automatic transmission fluid is good. I used to use ATF in my British motorcycles with wet clutches, the clutch worked great and did not have the sticking problem when cold.

[Guest Al Brass]

I am using a regular 15 w 40 motor oil, not synthetic. It is an awkward one because you like to think you can provide the engine and gearbox with the most slippery available but the clutch won't like that. I have tried a few different oils, so the thought had crossed my mind but but none made any real difference.

The engine, clutch, gearbox and front drive coupling are all lubricated with crankcase oil.

I do think those wear ridges we have discussed will be the main reason but at least I know know everything is as right as it can be in there. My father did that part of the car up but he is not around to ask about it but I can see that he didn't take the clutch apart. At the very least, I now fully understand how the clutch works, something I didn't know before. If it slips now, I can change oils and try some other things.

Regards

Al

Edited July 28, 2011 by Al Brass (see edit history)