Hup 20 - Clutch Slipping

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Hello All,

I’m almost embarrassed to say that, after 2 years of ownership, I have finally found the time to delve into my 1911 Model 20. After a test drive, the clutch seems to be slipping when I shift from 1st to 2nd. It shows up most on a small grade where, after completing the shift with the clutch fully engaged, the engine speeds up (from acceleration), but the car is slowing down (from gravity). Eventually, by letting off the gas some, the engine and speed of the car seem to get in sync and acceleration seems normal enough for 2nd gear on a small hill.


I noted that sometimes, in neutral, there seems to be a slight rattling from the clutch/transmission area. It almost sounds like large washers rattling. This is an intermittent sound that only happens once in a while. I’m not sure if this is related to the clutch slipping or if it indicates a second problem.


Also noted, when I press hard on the clutch pedal (in neutral) the engine will slow down some. From other threads on the forum, it seems this is due to worn thrust washers between the engine and the clutch. When I pulled the clutch off the engine, there was only 1 bronze washer (0.052” thick) against the clutch pack and 1 fiber washer (0.030” thick) against the engine block. There is about 0.045” of wear into the block.

Because the car has had an older cosmetic restoration and at a separate time, the engine was restored with some work done on the transmission, I suppose anything and everything is suspect. Any help in guiding me to fixing these problems would be appreciated.

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You appear to be missing one more washer/spacer.  I've attached a picture (that was sent to me by Ken on this forum, he'll possibly chime in ) showing the correct spacers for the clutch.


While you have things apart, I'd recommend you take the transmission apart, checking the rear bushings.  There's one large one in the back that is usually quite worn, and it affects the alignment of everything.  The transmission is very easy to take apart, but it has to be done in a specific order of parts removal, and put back together the same way. 


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The slipping is pretty much normal when you shift,it takes a few seconds for the oil between the plates let them grab.Not good if it continues to slip obviously.

The photo David posted shows one bronze was riveted to the clutch drum so actually there should be the fibre and one more bronze.

I don't know who did that or why,I would not.

Also recommend you very carefully open the clutch to check the bushing for the forward end of the main shaft.

Also note how clutch came off crank,and replace same way.

And check end clearence once bolted up,I think the gentlemen from down under might be more knowledgeable on that topic.

Good luck,Ken

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Hi David, Ken,


Thanks for your replies. I recall seeing this photo on one of the threads and was surprised to find only two washers when I removed the clutch. Judging by the wear on the engine block and that the wear matched the fiber washer perfectly, I suspect the last restorer only put in the two. Perhaps the 3rd one was worn completely away when he restored the engine and didn’t know any better?


Do you (or Ken) have any idea of what thickness each of these washers should be? They look like about 1/8" or a bit under in the photo. Is it highly critical?


I checked the transmission bushing for wear against the main shaft. The clearance (difference) measures about 0.007” and appears to be round. I also checked the clearance between the main shaft and the rear of the clutch and it too was 0.007". Some wear, but not to the point where I think I have to replace them at this time. I didn’t have to take the transmission apart since I could reach the bushings with a telescoping gage. The service history of the car indicated some work was done on the transmission in the mid-eighties, I assume this bushing was replaced at that time.


Ken – Both the clutch slots and crank keys appear to be symmetrical, so I’m not sure why the rotation of the clutch when reassembling would make a difference, unless of course I don’t know where to look for a difference (or the design was altered slightly from 1910 to 1911). The main shaft does have a “front” and “back” orientation, and is so marked “F” and “R”.


When I was removing the main shaft from the clutch I noted about 1/16” of each key end was worn down to the diameter of the shaft along with some wear on the shaft itself. When playing with it, sometimes it would not seat all the way in. If it was hanging up, I suppose that could be a cause for the clutch slipping. Each key was also worn on the “drive” side, which you would expect.  Are those pins that hold the keys in the main shaft?


post-154239-0-30301000-1439406721_thumb. post-154239-0-00766000-1439406754_thumb.


Looks like it is time to take the clutch apart and examine it for wear and/or damage.

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G,day to all Huppers. The alignment marks will be seen on the end of the crankshaft and on the forward end of the clutch drum.

They are in the form of heavy centre punch marks and are there because the rear main bearing which is the outer surface of the

clutch spigot only runs true when assembled in the position that it was originally ground. On some engines the clutch will not

slide onto the crankshaft unless the dots are lined up . In other words the alignment of the crankshaft is dependant on the

alignment of the clutch. Clutch slip for a few yards upon changing gear is standard and the heavier oil in the gearbox the further the clutch will slip. Never use red fibre in the centre of the three unit thrust washer pack, use the material that fibre timing

gears are cut from. We use a centre washer of stainless steel between two of PB1 and we fix the one on the engine with 3/16 screws to prevent it spinning . Old age and long use sometimes lets these washers wear into the clutch spigot Max Burke Nulkaba 2325


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Hi Max,


Thank you for your post regarding the alignment marks. It really helps to know WHY things are the way they are. I looked thoroughly at the end of my crankshaft and I could not find any alignment marks as you describe (although I did see a pair on the top right rear of the block which have to have some other meaning). I also looked carefully on the clutch housing, but couldn’t find any there either. But as you can see from the photo in my first post, I believe it has been machined to remove wear, the kind similar to what to what has happened on the end of my block.


Since I couldn’t find any marks, but your explanation told me why they were there, I measured the trueness of the clutch in the bearing with it installed on the crankshaft in either orientation. While the runout was 0.020” (who is to say the housing is perfectly concentric), it was the same with either orientation, meaning there was no “adding” or “subtracting” caused by the trueness of the bearing.


As to the 0.045” wear on the block, I believe it was caused by the fiber washer being in direct contact instead of bronze. Since the engine has been restored not too many miles ago and runs absolutely perfect, tearing the engine down and mounting the block onto a lathe and turning it down is not an attractive option. I have to think of some alternate. If anyone has any good ideas, I’m open to them.


When I pulled the clutch apart, I think I found the reason for the slippage. I believe the clutch plate tabs were getting “hung up” on the steps on the rear clutch housing, not allowing them to fully engage each other when the clutch pedal is released. I can mill a new set of ½” slots in the housing which will eliminate the steps.


It is interesting that each tab on the clutch plate stack has worn to a different width. All three tabs and their respective slots in the housing have a similar amount and type of wear. Otherwise, the plates are in good condition and do not show any signs of bluing. I’m debating if I need to have new clutch plates made. The tabs are certainly strong enough as they are, but there would be some radial movement each time the clutch is engaged. Does anyone have any thoughts or opinions?




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G,day Huppers. Yesterday evening a friend who has a Hup 20 called me to relate a sad tale. Whilst on a short journey on his Hup he had to stop at a rail crossing . Upon proceeding away again he found that he could not. He had to have the Hup loaded onto a tilt bed truck and taken home. Later in the shop after removing the gearbox he found that the needle roller bearing which he had used to eliminate the thrust washer pack was responsible. That marvelous device had worn a groove right into the spigot of the clutch causing a weak spot and this is where the spigot and the clutch parted company .That,s right , snapped right off.Lucky ,he has a usable replacement and was wondering about having it hardened to avoid the same thing happening again. I suggested talking to his bearing stockist for advice as they may have a hardened sleeve to use rather than having a coating of some hard spray on substance  applied for when the next  needle roller bearing does the same trick. I have  seen a clutch which has grooves worn here  and another which has broken through the wear grove  and been welded up and put back into service.Neither had a needle race . We used neither of them. When attending to your clutch be sure to check this area. Max Burke Nulkaba 2325 Australia.

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Hi Edgar here,

Hupp 20s have tricks and traps for the unwary in their clutch design. As Max said mine was slipping more than usual until it finally didn't work at all. The unit which holds the plates broke at the clutch release bearing, causing lots of mischief. I fitted a needle roller bearing in place of the brass shims which worked well. However I failed to notice that this spigot was already warn badly from previous brass washers, so the needle bearing rolled around the spigot and eventually parted it off as clean as a lathe leaving the gear box oil heavily polluted with powdered iron. All four of my spare clutches were similarly worn, so I had the worst one built up with nickel bronze at red hot temperature and cooled very slowly in lime.

    I also have a needle bearing fitted between the clutch drum and crankcase so the engine doesn't stall when de-clutching at idling speed. These bearings are far better than brass and fibre washers.

    I found it easiest to drop the rear axle and undo the gearbox from the engine rather than lifting out the whole power unit. Here is a word of warning; because the clutch unit as a whole forms the rear journal of the crankshaft. Do not attempt to remove it from the engine to work on the clutch. Instead undo the 10 round slotted bolts after cutting out the wire which runs through each of their heads. If the wire is not bent at all, make up a jig to put the bolts in so that each one goes back into its original place otherwise you have to refit each one with washers so the holes for the tie wire, line up when you put it back together. Otherwise you will never get the wire back through them again. Because of the very strong spring inside, you need to take out 3 bolts and replace them with high tensile rods 3 inches long with 5/16 UNF thread and nuts screwed down to the clutch unit. Then remove all the other bolts with a short ratchet screw driver. Gradually undo the nuts on the threaded rods in turn until the unit comes undone.

    Inside the heavy spring impinges on a race of ball bearings in a brass holder. If this ball race is worn out it is easy to make a replacement. Just turn a new brass holder on the lather and bore a series of holes in it to hold new steel balls. Make the holes exactly the same size as the balls. Place the balls in the brass one at a time and crimp them in place with a steel hole punch (slightly bigger than the balls) on both sides of the brass ring.

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