Single clutch problems

roromac · Post by **roromac** » Tue May 12, 2009 12:02 pm

I though I was being clever - or practical. A clutch sudden clutch drag seemed like a pressure plate fault. Having split the single clutch Super Dexta and found the expected fault with the pressure plate, I repaired - i.e. replaced split pins and finger bolts. The old finger bolts were worn to paper thin on top or in one case away to the thread so I replaced them. The bolts I put in were similar in length, without the domed (I assume) top.
When we reassembled, (with new friction plate), the clutch pedal was very light and seemed only to be overcoming the spring on the release bearing.
We haven't started the tractor; our suppositions come from engaging a gear and turning the engine by hand.
Can I assume
1. The finger bolts are not proud enough, (i measured their protrusion against another pressure plate) so the release bearing never contacts them?
2. The release bearing was pushed backwards towards the gearbox? (Seems impossible given it's cradle)
3. I've missed something obvious.

I know in the instruction manual it says don't mess with the finger bolts but they were worn away. On another BB (sorry) an illustration is given for MF (sorry again) adjustment and suggests that the bolt heads be level with the preesure plate housing - this is more or less what I have.

Any questions or suggestions? I expect I'l have to split again but then do what?

Rob

Post by **Brian** » Tue May 12, 2009 6:07 pm

Check the bolt/pins in the release bearing clutch fork.

roromac · Post by **roromac** » Tue May 12, 2009 9:21 pm

Thanks Brian - that I will check. That seems consistent with the wear on the bolt heads; I had wondered how so much wear could occur on bolts that press against a bearing - they should mostly be still whilst in contact.

Rob

Post by **Brian** » Wed May 13, 2009 8:02 am

Driving with the foot resting on the clutch pedal or having the clutch free play adjusted wrongly were the most common causes. It could also be "fair wear and tear" if you are looking at a clutch pressure plate that has done over 40 years.

roromac · Post by **roromac** » Wed May 13, 2009 10:54 am

The first seems quite likely - the tractor has been used by many different people who don't usually drive tractors.
Looking at the workshop manual, the fork seems to be attached to the shaft by two pins. There is still light pressure on the pedal so I assume those are still intact. Does that sound like a fracture in the cradle?
Rob

Post by **Brian** » Wed May 13, 2009 2:00 pm

Then it sounds like the release bearing is not reaching the clutch fingers. The cause could be the wrong clutch friction disc. If the plate was too thick the pressure plate springs would be compressed, the fingers would be a lot lower than normal and would not contact the release bearing.

As long as the adjusters were around the same height as they were originally they should not give you a problem as long as they are equal heights so they all release the disc at the same time.

Could the disc be fitted the wrong way round?

roromac · Post by **roromac** » Wed May 13, 2009 3:01 pm

I'm sure you're right that the thrust race isn't reaching the fingers. The clutch plate is fitted the same way round as the one it replaced and is from Forge Services for this tractor.
If I remember correctly, the flare is towards the gearbox and is consistent with the workshop manual pictures. The finger bolt heads are about 3mm proud of a level line taken across the top of the cover plate before fitting. I have no way of knowing what the original height was but I have a Major cover plate to compare, (same part) and the guidance from the BB mentioned earlier in the postings. When clamped to the flywheel, the fingers lowered as pressure was applied but that was as expected for the friction plate to work.
I like your idea, Brian, of a fault in the release bearing carrier but I can't think what it could be.
Rob

Post by **Brian** » Wed May 13, 2009 4:26 pm

Something that might be "teaching my grand mother to suck eggs" but you have adjusted the clutch rod to try and get the clutch to free haven't you?

roromac · Post by **roromac** » Wed May 13, 2009 4:30 pm

I have indeed. In fact if you use a bg adjustable directly on the lever at shaft end for leverage, you run out of movement before the clutch clears - most of the travel is against light spring tension.

roromac · Post by **roromac** » Mon May 18, 2009 6:53 pm

Had time to split the tractor again today. Release bearing fine, works as it should. Removed cover plate and compared with a much newer one. There were two differences: Stronger springs on the newer one and 2 or 3 mm more clearance between pressure plate face and a line level across the bolted face. This made me think you were right about the friction plate thickness.
Test fitted the newer cover plate and gained some movement that felt like the release fingers - but not enough. It's convinced me that the plate thickness is the problem so I'll wind out the finger bolts enough to give good adjustment.
One thing - the original cover plate had one over-sized hole which suggests only one position suits on the flywheel. I can't see why that should be so so I intend to drill out one of the smaller holes on the newer cover plate. Does anyone know if there is a reason why I shouldn't?
Rob

Post by **Brian** » Mon May 18, 2009 8:34 pm

I have heard that clutches were balanced in the US but we never used to bother with that. There is no reason why you have one larger bolt unless someone has broken a bolt off at some time and replaced it with the next size up.