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Discussion Starter #1
Hi,

So... I have been restoring a 94 748 all the way through, and it has been a troublesome project with a steep learning curve. I have clocked 700km on it after the restoration now, first with some gear shift problems, but I fixed those last weekend, and today was the big test day. Gear problems fixed with success :) But after 20km or so the clutch started slipping when I revved up quickly and I thought that was odd, I was on the highway so I decided to get off at next exit, but 800m before that exit the engine was very quickly getting a harder time spinning the wheel and the bike was slowing down quickly, so I pulled to the side and pulled the clutch. Now, it was a bit of a stressed situation with all the cars going fast right by me, and thus I forgot to be in diagnose mode and my observations might not be 100% correct. But I am quite sure that the engine ran fine when the clutch was pulled, so the clutch was working and nothing was stuck in the crankshaft I think. I switched the engine off, and realised I was very close to the road and tried to push the bike to the side, but it was totally stuck even with the clutch pulled. After some minutes, talking on the phone and being very frustrated, I tried to push the bike again and it was totally fine again. After maybe 30 minutes i started it up, and drove slowly and carefully home without any problems.

So... Something gets stuck when it gets hot, and it works again when it cools down? If I remember everything right, it is not the crankshaft and not the clutch, so it must be either in the gearbox or rear hub, right? I did drive 700km before this where the engine got much hotter, and did not have this problem at all (I did have a gear problem though), so did I do something to cause this in between or has i developed over time? I had the engine cover on the clutch side off last weekend, including the little green o-ring, but I did not replace it as it was almost new (it had the 700km on it), but does that little o-ring somehow ensure some vital part gets oiled and does not run hot and get stuck (what does that o-ring do there? it is nr. 12 on the attached photo)?

How do I diagnostic this problem? Any ideas?

Thank you
Søren
 

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Hi,

So... I have been restoring a 94 748 all the way through,
By this do you mean just the engine only or are you meaning the bike as a whole?

& what were the gear shift issues you had to fix? Cancel that,,,,just read your other thread

If it were me ( & actually knowing what work I'd previously done to the bike/engine ) I'd be looking at the rear axle assembly then work my way forward ,, process of elimination.
 

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Discussion Starter #3
The whole bike. The rear axel assembly has been totally rebuild also, but that part was done by a Ducati mechanic and not me. I did suspect that part also, but how do I check it? Disassemble it and look for wear that indicates metal/metal grinding contact?

That o-ring there, does anybody know what it does? I have always wondered, because it sits between the engine casing and the engine cover, and seem to not really have a function? I am asking about that o-ring, because I know that it can be dislocated or even fall off, when installing the engine cover without any chance of noticing I think, and if it does indeed sit there to ensure some lubrication of some bearing or something, then this might be the source? Also because I did not have this problem for the first 700km, but now after I had the engine cover off and on again I have this problem.

Thank you
Søren
 

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If the rear brake has too little free-play in the master cylinder/pedal then the fluid gets over hot, expands and can lock the rear wheel, after it cools down it will be OK again (for a while).

I had this after the first service on my 916 where the dealer adjusted the brake too tight and on the way home it slowly got tighter until I was left at the roadside with the rear brake locked and the pads on fire!

They collected me and fitted new pads/adjusted correctly but a year or so later I needed a new caliper as the seals were leaking which, I assume was probably caused by the overheating...
 

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Discussion Starter #5
I will check the brakes, there should be some visual clues if the disk has been this hot? Had it been red, I think I would have noticed it right there in the situation.

Thank you
Søren
 

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Agree with desmoduke here. Have seen this a number of times on not only dukes but Mv's and aprillia's. Customers take all the play out of the shaft that does into the master. Great when cold, locked when hot.
 

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But, if that's not the problem then it's a series of elimination to diagnose what may be the cause of the lock up. Not difficult to do.
 

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I will check the brakes, there should be some visual clues if the disk has been this hot? Had it been red, I think I would have noticed it right there in the situation.

Thank you
Søren
My disc was 'blued' from the heat but it also burnt off the gold paint around the rim...
 

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Discussion Starter #9
But, if that's not the problem then it's a series of elimination to diagnose what may be the cause of the lock up. Not difficult to do.
Ok, I will get back to you on that xracer if this is not the problem, I need some help on how to progress :)

Thank you
Søren
 

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Discussion Starter #10
I checked the brake disc and calibers, there is no blue, not even a hint and the disc still have some rust on it, so they do not look like something that was abused hard or anything in that direction. I think we can rule that one out.

That o-ring i keep rambling about, well I removed the clutch and engine cover and it was right where it should be. Yeah it is a little flat, I did not replace it, but I doubt that this would cause this lock up.

So, what next... The rear hub? Should there be any outer signs if that has been hot and locked up? Would it be a good idea to go for a ride again, and take note of some specific behaviour? Like, is the rear totally locked or will it flex the amount the chain allows? Is it stuck in neutral also?

Thank you
Søren
 

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You should be checking the cause not the symptom.
Doesn't mean a thing if the brake is blue or not... check the rear master cylinder pushrod has freeplay.
I had mine stop the bike from the same cause and there was no visible evidence on either the caliper or the disc, simply brought the bike to a stop as in a normal heavy brake application.
That little green O ring links the oil supply from the pump to the end of the crankshaft so yes it is a bit important.
 

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Discussion Starter #12
I checked rear breake master freeplay and I checked the o-ring and it was in place, I put in a new o-ring and loosened the rear master freeplay even more and went on a test drive. I did not touch the rear brake, and very quickly my clutch started slipping again when revving up. I drove home and put my hand on the rear disk, it was ice cold, my front disk was hot but I think that is to be expected, and the font disk break fluid was cold so no heating up there. It was a very short test drive, and it did not lock up, but the early symptoms with the clutch slipping was there right away.

What do I look for next? Could it actually be the slipping clutch that is causing the lock up, I mean could it be that the clutch is constantly slipping and it heats so much up it gets stuck? I did not look damaged in any way when I opened it up though.

Thank you
Søren
 

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Is the rear hub hot?
 
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What do I look for next? Could it actually be the slipping clutch that is causing the lock up, I mean could it be that the clutch is constantly slipping and it heats so much up it gets stuck? I did not look damaged in any way when I opened it up though.

Thank you
Søren
That's simply ridiculous....

If by some chance that the clutch was able to get so hot that it actually welded itself together, then you would have constant drive not lock up.

Something is happening at the backend of your bike if the rear wheel is locking up (if that is what's actually happening),,,, brake ,, axle/hub ,, or even gearbox .

Are you positive that the rear wheel is actually locking up?
Could it be your that front brake setup is incorrect? I'm sure that this has happened more than once
 

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Discussion Starter #16
Ridiculous... maybe... It took some time, because I examined different parts one bye one and because I only have time to work on it in between family time and what not (like most other I think), but it seems I have found the problem. This problem started after I found the gear problem and re-assembled the right hand side of the engine, the drive gear and clutch. When I took the clutch out, I stacked all the clutch plates in the order I took them out, and when I re-assembled I put them in in the same order. I did that with every take-apart/re-assembled after the gear fix and was continuously having the clutch slip problem. So I did it again and again taking special care to check that all was in order pice by pice, but this time I also got a drawing of how the clutch plates should be just in case and compare with those. One of the plates where missing, in my setup (not original) it should start with two metal plates, and then every second plade is a grip pate and a metal plate, but one of the first metal plates where missing and since I know I stacked them in order and put them in in the same order I just never noticed this. So I went searching for that plate, I know I never moved it so it was strange, and it was nowhere to be found... So... I went to that one person in the house that really likes shiny metal stuff, like bolts and screws and what not, my 6yo daughter, and told her that I had a mystery, that this metal plate was gone like magic. She confessed, so she had taken it and I just never noticed it or guessed anything in that direction :grin2:

I re-assembled it, slipping was gone so now some long drives to test if the lock-up was gone also. I have since then driven 800km on freeway at high speed and smaller roads, and the bike performs flawless now. The clutch plates has been very very hot, they have visual signs there of, but they do seem to work just fine.

Thank you
Søren
 

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Discussion Starter #18
Yes, I don't blame her, she is simple curious of mechanical stuff :smile2: I will measure always in the future.
 

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1 plate missing still does not explain or contribute to a rear wheel locking up.

Somebody please correct me if I'm wrong ......clutch slip yes , but a rear wheel lock up I don't think so.
 
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