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2004 ktm 250 exc hydraulic clutch leaking fluid?

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Hey guys, I let a friend ride my KTM a few times and on the 3rd or so ride it sounded like he wasnt even using the clutch when starting off from neutral, it was making a HUGE "clunk" sound.

turns out the clutch leaked, and basically wasnt even engaging and he couldnt even tell the difference and rode with it like that all day 🙂👍:applause:🤣:cheers::jawdrop:

so I got 2 questions.

1. I cant see where its leaking from... any ideas? im sure its just a simple gasket but these KTMs are very weird to work on IMO.

2. is it safe to just keep filling it with normal ol mineral oil (like it says on the cap) from walmart? it doesnt have to be special mineral oil? (I also heard you can use ATF or low weight fork fluid in these hydraulic clutches so im sure the mineral oil is nothing special.. just wanna make sure)

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Hey guys, I let a friend ride my KTM a few times and on the 3rd or so ride it sounded like he wasnt even using the clutch when starting off from neutral, it was making a HUGE "clunk" sound.

turns out the clutch leaked, and basically wasnt even engaging and he couldnt even tell the difference and rode with it like that all day 🙂👍:applause:🤣:cheers::jawdrop:

so I got 2 questions.

1. I cant see where its leaking from... any ideas? im sure its just a simple gasket but these KTMs are very weird to work on IMO.

2. is it safe to just keep filling it with normal ol mineral oil (like it says on the cap) from walmart? it doesnt have to be special mineral oil? (I also heard you can use ATF or low weight fork fluid in these hydraulic clutches so im sure the mineral oil is nothing special.. just wanna make sure)

There is a write up on bleeding the hydraulic clutch here in the KTM 2 strokes FAQ's section under General FAQ's https://thumpertalk.com/forum/showthread.php?p=5156936#post5156936

The master cylinder could be bypassing internally in which case you would need a rebuild kit.

It could have leaked air in from the master cylinder if tipped over or in some unusual attitude in which case it needs to be bled.

I could be leaking past the slave cylinder which uses an o-ring on the piston for a seal. You wont see it come out because it will go into and mix with the oil in your trany. There is no rebuild kit or o-ring offered by KTM for the slave. They want you to buy a new one. There is one available with a KTM P/N that fits that is used elsewhere on a KTM. The P/N give in the FAQ's write up is wrong (typo). It should be Clutch Slave Cylinder O-Ring 23.52 X 1.78 mm KTM P/N 770020210, or you can get the same size 23.52 X 1.78 mm from McMaster-car.

The slave seal o-ring to the case is listed I think but it is a 30,00X1,50 nitrile o-ring, KTM P/N 770300015 (at least on the big bikes it is).

For the fluid you can use ATF or light weight fork fluid like 2.5 or 5 wt. The stuff that is supposed to go in there is Magura Blood. ATf or Drug Store mineral oil both work fine too. They may be a little heavy and sluggish for some folks taste. The 5wt fork oil is your best bet.

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ok, so according to that link, it tells me that "If after a ride or two the clutch goes away again then you need to check the resevoir. If its low again then you have a bad o-ring in the slave. The oil probly wont run out anywhere as it goes into the gearbox along the clutch rod."

so I have a bad o-ring in the slave? surely that o-ring can be found anywhere like in most o-ring kits, right? would it be a standard or metric o-ring?

Searching for "770020210" brings up nothing...

thanks for the help, keep it coming lol!!!

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OK, so you are saying the level didn't drop, I guess. If that's the case then your troubleshooting sounds plausible.

23.52 X 1.78 mm means it is metric. You probably wont find it in an o-ring kit or at the hardware. I gave you the size, a KTM P/N and a McMaster-car P/N, but if you find it somewhere else ..... good luck.

How are you searching for it?

I just did a search on that part number by putting it in the search box while in the KTM World web site and got this returned:

O-RING 23,52X1,78

770020210

Price: $1.89

Like I said, it's not listed in the parts break down if that is what you are looking for.

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oh ok perfect, I was searching for it on ebay, and on google... usually if google cant find it no one can!

but I just came back from the shop.. kinda bad news.

I took the 2 screws + the cap out of the reservoir by the clutch lever, and the remaining fluid (not much) was like old clutch oil... it was grey and had tiny tiny metal dust/shavings in there it seemed like.. why?

I also topped it off with mineral oil, put the cap back on, screwed it down, and 10-15 pulls of the clutch lever and still nothing, even with topped off fluid the clutch still wasnt engaging. now I think its serious :'(

how hard are these hydraulic clutches to take apart and diagnose/fix? I dont know if I have the time nor the patience for something like that so it might just end being brought back to the guy I bought the bike from, who also owns his own bike shop, and I could get him to fix it for cheap as he knows the bike inside and out whereas ive never turned a bolt on a KTM before!!!

thanks.

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Ok, you (we) are back to square one.

If the level has drooped, and there is no external leak then it is leaking out the slave piston seal.

If air got in it could just need to be bled but the level wouldn't have dropped. It could have leaked air in from the master cylinder if tipped over or in some unusual attitude in which case it needs to be bled.

If the level didn't drop the master cylinder could be bypassing internally in which case you would need a rebuild kit for the master cylinder which KTM does sell and then bleed the system.

The dark residue is probably from the bladder/diaphragm on the reservoir cover or from the master cylinder piston seals.

If you don't know if the level dropped or not then try bleeding it first and see if that fixes it temporally or permanently. Did you get enough from that link to be able to bleed it? You need a syringe and short piece of tubing (clear vinyl is nice) and back bleed it from the slave up to the master.

Do you think you are going to be comfortable working on this? It is much like rebuilding and bleeding brakes. Ever done anything like that?

If you do we can go on.

Edited by Gary jp4
add diaphragm for possible source of black residue

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ok everything you said makes sense. I had a friend bleed my mountain bike brakes when I was young so im 99% sure I know how its done and understand its concept. ive bled brakes before but never rebuilt one. I can rebuild a fork and a crf engine from the inside out so im sure I can handle the ktm clutch 👍

I suppose I could tackle it, im working for the next 12 days so I can tackle it after work and find out what I need to order to fix it.

so first thing is to try bleeding it? where exactly is the nipple on the bottom? how big (capacity) of a syringe am I going to need? and a bottle of 5wt fork oil? what do you figure needs to be replaced?.. im kinda doubting that a bleeding will fix it.

thanks for the help.

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Bleed it first. You need a syringe, a 60 ml/cc syringe from a farm supply would be great. A length of 1/8 vinyl tubing run to the nipple.

The bleed nipple/fitting is on top of the slave cylinder. If it has not been covered you need to take it off an clean it out so you are not pushing dirt into the system when you back bleed it.

It sounds like you will probably end up needing:

A master cylinder rebuild kit P/N 59002032000 REP.KIT PISTON 9,5MM RAC. 2000 (about $50)

The o-ring for the slave piston 23.52 X 1.78 mm KTM P/N 770020210

The o-ring for the slave cylinder seal to the case 30,00X1,50 nitrile o-ring, KTM P/N 770300015

Fluid

A syringe

Clear tubing

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ouch, wasnt expecting it to be that expensive but oh well, I will try what you mentioned when I have time (hard to run to store working from 6 to 6) and report back when I am able to bleed it.

thanks for the help.

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Thanks Mike

It keeps my service rep skills tuned up.

Your knowledge of KTM's and common problems is invaluable.

Edited by Gary jp4
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Bleed it first. You need a syringe, a 60 ml/cc syringe from a farm supply would be great. A length of 1/8 vinyl tubing run to the nipple.

The bleed nipple/fitting is on top of the slave cylinder. If it has not been covered you need to take it off an clean it out so you are not pushing dirt into the system when you back bleed it.

It sounds like you will probably end up needing:

A master cylinder rebuild kit P/N 59002032000 REP.KIT PISTON 9,5MM RAC. 2000 (about $50)

The o-ring for the slave piston 23.52 X 1.78 mm KTM P/N 770020210

The o-ring for the slave cylinder seal to the case 30,00X1,50 nitrile o-ring, KTM P/N 770300015

Fluid

A syringe

Clear tubing

Revision. The o-ring part numbers I listed should have a 0 in front of them. It was entered as a number in a spread sheed where I stored them and it dropped the leading "0".

It should have read like this:

The o-ring for the slave piston 23.52 X 1.78 mm KTM P/N 0770020210

The o-ring for the slave cylinder seal to the case 30,00X1,50 Nitrile o-ring, KTM P/N 0770300015

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