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scooterspal

Gas Gas JTR160 clutch issues

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Hello All. Purchased this 1996 Contact Gas Gas JTR160 last week and in the process of getting it back in shape. I have no manual for this bike and there appears there never was any that I can find. Flying blind on most of this but I have worked on my Honda's so not a complete novice on repairs.

My problem is the clutch not fully disengaging. I'm used to bikes with cabled controls and this bike is all hydraulic. Where there usually is a way to adjust the cable tension at the lever on the motor, there is none on this bike. Comparing the right brake lever to the left clutch lever... the brake lever has a hard stop when you squeeze it. The clutch lever is more mushy.  I have bled the fluid (there was air in the line at first) and have even done the reverse bleed injecting DOT4 at the nipple forcing it back up the line to the reservoir so pretty sure this is not my issue.

The prior owner was running Royal Purple synthetic (5W30) oil, which is a no-no according to what I have read. I drained that and put in 75W conventional gear oil. Before I go and crack these cases I'd like to get some feedback or help with this repair. How is the clutch adjusted inside the case and is there a way to do so? Is it worth filling the case with mineral spirits to try and wash off the oil still in there and add fresh. Even with the oil drained, now, I still have partial engagement of the clutch. I can push the bike forward but not like being in neutral.

Thanks!

 

 

bike.jpg

case.jpg

brake.jpg

clutch.jpg

Edited by scooterspal

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 Chances are the friction plates have come apart. Only thing to do is pull the clutch apart and see. Just lay the bike over on the left side, pop off the round clutch cover which has an oring. Take the 6 bolts and springs out and remove the plates. Good chance the friction material has separated from the steel.

Edited by lineaway

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Thanks both of you.

The first outer fiber was pulling away from the plate for about a third of it. None of the others were separating. I cleaned all of them with mineral spirits and cemented the fiber back on. Since that one has the same keying as the back most ring, I swapped them hoping the release pressure will be less at the back. Will see if I can still get these rings somewhere.:unsure:

There were only four springs in this clutch but room for the six. Not sure what that is all about but not having trouble with it grabbing. Anyway, when back together it made no difference. Still not fully releasing when engaged.

I do notice there is very little movement in the outer plate cover. Measures only 3/64" which seems way too small. I'm used to much more outer movement in my other clutches. I took off the clutch slave on the other side and you can see there is just a small amount of change from fully engaged (first picture) to not engaged (second picture).

I can try doing the bleed again, but from what I can see, moving the clutch lever causes the slave piston to move smoothly and consistently, so it does not appear there is still any air in that line. It's just not moving enough, IMHO.

There is another video on Youtube showing a guy (not Jim Snell) replacing the guts to a Gas Gas slave although he never explains why he is doing so.

I'm going to take this slave off the hose and open it up. Maybe I will find the problem in there. If that does not pan out the problem may be in that master cylinder. Hoping that's not the case, though.

 

 

 

slave out.JPG

slave in.JPG

Edited by scooterspal
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Looking at the photo of the slave cylinder, there is a 5 or 6mm diameter ball bearing that, from memory, sits flush with the top surface of the hole in the slave piston. These ball bearings have been known to become pushed further in over the course of time, eventually going in so far as to give the symptoms of what you are experiencing. The slave piston, when actuated would come to a mechanical stop on the crank case before the clutch was fully disengaged and the clutch lever would feel as though it has reached it's actuating limits. A replacement slave cylinder kit is needed, if this is the case. You may be able to try inserting an extra ball bearing, that can be removed, just to try this out to make sure that this is the problem. With regards to the gearbox oil, for over 25 years we have run ATF rated to Dexron III in all models of Gas Gas trials bikes without problems. For your model, the gearbox is stated taking 700ml, you are absolutely fine to run with 600ml, from the factory. Bye, Peter B.

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Thanks much!

I can see that ball bearing way back there. Was not sure if it was a ball or the way this piston was milled. It also has a bit of a flat on it.

I will try and freeze this piece to see if the ball will dislodge upon a good whacking against a table top. If that does not work I can drill a wire size hole at the back and push it out. Can fill that tiny hole easy enough.

Off to Ace Hardware to see if I can source a 6mm ball baring and some 25mm O rings to replace the seals that are around the piston. Also noticed some scoring on one side of the piston and inside the slave. Have removed it with some crocus cloth.

 

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23 hours ago, oni nou said:

 

You do realise that this is a video and you clic on the arrow in the center to see it .......you said that your clutch has 4 springs and you do not know why ....if you watch the video it tells you why................JHC

Edited by oni nou

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I wouldn't drill out the back of the piston as that would weaken it. I have a new slave kit that I would need to locate first, that I could take a photo of the bearing height, measure it and let you know. I tried running 4 clutch springs on a 330 GG years back, was much easier on your finger, but would slip with a handful of revs in 4th, probably fine on a 160. Bye, Peter B.

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Well Jim you tried to inform people but it looks like with some that they prefer to ignore your efforts.....shame really.....all that effort amounting to diddlee

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Could not find a 6mm ball bearing locally so I took a 6mm cap nut and machined it to fit the hole. Raised the point of contact up quite a bit so the piston does not have to travel as far as before.

I have not put the 30W oil back in as yet but already I'm getting a vast improvement over before. I have an email in to Jim Snell to see if he still has the parts to replace. May have to get the entire slave with the casing as I'm getting a bit of leaking where the inside of the piston shaft was scored. Probably why it was losing its power over time.

If you can take a picture of what a new one looks like Peter, I can compare it to my handy work.

Thanks much!

bering fix.jpg

Edited by scooterspal

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13 minutes ago, oni nou said:

Well Jim you tried to inform people but it looks like with some that they prefer to ignore your efforts.....shame really.....all that effort amounting to diddlee

Good informative video, it’s all there to be absorbed🤷🏻‍♂️👍🙂

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Several issues here.

First, the spring is missing from the back of the piston. It is that spring that keeps the piston pushed out and against the rod (when you go to fill the system with DOT4 hydraulic fluid) that runs to the other side to release the clutch plate pressure. If it's not there and you assemble the slave with the piston fully pushed back there will not be enough travel when you squeeze the arm to move the piston far enough to fully engage the rod.

Mine also is leaking from wear in the cylinder wall. Jim has the entire assembly for a very reasonable price, so I've ordered the complete package from him, but at least I know (as do you, now) how it works for future repair issues.

Edited by scooterspal

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