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Old 07-16-2013, 05:28 PM   #1
Seavoyage OP
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Location: San Francisco
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GasGas Pro clutch drag

Many GasGas Pro owners experience clutch drag. The GasGas Pro clutch is very sensitive to the 'finger height' and the currently available complete clutch pack is too thick resulting in noticeable drag - the slave cylinder 'top hat' can't engage the 'shallower' finger height to hold tension or complete disengage. If a 2.00mm steel plate is replaced with a 1.30mm-1.50mm steel plate, the finger height will be too high resulting in slip - top hat stays engaged.

The GasGas Pro uses a diaphragm clutch design that is different from mainstream motorcycle clutches:



I recently replaced my Pro clutch pack and discovered the following:

GasGas only sells the complete clutch pack MT280232055 : 3 Friction plates MT280232051 and 2 steel plates.MT280232050 . See note below..

Each steel plate in the complete clutch pack is 2.00mm thick.

2002-2003 clutch packs were different MT280432055 . Early 2002 friction plates MT280232051 were prone to swelling; current friction plates do not swell in ATF.

The 1.50mm MT280232050 , 1.40mm MT280232050/4 , and 1.30mm MT280232050/3 steel plates are no longer available. If used with the current clutch pack to replace one of the 2.00mm steel plates, the overall thickness will be too thin.

If, post 2006 model, both steel plates measure 2.00mm and the friction plates vary in thickness: one friction plate is 2.20mm and the other two are 1.80-1.85mm for a overall thickness of 10.00mm? ( I realize the math doesn't add up from the factory specs)

AND

The correct specification is: No less than 9.75mm and not more than 10.05mm

How do we build a clutch pack that measures 9.75mm +/- 0.1mm to acheive the desired 17mm +/- 1mm 'finger' to inner hub depth?


I ended up going through all my old friction discs to build the appropriate clutch pack.

I had trouble reverse bleeding the clutch and discovered one of the two orifices in my AJP master cylinder (small reservoir) was blocked. I couldn't clear the blockage; so I replaced the master. I discovered that the master cylinder bore and stroke was relatively the same between the AJP long and short reservoir styles.

Replaced the O-rings in the slave cylinder for good measure. The GasGas Technical Bulletin (10/2006) updated 10/2012 http://www.trialspar...ober_2_2012.doc recommended conversion from DOT4 to mineral oil. We since converted back to DOT5 by replacing the slave cylinder O-rings with MT280432047..

We found the Carquest part number CTC407008 for Viton® O-rings for the slave cylinder a bit tighter fit than the OEM MT280432047

Note:
Quote:
2006 and newer model Installation note: The clutch fiber and steel discs were changed in the 2006 model year. The three fiber discs have a variation in thickness and the two steel discs are thicker than the previous models. There may be slight variations in thickness of the fiber discs, this is done at the point of manufacture to ensure precise total pack width. The total pack width is 10.0~10.01mm – The two steel discs measure 2.0mm each – Two of the fiber discs measure approximately 1.80~1.85mm thick and the third one is 2.2mm thick. All steel and fiber discs are symmetrical (there is no specific front or back side)
IMPORTANT: Of the three fiber clutch plates, one is noticeably thicker. (about 2.2mm thick) This thickest plate MUST be the one that is placed into the engine first. (Farthest into the interior and against the rear surface of the center clutch driven hub.)
ADDENDUM:

The current replacement is the complete clutch pack which:
Quote:
There may be slight variations in thickness of the fiber discs, this is done at the point of manufacture to ensure precise total pack width.
The critical requirement for proper clutch operation is the depth of the finger height to inner hub (essentially the angle): 17mm +/-1mm which is usually achieved with thecurrent OEM replacement clutch pack, but probably on the thicker side as the new clutch packs measure
Quote:
The total pack width is 10.0~10.01mm
according to the factory: The ideal clutch pack thickness is 9.75 +/-0.1mm which currently can only be acheived by using thinner (i.e. used) discs.

For those that run the smaller slave cylinder volume (Magnesium cases: 2002, Raga, S3, etc). the tophat travels slightly further with the same AJP master cylinder, and this makes the issue more prominent. 16.8mm-17.0 mm finger height to inner hub measurement seems ideal. A shallower finger to inner hub height due to a thicker pack increases drag; which seems acceptable to most riders, the opposite slip occurs with too thin a clutch pack (worn out discs). Using any of the previous 1.30mm-1.50mm steel plates (or the mentioned Jitsie 1.6mm) with the current fiber plates will likely result in too thin a clutch pack.
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Seavoyage screwed with this post 07-18-2013 at 09:15 PM
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Old 07-16-2013, 05:59 PM   #2
lineaway
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Good info. Was the car quest O-rings for the old style case?
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Old 07-16-2013, 07:26 PM   #3
Seavoyage OP
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Quote:
Originally Posted by lineaway View Post
Good info. Was the car quest O-rings for the old style case?
The Carquest O-ring is Viton® synthetic rubber which addressed the swelling issue in the early clutches, and is readily available. It appears to replace any of the designs: 2002 old style two O-ring; 2003-2006 one O-ring; 2007 onward two O-ring. But as I mentioned it was a tight fit when I tried it, so I went back to the current OEM O-rings which are resistant to swelling. Replacing the O-rings allows me to run DOT5 rather than mineral oil.

Seavoyage screwed with this post 07-16-2013 at 08:31 PM
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Old 07-21-2013, 06:42 AM   #4
motobene
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Quote:
Originally Posted by Seavoyage View Post
The Carquest O-ring is Viton® synthetic rubber which addressed the swelling issue in the early clutches, and is readily available. It appears to replace any of the designs: 2002 old style two O-ring; 2003-2006 one O-ring; 2007 onward two O-ring. But as I mentioned it was a tight fit when I tried it, so I went back to the current OEM O-rings which are resistant to swelling. Replacing the O-rings allows me to run DOT5 rather than mineral oil.
Fantastic job on detail, Seavoyage!

I ride GasGas and just absolutely love the clutch design. I was very happy with Sherco clutches (my last Sherco was 2002 model). I had problems with older Beta clutches... really bad drag. I detest the light switch clutches on the 4RT and Beta 4Ts. Just don't get that. The Bellville spring and low number of plates GasGas clutch has so far my favorite, predictable, and controllable slip range in the clutch. Zero tendency to be light switch on engage and disengage.

With such a wide disengage bandwidth relative to the lever pull, there is some clutch drag with lever fully pulled in, even when running thinner and slicker ATFs like my fav, ATF+4, an economical full synthetic. The drag is not bad enough to create an irritating forward impulse when coasting in sections, clutch in, but it does put pressure on the gears making it hard to get into neutral when stopped.

BTW, a trick for getting into neutral, engine idling and bike stopped: Rev the motor up and snick the tranny into neutral just as the rpm drops. The gears will unload and slide easier at that moment. Or just kill the bike before snicking into neutral just before you get off.

As for Viton, it is a fluoropolymer, like Teflon. More expensive than Buna-N or Nitrile O-rings, so factories often just go with what is common more affordable and still works well. Theoretically less issues with swelling, so more options for fluids.

You can find out more about fluoropolymers here:

http://en.wikipedia.org/wiki/Fluoropolymer

motobene screwed with this post 07-21-2013 at 06:49 AM
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Old 07-21-2013, 06:58 AM   #5
motobene
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An additional point, Seavoyager. You say the slave cylinder volume (diameter) is less on the Mg primary cover. That would make the top hat piston travel more as you say, but it would also disengage the clutch more with the same lever pull.

I comparison rode for 5 hours my TXT with aluminum centers cases and primary cover and my Raga yesterday and found the Raga with Mg primary cover felt like it has a larger diameter slave cylinder for less top hat stroke relative to lever stroke. In other words, a wider engagement-disengagement band and more tendency to be stickier trying to get into neutral and parked and idling.

Could you please reconfirm the diameter differences between the aluminum and magnesium primary covers? Di you measure the piston diameters?

I'll be deep into a TXT and Raga motors in the next week and will make a not to measure the slave cylinder diameters of both.

motobene screwed with this post 07-21-2013 at 07:04 AM
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Old 07-22-2013, 02:16 PM   #6
Sting32
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Quote:
Originally Posted by motobene View Post
An additional point, Seavoyager. You say the slave cylinder volume (diameter) is less on the Mg primary cover. That would make the top hat piston travel more as you say, but it would also disengage the clutch more with the same lever pull.

I comparison rode for 5 hours my TXT with aluminum centers cases and primary cover and my Raga yesterday and found the Raga with Mg primary cover felt like it has a larger diameter slave cylinder for less top hat stroke relative to lever stroke. In other words, a wider engagement-disengagement band and more tendency to be stickier trying to get into neutral and parked and idling.

Could you please reconfirm the diameter differences between the aluminum and magnesium primary covers? Di you measure the piston diameters?

I'll be deep into a TXT and Raga motors in the next week and will make a not to measure the slave cylinder diameters of both.
It is more than that, the "un Initiated" trials riders, or newbies... Most hate the idea that they pull the clutch, and they think the bike "should free-wheel" like a street bike... It can unnerve a beginner a little thinking they dont have control when pulled clutch but bike is ever so slightly pulling them forward still.

But, I am like you, plus the tune-ability of the slip/stroke just with oil in transmission alone is almost guarded secrets, yet is wonderful. Test this yourself some time you have time. I used to Use Type f ATF. seems to get closer to the 4 strokes, not quite ON/OFF but it was smaller subset of what I like now that is for sure. Then, try dextron, then Goto 5w/30... To me, each one is more what I call progressive, I use synthetic Yamalube, and it seems to be just like I loved when all adjusting of finger heights was completed, while using Auto-Track 2.

IF I was a PRO or even better than me I might need to go back to ATF, because I don't ever "WFO & Dump the clutch" to get up stuff, I hop only in emergencies most the time, so I am usually trying to moderate the slip of the clutch to make a turn or what have you... when I get good enough to hop all turns, and ZAP the crap, then I wan to have the 4stroke type on/off clutch maybe...
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