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Sticky gear change, clutch disengagement problems

 
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CÚdric  



Joined: 27 Aug 2004
Posts: 1717
Location: Sweden

PostPosted: Mon Aug 15, 2016 7:47 pm    Post subject: Sticky gear change, clutch disengagement problems Reply with quote

Hi !

After last winter I have had some issues with the gear change. I thought I got some air in the lines after a front brake rebuild, but that didnt fix the problem.

It works fine when you drive around sub 4k rpm, but if you pull all the way up to redline its really tough to get out of gear and in to another.

The car has worked great on road and track before for a couple of years. Only hassle has been that it sometimes doesnt want to slip into first gear that easily. Which could be a sign.

Have anyone had similar issues?

Specs:
-Refreshed box(rebuilt gear 1-3)
-Short shifter from ideola+ brass bushings, all other bushings are new and the linkage is VERY tight and precise.
-Engine was bought second hand, the so called "new" clutch was actually just a new friction disc. Changed throwout and pilot bearing due to noise. Pressure plate was really good condition (but here lies my suspicions)
-Master and slave units were change a couple of years ago.
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morghen  



Joined: 21 Jan 2005
Posts: 7832
Location: Romania

PostPosted: Tue Aug 16, 2016 3:08 am    Post subject: Reply with quote

My 931 has similar behaviour. Not too pronounced but making a comparrison between my 924 with 944S2 gearbox and the 931 i can say that sometimes the 931 require a small amout of force to get out of say 4th even tho the clutch pedal is fully pressed.

I also have a freshly rebuilt clutch disk, fresh linkage bushings and a very good snailshell. I suspect there is some wear in the fork...or maybe the bearing has worn that much that the clutch does not get enough off the surface.
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 1549
Location: Not Detriot - NMI

PostPosted: Tue Aug 16, 2016 4:30 am    Post subject: Reply with quote

Try starting to pull on the shifter a little before you drop the throttle and depress the clutch..

When your RPMs are climbing and your getting ready to shift put some pressure on the shifter before you let off the gas and push the clutch.

The instant between when the gears are seeing engine torque to overrun drag, that moment of neutral force, it should slip out of gear easily, as if you were going to float gears but just to get it out..

Maybe your torque tube bearings are exerting enough resistance at high RPM to keep it from easily popping out of gear while disengaged from the engine..

The same principle as if you are coasting in gear and want to pop it in neutral without clutching it will not pop out with drag on the gears so you have to touch the throttle a tiny bit with pressure on the stick to get it to pop out of gear.. It will pop out at that moment of neutral torque inbetween coast drag and acceleration..


My dad's 64 Norton has a momentary ignition kill button, right side shift, 1 up 4 down. You just get the holeshot with the clutch and then hold down on the shifter, when you want to shift just flick that kill button while standing on the shifter and that momentary kill will let it pop into the next gear..
Still holding WOT you shifted with the button, while you are gaining RPMs in the next gear just let off the shifter and put pressure back on it to reset the shifter. When its time to shift to the next gear again just flick that switch with pressure on the shifter and you are in the next gear still WOT..
Just barely bump that kill button at redline with pressure on the shifter toward the next gear and away you go.. Bang bang bang fastest shifts in the west..

64 Norton Atlas 750 bored to 810 with big mikuni carbs and some other tricks. He bought it in 66, modified it a bit, and says it would kill any other bike on the road until the jap inline 4s started getting fast in the mid 70's..

Ha, sorry for the rant..
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1980 931S - LSD - FMIC - GTS fuel - hobby
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Rasta Monsta  



Joined: 12 Jul 2006
Posts: 11354
Location: PacNW

PostPosted: Tue Aug 16, 2016 7:18 am    Post subject: Reply with quote

Fasteddie313 wrote:
Try starting to pull on the shifter a little before you drop the throttle and depress the clutch.


Never do this. Bad for dog teeth/selector collar.
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CÚdric  



Joined: 27 Aug 2004
Posts: 1717
Location: Sweden

PostPosted: Tue Aug 16, 2016 7:29 am    Post subject: Reply with quote

Atm its hard to actually pull out of gear without significant force, which of course isn't good at all.

In calm driving conditions you can slip out of gear easily if you time the the shift, without clutch. As you can on almost any car ive driven, all about timing. But im not sure how that is connected to my problem. I'm thinking maybe the pressure plate Springs are giving up, hard to measure but ideally i would like to compare pressure plate travel on a healthy car and my car to find the actual problem. Clutch change isn't exactly fun, definitely an engine out project.. Not so good timing wise in my life though :/
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http://www.garaget.org/show.php?car=211
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 1549
Location: Not Detriot - NMI

PostPosted: Tue Aug 16, 2016 8:20 am    Post subject: Reply with quote

CÚdric wrote:
Atm its hard to actually pull out of gear without significant force, which of course isn't good at all.

In calm driving conditions you can slip out of gear easily if you time the the shift, without clutch. As you can on almost any car ive driven, all about timing. But im not sure how that is connected to my problem. I'm thinking maybe the pressure plate Springs are giving up, hard to measure but ideally i would like to compare pressure plate travel on a healthy car and my car to find the actual problem. Clutch change isn't exactly fun, definitely an engine out project.. Not so good timing wise in my life though :/


Part of the diagnosis..
Exactly what I was talking about.. That makes me think that inside your trans is ok, but some external forces are making it act like there is a load on the gears not letting you pull it out..

Torque tube bearings - high friction causing load..

clutch springs - I think it is possible if the center of your clutch was giving out letting the disk cock sideways it could cause this, if it cocks enough to still rub between the PP and the flywheel and cause that gear load..

Clutch hydraulics - maybe you have air in your clutch line to where it is letting you give enough force to make the clutch slip but not fully disengage.. Or a cylinder (master/slave) that leaks only once it reaches X psi acting like a pressure regulator..

pilot bearing - not likely to be able to provide that much load..

Something between the trans and crank, Either a high friction point or a malfunctioning clutch..
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1980 931S - LSD - FMIC - GTS fuel - hobby
95 M3 manual coupe - summer DD
06 X5 3.0 auto - winter DD
01 RS25 coupe - 90% Retired
06 MDX - bought for mom to DD
81 Rambler BBC 454
97 Tercel long retired/sitting
77 gs750 - 95 300ex - 89 blaster
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morghen  



Joined: 21 Jan 2005
Posts: 7832
Location: Romania

PostPosted: Tue Aug 16, 2016 5:40 pm    Post subject: Reply with quote

CÚdric wrote:
Atm its hard to actually pull out of gear without significant force, which of course isn't good at all.

In calm driving conditions you can slip out of gear easily if you time the the shift, without clutch. As you can on almost any car ive driven, all about timing. But im not sure how that is connected to my problem. I'm thinking maybe the pressure plate Springs are giving up, hard to measure but ideally i would like to compare pressure plate travel on a healthy car and my car to find the actual problem. Clutch change isn't exactly fun, definitely an engine out project.. Not so good timing wise in my life though :/


Than be happy that you have a snailshell as you can remove the gearbox and do the clutch refresh like that.
My 931 shifts just perfect when warmed up, but kind of restrictive when cold. Did you get yours warmed up this year?
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CÚdric  



Joined: 27 Aug 2004
Posts: 1717
Location: Sweden

PostPosted: Tue Aug 16, 2016 7:09 pm    Post subject: Reply with quote

morghen wrote:
CÚdric wrote:
Atm its hard to actually pull out of gear without significant force, which of course isn't good at all.

In calm driving conditions you can slip out of gear easily if you time the the shift, without clutch. As you can on almost any car ive driven, all about timing. But im not sure how that is connected to my problem. I'm thinking maybe the pressure plate Springs are giving up, hard to measure but ideally i would like to compare pressure plate travel on a healthy car and my car to find the actual problem. Clutch change isn't exactly fun, definitely an engine out project.. Not so good timing wise in my life though :/


Than be happy that you have a snailshell as you can remove the gearbox and do the clutch refresh like that.
My 931 shifts just perfect when warmed up, but kind of restrictive when cold. Did you get yours warmed up this year?


I would be careful to use the word happy in this case No, for me clutch is an engine out project, not worth the hassle to try to remove the clutch cover etc with the engine still in, just plain horrible. Problem is my garage is not finished on the inside, tiles, lights, paint etc. Since I want to change turbo aswell its not that bad to take the engine out.

haha, actually i have been driving my car a couple of times this year, since its in my own garage it has been much easier. And i also live super close to some awesome twisty roads. But no track driving, I want to do some autocross close by, but this problem is getting worse. Didnt notice it at the beginning of the season, but not its really bad, regardless of temperature.
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morghen  



Joined: 21 Jan 2005
Posts: 7832
Location: Romania

PostPosted: Tue Aug 16, 2016 7:39 pm    Post subject: Reply with quote

did you inspect the linkage since you noticed this problem?
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Dutch924-racer  



Joined: 23 Jul 2007
Posts: 1004
Location: The Netherlands

PostPosted: Tue Aug 16, 2016 9:26 pm    Post subject: Reply with quote

Do you have a clutch disc with a rubber centre?
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CÚdric  



Joined: 27 Aug 2004
Posts: 1717
Location: Sweden

PostPosted: Tue Aug 16, 2016 10:05 pm    Post subject: Reply with quote

Dutch924-racer wrote:
Do you have a clutch disc with a rubber centre?


No, its a steel springed clutch disc. sachs 1878066531
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CÚdric  



Joined: 27 Aug 2004
Posts: 1717
Location: Sweden

PostPosted: Tue Aug 07, 2018 5:13 am    Post subject: Reply with quote

Found this old thread by coincidence, for future reference for people who have similar issues i will just write down what the issue actually was. I pulled everything apart and it was actually the clutch plate that was the problen, there were alot of meat left on it, but a chunk of the friction surface was broken of and barely hanged in there. So when rpms increased it kind of wedged itself stuck and i couldnt get out of gear, hence the problems only occurring at high rpm.

New clutch solved everything and made the gear change ver very nice, but i got some other problems instead, but thats for another thread
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