If the slave seal is worn enough to be not able to withstand a few psi of vacuum, can it withstand 600 psi of clutch actuation pressure and not leak? This is going to depend on the design of the seal and perhaps pressure helps the seal do its job and, in the absence of positive pressure the worn seal does not function well and allows air in.
Clutch drag
- Thread starter SHOZ
- Start date
- Status
Originally Posted By: George7941
... and perhaps pressure helps the seal do its job ..
Well, no "perhaps" about it, George, of course the seals depend on positive pressure. And for lip seals, that clearly only works in one direction.
Think of how the master cylinder front seal works when you do a pedal-type bleed - it is specifically intended to allow reservoir fluid to pass by when a vacuum is present in the system as you return the pedal with the caliper bleed valve closed. In that instant, if the caliper had a single lip seal with the same pressure characteristics, air might enter. They use a square O-ring design that works both ways.
This particular car was an early Saab 900 and in my opinion the designers of that clutch concentric slave cylinder assumed that the system pressure was always positive and used a single lip seal (which I confirmed was present.) It worked as long as it was new and tight.
Those Saabs always had a reputation for hard shifting and I'll bet that's why.
... and perhaps pressure helps the seal do its job ..
Well, no "perhaps" about it, George, of course the seals depend on positive pressure. And for lip seals, that clearly only works in one direction.
Think of how the master cylinder front seal works when you do a pedal-type bleed - it is specifically intended to allow reservoir fluid to pass by when a vacuum is present in the system as you return the pedal with the caliper bleed valve closed. In that instant, if the caliper had a single lip seal with the same pressure characteristics, air might enter. They use a square O-ring design that works both ways.
This particular car was an early Saab 900 and in my opinion the designers of that clutch concentric slave cylinder assumed that the system pressure was always positive and used a single lip seal (which I confirmed was present.) It worked as long as it was new and tight.
Those Saabs always had a reputation for hard shifting and I'll bet that's why.
Originally Posted By: The_Eric
If this has been happening since new and other installers of this kit are experiencing this too, is it possible the master/slave combo isn't yielding enough stroke?
Are the bore diameters the same as OE on the master and slave?
OE is the only Clutch Master Cylinder and Clutch Slave Cylinder that there is for the car.
If this has been happening since new and other installers of this kit are experiencing this too, is it possible the master/slave combo isn't yielding enough stroke?
Are the bore diameters the same as OE on the master and slave?
OE is the only Clutch Master Cylinder and Clutch Slave Cylinder that there is for the car.
I've bleed the slave three times since. It is a bit better but still creeps and is hard to get into 1st and rev with the engine running.
I think the slave just isn't up to the pressure needed for that clutch disc.
I have a used low mile 2013 OEM pressure plate, disc and flywheel to install. It is built to take more power unlike the original OEM setup which would slip when adding 40 or so HP.
I think the slave just isn't up to the pressure needed for that clutch disc.
I have a used low mile 2013 OEM pressure plate, disc and flywheel to install. It is built to take more power unlike the original OEM setup which would slip when adding 40 or so HP.
Have you tried reverse bleeding from the bleeder screw? I ran into this on an MG years ago and this method was the only thing that fixed it.
It helps to put a little teflon tape on the blleder threads when doing this.
It helps to put a little teflon tape on the blleder threads when doing this.
I see, yes that wont work. It sure sounds like it still has some air in it.
Is there any way of removing the line from the MC and draw fluid up under a vacuum while feeding it fluid through the bleeder?
Then you could reverse bleed the MC, I dont know I am just thinking about how this works.
Is there any way of removing the line from the MC and draw fluid up under a vacuum while feeding it fluid through the bleeder?
Then you could reverse bleed the MC, I dont know I am just thinking about how this works.
Does this car have a clutch delay valve in the line? Usually, some tiny orifice somewhere. If you have air in the line, it will be just about impossible to bleed the air out if you have a clutch delay valve in it. Basically, you'd need to disassemble.
Reverse bleeding as Trav suggested earlier can help since if the air bubble is on the other side of the orifice, you have a shot of pushing it out to the master. You can use a clean new oil squirter to pressurize brake fluid for reverse bleeding rather than a ripoff specialty tool. Cheap.
If (big if) your car has a clutch delay valve, I'd start by removing it, however.
Here are some links.
http://www.hyundai-forums.com/rb-2012-accent/299169-slave-cylinder-delay-valve-present.html
http://www.veloster.org/forum/58-hyundai-veloster-turbo-discussion/8735-clutch-delay-valve.html
Reverse bleeding as Trav suggested earlier can help since if the air bubble is on the other side of the orifice, you have a shot of pushing it out to the master. You can use a clean new oil squirter to pressurize brake fluid for reverse bleeding rather than a ripoff specialty tool. Cheap.
If (big if) your car has a clutch delay valve, I'd start by removing it, however.
Here are some links.
http://www.hyundai-forums.com/rb-2012-accent/299169-slave-cylinder-delay-valve-present.html
http://www.veloster.org/forum/58-hyundai-veloster-turbo-discussion/8735-clutch-delay-valve.html
No valve like the older ones. Sachs makes a slave for it but it looks to be identical the Hyundai with only one line going to it.
With the bleeder where it is forcing fluid into it would just have it all go up to the master cylinder. I put a new clutch master cylinder in it last summer.
Others have popped the slave and lost all pressure I assume due to too much force being applied.
With the bleeder where it is forcing fluid into it would just have it all go up to the master cylinder. I put a new clutch master cylinder in it last summer.
Others have popped the slave and lost all pressure I assume due to too much force being applied.
Was the flywheel machined correctly prior to installatio.?
What bleeding method are you using?
I had trouble bleeding a Honda clutch that would only fully bleed after I got a full catch cup of fluid into my mityvac, which meant that I needed a helper to pour fluid into the reservoir while I pumped the vac until the catch cup was full.
Gravity bleed method, two man "up, up, down, down" method and solo mityvac method all failed before getting it done with the above method.
I had trouble bleeding a Honda clutch that would only fully bleed after I got a full catch cup of fluid into my mityvac, which meant that I needed a helper to pour fluid into the reservoir while I pumped the vac until the catch cup was full.
Gravity bleed method, two man "up, up, down, down" method and solo mityvac method all failed before getting it done with the above method.
Originally a gravity bleed. The bleeder would empty the shared brake master cylinder if you let it. Later the traditional up /down. Then a vacuum on the slave with the feed line from the MC clamped shut. Lastly a one man up/down. The last time no air came out.
I would use a 30" 2x4 to pump the pedal rapidly 10 times leaving it down and then holding it down by moving the seat forward to hold the clutch pedal down. Then under the car. Repeat this 4 times. It is the way Hyundai says to do tings.
The slave is on a dead end of about 6" of tubing and a terrible design.
I would use a 30" 2x4 to pump the pedal rapidly 10 times leaving it down and then holding it down by moving the seat forward to hold the clutch pedal down. Then under the car. Repeat this 4 times. It is the way Hyundai says to do tings.
The slave is on a dead end of about 6" of tubing and a terrible design.
In my case I hypothesize that I needed to get the full volume of fluid from the reservoir to the bleeder out in one go, so I just kept pumping while a helper kept it topped off until my little hand held mityvac was full. If it didn't work I was going to get a bigger mityvac or at least a bigger reservoir for it.
I picture a bubble somewhere in the line that is trapped and just moves back and forth.
I picture a bubble somewhere in the line that is trapped and just moves back and forth.
It may be but it has to be between the slave and bleeder screw. The CMC end comes out does a 90* turn up for about 3/4" then it's all downhill to the bleeder. When filling it initially and other times doing a gravity feed will purge the pipe going up easily.
And when it did have air in there some double triple pumping would help get it into gear.
It could very well have air in the slave but I don't have any idea how to get it out anymore.
And when it did have air in there some double triple pumping would help get it into gear.
It could very well have air in the slave but I don't have any idea how to get it out anymore.
Well I've bled and bled and still have the issue with 1st and rev. With the engine off they both slip into gear easily. When the engine is running it is very difficult, sometimes you have to shut the motor off.
I believe BMW is the first to use this trans and the concentric slave. Sachs has an identical to OEM slave but it is not available. I think it is listed as a ZF S6-40?
I did find this info from ZF with regard to some of the OEM slaves and the problem was the seal was installed backwards.
Technical Information on the ZF S6-40
http://www.zfdoc.com/techinfo.htm
A Common Problem with - the clutch hydraulic slave (actuator) cylinder is that they are susceptible to developing a hang up spot between the seal and the bore at the fully extended end of the cylinder's travel range. Recently (June 2006), we discovered that GM and NAPA replacement slave cylinders (TRW manufactured) have been assembled and sold to customers all over the country/world with the piston seal installed backwards. The problem with this condition is that the clutch hydraulic system will bleed out normally but still have a hang up spot present. This condition creates a problematic operational situation in the system where even a full clutch pedal depression will not allow complete disengagement of the clutch for more than just a brief instance when the pedal is depressed and held to the floor. The initial hydraulic fluid surge within the slave cylinder presses the actuation rod far enough for complete disengagement only to spring back slightly when pedal movement is halted in the fully depressed state. The spring back is caused by flex in the slave cylinder seal getting hung up and stretching a bit further only to return to its normal shape when surge pressure subsides. This manufacturer induced fault condition will mislead most technicians into believing that the clutch hydraulic system is operating at an acceptable level. Under these conditions, exactly timed quick shifts will occur fairly smoothly because the brief instance that the slave cylinder bore seal stretches is the same instant that the shift occurs. When the shift sequence is slowed down, the spring back of the slave cylinder occurs before the shift lever actuation causing a not-so-smooth gear engagement event. This causes the synchronizer to work much harder than necessary and is exposes the synchronizers and dogteeth to potential damage especially during higher RPM shifting.
The best way to verify the presents of a " hang up" condition in the hydraulic clutch system is to have the vehicle at running temperature, coast down to a full stop until completely stationary and in neutral with the clutch pedal all the way up. Wait for a few seconds then depress the clutch pedal completely to the floor then wait for another 2 seconds before shifting from neutral to either 1st or reverse gear. If there is any resistance at all when actuating the shift lever into either gear from this state, it is likely that some degree of seal hang up is present. Hydraulic clutch systems that have this type of problem can cause the synchronizers to wear much more quickly. A healthy clutch hydraulic system should provide silk-smooth gear engagement during this type of test.
I believe BMW is the first to use this trans and the concentric slave. Sachs has an identical to OEM slave but it is not available. I think it is listed as a ZF S6-40?
I did find this info from ZF with regard to some of the OEM slaves and the problem was the seal was installed backwards.
Technical Information on the ZF S6-40
http://www.zfdoc.com/techinfo.htm
A Common Problem with - the clutch hydraulic slave (actuator) cylinder is that they are susceptible to developing a hang up spot between the seal and the bore at the fully extended end of the cylinder's travel range. Recently (June 2006), we discovered that GM and NAPA replacement slave cylinders (TRW manufactured) have been assembled and sold to customers all over the country/world with the piston seal installed backwards. The problem with this condition is that the clutch hydraulic system will bleed out normally but still have a hang up spot present. This condition creates a problematic operational situation in the system where even a full clutch pedal depression will not allow complete disengagement of the clutch for more than just a brief instance when the pedal is depressed and held to the floor. The initial hydraulic fluid surge within the slave cylinder presses the actuation rod far enough for complete disengagement only to spring back slightly when pedal movement is halted in the fully depressed state. The spring back is caused by flex in the slave cylinder seal getting hung up and stretching a bit further only to return to its normal shape when surge pressure subsides. This manufacturer induced fault condition will mislead most technicians into believing that the clutch hydraulic system is operating at an acceptable level. Under these conditions, exactly timed quick shifts will occur fairly smoothly because the brief instance that the slave cylinder bore seal stretches is the same instant that the shift occurs. When the shift sequence is slowed down, the spring back of the slave cylinder occurs before the shift lever actuation causing a not-so-smooth gear engagement event. This causes the synchronizer to work much harder than necessary and is exposes the synchronizers and dogteeth to potential damage especially during higher RPM shifting.
The best way to verify the presents of a " hang up" condition in the hydraulic clutch system is to have the vehicle at running temperature, coast down to a full stop until completely stationary and in neutral with the clutch pedal all the way up. Wait for a few seconds then depress the clutch pedal completely to the floor then wait for another 2 seconds before shifting from neutral to either 1st or reverse gear. If there is any resistance at all when actuating the shift lever into either gear from this state, it is likely that some degree of seal hang up is present. Hydraulic clutch systems that have this type of problem can cause the synchronizers to wear much more quickly. A healthy clutch hydraulic system should provide silk-smooth gear engagement during this type of test.
It looks like the problem is the bushing CC uses in their flywheel. The fix is to use the OEM one from the original flywheel.
Not Fully Disengaging
So when they removes the transmission bolt, they tried pulling on it but it wouldn't come out ... something was stuck in there ... they had to put bolts to push the transmission out and then the culprit showed up
TADAA!
This is the brass bushing that comes with the clutch kit ... you have to press it in the flywheel and grease it a bit and the input shaft should spin freely in that bushing instead of the OEM bearing .. but the reality is ... the bushing doesn't fit loose enough on the input shaft so when they pulled the transmission, that bushing was stuck on the input shaft and they had to use a puller to pull it out .. so we ended up putting the stock bearing but the fitment wasn't as tight as they would've liked (because of what happened with the bushing) .. they ended up putting a bit of loctite or something similar to make sure it doesn't get out
Not Fully Disengaging
So when they removes the transmission bolt, they tried pulling on it but it wouldn't come out ... something was stuck in there ... they had to put bolts to push the transmission out and then the culprit showed up
TADAA!
This is the brass bushing that comes with the clutch kit ... you have to press it in the flywheel and grease it a bit and the input shaft should spin freely in that bushing instead of the OEM bearing .. but the reality is ... the bushing doesn't fit loose enough on the input shaft so when they pulled the transmission, that bushing was stuck on the input shaft and they had to use a puller to pull it out .. so we ended up putting the stock bearing but the fitment wasn't as tight as they would've liked (because of what happened with the bushing) .. they ended up putting a bit of loctite or something similar to make sure it doesn't get out
- Status
