The black Sentra I sold a friend of mine is giving him some problems. When I owned it, I once had the clutch pedal go soft, but a fluid change fixed that right up. My friend had the clutch go away completely on him recently, so he replaced the slave cylinder, which mostly fixed the issue. Now, however, there is something very strange going on. He has only a couple of inches of travel down near the bottom of the stroke, and neither one of us can properly bleed the system. I tried last night with my trusty MightyVac, which has never failed me yet, but I couldn't pull more than a couple of drops of fluid out of the bleeder. It's acting like there's a check valve or something jammed closed. What could cause this? My bet is either he got a bad slave cylinder from the auto parts store, or there's something funky going on in the master cylinder. Any guesses?
Flex hose collapsed internally?
Try gently cracking the line at the clutch master cylinder side of the hose and see if regular pedal pumping can push more fluid there. Then close the fitting and open it at the other end of the flex line, repeat.
Also build yourself a pressure bleeder, they tend to work better on clutch hydraulics.
http://faculty.ccp.edu/faculty/dreed/campingart/jettatech/bleeder/index.htm
In reply to jstein77:
Jerry,
Sometimes air gets in a long vertical run in the tubing and doesn't want to migrate out toward the slave cylinder during the bleeding process.
I have used a suggestion by Bill Burris of PCA to "reverse bleed" the clutch, using a old fashioned hand-pump type oil can full of clean brake fluid. Connect to the bleed nipple on the slave cylinder with a rubber hose and push fluid back up into the line so any air is expelled through the master cylinder. Be careful not to overflow the master reservoir.
Dan
My 240sx had the same thing. It has a odd slave cylinder on the frame rail between the master and the actual clutch slave. Don't know what it was for, but it trapped a bit of air that I could not bleed out. I bypassed the thing and all was well.
Well, when I owned it I was never able to succesfully bleed the system using the clutch pedal. There was something in the line that introduced more air with every stroke. I'm not sure if there is a damper in the line somewhere, but there's nothing obvious between the master and slave cyclinder like you had, Bear.
I've always been able to pump it out with the MightyVac with just a few pumps. In fact, that's how I changed the fluid - I could completely drain the reservior in about 5 pumps. Now, however, I can't even get it to draw any fluid at all. My first theory was that whatever caused the air to be introduced when using the clutch pedal (damper, check valve, whatever) has jammed open and keeps pumping more air in every time I pump the MightyVac.
It needs to be reverse bled. Push the fluid from the slave back through the system. I like Icondrivers idea of using an oil pump can. I've always used a mighty vac with fresh fluid in the resevior, and the suction hose connected to the pressure side if the mighty vac pump, to push the fluid out of the resevior to the slave cyl and back up through the system.
What has probably happend with the Sentra is that the piston in the MC is stuck in the bottom of the bore. Reverse bleeding will oush it back up. Trying to pull fluid through with the vac will just get it stuck worse. Also, the piston being stuck doesn't mean its bad, clutch MCs don't often have a return spring for the piston.
bearmtnmartin wrote:
My 240sx had the same thing. It has a odd slave cylinder on the frame rail between the master and the actual clutch slave. Don't know what it was for, but it trapped a bit of air that I could not bleed out. I bypassed the thing and all was well.
Clutch regulator valve?
Make sure the Sentra doesn't have one.
HappyAndy wrote:
What has probably happend with the Sentra is that the piston in the MC is stuck in the bottom of the bore...
The funny thing is that is still has a semi-functional clutch, with a couple of inches of travel at the bottom of the stroke. You would think that if the piston were stuck at the bottom of the stroke, there would be no clutch whatsoever. He drove it over to my house and back.
Have you tried a power bleeder from the other direction?
Not yet - the two of us only have vacuum pumps. We'll try the idea of using the mighty vac to pump fluid in.
