Clutch Hydraulics and RPV's
Discussion
I have a scratch built car with a Wilwood master with integral reservoir and a Ford concentric slave.
Rear wheel drive, Getrag box on a Lotus engine.
The pedals are floor mounted so the master is lower than the slave.
Someone has recommended fitting a 2psi residual pressure valve in the line to prevent syphon back.
Good idea on not ?
Anyone done this ?
Cheers in anticipation,
Paul G
Rear wheel drive, Getrag box on a Lotus engine.
The pedals are floor mounted so the master is lower than the slave.
Someone has recommended fitting a 2psi residual pressure valve in the line to prevent syphon back.
Good idea on not ?
Anyone done this ?
Cheers in anticipation,
Paul G
I am no expert & others may know more but here is my 2p.
NO!
Residual pressure in the system will surely keep the brakes slightly on. Therefore the brakes will get f+*&^%$g hot & the pads will last no time at all.
When you bleed the brakes and finally close off the bleed nipple, that locks the hydraulic fluid in place as it has nowhere to go, so surely that will solve the non-existent problem you are trying to overcome.
NO!
Residual pressure in the system will surely keep the brakes slightly on. Therefore the brakes will get f+*&^%$g hot & the pads will last no time at all.
When you bleed the brakes and finally close off the bleed nipple, that locks the hydraulic fluid in place as it has nowhere to go, so surely that will solve the non-existent problem you are trying to overcome.
E-bmw said:
I am no expert & others may know more but here is my 2p.
NO!
Residual pressure in the system will surely keep the brakes slightly on. Therefore the brakes will get f+*&^%$g hot & the pads will last no time at all.
When you bleed the brakes and finally close off the bleed nipple, that locks the hydraulic fluid in place as it has nowhere to go, so surely that will solve the non-existent problem you are trying to overcome.
Who mentioned brakes ?NO!
Residual pressure in the system will surely keep the brakes slightly on. Therefore the brakes will get f+*&^%$g hot & the pads will last no time at all.
When you bleed the brakes and finally close off the bleed nipple, that locks the hydraulic fluid in place as it has nowhere to go, so surely that will solve the non-existent problem you are trying to overcome.
Please, please, if you do have an answer can you make it at least resemble the question.
Paul G
Sorry, my mistake, I know the title said clutch, but as soon as you mentioned Wilwood I assumed you were talking about brakes.
However the second half of my answer is still 100% true, once the bleed nipple is closed where can the fluid go?
The laws of physics apply to all hydraulic systems!
Does that resemble the question enough for you?
However the second half of my answer is still 100% true, once the bleed nipple is closed where can the fluid go?
The laws of physics apply to all hydraulic systems!
Does that resemble the question enough for you?
The second part of your statement isn't 100% true at all, 2psi is f**kall when it comes to brakes, you won't even overcome the seal retraction forces with that, just negate some of it.
I've run 2 and 10psi valves on road cars for years without issue.
Anyway, back to the original question, 2psi valve should do the job fine.
2psi in a what, .75 or .875" cylinder for a clutch I'd guess? So ~1.2lb of force on the clutch bearing and pressure plate that will need 2 orders of magnitude more to release it - it's probably only just enough to keep the bearing from rattling on the shaft.
I've run 2 and 10psi valves on road cars for years without issue.
Anyway, back to the original question, 2psi valve should do the job fine.
2psi in a what, .75 or .875" cylinder for a clutch I'd guess? So ~1.2lb of force on the clutch bearing and pressure plate that will need 2 orders of magnitude more to release it - it's probably only just enough to keep the bearing from rattling on the shaft.
Edited by PhillipM on Friday 1st April 21:23
First a photo to show the set up.
Bottom left shows the Wilwood 11/16" m/c mounted on the end of the footwell, and centre of the photo shows the concentric slave.
Difficult to assess the size of this as it's a cylinder with gearbox shaft passing though it. ( pi r squared minus pi r squared ? )
The flexy pipe has been removed but I have drawn it in on Photoshop.
I was stupid enough to use a second hand slave and the car has done 400 miles since first registration. Bought a new one.
My mate, who suggested the residual pressure valve, is working on the possibility that with the slave higher than the master the weight
of the fluid in the line could suck air into the slave, as hydraulic seals are designed to seal ( against pressure ) one way but not
necessarily the other. Fluid might have the tendency to want to return to the master when the car is not in use.
The problem is a dragging clutch, making it difficult to engage gears from standstill.
Advice is appreciated,
Paul G
Bottom left shows the Wilwood 11/16" m/c mounted on the end of the footwell, and centre of the photo shows the concentric slave.
Difficult to assess the size of this as it's a cylinder with gearbox shaft passing though it. ( pi r squared minus pi r squared ? )
The flexy pipe has been removed but I have drawn it in on Photoshop.
I was stupid enough to use a second hand slave and the car has done 400 miles since first registration. Bought a new one.
My mate, who suggested the residual pressure valve, is working on the possibility that with the slave higher than the master the weight
of the fluid in the line could suck air into the slave, as hydraulic seals are designed to seal ( against pressure ) one way but not
necessarily the other. Fluid might have the tendency to want to return to the master when the car is not in use.
The problem is a dragging clutch, making it difficult to engage gears from standstill.
Advice is appreciated,
Paul G
PhillipM said:
The second part of your statement isn't 100% true at all, 2psi is f**kall when it comes to brakes, you won't even overcome the seal retraction forces with that, just negate some of it.
I've run 2 and 10psi valves on road cars for years without issue.
Anyway, back to the original question, 2psi valve should do the job fine.
2psi in a what, .75 or .875" cylinder for a clutch I'd guess? So ~1.2lb of force on the clutch bearing and pressure plate that will need 2 orders of magnitude more to release it - it's probably only just enough to keep the bearing from rattling on the shaft.
That was the first part!I've run 2 and 10psi valves on road cars for years without issue.
Anyway, back to the original question, 2psi valve should do the job fine.
2psi in a what, .75 or .875" cylinder for a clutch I'd guess? So ~1.2lb of force on the clutch bearing and pressure plate that will need 2 orders of magnitude more to release it - it's probably only just enough to keep the bearing from rattling on the shaft.
Edited by PhillipM on Friday 1st April 21:23
The second part was the bit about hydraulic lock!
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