quote Originally posted by Tryxalon: yes, I lowered the volume of the slave with the "helper" by making the piston longer. Any modification of the rod length would have changed the geometry. Didn't want to do that.

But that's exactly what you did. Moving the piston further into the master cylinder has the same effect as increasing the pushrod length.

I was just pointed to this thread, and have a comment or two.

The slave couldn't be drawing in air as it's retracting because most of the restoring force is from the clutch diaphragm spring, not the pedal return spring. This reverses the role of master and slave while the pedal is retracting. The slave must be drawing in air after the pedal has fully returned.

Will, apparently I was not able to describe what I did effectively.

1) I did not change the master at all. The volume of the master was smaller than that of the slave already.

2) I did not increase the rod length, I increased the "length of the slave cylinder piston". The effective "moved volume" of the slave is now within .1cc of the master Even though the slave is .3 inches larger in diameter and .6 inches longer.

--B-------------------------------S
[................[added]{piston}..S.Rod to lever
--------------------------------- S

where B is bleeder SSS is seal "piston" is the original slave cylinder piston, and "added" is the part of the old piston I cut and added to reduce the volume inside the slave cylinder to near the same as the master (only slight differences in cylinder diameter, but almost an inch difference in length (ergo volume).

This is maybe a little better description? I don't have a camera.

It still is working perfectly. I've had the engine out of the car for some work and separated the engine and trans to check on the clutch since I was there. Could barely tell it was not a new one ... and this is almost 2 and a half years later!

It also bleeds, first time, every time. Crack the bleeder valve (remove the pressure)and you can work the clutch lever at the trans (need a prybar cause of the clutch springs, but ...) It doesn't increase or hold pressure on the lever, but it increases the amount of "oomph" the slave recieves from the master.

All I know is that it made sense to me and apparently it works well.

[This message has been edited by Tryxalon (edited 06-17-2002).]

quote Originally posted by Will: But that's exactly what you did. Moving the piston further into the master cylinder has the same effect as increasing the pushrod length. The slave couldn't be drawing in air as it's retracting because most of the restoring force is from the clutch diaphragm spring, not the pedal return spring. This reverses the role of master and slave while the pedal is retracting. The slave must be drawing in air after the pedal has fully returned.

I think that both of you guys (will and tryxalon) are both correct.

lengthening the piston has the same effect as lengthening the push rod. Lenghthening the push rod also has the effect of changing the geometry. The change, however, is so minute that it has nominal effect on slave's efficiency. In fact, if I remember my geometry correctly, a longer push rod will move the clutch arm a greater distance than its stock counterpart.

I think most of the people who suffer from air bleeding into the system have a problem with air bleeding into the system while the car is at rest. However, I do know that air can bleed into the system while the slave piston is in motion. Remember, I complained about how a substantial amount of air would bleed into the system after a short 1/4 mile pass? I don't think that that amount of air could bleed into the system during a short 10 second pass (Ok, i lied. Make that 13 sec.) It must have something to do with what happens when I sidestepped the clutch peddle. My thinking on this is that if the speed at which the piston in the master returns exceeds the speed at which the slave piston return, a vacuum condition will be created, allowing air to bleed past the slave piston seal. The only way to prevent this from occuring is by increasing the speed at which the slave piston returns to its resting position. Before installing the RPV, I tried to do this by attaching return springs to the slave and the clutch arm. It didn't work, however.

Farknocker

quote Originally posted by Mr. Farknocker: I think most of the people who suffer from air bleeding into the system have a problem with air bleeding into the system while the car is at rest. However, I do know that air can bleed into the system while the slave piston is in motion. Remember, I complained about how a substantial amount of air would bleed into the system after a short 1/4 mile pass? I don't think that that amount of air could bleed into the system during a short 10 second pass (Ok, i lied. Make that 13 sec.) It must have something to do with what happens when I sidestepped the clutch peddle. My thinking on this is that if the speed at which the piston in the master returns exceeds the speed at which the slave piston return, a vacuum condition will be created, allowing air to bleed past the slave piston seal. The only way to prevent this from occuring is by increasing the speed at which the slave piston returns to its resting position. Before installing the RPV, I tried to do this by attaching return springs to the slave and the clutch arm. It didn't work, however. Farknocker

Air seems to bleed out of my system while it's sitting. It frequently comes closer to releasing in the morning.

The way I look at it is that the lion's share of the pedal load is transmitted through the hydraulics from the clutch diaphragm spring. If you've never worked with an empty master, trust me, the return spring is only enough to move the pedal.
Since the hydraulic force exerted by the diaphragm is greater than the mechanical force exerted by the return spring, the pedal is returned by the diaphragm spring, not the retun spring, and the hydraulics are under positive pressure whenever the pedal is displaced from zero. I don't know exactly how much pressure is in the system as it returns, but it's got to be above atmospheric.

Great thread!!! I just ordered a 2 lb valve, will receive it tomorrow. Won't be able to install until next week but I will report back. The prices(in Canada) are a laugh... anywhere from $29.95-(in next day) to $90.00(7-10days) ...guess who I went with??? I have 2 slaves, both fairly new that need bleeding every 10 days. I am praying for this to be an answer to all this clutch BS.
thanks,Sandy

1st! I have to thank 'Farknocker' for this topic. I installed a 2 lb RPV and, at the same time, rebuilt my Master Cyl (Wagner rebuild kit, I know,I know!!!). The clutch operates so well, I've had to re-learn how to shift! (ie: stop double-clutching) I can actually adjust where, on the pedal-travel,(I use an adjustable banjo) that my clutch will engage. No more grinds into reverse! I can honestly say that my car has a 'CLUTCH' and not just 'Speedshift' out of the driveway. Now, I cannot prove that the RPV is the answer as I rebuilt my Master Cyl at the same time, but hey, spent $30Can(RPV) and $35Can(Wagner rebuild kit) and my car is a whole new world. I will also state that I took a little time playing with my banjo adjustment. Thanks again 'Farknocker', my prayers have been answered!
Sandy

[This message has been edited by cowans (edited 07-04-2002).]

NP.

Where do I send the bill?

Farknocker

I have enjoyed reading this thread - what a great exchange of ideas! I might like to try an RPV on my 1988 Coupe. Would it be feasible to install the RPV between the flex line and the slave cylinder? That way, you wouldn't have to mess with bending /flaring tubing and so forth - the RPV would "plug right in." And you could easily delete the RPV if you changed your mind.

I measured the threads on the bleeder valve, and they seem to be a metric size: M12x1.0. I assume the flex line has the same thread.

Wilwood's data show 1/8" MPT on their RPV. I don't suppose fittings are available to mate those 2 threads?

quote Originally posted by StuGood: Would it be feasible to install the RPV between the flex line and the slave cylinder? That way, you wouldn't have to mess with bending /flaring tubing and so forth - the RPV would "plug right in." And you could easily delete the RPV if you changed your mind. I measured the threads on the bleeder valve, and they seem to be a metric size: M12x1.0. I assume the flex line has the same thread. Wilwood's data show 1/8" MPT on their RPV. I don't suppose fittings are available to mate those 2 threads?

I don't think there are any fittings out there that would allow you to install the flext line directly to the RPV and the RPV directly to the slave. My guess is that you will have to cut the hard line, right before the flex line, and install compression fittings in which case, you might as well do it at the master where it's easier to access. I would, however, encourage you not to give up on your idea. After all, that's how I came up with the fix in the first place.

Farknocker

[This message has been edited by Mr. Farknocker (edited 07-22-2002).]