RWD - Clutch Slave Cylinder Rubber Boot

Volvo RWD 120-130 Forum

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Clutch Slave Cylinder Rubber Boot 120-130

It looks like you've spent quite a while thinking about these clutch slave cylinders...

I admit I was slightly skeptical that they'd have left enough clearance in the design for the piston to cock, as you indicate on your webpage (if I had to tender a guess I'd have guessed maybe a 0.001" clearance on the diameters).

I just took apart my old and new and these are the results:

Piston: OD* = 0.81035 +/- 0.00005 in
Cylinder: ID** = 0.8125 +/- 0.0005 in
clearance ~0.002

Piston: OD* = 0.80730 +/- 0.00005 in
Cylinder: ID** = 0.8120 +/- 0.0005 in
clearance ~0.005

* OD's measured with micrometer
** ID's measured with caliper, as my inside mic couldn't reach deep enough into the bore for an accurate reading.


I'm going to have to agree with you; this is a faulty design. There is nothing to keep the piston from cocking and rubbing against the cylinder wall except a thin fluid bearing. To make matters worse, my new slave is destined to fail in this manner even more quickly than the one it's replacing!

On the bright side, the leading (dry) edge on my old piston was very rough, and the piston itself had only a lathe finish. The new piston has a very nice radius on the end and appears to have a ground finish. The nicer sidewall finish won't do anything for me, but hopefully the clean radius will prevent premature scouring.


In an effort to get my car back on the road ASAP (I'm borrowing a car right now), I'm going to throw the thing together this evening with:

- the new slave assembly
- a rubber balloon & zip-tie acting as a boot

But I DO like your O-ring upgrade...

Are you using 1/8" thickness or 3/32" thickness O-rings on your upgraded pistons? Buna, Viton, Silicone? Also, do you turn the groove or grind it in? I'll probably re-build my old slave with a RKwas piston when this new one starts to show signs of failure.

...happy motoring...


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New Clutch Slave Cylinder Rubber Boot [120-130]
posted by  Mr. Happ  on Mon Apr 24 05:19 CST 2006 >

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