Hydraulic Handbrake

[Carpmart]

Hi Chaps

I have a hydraulic handbrake I am fitting to my race car. My question is with this brake cylinder on the handbrake pictured (http://www.demon-tweeks.co.uk/products/ProductDetail.asp?cls=MSPORT&pcode=RIX650), which is the in and out for the brake lines?

Thanks in advance for your help!

[GreenV8S]

Can't see any detail on the DT pics, but I'd expect to find the handbrake lever pushed a rod into the cylinder, the outlet would then be the one furthest from the rod. If it isn't obvious, you could always ask the supplier.

[Carpmart]

GreenV8S said:

Can't see any detail on the DT pics, but I'd expect to find the handbrake lever pushed a rod into the cylinder, the outlet would then be the one furthest from the rod. If it isn't obvious, you could always ask the supplier.

That seems logical, thanks for your quick reply!

[RT106]

No, the union furthest from the handbrake lever is the inlet.

[GreenV8S]

RT106 said:

No, the union furthest from the handbrake lever is the inlet.

How does it work then? I've never used one myself, but the ones I've seen look like basically ordinary master cylinders with an input from the real master cylinder where the reservoir input would normally go. Perhaps they do clever stuff with the seals internally to cope with the extra pressure on the 'unpressurised' side of the piston, but externally they looked pretty straight forward.

[RT106]

GreenV8S said:

How does it work then? I've never used one myself, but the ones I've seen look like basically ordinary master cylinders with an input from the real master cylinder where the reservoir input would normally go. Perhaps they do clever stuff with the seals internally to cope with the extra pressure on the 'unpressurised' side of the piston, but externally they looked pretty straight forward.

I don't have a clue how they work! The cylinders supplied with the handbrake kits are exactly the same as the cylinders used with twin MC bias pedal boxes. I think the design originates from old Land Rovers...

Regardless, whether fitted in a pedal box or handbrake the inlet is furthest from the 'pedal'. I've had a few of these in my time, and before posting I dug out some pics of my old rally cars to assure myself that I wasn't going mad!

As an aside, the cylinders supplied with these kits (Girling/Lucas) tend to cause the handbrake to lock on if used in conjunction with the footbrake. This is due to them not being designed to cope with pressure on the 'unpressurised' side. AP cylinders are much more expensive but don't have this problem, and interestingly are plumbed as you might expect with the inlet closest to the 'pedal'.

[Mr2Mike]

It depends on the particular master cylinder used. The popular Girling type has the outlet closest to the pushrod and the inlet/reservoir fitting furthest away. The AP racing master cylinders used in this application work the other way.

[GPR_TECH]

The cylinder supplied in the kit is a Girling (or a copy of) which have been standard fair on competition cars since the 50's. The vertical port at the rear is the inlet and the angeled port is the outlet, this is not the same for all makes of cylinders but generally the easy way to differentiate between the two ports is that the inlet is larger than the outlet, in this case the inlet is 7/16 UNF and the outlet is 3/8 UNF and that is consistent with the AP cylinders. The cylinders used are identical to those used on the main braking circuit, you only use the hydraulic handbrake when you are not using the footbrake, so as the main cylinder is is in its relaxed mode the piston is behind the cut off ports which allows the handbrake cylinder to draw fluid from the main reservoir through the main braking cylinder.