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Fri Apr 11, 2008 7:21 am

My buggy runs a disc brake master cylinder (Superbug) however it has drum brakes.
The pan was made from a Superbug pan and the front end has been converted to a link pin beam. I am using the stock drums.

I have bought a residual pressure valve for the front brakes but I'm not 100% sure how to fit it.
The valve (in the pic below) has an arrow at the same end as the 10lb stamp and it points towards the other end.
Would I fit this end to the master cylinder with the arrow pointing away from the master cylinder?

Fri Apr 11, 2008 8:58 am

With drum brakes you don't need a residual valve at all
Drum brakes have springs to pull the pads away from the drum when you aren't using them.

Calipers are sort of opposite, by that I mean there has to be a small pressure there to hold the pads against the rotor slightly. The pistons float in their bore so without the residual valve they may feel spongey. Having these installed you won't have to push the pistons into position as well as apply force to the rotor.

I think that because of the drum brakes in the rear and discs in front that by NOT installing the residual valves it may help counter ballance the locking of the front brakes befor rears which seems like a common buggy problem.

Another solution would be a perportioning valve. this device would let you manually dial the pressure of the front brakes as you drive, then you can lock in that setting

yet another solution in you case would be to switch rear wheel cylinders to the fronts and vise versa. In other words use the larger ones in the rear and the smaller ones in the front (opposite of the stock Beetle configuration)

As for the answer to your question regarding the arrow -
yes , the flow is going from the master toward the caliper.

The residual valve is basically a check valve that holds a certain pressure( a check valve won't let any fluid drain back and wouldn't release the disc)This happens quite often to any system when the rubber hose goes bad - fluid goes in and can't release pressure.
Bart

Fri Apr 11, 2008 3:19 pm

It has drum brakes in the front but it has a master cylinder for disc brakes in the front.

I was told that this is the problem by a VW service mechanic. I don't think he has much experience with custom set-ups though.

I'll give the valve a try as I have already bought it and I'll post my findings here.

Sat Apr 12, 2008 12:11 pm

manxmark wrote: I was told that this is the problem by a VW service mechanic. I don't think he has much experience with custom set-ups though.

Believe it! It's amazing how many "Factory VW techs" out there think that anything other than stone stock is doomed to failure or just will not work in any way.

Sat Apr 12, 2008 3:45 pm

You need the residual valve to keep the DRUM brake springs from pushing all the fluid back to the master cylinder. The fluid that is pushed all the way back to the master cylinder has to be moved back to the wheel cylinders and sometimes that can take a pump or 2 on the brake pedal,unless there is a residual valve in the line to keep some of the fluid in the wheel cylinders.

Tue Apr 15, 2008 2:21 am

I fitted the valve today and it made a huge improvement.

Thanks for everybody's help and info.

Tue Apr 15, 2008 8:38 am

What do you mean it made a "huge improvement"?

and

what way did you install it?

Bob E

Tue Apr 15, 2008 2:46 pm

It has a really firm pedal now. The brakes are working just as they should.

Before the valve was fitted the brakes had to be pumped a couple of times to get a decent brake pedal......and then as soon as you took your foot off the brakes you had to repeat this process again to apply the brakes. This was far from ideal!

The valve was installed with the arrow pointing away from the master cylinder.

Thu Apr 17, 2008 5:51 pm

I have a sandrail and had to install a residual pressure valve because the calipers are above the master cylinder.
If you're running drums, you should be able to adjust them so there isn't so much slack pedal movement.
Also, the disc brake master will have a higher volume output at a lower pressure than a drum master. It'll work, but the pedal will be harder to push.

Fri Apr 18, 2008 3:48 am

Hmmm, I have discs on my vert with a single circuit master and no problems what so ever. Is there a specific combo that needs this?

Mon May 12, 2008 11:55 am

So I started another thread on this subject because a search turned up nothing..I must have misspelled, because google kicked this one right to the top.

I have discs in the rear and a cutting brake. Should the pressure valves for the rear discs be behind(downstream from) the cutting brake?

For the front valves, should you mount them right on the master?

Mon May 12, 2008 12:04 pm

It sounds to me that installing a residual valve is a poor way of keeping the drum shoes close to the drum. I get the same solid peddle feel from just adjusting the brakes on each wheel until the shoe just lightly drags. VW's do not have automatic shoe adjusters so this maintenance is required frequenty to maintian good peddle feel and safety.

Mon May 12, 2008 2:48 pm

wythac wrote:
I have discs in the rear and a cutting brake. Should the pressure valves for the rear discs be behind(downstream from) the cutting brake?

For the front valves, should you mount them right on the master?

I would say yes, mount them downstream of the cutting brake (which acts like a couple of master cylinders).

As for the front, we mounted ours right on the master. Granted, we're running disks, but it should work the same.