Brake residual pressure valve

markmark · Post by **markmark** » Fri Apr 11, 2008 11:03 am

My buggy runs a disc brake master cylinder (Superbug) however it has front and rear drum brakes. This is because my pan was made from a superbug pan and the front end was converted to a link pin beam front. I am still using the stock drums. I need to use the Superbug master cylinder as it is the only one that will fit. 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?

mel hubbard · Post by **mel hubbard** » Fri Apr 11, 2008 2:31 pm

[QUOTE="markmark"]My buggy runs a disc brake master cylinder (Superbug) however it has front and rear drum brakes. This is because my pan was made from a superbug pan and the front end was converted to a link pin beam front. I am still using the stock drums. I need to use the Superbug master cylinder as it is the only one that will fit. 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?

[/QUOTE] Mark, Im no big brake expert,, but I would say the arrow would indicate the flow of fluid to the drums, so Im guessing its just a 10lb one way valve. On some master cylinders they have one feed to the rear T piece & 2 separate feeds to each of the fronts, so Im gessing if thats the case you would have to blank one front one & run a single pipe with the inline valve to a front T piece to feed the two front drums. Can you tell me why you need this valve? I thought they were just for vehicles with very low master cylinders (to stop flow back to the MS) maybe Im wrong.

markmark · Post by **markmark** » Fri Apr 11, 2008 3:03 pm

The valve is meant to give a much firmer brake pedal. I'm told that if you run a disc brake master cylinder with drum brakes that you lose all the pressure in the brake lines, which gives a spongy pedal. I have tried bleeding the brakes several times and I'm quite confident that there is no air in the system. The brake pedal does firm up if it is pumped a few times. As soon as you take your foot off the brake pedal and then try the brakes again the pedal nearly travels to the floor. I'm certainly not happy with it like this. Hopefully the residual pressure valve does the trick.

mel hubbard · Post by **mel hubbard** » Fri Apr 11, 2008 4:41 pm

Mark, have you set the adjustable pedal rod to master cylinder at the correct length?, my buddy had a similar problem & thats what it turned out to be. Those residual valves (I think) just keep a 10lb pressure of brake fluid from the valve to the wheel cylinders to stop any bleed back, you should not get that on a VW based buggy.

mel hubbard · Post by **mel hubbard** » Sat Apr 12, 2008 12:16 am

Hey Mark, I've been thinking more about your brake problems,,,,, the 1302 (super bugs) here in UK had a wider Napoleans hat section. You say you've put a link pin front on it,,,, Im wondering if you also changed the Napoleans hat section of the chassis with the narrower non superbug one and are using the superbug pedals & MS push-rod. If so this would make the superbug push rod too long, which to me sounds like the 'bleeding' problem.

newmanx59 · Post by **newmanx59** » Sat Apr 12, 2008 1:25 am

[QUOTE="markmark"]The valve is meant to give a much firmer brake pedal. I'm told that if you run a disc brake master cylinder with drum brakes that you lose all the pressure in the brake lines, which gives a spongy pedal. I have tried bleeding the brakes several times and I'm quite confident that there is no air in the system. The brake pedal does firm up if it is pumped a few times. As soon as you take your foot off the brake pedal and then try the brakes again the pedal nearly travels to the floor. I'm certainly not happy with it like this. Hopefully the residual pressure valve does the trick.[/QUOTE] The valve should do it. The springs on the brake shoes pump all the fluid back to the master cylinder and that requires more pedal travel to fill the wheel cylinders back up before the shoes contact the drum.

markmark · Post by **markmark** » Tue Apr 15, 2008 11:11 am

The valve did the trick. The pedal is really good now. Thanks for everybody's help.

Manx-Australia · Post by **Manx-Australia** » Tue Apr 15, 2008 11:40 pm

Just for peoples info the reason you get this issue when you use a M/C which comes from a brake system which was designed for disc brakes is due to the fact the tha Disc Callipers do not force the fluid back into the M/C like a drum brake setup does. This means when you use a Disc M/C on a drum brake setup the fluid is forced back into the M/C and has a negative effect as the M/C is designed to build up some residual presure and thus maintain a hard pedal with minimal fluid movemnet. You usually see the effect in reverse when people upgrade drum brakes to disc and keep their drum M/C which then causes the callipers to ride on the rotors as the M/C has an internal residual presure valve and the callipers do not have the fluid return ability of the drums. Anyway this residual presure valve on a Dual Circuit T1 Drum Brake M/C is around 9lbs.

mel hubbard · Post by **mel hubbard** » Wed Apr 16, 2008 12:24 am

[QUOTE="Iguana"]Just for peoples info the reason you get this issue when you use a M/C which comes from a brake system which was designed for disc brakes is due to the fact the tha Disc Callipers do not force the fluid back into the M/C like a drum brake setup does. This means when you use a Disc M/C on a drum brake setup the fluid is forced back into the M/C and has a negative effect as the M/C is designed to build up some residual presure and thus maintain a hard pedal with minimal fluid movemnet. You usually see the effect in reverse when people upgrade drum brakes to disc and keep their drum M/C which then causes the callipers to ride on the rotors as the M/C has an internal residual presure valve and the callipers do not have the fluid return ability of the drums. Anyway this residual presure valve on a Dual Circuit T1 Drum Brake M/C is around 9lbs.[/QUOTE] Would adjusting the drum brakes ''FULL ON'' overcome this problem when bleeding? Maybe I've just been lucky in the past, but have used D/C master cylinders with drums & discs in the past without any problems. Not sure how different the super beetle M/C's are to the standard D/C ones though.

mel hubbard · Post by **mel hubbard** » Thu Apr 17, 2008 1:05 am

Mark, Jerry & Iguana,, this subject intrigues me,, Im no way a brake guy, but would like to know a little more about it. How I read the quote > ''the reverse effect can be got by upgrading a drum brake MC to disc brakes'' SO, does this mean a VW drum brake MC has a built in 10 lb one way valve?? If so a 10lb shot of fluid should come from the bleed nipple when undone, which I've never experienced. I DO understand that a 10lb valve would cause disc pads to hold on due to not having the same return strong BD springs. Glad you got it sorted Mark :rock:,, maybe I should just stick to the FG

markmark · Post by **markmark** » Mon Jul 20, 2009 1:40 pm

I have been driving this thing like this for 6 months and the brakes are still good. One thing I learnt also was to make sure that the brake shoes are really well adjusted. I adjusted the shoes so that they were all just scraping the drums. This made the pedal a million times better also.

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Brake residual pressure valve

Brake residual pressure valve

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