Fitting a brake proportioning valve.??

[Gene-C]

I've got a JAMAR hydraulic pedal assy fitted to a f'glass dune buggy i am building for the street. ( Tube chassis,2276cc,Autometer gauges,ERCO wheels etc ) I want to plumb in a brake proportioning valve to adjust the brake bias, due to the front end having not a lot of weight. I also need to fit a residual brake pressure valve due to having discs all round, and the m/cylinder being lower than the brake calipers. The master cylinder is attached to the pedal assy. A line will come out from the m/c and into a t-piece, then a line to the front with t-piece, and a line to the rear with a t-piece and brake light switch. The t-pieces at the front and the rear of the system then branch off to the brake calipers. Should i have the proportioning valve between the front and rear t -piece's, and the residual pressure valve to the rear of the proportioning valve.? Or should the residual pressure valve be as close to the master cylinder as possible, and the proportioning valve plumbed between the front and rear system.? It's a single circuit system because of the hydraulic pedal assy if it makes any difference. Cheers Richie :help:

[Gene-C]

I personally don't see why you need either of those. I had a buggy with 4 wheel disk and I didn't have a proportional valve or residual valve and It worked perfect. But as for where you should place them I would suggest putting the proportioning valve somewhere in the cab with you. Maybe next to the seat or something. Then you can adjust it very easily if you need to. I really don't see a need for both. You use a residual valve for when the back end or the car lifts up and it purportions the braking so the rears don't lock. A buggy doesn't have enough weight in my opinion to need one. Just my :2cents:

[croakintowd]

Hello, I am in the same predicament as you. I read what I could find on the Internet, and was amazed at how wrong some "official" sites were with respect to braking systems. The Proportioning Valve goes in the line to the rear brakes. It lowers the pressure to the rear brakes so they won't lock up when the weight transfers to the front brakes during braking. I'm going to stick my valve under the dash, out of sight. I figure someone would be less apt to mess with it, if it's out of sight. The Residual Pressure valve is a good idea. From what I can tell, it simply applies about 2 lbs. of "residual" pressure so the fluid doesn't drain back to the master cylinder. I could be wrong, but for some reason I thought each wheel had to have its own valve(?). But, it seems like one per circuit would do just as well. You are right about the requirement to place a Residual Pressure valve in the line if the M/C is lower than the Calipers. I'm going to try my car without the Residual Pressure valve, just to see if I can get away with it. My M/C is just about even with the Calipers. I'm hoping to get out cheaper, I guess. Good luck,

[newmanx59]

The Proportioning valve should be in the front brake circuit so you can reduce the braking to the front wheels as needed. Here is a little info about RESIDUAL PRESSURE VALVES: These in-line pressure valves retain a minimum brake line pressure to help eliminate excessive pedal travel in both disc and drum brake systems. The two pound valve is used in disc brake applications where the master cylinder is mounted below the horizontal plane of the calipers and fluid drain back occurs from gravity and vibration, thereby causing excessive caliper piston retraction and a longer brake pedal stroke. The minimal two pound residual pressure prevents fluid from flowing back without causing the brakes to drag. With drum brakes, a ten pound valve is used to compensate for return spring tension in the drums. I have run residual valves with a valve screwed directly into each caliper and I have also run them with 1 inline for both front calipers and 1 inline for both rear calipers. They worked great both ways. The first time I installed them I really didn't think they were needed, boy was I wrong. They made the pedal higher and harder. Since I posted this I did a bit of research and found this: INSTALLATION NOTES: ? On Disc front, Drum rear combinations with a single master cylinder, be sure to remove the residual check valve, or purchase a master cylinder without a check valve. You must then install an in-line residual check valve in the line to the rear drum brakes. The valve should be installed on the brake side of the proportioning valve as shown in the diagram. ? When using a dual master cylinder with Disc front, Drum rear combinations you won't need to remove the residual check valve as it only applies pressure to the rear brake line. On dual master cylinders, the large reservoir side is for the disc brakes, and the small reservoir side is for the drum brakes. ? Do not use a residual pressure valve with 4 wheel Disc brake systems. The residual pressure will cause the calipers to drag. ? An adjustable Proportioning valve allows you to balance the pressure between the front and rear brakes for smooth safe stops. This is a must for disc/drum combinations, as disc brakes require considerably more pressure to operate than drum brakes. Without a properly adjusted proportioning valve, the drum brakes will lock up before the discs do which can result in handling problems. Proportioning valves are also useful on 4-wheel disc or 4-wheel drum brake systems, giving you the ability to compensate for tire size differences, weight distribution, etc. ? Make sure that the bleeder valves on the calipers and the power booster point up when installed. Air cannot be fully bled from the system unless the valves are installed in the up position.

[subimanx]

[QUOTE="newmanx59"]The Proportioning valve should be in the front brake circuit so you can reduce the braking to the front wheels as needed. [/QUOTE] I would disagree. I run 4 wheel disc brakes and a dual master cylinder.My REARS locked up during the brake test and a proportional valve was required to be installed into the rear system,to lessen the braking ability of the rears.I would instal neither untill there was a valid reason for doing so; ie if the front locks up instal the proportional valve in the front line or in the rear if required. I would steer away from a residual pressure valve unless it is neaded.Try the brakes out first,the less joins in the line the better! Just my 2 cents.....

[croakintowd]

HI folks, I don't want to start an argument, but the deal with the proportioning valve is to reduce the pressure in one of the brake circuits. To my way of thinking, if you reduce the pressure in the front circuit, you would need more pedal pressure to stop, and that would increase the pressure to the rear brakes, causing them to lock up earlier. The front brakes do most of the stopping. For some reason it seems the right front wears more than the other wheels. I don't know why. By using the Proportioning Valve to reduce the pressure to the rear brakes, the rears would be less apt to lock up when the weight transfers to the front of the car during braking. I have read articles on the internet, and one article would profess installing the valve in the front circuit, and another on the rear. Perhaps, on some applications, it is correct to install the valve in the front circuit? I don't think that's the case with buggies. I guess I'll know when I stick it in and hit the brakes! Thanks,

[newmanx59]

I have tested my buggy brakes on a brake test stand and found that the front braking is marginal to the point that the sensors that measure the braking force of the front brakes/tires was not even measurable until I persuaded my 250lb friend to stand on the front bumper. With the brakes sized properly for a full bodied Bug and installed on a Manx buggy the front brakes will lockup well before there is enough braking in on the rear tires. Take any buggy with brakes properly sized for a stock bodied Bug on a wet street and lock up the brakes at speed, the buggy will lock up the front brakes long before the rears even start to make a difference. Most of the weight in a buggy is on the rear wheels to add braking to the rear wheels is only logical. Weight transfer to the front wheels is minimal due to the fact that the engine is behind the rear axle, the buggy is so short and the typical buggy has front suspension that is too stiff to allow the nose to dip properly and initiate the weight transfer under braking. The fact that most Manx style buggys have smallish front tires which will loose traction sooner due to a smaller footprint and less weight and rear tires that are considerably larger then stock and will welcome more braking pressure because the footprint is larger and there is more weight is on the rear tires is also a factor. If you install an adjustable proportioning valve in the front brake circuit the difference in pedal pressure is not noticable.

[Gene-C]

Interesting topic for a change. My question is if a proportioning valve or residual pressure valve is required for whatever reason, why did the disc brake Ghias not have either one? Granted that style car is heavier than a buggy with all the sheet metal, etc., but why didn't VW bother to include all that stuff on those cars?

[Gene-C]

Jerry aka Newmanx59 is correct. The adjustable proportioning valve goes in the front brake circuit, because you want to be able to reduce the braking to the front. On a regular car, 60%-70% of the braking is by the front... On a F/G Buggy due to its extra light frontend & heavy rear weight bias, it is just the opposite, 60%-70% or more at the rear. Adjusting an adjustable proportioning valve works opposite of what you would think too, screw it in & it opens it up... screw it out & it closes it off. It's ALL Fun, Fun, Fun... ManxManiac

[croakintowd]

Hello, I guess I figured everything backwards! That's the beauty of these sites, good info can be found, and save a guy a lot of trial and error. Jimmler: I read up on the disc brake conversion from VW to Ghia, and if memory serves, the Residual Pressure Valve is integral to the Master Cylinder. I used to know the part number of the M/C. I even bought one. But I think I've decided to go with a single single circuit M/C. Why? I don't know. (To tell the truth, I've been waffling on this). Thanks for setting me straight on the Proportioning Valve! C-Ya,

[Gene-C]

I have the same brake set up as you , i did not install a valve. I do not have any problems except that is is hard to lock them up on the street... the 31'' tires have something to do with that. I am going to swap the drum cylinders in the future or add rear disk. I had my buddy with me the other day we are both 250 ish and i was going 80 down hill and everyone locked them up.. holly cra** it did not stop as fast as i wanted .. and this is why i will add the disk rears.mean while i give a little more space between me and the front car..