Brake pressure regulator - Wayne's question of the week

Randy in Maine · Post by **Randy in Maine** » Wed Mar 21, 2007 2:30 pm

I guess only wayne can get by with that line, eh?

Why do we have brake pressure regulators?

Is it because our brakes are disc up front and drum in the rear and they (disc vs drum) require a different pressure "signature"?

Or is a weight issue where most of the weight is in the rear of the bus (or truck or whatever) and we do not want the lighter rear to "lock up" when there is no weight back there?

Or is because the front brakes do most of the braking and we want to send more fluid pressure there for that reason? Possibly a "power brake thing?

Did cars with 4 wheel drum brakes use them? Cars with 4 wheel disc brakes use them? My first one that I can recall was my 71 Datsun PL-521 pick up (disc/drum) and my 77 Jeep J-20 Pick up (disc/drum)

I cannot remember if my splitties or non-fat beetles had them. I had a 72 gia and I never looked to see if it had a brake pressure regulator.

Just wondering.

Randy in Maine

Post by **Amskeptic** » Wed Mar 21, 2007 8:02 pm

Randy in Maine wrote: I guess only wayne can get by with that line, eh?
Why do we have brake pressure regulators?

The fluid pressure dynamics favor drum brakes. Drum brakes have this great leverage between the anchor and the wheel cylinder that disk pads do not. Because disk circuit pressures have to be higher and use more volume than drums, the master cylinder is more likely to lock up the rears on disk/drum than drum/drum. VW's lovely little system turned out to be elegant and extremely adaptable to the bus chassis because the VW bus has probably the greatest pitch under braking of any vehicle ever sold. The inertia style regulator is right at home in a bus when that chassis does the nose-drop, and it works extremely well on steep downhills too even when you are not braking like a maniac. Most every disk/drum set-up requires a regulator to synchronize brake application between the disk circuit and the drum circuit.
Colin

covelo · Post by **covelo** » Wed Mar 21, 2007 10:22 pm

Don't try the reverse: backing down a steep dirt track with bad traction. You touch the brake, the front locks up, and no steering. This is how we ended up having to be towed by a Nissan pickup in Covelo one rainy spring day.

Post by **Amskeptic** » Thu Mar 22, 2007 7:48 am

covelo wrote:Don't try the reverse: backing down a steep dirt track with bad traction. You touch the brake, the front locks up, and no steering. This is how we ended up having to be towed by a Nissan pickup in Covelo one rainy spring day.

You are so correct, covelo. But you try to save yer ass in that circumstance by very aggressive stab-n-steer cadence braking. That is where you hit the brakes hard so the rears can slow you down, release to steer, hit the brakes hard, release to steer, hit the brakes hard, etc.
Try to avoid it though.
Colin

Gypsie · Post by **Gypsie** » Sun Mar 25, 2007 6:10 pm

Just wondering if a bit of parking brake would help balance the braking load in this backing down situation? I have used this method and wonder if there is any reason that I should not. I use this method for uphill starts as well.

Post by **Amskeptic** » Mon Mar 26, 2007 8:07 am

Gypsie wrote:Just wondering if a bit of parking brake would help balance the braking load in this backing down situation? I have used this method and wonder if there is any reason that I should not. I use this method for uphill starts as well.

An excellent suggestion. Automatic transmission buses can stay in forward low while backing down also (see PV4 mag 1972-3 bus at Saddleback Hill)

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Brake pressure regulator - Wayne's question of the week

Brake pressure regulator - Wayne's question of the week

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