Technical removing brake compensator

[flisko]

i often wonder if rear brakes would be affected without rear brake compensators

failed mot once cuz of a rear brake compensator, rear foot brake with the faulty compensator wasnt braking sufficiently enough as oppose to other side, replacing the aforementioned compensator fixed that

did anyone actually try to remove it and wire brake pipe directy to rear brake cylinder

 

[portland_bill]

Don't remove it. If you by-pass it, you are likely to lock up the rear wheels when braking. This will make the car unstable as the locked rear wheels will try to overtake the front, so you spin. After the crash, the police will impound your car for inspection, they will find that you have by-passed the compensator, and your insurance company will abandon you.

 

[flisko]

rear wheels lock anyway when braking

 

[oldhammer]

rear wheels lock anyway when braking

Your car has defective brakes then if so,



The proportioning valve reduces the pressure to the rear brakes. Regardless of what type of brakes a car has, the rear brakes require less force than the front brakes.

The amount of brake force that can be applied to a wheel without locking it depends on the amount of weight on the wheel. More weight means more brake force can be applied. If you have ever slammed on your brakes, you know that an abrupt stop makes your car lean forward. The front gets lower and the back gets higher. This is because a lot of weight is transferred to the front of the car when you stop. Also, most cars have more weight over the front wheels to start with because that is where the engine is located.

If equal braking force were applied at all four wheels during a stop, the rear wheels would lock up before the front wheels. The proportioning valve only lets a certain portion of the pressure through to the rear wheels so that the front wheels apply more braking force. If the proportioning valve were set to 70 percent and the brake pressure were 1,000 pounds per square inch (psi) for the front brakes, the rear brakes would get 700 psi.

 

[flisko]

good explanation

 

[portland_bill]

rear wheels lock anyway when braking

You need to identify the cause and fix it. Changing the spec by removing the compensator will only make diagnosis and cure more difficult.

Check the compensator is working correctly.
Remove both rear drums and inspect for free movement, nothing seized, and no leaks and contaminated shoes.
Check both front brakes for proper operation. Rears seizing could be ineffective fronts.

 

[flisko]

You need to identify the cause and fix it. Changing the spec by removing the compensator will only make diagnosis and cure more difficult.

Check the compensator is working correctly.
Remove both rear drums and inspect for free movement, nothing seized, and no leaks and contaminated shoes.
Check both front brakes for proper operation. Rears seizing could be ineffective fronts.

how can i check for that

 

[portland_bill]

how can i check for that

I've not crawled underneath a Punto, but it looks similar to others I've seen. If there is a actuator of some sort, usually a rod that moves with the suspension, check that it moves freely, and that the piston inside the actuator moves with it. The rod changes the amount of pressure allowed through according to vehicle loading. A seized piston may cause too much or too little pressure according to where it has seized.

 

[flisko]

i posted a picture how it looks above, dont think u can check if it works, unless u are on those rollers where they check braking efficiency

 

[portland_bill]

The pic shows what it looks like, not how it is fitted or actuates. Without a diagram of how it is fitted, or a description of how it works, it is difficult to help further.

The brake roller tester will not test this, unless it is blocked. The roller tester checks if the brake is working within quite wide parameters, but is not affected by load or vehicle movement, as it is not moving.

Just looked at the classic Panda Haynes. Probably a similar unit. It is not like the ones on the Mirafiori and Argenta that are actuated by a lever form the suspension, so that operation cannot be tested.

To quote Haynes:
"The device is designed to prevent rear wheel lock up by limiting the pressure to the rear brakes during heavy applications of the foot pedal.
If the valve fails to function correctly and the rear wheels are found to lock then the regulator valve must be renewed as it is a sealed unit and cannot be repaired."

First check the brakes, front and rear as described earlier, to ensure condition and operation are good. Seized or partially seized calipers, seized or leaking wheel cylinders, contaminated linings, etc., must all be fixed first.

Find a quiet road and brake normally from 30mph.
Repeat, gradually braking harder each time, through to a full emergency stop.
The rear brakes should not lock. If they do, replace the compensator.

 

[flisko]

well i took them off and blew air in them, they are not blocked

maybe just got bad after 20 years

 

[oldhammer]

https://www.fiatforum.com/punto/304463-back-brakes-valves-99-punto.html

worth aread, @ flisko.

 

[flisko]

already read all the threads about it, but its not the same as that spring valve

 

[portland_bill]

The pic shows what it looks like, not how it is fitted or actuates. Without a diagram of how it is fitted, or a description of how it works, it is difficult to help further.

The brake roller tester will not test this, unless it is blocked. The roller tester checks if the brake is working within quite wide parameters, but is not affected by load or vehicle movement, as it is not moving.

Just looked at the classic Panda Haynes. Probably a similar unit. It is not like the ones on the Mirafiori and Argenta that are actuated by a lever form the suspension, so that operation cannot be tested.

To quote Haynes:
"The device is designed to prevent rear wheel lock up by limiting the pressure to the rear brakes during heavy applications of the foot pedal.
If the valve fails to function correctly and the rear wheels are found to lock then the regulator valve must be renewed as it is a sealed unit and cannot be repaired."

First check the brakes, front and rear as described earlier, to ensure condition and operation are good. Seized or partially seized calipers, seized or leaking wheel cylinders, contaminated linings, etc., must all be fixed first.

Find a quiet road and brake normally from 30mph.
Repeat, gradually braking harder each time, through to a full emergency stop.
The rear brakes should not lock. If they do, replace the compensator.

Can't see where I suggested blowing air through them.:bang:

well i took them off and blew air in them, they are not blocked

maybe just got bad after 20 years

Blowing air through them is unlikely to diagnose any fault.
Have you done ALL of the other checks as suggested?

The valves allow some pressure through, but close off when the pressure rises to a set amount, to prevent the back brakes locking. Air will go through easily where the "normal" pressure goes.
If the valve is stuck, it will not operate to restrict the pressure when it should and may allow the brakes to lock.
Carry out the stopping tests a described.

 

[oldhammer]

.
.
v

Read from where it says : Note,

 

[flisko]

when i was bleeding all brakes, fresh brake fluid came out in front and rear brakes, so that means rear brake compensators were opened or else i wouldnt see fresh fluid going out, there is a real difference in color between old and new fluid so cant mistake the two

only thing i didnt do is bleed in the sequnce u posted above, but that probably doesnt matter as car passed mot on 21.1.2014, after i changed rear compensator and cylinder

rear brakes lock if i slam the brakes rly hard on gravel road, havent tried on asphalt yet

 

[fingers99]

Need to try on tarmac. Most competition cars will have an adjustable brake bias to account -- in part -- for different road conditions.

 

[portland_bill]

when i was bleeding all brakes, fresh brake fluid came out in front and rear brakes, so that means rear brake compensators were opened or else i wouldnt see fresh fluid going out, there is a real difference in color between old and new fluid so cant mistake the two

rear brakes lock if i slam the brakes rly hard on gravel road, havent tried on asphalt yet

Pressure and flow are NOT the same.
When bleeding you are seeing flow, not pressure, so your logic is flawed.
The compensators will always allow some fluid to pass, even when seized. They then close completely when pressure rises above a preset level. This will not happen if seized.

Testing on a gravel road, like blowing air through, will achieve nothing in terms of diagnosis.

Are you sure you should be playing with brakes?:bang:

 

[flisko]

how do u actually test it then

 

[fingers99]

The only way to test for pressure is a pressure gauge. That said, unless you know what results to look for, it won't get you very far.

Tarmac is cheap and readily available on a road somewhere near you.