R600 Brakes Not Releasing

[r600]

hi,can anyone help me with the rear brakes not releasing properly when i let the maxi brake switch off on the dash,all four brakes are slow to come off,maybe its the foot valve because both release at the same slow speed if it was a relay valve in the chassis i think one side maybe slow and the other fast and seems to be better when service brake used???maybe its not the foot valve ???help thanks adrian

[DigDug]

Have you checked the brake pedal for corrosion or dirt build up? Sounds silly but its where to start. Good luck. doug

[Mike]

hi,can anyone help me with the rear brakes not releasing properly when i let the maxi brake switch off on the dash,all four brakes are slow to come off,maybe its the foot valve because both release at the same slow speed if it was a relay valve in the chassis i think one side maybe slow and the other fast and seems to be better when service brake used???maybe its not the foot valve ???help thanks adrian

Adrian,

How old are the diaphrams? And is it passing much oil? If not, then I would be checking the foot valve and other valves for freedom to operate.

mike

[mopar]

I does sound like one for the vavle might be plugged along with the vavle I would check the wheel seals too

of course some thing I would ask Rob on.

[r600]

ok,no the pedals not stuck work freely,the chambers are old but what i dont thik its that because its all 4 rear release at the same slow pace and awhile ago i caged the spring and there was still heaps of tension on the spring,i have painted the chassis and dont want to pull every thing off if it can be helped,maybe rob will read this and throw some light on it ,cheers adrian

[Rob]

ok,no the pedals not stuck work freely,the chambers are old but what i dont thik its that because its all 4 rear release at the same slow pace and awhile ago i caged the spring and there was still heaps of tension on the spring,i have painted the chassis and dont want to pull every thing off if it can be helped,maybe rob will read this and throw some light on it ,cheers adrian

Hi Adrian, I would follow the air line from the emergency side of the brake chambers back to the quick release valve, the relay valve on frame fed from air tank, and the air tank check valve if there is one. It sounds to me like you have a valve that is very slow to function. Do the parking/spring brakes apply as soon as they are set? If they do then you can rule out the quick release valve as it's function in that application is to exhaust the air that is holding the parking brakes released quickly. Don't forget to evaluate the PP-1 valve in the dash that you actuate to release the brakes. If it is passing air through it slowly the relay valve will be slow to operate and you will have a slow release as you are experiencing. A slow relay valve will do the same thing in delaying the needed air to release the brakes.

Here is what I would do: Take the air line off at the pilot port of the relay valve. With the air built up in the truck but engine off, push the PP1 valve, (yellow handle) in and listen for a sudden rush of air at the disconnected fitting. You should hear this air escape immediately without delay or ramp up. If the air starts slow and increases in flow, replace your PP-1 valve in the dash. If the air rush is immediate and without delay, reconnect this pilot line and disconnect the lines that run to the emergency side of the brake chambers. Repeat as mentioned earlier. There should be no delay, or ramp up of escaping air pressure.

A relay valve has tank pressure on one side of it at all times. When the pilot port has air pressure applied to it, the relay valve opens allowing air pressure to pass through it to perform a function downstream. In this case, release the brakes.

Rob

[r600]

Hi Adrian, I would follow the air line from the emergency side of the brake chambers back to the quick release valve, the relay valve on frame fed from air tank, and the air tank check valve if there is one. It sounds to me like you have a valve that is very slow to function. Do the parking/spring brakes apply as soon as they are set? If they do then you can rule out the quick release valve as it's function in that application is to exhaust the air that is holding the parking brakes released quickly. Don't forget to evaluate the PP-1 valve in the dash that you actuate to release the brakes. If it is passing air through it slowly the relay valve will be slow to operate and you will have a slow release as you are experiencing. A slow relay valve will do the same thing in delaying the needed air to release the brakes.

Here is what I would do: Take the air line off at the pilot port of the relay valve. With the air built up in the truck but engine off, push the PP1 valve, (yellow handle) in and listen for a sudden rush of air at the disconnected fitting. You should hear this air escape immediately without delay or ramp up. If the air starts slow and increases in flow, replace your PP-1 valve in the dash. If the air rush is immediate and without delay, reconnect this pilot line and disconnect the lines that run to the emergency side of the brake chambers. Repeat as mentioned earlier. There should be no delay, or ramp up of escaping air pressure.

A relay valve has tank pressure on one side of it at all times. When the pilot port has air pressure applied to it, the relay valve opens allowing air pressure to pass through it to perform a function downstream. In this case, release the brakes.

Rob

thanks rob,i'll check that on the weekend and let you know,cheers adrian

[Rob]

thanks rob,i'll check that on the weekend and let you know,cheers adrian

Forgot to mention to check for air leaks at hoses, and connections etc. Use soapy water if necessary. When the brakes are released does the truck leak air at any of the chambers? You may need to have the engine shut off with the brakes released to hear this. If air is escaping as the emergency, (spring brake) side of the chambers are charged, they will be slow to release. A rapid leak of air pressure will be easily detected without the engine running.

I always check air functions and operations with shop air supplied to the truck under test so I don't have the engine running.

Rob

[fjh]

Forgot to mention to check for air leaks at hoses, and connections etc. Use soapy water if necessary. When the brakes are released does the truck leak air at any of the chambers? You may need to have the engine shut off with the brakes released to hear this. If air is escaping as the emergency, (spring brake) side of the chambers are charged, they will be slow to release. A rapid leak of air pressure will be easily detected without the engine running.

I always check air functions and operations with shop air supplied to the truck under test so I don't have the engine running.

Rob

I have run across the main air line that feeds the spring brake relay plugged with goo causing a slow or no release problem just another thingto look for.