CA Trucking Posted March 30, 2017 Share Posted March 30, 2017 Good morning, I'm new to this site and to dump trucks. I have a 2004 Mack Granite and when I engage the parking brake it doesn't engage right away. Any ideas on where to start. I have checked for air leaks at the brakes and didn't find any. Any advise would be much appreciated Quote Link to comment Share on other sites More sharing options...
j hancock Posted March 31, 2017 Share Posted March 31, 2017 Plugged line somehow? Has this been going on for a while or all of a sudden? Quote JimIt doesn't cost anything to pay attention. Link to comment Share on other sites More sharing options...
CA Trucking Posted April 1, 2017 Author Share Posted April 1, 2017 Hi Jim, Thanks for the reply. I noticed it after buying it. So with me it's been the whole time. it does engage but takes about 5 or 10 seconds. Also I just replace an abs solenoid. it was pouring out Air and couldn't build up enough air pressure to release the parking brake. The parts guy stated that I had blow back coming from the out side of the solenoid. Quote Link to comment Share on other sites More sharing options...
j hancock Posted April 2, 2017 Share Posted April 2, 2017 If under normal driving the brakes are working well, the adjustment and lubrication of the cams is probably good. There is mega pressure from the spring in the brake chamber to engage the shoes so something is not dumping air like it should. Control valve or QR??? This Bendix info may be helpful. http://www.suspensionspecialists.com/techinfo/Bendix_Brake_Handbook_2009.pdf Quote JimIt doesn't cost anything to pay attention. Link to comment Share on other sites More sharing options...
BGarofalo Posted April 2, 2017 Share Posted April 2, 2017 Kinked or blocked vent line from dash valve will cause slow engagement of park brakes. Just trace line from back of dash valve. Usually just dumps out side of firewall. Quote Link to comment Share on other sites More sharing options...
CA Trucking Posted April 3, 2017 Author Share Posted April 3, 2017 Thank you Both I will check on Both of those today Quote Link to comment Share on other sites More sharing options...
MackTech Posted April 9, 2017 Share Posted April 9, 2017 I could also be the spring brake inversion valve (I think they used the Bendix SR7 valve back then in Granites, nowadays they use the Wabco IR2 valve) there could be problems there or with any of the lines connected. On the SR7 there typically was a supply line from the secondary to a check valve on the SR7, a trigger line from the firewall, a balance line from the service relay, and delivery lines to the spring brakes. There might have been one other line that went to the front secondary brake circuit as well. Quote Link to comment Share on other sites More sharing options...
Swishy Posted April 9, 2017 Share Posted April 9, 2017 When U add up all the air to release the parking brake = a lot of air n if it was to return to where it came from (dash control) it would take quite a few seconds to get the spring to apply the parking brakes so to dump the air quicker they have a Quik Release Valve @ each axle th@ has the spring parking brakes on normally parking brakes will apply with in a millisecound (give or take a duz) check out u're QRV cya §wishy 1 Quote Link to comment Share on other sites More sharing options...
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