hi everyone well here s my headache i have going for me now I got a 769d that the brakes were not holding ! We tore it all down to find plates and discs had had it,so we replace them all and all 36 springs for the mechanical side of the parking brake.We also rebuilt the calipers while we were at this point . Put machine back together bleed service side and parking brake side . Now we go to test it out release parking brake put it in gear and the parking light is flashing and the alarm is going off ????? Where do I go from here I have no manuals so I m here reaching out for help?????
Does the truck actually move (or can you push/pull it) when you release the parking brake while it is still in neutral...? Either that or a pressure test will tell you if the parking brake is actually releasing. I know from experience it's easy to "shave" brake piston seals when you install the piston into the housing and cause them to fail the first time they get pressure one them.
Do you have the S/N or prefix? I might be able to find a trouble shooting chart or something that might help.
IIRC the parking brake/transmission interlock looks for pressure in the parking brake circuit. Engaging any gear if the pressure switch is not closed will set off the alarm. Hence my question if the truck wants to move or exhibits any signs of the park brake coming off without putting it into gear. If it does move then troubleshoot the park brake pressure switch, if it doesn't troubleshoot the recently-rebuilt brakes
I pressure tested the calipers on the truck and both sides hold pressure . It almost seems like the right side is a little lazy to release but then wouldnt the left side be that way too???
What we need right now is a Serial Number. I'm looking at BBB-prefix just as an example but I'll bet they are all the same. With the truck in neutral if you put the park brake control valve in the "off" position do you have any pressure in the hydraulic lines at the front calipers..? You should have nothing. Rear brakes you need to test the pressure in the parking brake release line at each brake with the park brake in the off position, engine idling, trans in neutral.
While bleeding the brakes did you over/stroke the air over hydraulic cylinder? Look for a switch on the side of the cylinder. Switch is #7 in picture. If cylinder was overstroked rod # 9 will be sticking out. You should be able to push it back in flush. Sometimes if the switches have not been used for a long time they will fail to reset. Off the top of my head I can't recall if they are open or closed in normal use. You could disconnect the two wires and if that doesn't shut off the alarm try connecting them together. DO NOT leave this switch by-passed do this only to prove where the problem is, leaving it by-passed could lead to serious loss of control do to lack of warning when there is a fluid leak.
5TR00473 thank you guys for helping I been pulling my hair out
KSH, if it's a brake overstroke switch surely the alarm would come on immediately the key switch was turned on. According to the OP the alarm comes on when he releases the park brake and puts the transmission in gear. I still think it's the park brake interlock. The overstroke switches are normally closed and are wired in series through however many rotochambers there are on the machine. Open any switch and the alarm will go off. It won't stop until you push the pin back in unless there is something wrong with either the rotochamber or the switch itself. Thought to self. I wonder if a rotochamber got overstroked while they were bleeding the brakes..?
Was not 100% sure if the OP meant the alarm only came on when it was put in gear, but on second reading I think that was implied. From the operators manual: If the parking brake is engaged and the transmission is engaged, the alert indicator will come on, the action light will flash and the action alarm will sound. Release the parking brake. NOTE: If the overstroke switch is activated, the action light will flash and the action alarm will sound.
just wanted to thank you all it was the overstroke switch that was activated reset it problem solved thanks guys
Just let me know where to send the bill, late night and early morning trouble shooting is a little high priced than normal hours
Well done that man.............. To the OP - it's easy to not get all the air out the first time. I'd go back and bleed the brakes again after a week or so. You might be surprised how much air you get out. BTW, did you replace or recondition the slack adjusters..? I'd bet money they were the root cause of your rear brakes being worn out.