seyser Posted July 18 Share Posted July 18 I have what I believe to be a faulty front relay valve. When I first air the truck up and release the parking brake I can move the truck as normal until I first press the service brake then the brakes are locked on. We removed and capped the air line that goes from the relay and feeds the front axle and then the brakes act as normal. Does this sound like a bad relay valve? I found the same one on ebay and it should be here today. Haldex 28071. When I remove the nylon air lines can I reuse them as is or do they need to be cut shorter with a new ferrule added? They are already as short as can be so that would involve making a junction on all lines or replacing the whole length which I hope I don't have to do. Quote Link to comment https://www.bigmacktrucks.com/topic/74353-replacing-air-relay/ Share on other sites More sharing options...
Geoff Weeks Posted July 18 Share Posted July 18 By "front axle" I think you mean front drive axle and not steer axle? You have a black line that is next to the one you capped, where does it go, and does the thing it is connected to work? Put a pressure gauge in the plugged port and see if there is pressure there when the brake is applied and then released. You should see pressure when applied and none when released. Relay valves are similar to electric relays, in that they have a control that manipulates the output. They can fail in the same way. either the input can be faulty or the output is not following the input. The first is not the relay's fault it is what ever supplies the input. In short it could be, but it isn't 100% what is at fault you need more diagnoses. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/74353-replacing-air-relay/#findComment-555476 Share on other sites More sharing options...
seyser Posted July 18 Author Share Posted July 18 (edited) Correct yes the front drive axle. I would have to follow the other lines but I know one or two go back to another relay for the brakes on the rear drive axle. After first applying the service brakes there is air coming out of this plugged port regardless if the pedal is pressed or not. I assume it should only be pressurized when the pedal is pressed as to activate the brake cans. Edited July 18 by seyser Quote Link to comment https://www.bigmacktrucks.com/topic/74353-replacing-air-relay/#findComment-555477 Share on other sites More sharing options...
Geoff Weeks Posted July 18 Share Posted July 18 That should be the one on top that "T"s into the relay and the large one at the far left of the picture. Disconnect the other black one that was next to the one you plugged. When you step on the brakes air should come out the valve but none out of the disconnected black line. If the rear relay is working correctly, and you don't get air out of the black line next to the one you plugged, then the relay is a good bet to be the problem. If you have air coming out the black line, then you have more work to do. Quote Link to comment https://www.bigmacktrucks.com/topic/74353-replacing-air-relay/#findComment-555480 Share on other sites More sharing options...
seyser Posted July 18 Author Share Posted July 18 Can I just unscrew the nut holding the air line and pull it out? Can they then be reinserted and reused as is? Quote Link to comment https://www.bigmacktrucks.com/topic/74353-replacing-air-relay/#findComment-555481 Share on other sites More sharing options...
Geoff Weeks Posted July 18 Share Posted July 18 yes. as long as the nut isn't bound to the Ferrel on the tube, where the tube want to turn with the nut. Often you can work it back and forth with a little oil and get it to break free. Quote Link to comment https://www.bigmacktrucks.com/topic/74353-replacing-air-relay/#findComment-555482 Share on other sites More sharing options...
seyser Posted July 18 Author Share Posted July 18 Sounds good! Quote Link to comment https://www.bigmacktrucks.com/topic/74353-replacing-air-relay/#findComment-555483 Share on other sites More sharing options...
Geoff Weeks Posted July 18 Share Posted July 18 Here are some picture of shoes with wear limits on them. On the picture of the V notch, you can clearly see where the V goes to a vertical slot. Once the shoe has worn to that point it is time to change. The next picture shows a line on the side of the lining, the lining becomes a little wider at that point, when the shoe has worn to the line, it is time to change. I don't have a shoe with the 1/2 moon ground on the lining to show you. Quote Link to comment https://www.bigmacktrucks.com/topic/74353-replacing-air-relay/#findComment-555484 Share on other sites More sharing options...
seyser Posted July 18 Author Share Posted July 18 Very good! That's a great referance. Quote Link to comment https://www.bigmacktrucks.com/topic/74353-replacing-air-relay/#findComment-555485 Share on other sites More sharing options...
Joey Mack Posted July 18 Share Posted July 18 so 1 brake appication locks the brakes? for how long? do you hear a slow hissing before the brakes reales with foot off the pedal? that valve looks crappy anyway, change it, what condition is the park brake valve. likely an R-12 valve.. Quote Link to comment https://www.bigmacktrucks.com/topic/74353-replacing-air-relay/#findComment-555501 Share on other sites More sharing options...
Mark T Posted July 19 Share Posted July 19 Sure it's not a quick release valve gone bad ? Pedal isn't sticking ? If it sat around, sometimes those bugs that make their house out of mud love doing it in air exhaust ports . Then stuff won't work because it doesn't exhaust. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/74353-replacing-air-relay/#findComment-555502 Share on other sites More sharing options...
Joey Mack Posted July 19 Share Posted July 19 well the profile picture is an 'R' model.. definatley possible that the plunger under the brake pedal is sticking.. 1 1 Quote Link to comment https://www.bigmacktrucks.com/topic/74353-replacing-air-relay/#findComment-555503 Share on other sites More sharing options...
seyser Posted July 19 Author Share Posted July 19 Yes the brakes lock on with 1 application of the foot brake. The cap that was put on the relay is the wrong threads but it kinda seals. After the brakes lock on I can hear constant air blowing out of that port. I purchased the truck in this condition. The original owner died and his wife consigned the truck through the local CAT dealer. The brakes were locked and the mechanic removed that hose and capped the relay so it could get loaded on the lowboy. Quote Link to comment https://www.bigmacktrucks.com/topic/74353-replacing-air-relay/#findComment-555506 Share on other sites More sharing options...
Joey Mack Posted July 19 Share Posted July 19 is the rubber boot still under the brake pedal? just for fun, spray Kroil into the piston inder the brake pedal, with full air pressure on the truck, and use short strokes to work the Kroil into the piston, you may get lucky, or at leaste find the issue, and know where to go to fixi it. Quote Link to comment https://www.bigmacktrucks.com/topic/74353-replacing-air-relay/#findComment-555507 Share on other sites More sharing options...
seyser Posted July 19 Author Share Posted July 19 I can give that a try too. The brake relay will be here tomorrow so I will probably put that on. The brakes act like normal with that hose removed and port capped. Makes me think it’s the relay. Quote Link to comment https://www.bigmacktrucks.com/topic/74353-replacing-air-relay/#findComment-555508 Share on other sites More sharing options...
Joey Mack Posted July 19 Share Posted July 19 all good. just know that those floor mounted treadle valves will stick. everything on your boot lands on the pedal, hinge, and plunger.. any pen. oil on a regular basis will help.. anti sieze it when you have it apart.. you got this... Quote Link to comment https://www.bigmacktrucks.com/topic/74353-replacing-air-relay/#findComment-555509 Share on other sites More sharing options...
seyser Posted July 19 Author Share Posted July 19 Quote Link to comment https://www.bigmacktrucks.com/topic/74353-replacing-air-relay/#findComment-555510 Share on other sites More sharing options...
Joey Mack Posted July 19 Share Posted July 19 yep... looks clean on the outside, pull the pedal pin and pull the plunger out of the hole and see if it could use some lube,, maint. thingy is all.. Quote Link to comment https://www.bigmacktrucks.com/topic/74353-replacing-air-relay/#findComment-555511 Share on other sites More sharing options...
seyser Posted July 19 Author Share Posted July 19 Just looking under the relay and it looks pretty cruddy. Quote Link to comment https://www.bigmacktrucks.com/topic/74353-replacing-air-relay/#findComment-555512 Share on other sites More sharing options...
Joey Mack Posted July 19 Share Posted July 19 It does,, but one good thing I dont see.... is black oil... Know what I mean.. ? Quote Link to comment https://www.bigmacktrucks.com/topic/74353-replacing-air-relay/#findComment-555513 Share on other sites More sharing options...
seyser Posted July 19 Author Share Posted July 19 I hear ya! 1 Quote Link to comment https://www.bigmacktrucks.com/topic/74353-replacing-air-relay/#findComment-555517 Share on other sites More sharing options...
seyser Posted July 22 Author Share Posted July 22 (edited) Well I installed the new relay and still have the same problem. Possible bad quick release was mentioned. I will have to dig further into this. Edited July 22 by seyser Quote Link to comment https://www.bigmacktrucks.com/topic/74353-replacing-air-relay/#findComment-555666 Share on other sites More sharing options...
Joey Mack Posted July 22 Share Posted July 22 Did you clean the plunger under the brake pedal? Quote Link to comment https://www.bigmacktrucks.com/topic/74353-replacing-air-relay/#findComment-555667 Share on other sites More sharing options...
seyser Posted July 22 Author Share Posted July 22 I didn't get that far. The service brakes appear to work great though with that rubber hose unhooked and relay capped. It appears to just be an issue with the parking brake? Could I possibly have a bad air chamber on the front drive axle? This is the only place that uses the parking brake style air chambers. Quote Link to comment https://www.bigmacktrucks.com/topic/74353-replacing-air-relay/#findComment-555672 Share on other sites More sharing options...
fjh Posted July 22 Share Posted July 22 18 minutes ago, seyser said: I didn't get that far. The service brakes appear to work great though with that rubber hose unhooked and relay capped. It appears to just be an issue with the parking brake? Could I possibly have a bad air chamber on the front drive axle? This is the only place that uses the parking brake style air chambers. If its a spring brake chamber with brakes released you should have air coming out the bottom of the relay an or the foot valve with the brakes released! the piggy back shown in the pic looks fairly new how old is the other side? Quote Link to comment https://www.bigmacktrucks.com/topic/74353-replacing-air-relay/#findComment-555677 Share on other sites More sharing options...
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