Parking Brake Won’t Release

[JoeShahan]

I have a 2005 International CE300, with hydraulic brakes. I can’t get the parking brake to release and need to move the bus. I know how to compress the spring brakes on a bus with air brakes, but don’t even know how the parking brake works in this one, other than it being activated via an electrical switch. And the fuse for that that circuit is not blown. I appreciate and wisdom that anyone can share with me on this. Mahalo from Hawaii. Joe

 

[BamaBus]

Use the search bar and look for "brake release". Have you done any demo or any changes to the wiring? Could be an issue with the interlock system related to a door being open or removed.

 

[nikitis]

I have no experience with hydrolic brakes, however I do know the principle behind how they work and if a brake is hydrolickly locked it usually means its under pressure somewhere and that pressure will need to be released. I would think there has to be a relief valve or screw somewhere to release pressure which will get you moving but you'd have to also retighten the relief valve or screw before driving or you'll have no brakes, and if they aren't in working condition it may not be safe to move as you won't be able to stop. Might have to have someone come out to fix them in place.

I wish you luck. Someone else more experienced should comment and help this person out.

 

[Samarath]

If you have Wabco brakes, and it is the sustem I have, then there is a collar on your driveshaft with brake shoes. This system uses Spring Applied Hydraulic Release. If your rear hydraulic circuit isn't building/holding pressure, then the pb will not release. Is your brake psi light on? A scangauge can see brake psi, or you can subscribe to wabco software and use a nexiq to monitor brake psi on a laptop. In a situation that you have to move, and your front brakes seem to function, you can remove the cable goong from the SAHR canister on the inside of the driver side frame rail to the PB drum just in front of your rear diff.

Obviously there are saftey concerns and you shouldnt do this if you plan on going on the road. The reason your PB wont unlock is a saftey feature. If your brakes fail in motion, your PB is an emergancy feature and locks up via the spring applied brake drum on the driveshaft.

Maybe it is something else. I have an 07 IC CE 200 with hydraulic brakes.

 

[JoeShahan]

Use the search bar and look for "brake release". Have you done any demo or any changes to the wiring? Could be an issue with the interlock system related to a door being open or removed.

Hi Bama Bus. No modification yet. Got it home, then went to move it and no go. When I have searched Google, the only results showed how to apply the brake with the switch, which was really useless. I’ll try searching here to see what shows up.

 

[JoeShahan]

If you have Wabco brakes, and it is the sustem I have, then there is a collar on your driveshaft with brake shoes. This system uses Spring Applied Hydraulic Release. If your rear hydraulic circuit isn't building/holding pressure, then the pb will not release. Is your brake psi light on? A scangauge can see brake psi, or you can subscribe to wabco software and use a nexiq to monitor brake psi on a laptop. In a situation that you have to move, and your front brakes seem to function, you can remove the cable goong from the SAHR canister on the inside of the driver side frame rail to the PB drum just in front of your rear diff.

Obviously there are saftey concerns and you shouldnt do this if you plan on going on the road. The reason your PB wont unlock is a saftey feature. If your brakes fail in motion, your PB is an emergancy feature and locks up via the spring applied brake drum on the driveshaft.

Maybe it is something else. I have an 07 IC CE 200 with hydraulic brakes.

Hi Samarath, Thank you for the info. That gives my some things to explore.

 

[Samarath]

Hi Samarath, Thank you for the info. That gives my some things to explore.

Also, Wabco has a pretty great tech support. I won't say that I like the system/design, but they walked me through some diagnosis and repairs. I have some manuals that may apply to you.

I cant upload them.

https://www.zf.com/products/media/automotive/cv/literature_downloads_wna/truck_solutions/hydraulic_power_brake_maintenance_manuals/MM0401_web.pdf

If you can get the manual, then you can do some electrical testing. When you turn the key on, do the electric pumps kick on? You should hear two motors. If you only hear one, you're not building pressure in the front or rear circuit. On my bus, there is a 30amp maxi fuse inside the battery box, and two 30amp maxi fuses under the hood against the firewall.

 

[JoeShahan]

You nailed that one Samaranth. I would never thought to look on the drive line. There is the main pump near the front which comes on, and what appears to be a secondary pump, or maybe relay, toward the back with a line going directly to the brake on the drive line. That one is silent. The mechanics at the the bus yard who got the bus ready for me, had this issue, and they said they simply replaced the fuse, then it worked. I suspect that was just a coincidence that it worked, though it still worked when I brought it home a week later. A quick look at the manual you sent the link for doesn't show the rearward pump, at least not on my quick look so far. I'll read further when I have more time. I may go ahead and try the fuse trick just to see, though none of the fuses are blown, just as they weren't when the mechanics swapped the fuses.

 

[Samarath]

You nailed that one Samaranth. I would never thought to look on the drive line. There is the main pump near the front which comes on, and what appears to be a secondary pump, or maybe relay, toward the back with a line going directly to the brake on the drive line. That one is silent. The mechanics at the the bus yard who got the bus ready for me, had this issue, and they said they simply replaced the fuse, then it worked. I suspect that was just a coincidence that it worked, though it still worked when I brought it home a week later. A quick look at the manual you sent the link for doesn't show the rearward pump, at least not on my quick look so far. I'll read further when I have more time. I may go ahead and try the fuse trick just to see, though none of the fuses are blown, just as they weren't when the mechanics swapped the fuses.

The SAHR canister isn't manufactered by Wabco. It is an optional feature that Wabco supports. The manual invludes info on how to bleed the system, but it doesn't go into detail on the canister itself. Under the driver seat, or a little back is the Hydraulic Compact Unit which includes two electric pumps, two hydraulic fluid accumulators (storing 2k psi normally), a second hydraulic fluid resevior, and the ABS Electronic Control Unit. There are two wire harnesses. One is direct power from the battery to the front(I think) hydraulic pump. The other harness has the communication as well as power for the other pump. When you turn the KOEO, you should hear both pumps harmonizing and you should also see the brake fluid resevior empty a considerable amount as the accumalators are filled. The only reason to mess with the SAHR Canister is to crawl to another location. I should add that it is an unsafe crawl. I learned these details about my brake aystem when my brakes completely failed in Craig Colorado. I was ignorant of the system and the original owners had cut the PB cable. We used chocks when we stopped. Anyway, we survived a scarey day, so be careful. If you diagnose the HCU, you can load test some power supply and check for all of the continuity issues, shorts, etc with the proper manual and a few basic tools. Maybe jumper cables, a headlight, and a multimeter.

 

[Samarath]

One more thing. They may have replaced a fuse and it worked again, not because the fuse was bad, but because the fuse terminals could have been sloppy or corroded. I gave my terminals for the 30amp fuses under the hood at the firewall a squeeze with a pair of needlenose when one of my pumps didn't kick on. It saved the day that day. Anyway, good luck and hopefully you know what to look for anyway.

Oh, and also make sure your brake lights come on when you hit the brakes. It could be a switch not communicating that your brakes are applied and that it's okay to disengage the PB

 

[JoeShahan]

Well, I'm not entirely sure what's going on with the parking brake, I started the bus after recharging the batteries yesterday, and got it to move once, put the brake back on, released it again, the bus moved again, then I put the brake back on again, and then it wouldn't release. We just needed to move the location of the bus within our property as we're turning it into place for guests. Today I tried it, no go, so I removed and either replaced (where I had the proper fuse on hand) or repeatedly removed and inserted the existing fuse where I didn't have a replacement. Only this time we had the path clear to move the bus. As soon as I got it to move, we got it moved to it's final resting place. The only reason I even needed a running bus is that our driveway is too hilly and twisty to get for a large tow truck and the bus to navigate it. Plus we knew we would need to relocate it to a final place on the property. The only reason I knew I would be able to drive the bus in, is that we have had 5,000 gallon water trucks navigate our driveway to refill our water catchment tank. Thank's for all the help. Mahalo

 

[Samarath]

If there are no warning lights, and your brake lights function, it is potentially the PB knob/wiring.

If it is an issue with your brakes, you should have a red lamp and an audible warning. Your brake pedal sends a low psi hydraulic signal to the HCU and the HCU computer uses that to apply the brakes at each wheel via valves, adjusting for wheels that may be sliding with information from the Vehicle Speed Sensor at each wheel.

The VSS gauges speed from teeth on the inside of your rotors. Someone somewhere (schoolbusfleet.com?) said something about an error with that system causing an interlock situation.

It could also be that the PB is actually rusted inside the drum.

Did I already ask if both electric pumps are kicking on when you turn the key on? Also, even with the key off, when you hit the brakes, you should have one electric pump kick on.