Low Air presure - Park Brake

[iamduane]

Low Air Pressure while driving and Park Brake Leaking air thru Actuator.

2006 Alpine 38FD

I had about 58,000 miles when I first noticed that it took a long time for the air to build up in order for the low air pressure alarm to stop even though the air bags were up. It took longer and longer for the low air pressure alarm to stop. I now have 60,000 miles on my 2006 Alpine 38FD and at first they thought that it was the air dryer and this may have contributed to the slow build up of air. An Air Pressure gauge was put on the air tank and it maintained 117 pounds; however, we found that the problem only occurred after the Park Brake was released, then we could hear air leaking for several seconds and the air pressure dropped to 50 pounds.

This can be tested with the engine off after air pressure is built up.
Unfortunately someone had to crawl under the RV to find the leak - be sure and block the RV and have someone with their foot on the brake when releasing the Park Brake. The final culprit seems to be that the Air Actuator for the Park Brake is leaking Air when release so it does not fully disengage the Park Brake.

The Original actuator part number KSHR2PT03A475YN or (HR2PT03A) from Haldex
- Midland - Maxibrake (It is no longer built except by special request). There is a rebuild kit from Haldex # MQ15708. The bad news is that it the parts have to made in Mexico and can take 3-6 weeks.

Mike was able to help me find the part and it seems to be working OK now. A replacement part number HP2PT04A was used. The difference seems to be in a slight difference in air pressure to activate the Actuator, a longer shaft that will need to be cut and the clevis assembly has a larger hole and pin (so I had to use the old pin that screwed onto the new Actuator. See picture below)



If the Air Park Brake is leaking then it will only show up when the Park Brake is released. Block the wheels, build air pressure, turn off the engine, then have someone step on the brake and release the Park Brake. That is the only time that air will leak out of the park brake and it will also do this while driving.

[jerichorick]

How long has it been since your air dryer was serviced?

[Algoma]

Originally Posted by iamduane

Low Air Pressure while driving and Park Brake Leaking air thru Actuator.

2006 Alpine 38FD

I had about 58,000 miles when I first noticed that it took a long time for the air to build up in order for the low air pressure alarm to stop even though the air bags were up. It took longer and longer for the low air pressure alarm to stop. I now have 60,000 miles on my 2006 Alpine 38FD and at first they thought that it was the air dryer and this may have contributed to the slow build up of air. An Air Pressure gauge was put on the air tank and it maintained 117 pounds; however, we found that the problem only occurred after the Park Brake was released, then we could hear air leaking for several seconds and the air pressure dropped to 50 pounds.

This can be tested with the engine off after air pressure is built up.
Unfortunately someone had to crawl under the RV to find the leak - be sure and block the RV and have someone with their foot on the brake when releasing the Park Brake. The final culprit seems to be that the Air Actuator for the Park Brake is leaking Air when release so it does not fully disengage the Park Brake.

The Original actuator part number KSHR2PT03A475YN or (HR2PT03A) from Haldex
- Midland - Maxibrake (It is no longer built except by special request). There is a rebuild kit from Haldex # MQ15708. The bad news is that it the parts have to made in Mexico and can take 3-6 weeks.

Mike was able to help me find the part and it seems to be working OK now. A replacement part number HP2PT04A was used. The difference seems to be in a slight difference in air pressure to activate the Actuator, a longer shaft that will need to be cut and the clevis assembly has a larger hole and pin (so I had to use the old pin that screwed onto the new Actuator. See picture below)



If the Air Park Brake is leaking then it will only show up when the Park Brake is released. Block the wheels, build air pressure, turn off the engine, then have someone step on the brake and release the Park Brake. That is the only time that air will leak out of the park brake and it will also do this while driving.

Doesn't make sense since you were reporting low build up while the parking brake was ON.

[iamduane]

I have only owned the 2006 Alpine 38FD since July or 2013 and it had about 56,000 miles. I don't know if the air dryer had been replace so I replaced it a couple of days before finding the Park Brake Acturator leak.

[EngineerMike]

John- It appears that once this issue presents due to the air release on parking brake developing a leak, it is an intermittent thing & it can "stick" the leak open when its cold. Old Forester was having the same issue, slow pressure build when cold sometimes, then more frequently. Others have had similar experience w/the leak impeding building of chassis air pressure.

[Algoma]

Mike, I understand what you are saying but to quote iamduane:
"we found that the problem only occurred after the Park Brake was released, that is the only time that air will leak out of the park brake".
Maybe his description is not totally accurate.

[docj]

Originally Posted by Algoma

Mike, I understand what you are saying but to quote iamduane:
"we found that the problem only occurred after the Park Brake was released, that is the only time that air will leak out of the park brake".
Maybe his description is not totally accurate.

Don't forget that "releasing" the parking brake pressurizes the actuator. The parking brake is held in the "OFF" position by air pressure so that it is fail-safe and actuates if pressure is lost.

I may not own an Alpine, but we have a very similar parking brake actuator on our Beaver (part #HR2PT02A). Ours failed almost totally last summer and it was evidenced by an inability to release the brake and a loud hissing of air when we tried to do so. Fortunately, by repeatedly taking it on and off, we were able to get it to release enough to drive to where we could get it replaced. Because the actuator is only pressurized when the brake has been released the only time you experience the problem noted by the OP is when the brake is OFF!

During the repair we did discover that the failure had probably been taking place slowly over time long before the catastrophic failure we had noticed. Our parking brake is on a caliper/rotor system attached to the drive shaft and it appeared as if the actuator had been failing enough for the brake pads to have been dragging on the rotor for quite some time. One pad was completely worn through to the point where the underlying metal substrate was almost gone. After replacing the actuator and the brake pads, it appeared to me that the coach's air usage during driving had been reduced, as if there had been a slow leak possibly for a long time; that's hard to prove but I think it was the case.

[EngineerMike]

My comments were/are intended to pull together a series of experiences so that future searches will lead anybody having issues to a full discussion of whuzzup (either actually or potentially).

[jerichorick]

Originally Posted by iamduane

I have only owned the 2006 Alpine 38FD since July or 2013 and it had about 56,000 miles. I don't know if the air dryer had been replace so I replaced it a couple of days before finding the Park Brake Acturator leak.

That was a good call on your part. But now the leak? I wonder if dirt got pushed through some how. That thought is not fixing your problem.

Freightliner has RV service stations at several of their truck repair centers. It is called Oasis Service. I have no idea if they will work on your coach but I would give them a shot. You have done a good job at finding and fixing problems to this point. I hope someone comes up with a better way to go than what I have suggested.

[docj]

Originally Posted by jerichorick

That was a good call on your part. But now the leak? I wonder if dirt got pushed through some how. That thought is not fixing your problem.

Freightliner has RV service stations at several of their truck repair centers. It is called Oasis Service. I have no idea if they will work on your coach but I would give them a shot. You have done a good job at finding and fixing problems to this point. I hope someone comes up with a better way to go than what I have suggested.

I don't know about the the cause of the OP's leak but ours was simply a mechanical failure at the "bellows" that permits the actuator rod to move in and out. It had nothing to do with dirt from the air dryer, etc. Since his actuator and ours are basically the same, I presume something similar happened to his.

[EngineerMike]

The "bellows" has an annular space around the can allowing air in & out as the o-ring-sealed piston moves. This space allows dirt, water spray, salt, gritty grease flung off the u-joints, etc in where it can wear the o-ring. This may contribute to actuator failure.
IMO an improved installation would be to add a strip of fabric covering the annular space, zip tied in place, as a filter for the air exchange to minimize dirt intrusion.
You can see the annular space on the photos where the circumference necks down maybe 3/16" between the radial bolt heads & the fat 2-bolt flange.

[docj]

Mike:

I don't at all disagree with your approach. However, the installation procedure for our MH was extremely "tight" with barely enough room for the tech to reach the parts. I'll be content if I can get another 10-12 years on this actuator. I probably won't be driving any longer than that, anyway.

Joel

[jerichorick]

Originally Posted by iamduane

I have only owned the 2006 Alpine 38FD since July or 2013 and it had about 56,000 miles. I don't know if the air dryer had been replace so I replaced it a couple of days before finding the Park Brake Acturator leak.

I am not even close to being a air break guru. With that said, you can understand how this is only speculation and a rough one at that.

I know there is a pressure relief valve in the system. I think I have heard it called a pop off valve. Has this thing been checked? As I understand the way it works, you can think of it as a T&P safety valve as on your water heater. If the pressure gets too high it releases until the pressure drops to safe limits. I hear my pop off valve release often. If this were not resealing correctly it would be a air leak in the happening.

Hope this helps.
Rick

[Algoma]

Originally Posted by jerichorick

I am not even close to being a air break guru. With that said, you can understand how this is only speculation and a rough one at that.

I know there is a pressure relief valve in the system. I think I have heard it called a pop off valve. Has this thing been checked? As I understand the way it works, you can think of it as a T&P safety valve as on your water heater. If the pressure gets too high it releases until the pressure drops to safe limits. I hear my pop off valve release often. If this were not resealing correctly it would be a air leak in the happening.

Hope this helps.
Rick

What you are hearing is the purge valve in the air dryer. This is not a pressure safety valve but is removing the moisture from the dryer.