Sticky parking brake

[MyPrevost]

After a mid winter drive through salt and calcium chloride (xmas 2010), our parking brake is hanging up. Been able to release it by rocking back initially and then forth. Does this mechanism have any exposure to the elements? Does it use the same drive axle shoes that the service brake uses? I presume so. The service brakes seem to release normally. I’ve heard from others that this is common with ABS systems, but there is a correlation between when this sympton started and our only drive in the corrosive environment. Bottom line: is there something that needs my attention?

Oh, we have no slide outs.
Thanks.

 

Dan and Barb 2004 Royale XLII Huntley, Illinois Grand Cherokee CRD, 911 GTS, C43 amg

[MyPrevost]

If you have to rock backward a little before driving forward it is likely the shoes or pads have stuck to the drum or disk. Usually this is because they might have been damp when the bus was parked or it was humid or wet outside.

Your parking brakes are released by air which uses a diaphragm to push against a spring that engages the parking brake. When you apply the brake you hear air escaping. That is air being released behind the diaphragm allowing the very heavy spring to push your bakes on.

Depending on your type brakes (drum or disk) you may have a grease fitting at the brake shoe pivot point and slack adjuster, but other than that there is no lubrication required. If you wish you can see the brakes release by laying on the ground and looking under and across the coach to the opposite side drive wheel and you can see the slack adjuster move forward or back as brakes are applied and released. It is unlikely you have anything wrong with your brakes.

However…..it sounds like you have limited experience with an air brake system and I would suggest you do an internet search to find a DOT air brake check procedure and I urge you to use that every time as a pre-trip check. A good source is usually the commercial driver road test manual which also explains how the brakes work.

Jon and Di 2006 Liberty Elegant Lady, 2021
Jeep Grand Cherokee, 1950 Ford
Knoxville, TN

Owner of three Liberty Coaches since 1990

 

[MyPrevost]

If yours has disc on tag There is a common problem here.  There is no lube on slides that caliper runs on and when seals fail they start sticking  result draging  brake= fires.  Your year model is close to change over year for disc brakes.  I’m correcting frozen disc brake problem now on 98. If they would not release (parking brake) on tag . the book says lift tag to move bus.  Just what I am learning.   Bob     See   Knoor-Bremse on techmanual list under manfacturer list at prevostcar.

98 XLE home built triple slide-SW Indiana

[MyPrevost]

If yours has disc on tag There is a common problem here.  There is no lube on slides that caliper runs on and when seals fail they start sticking  result draging  brake= fires.  Your year model is close to change over year for disc brakes.  I’m correcting frozen disc brake problem now on 98. If they would not release (parking brake) on tag . the book says lift tag to move bus.  Just what I am learning.   Bob     See   Knoor-Bremse on techmanual list under manfacturer list at prevostcar.

98 XLE home built triple slide-SW Indiana

[MyPrevost]

I don’t believe that vintage coach has the K-B calipers so he would be able to see the slack adjuster which is not on later coaches. I’m not sure he has a tag axle parking brake.

But Bob brings up an excellent point. If you have disc brakes the caliper has to slide. Unless you can take off your wheels yourself it might require you to take the coach to someone to have them check to see if the calipers do slide. If you have drum brakes you will not have to check that. Infrequent use of our coaches creates a lot of problems never experienced by owners who use the coaches routinely and corrosion is one of the problems on moving parts.

Jon and Di 2006 Liberty Elegant Lady, 2021
Jeep Grand Cherokee, 1950 Ford
Knoxville, TN

Owner of three Liberty Coaches since 1990

 

[MyPrevost]

Thanks very much for your replies.
Our bus has disc brakes on the steer and tag, and the drive axle has drums. The parking brake acts only on the drive axle.
Called my trucker brother tonight, said there shouldn’t be anything exposed to the elements that would corrode and cause the parking brake to hang up. But he will Harley his way 5 hours to our place to check it out this weekend.
Yesterday, went to fill up with fuel (241 gallons), took 40 minutes. When pulling away sounded like the shoes were screaching against the drums for say 50 feet, but didn’t have to back up first to go forward as I did when I left the house.
Brother asked if it seemed I was losing air pressure after releasing parking brake, i.e. a leaking diaphram, answer, no. I think some pivot action in the shoes need attention.
For reference, been wrenching my own stuff the past 45 years, but the bus is new to me (about 7 years) so I lack experience but have all the air jacks and tools needed. So far have changed all the tires, air bags, front brake pads, and the Bendix AD9 dryer cartridge myself and enjoy the “work”.

Dan and Barb 2004 Royale XLII Huntley, Illinois
Grand Cherokee CRD, 911 GTS, C43 amg

[MyPrevost]

grease fitting for pivot shaft inside drake drum .couple shots only.  actuwates cam that expands shoes.  external fitting. Just throwing out ideas here. To much gets on shoes.  Only one set of shoes.  Good luck  Bob

98 XLE home built triple slide-SW Indiana

[MyPrevost]

Dan,

You likely have automatic slack adjusters. I would start there and make sure you do not have an issue with them. I am going by memory so verify this as to the slack adjuster travel. When you apply the spring brakes the rod pushing the slack adjuster arm should travel somewhere around an inch, with a maximum of about 2″. If you do not see that amount of travel the issue may be the brakes are not adjusted properly and a new slack adjuster may be required. The can be adjusted, but they should not need to be adjusted if that makes sense.

If your slack adjuster arm travel is correct you are just experiencing what a lot of us have dealt with from time to time with a sticky brake. Usually a very small rocking of the coach is enough to loosen them. When mine would “lock” just the act of going from Drive to Reverse was all it took to free them up..

I would check to make sure the two grease fittings on the slack adjuster shaft have been greased because if that shaft is dry the brake chamber return spring may not be retracting the slack adjuster arm due to excessive drag. And as Bob points out the two fittings on the pivot end of the brake shoes do need a small shot of grease occasionally. On the steer and tag brakes be very careful to not over grease the slack adjuster shaft.

Jon and Di 2006 Liberty Elegant Lady, 2021
Jeep Grand Cherokee, 1950 Ford
Knoxville, TN

Owner of three Liberty Coaches since 1990

[MyPrevost]

Caution — As Jon pointed out, the disc brake calipers have two fittings. If you over grease one of them, the pads don’t release and you will over heat the rotor causing cracks and possible seal problems. I know from experience, thanks to a shop in Florida that cost me new rotors.

Tom & Nancy
7 Prevosts Owned

[MyPrevost]

What was the problem??  K-B is the parent company of Bendix FWIW

Bob

98 XLE home built triple slide-SW Indiana

[MyPrevost]

Bob…….I think the coach in question had Rockwell or Meritor calipers. The K-B were used on later model years.

The grease fittings Tom refers to are those on the slack adjuster shaft that provide lubrication for the rotation and excessive greasing inhibits the opening of the caliper upon brake release.

The K-B calipers do not have slack adjusters external to the caliper and no grease is required.

Jon and Di 2006 Liberty Elegant Lady, 2021
Jeep Grand Cherokee, 1950 Ford
Knoxville, TN

Owner of three Liberty Coaches since 1990

[MyPrevost]

Trucker brother came over to help with my brake problem. He drove to get a feel for the symtoms, then I drove a couple inches while he listened for the screech and felt the vibration in the  right drive. Based on that, he thinks the front brakes are ok but cannot conclude until we put the right drive back together and drive again. After taking the right drive apart, drum and shoes are good somehow. I sanded both a little by hand. The slack adjuster was stuck sortof. It would push the shoes against the drum, but would not retract. And in trying to adjust it, could not. So, from Prevost ordered a new one $111.01. I have Rockwell axles, and it takes a Rockwell slack adjuster, Prevost part number 641273. We tested the stroke on the rod coming out of the brake canister and found it to be proper.

Correcting my previous post: The parking brake acts on the drive axle AND the tag axle. The evidence being two air lines going to the tag brake canister.

I will post once more for closure on this thread.

Dan and Barb 2004 Royale XLII Huntley, Illinois
Grand Cherokee CRD, 911 GTS, C43 amg

[MyPrevost]

The two brake problems were both fixed by replacing slack adjusters. Right drive and left steer.

We have Rockwell axles and ordered the parts from Prevost. They came in a meritor box with a meritor part number.

The front slack adjuster part can be installed on either the left side or the right side. Prevost part number 641271 equals Meritor part number R801072. Prevost price $128.37, Meritor price at www dot truckpartswarehouseonline dot com $74.30.

Drive axle right, Prevost part number 641273 equals Meritor part number R802383. Prevost price $111.01, Meritor price, same website, $83.44.

Cost of discovery, eighty-two dollars. Hope this helps somebody.

Dan and Barb 2004 Royale XLII Huntley, Illinois
Grand Cherokee CRD, 911 GTS, C43 amg

[MyPrevost]

Excellent post. One thing everyone needs to be aware of is that it pays to check prices.

One thing you got for your cost of discovery is the right part. There is some real value there.

Jon and Di 2006 Liberty Elegant Lady, 2021
Jeep Grand Cherokee, 1950 Ford
Knoxville, TN

Owner of three Liberty Coaches since 1990

[MyPrevost]

one comment here; I have to pay tax if I go local at 7%: plus usually 2 trips to town $6 worth of gas and 2 hrs lost time.  So I factor that time into price savings. When you buy Quanity like air bags local can’t compete.

Bob

Shop around

98 XLE home built triple slide-SW Indiana

[Author]

Posts