-
Tag wheel disc brake froze up
Today was the first time we had the bus out in a while. Weather has been in the teens over night, i.e. cold for Oregon. Went to fill up about 15 miles away and noticed a very strong brake smell while fueling. Sure enough, the passenger tag wheel was very hot. Filled up and crawled back to home base checking temps every few miles. Once there, I jacked up the wheel but could not turn it. Well there is the problem I thought. But to make sure I blocked the duals and released the parking brake. Now I could turn the tag wheel.
Not quite sure what happened. I had the parking brake on in the barn. Prolonged temps in the teens seem to have frozen one of the brake valves, so it did not release air.
Several lessons for me:
1- Keep checking wheel and tire temps after 20 miles or so when leaving on a trip (even when it is freezing outside)
2- Know where your fire extinguishers are. I could have sworn we had one inside the bus
3- Don’t set the parking brake during long term storage in the barn. Block the wheels.
The parking brake operates on the tag wheels as well (I guess as long as you have air pressure). Can someone confirm this please
Gerald
-
13 Replies
-
Gerald,
The problem with not applying the parking brakes is you are counting on a perfect brake system because keeping the parking brakes released requires a totally leak free set of brake chambers and brake system. When the parking brake is applied you have no air pressure to brake chambers.
The problem could have been a parking brake that did not fully release. If it was moisture or rust that held the brake pad to the disc the heat and rotation of the wheel when driving would have gotten rid of that problem quickly.
-
Jon,
you are of course correct. Over several weeks the brake air pressure would likely bleed down and the spring operated parking brakes on the drive wheels would engage.
I was surprised that the parking brake system also operates on the tag wheels. Are the tag axle brake chambers also spring operated?
Gerald
-
For safety, all parking brakes are activated by spring pressure so if air pressure is lost, ur stopped. Service brakes require air pressure to activate, but if ur stopped, the need is moot.
-
Yes the drive axle and tag axle both have the parking brake or spring brake on them early model coaches did not have them on the tag just drive axle
-
We made it over the Siskiyous before the next snow fall and had no more tag axle brake issues. There may have been a bit of ice in one of the brake valves that melted as the wheel heated up. These buses don’t like sitting in subfreezing weather even inside.
My brake chambers are likely the original ones. Time to start thinking about replacing them. Need to get familiar with how to cage these spring chambers should one fail on the road.
Thanks for all the help,
Gerald
-
I cannot think of a scenario where a dragging brake is going to thaw frozen water that might have contributed to a dragging brake.
However if the brakes were not Knorr-Bremse I can easily imagine almost frozen excess grease in the slack adjuster pivot that has created a hydraulic lock for releasing a caliper being the cause. What style brakes Gerald, and if the Meritor / Rockwell type the problem was likely caused by excess greasing in combination with the cold.
-
Jon: Do you think if Gerald had polished his slack adjusters on a regular basis that might have prevented the freeze-up?
-
Polished slack adjusters lock up just as fast as dirty ones if the grease monkey just keeps pumping grease into the pivot points. The caliper will press the pads against the brake disc, but when the brakes are released the excess grease can block the caliper from retracting or releasing. If it is cold out the grease is thicker and even less likely to allow the caliper to release.
This does not apply to Knorr-Bremse brake chambers, but coaches with slack adjusters and conventional brake chambers.
-
I think I have Meritor Rockwell type brakes. Will have to double check next time I’m under the bus.
The grease monkey (me) got a new state of the art, high-performance 20V lithium ion battery-operated grease gun. And I was not afraid to use it when I lubed the chassis. There you have it – another maintenance induced failure.
So, the low temps combined with overgreasing the caliper prevented the pads from releasing. There is just never a dull moment owning one of these beasts.
Gerald
-
Don’t kick yourself Gerald. As Tom and others can tell you even professional shops, including Prevost have overgreased the slack adjuster pivot fittings on caliper equipped coaches with the result being a dragging brake.
I am not suggesting we do not have to be aware cold temps and moisture in our air systems is a bad combination, but it sounds like in this instance it was not a factor.
-
Gerald & Everyone:
If you have Meritor air disc brakes, here is the mx manual:
http://beamalarm.com/foretravel-links/PDF/brakes-maintenance-manual-mm4m.pdf
It explains the correct grease types and procedures for lubing “calipers & slack adjusters” starting at page 54 of this pdf file. There’s a lot of other good info about our Meritor air disc brakes throughout the rest of the document too.
-
Gerald, you posted Aug of 2015 that you thought you were having brake issues? Checkout the good info given then too(see link below)
http://prevostcommunity.com/forum/threaddetails.asp?Category=Chassis&ThreadID=4605
Everyone: just because something has a grease fitting on it(like calipers) that doesn’t mean it needs to be greased. There’s a schedule and when it comes to calipers thay’re not to be greased very often, and they take a different type of grease. I use Meritor clay based grease, part# A1779W283, meeting their spec 0-616A, NLGI 1
https://www.finditparts.com/products/2128958/meritor-a1779w283
Your asking for trouble anytime you let just any old grease monkey play w/your bus
-
Years a go I had bought a bus and wanted to have oil, filters and greased before heading home. I should have paid closer attention to the greasing knowing the problem of caliper over grease. That trip home cost me a set of front rotors due to over greasing. I don’t remember which fitting, but one of the caliper zerks should NOT be greased. I was lucky, it could have been much worse with a hub seal problem.
Log in to reply.