Patriot thunder brake problem

[Greg Kamper]

I have a 2000 patriot thunder and just had my rear brakes replaced. Thr mobile mechanic had never seen brakes like mine before... the air over hydraulic system. The right rear wore down and was metal on metal. He replaced both calipers and pads and rotors on the rear. Then he bled the brakes. The left rear would not push fluid out of the bleeder. That's probably why there was very little wear on that side and too much on the right side. Is there a bias control  that could be causing this?  Could the abs cause this? It looks like there is some sort of controller tucked up on top of the front axle. Any help would be greatly appreciated since we have a trip coming up.

Thanks in advance.
Greg.

[Vince Bunting]

I had a similar problem.  Turned out to be a restriction in one of the rubber flex hoses.  Replace all four flex hoses to more problems

[Eric Maclean]

Greg
As Vince pointed out it is possible a flex line has an issue.
There is no bias valve arrangement in these systems as they have two air operated master cylinders up front under the drivers platform.
It is possible you have a faulty ABS modulating valve .

If you have no fluid movement to one of the rear calipers start by disconnecting the flex line and see if you can get fluid movement there and work your way back to the ABS valve to see which component is at fault.
If the ABS valve is at the front there will likely two sets of lines one for the right rear and one for the left each may have two or three flex lines in it's path.

The ABS modulateing valve should not have any restriction in it until the ABS module recognizes a wheel speed discrepancy (lock up) It then starts to modulate the braking pressure to the wheel which is locking up .

If this was a full air brake system the modulator valve would be mounted near the wheel in question but this is a hydraulic brake system and most of those use a multiple valve configuration ( larger square valve with a pump and several lines exiting it) mounted closer to the master cylinder or in this case cylinders.
There where several manufacturers and I have no idea which system Beaver would have installed.
Unfortunately most of those valves are not supported for parts and are replaced as a unit

[Greg Kamper]

Thanks for the replies. I did loosen the two flexible lines near the rear caliper. There was no fluid in them. They looked fine on the outside and still in the shielded cover. Is there a schematic of the brake system online? The brake lines are very difficult to follow with all of the other lines that are tied together.
Thanks, Greg.

[Carl Boger]

Greg,

I am not aware of a diagram, but having recently replaced all m brake lines I believe you will be able to find another junction point in front of the fuel tank for the line running to the rear brakes.  You might want to check for fluid flow there.

On my MH the brake line to the rear brakes ran  up and over the fuel tank, along the inside rail in the storage bays and then exited.  I cut off the brake line at the front and back, and then ran a new line along a similar path.  Hopefully this will last me for as long as I need. 

The cost of the lines wan't all that bad, but getting them in was challenging.

[Eric Maclean]

Greg
If your coach does have ABS it will likely have two brake lines running to the front of the coach as apposed to the older coaches without ABS which only had a single brake line running from the front to the rear brakes .
As  Carl pointed out the older coaches had a pair of flex lines which ran from the two master cylinders to the inside of the driver's side frame rail just ahead of the fuel tank one flex line feed the front brakes and the other feed the rear line going to the rear brakes I surmise that on a coach with ABS those two flex lines will be connected to a pair of steel lines going to an ABS control valve block where there will be four lines leaving from one head to each wheel.

On many of the cars with ABS the only true way to bleed the brakes is by controlling the ABS valve and pump arrangement but this requires a scan tool connected to the vehicles ABS computer .
On a motorhome I'm not sure where or how to get connected to the system.
Maybe if we could get some picture of the ABS valve or controller we might find a manufacturer and possibly some literature on
Servicing it.
I believe it will likely be a Wabco unit likely  like this link below.(the fourth down)for bus and motorhome

https://www.google.com/search?client=tablet-android-lenovo-rev2&sxsrf=APwXEdeTUIm_OB6-V64q8lojz1_sml1n4w:1687219308979&q=wabco%20hydraulic%20abs%20troubleshooting%20manual&ved=2ahUKEwipm8fcxdD_AhX6m4kEHfWLAX0QsKwBKAB6BAhoEAI&biw=1103&bih=690&dpr=1.16#ip=1

[Vince Bunting]

Greg,
 Your rubber flex lines deteriorate from the inside.  They can look just fine on the outside. The rubber starts to soften up and becomes a check valve on the inside if they are twenty plus years old.  Think of it as maintenance.  Most people replace tires, radiator hoses, belts and other rubber items on their motorhomes way before twenty plus years.  If you checked the flow at the caliper (Banjo Bolt) and no fluid comes out, then check the steel line going into the flex hose at the frame for flow.   Be sure to use a line wrench or you will strip the line nut.  I replace my flex hoses with -3 Aeroquip hoses.  They have Teflon inside with stainless steel braid on the outside - not rubber.  And yes, they were pressure tested and DOT approved.  They silver braze the OE steel tube that comes off the caliper to an AN fitting to replace the rubber.  I did this 6 years ago when the brakes were replaced.  You can always do rubber replacement but the Aeroquip is once and done. Cost is more but peace of mind is worth it.  If it's good enough for airplane brakes it's good enough for my motorhome.  Just FYI, I own a specialty brake shop in Long Beach, CA that was established in 1931.  I bought it in 1981.  Brakes have been my business for a long time. 
Hope this helps, Vince

[Greg Kamper]

Greg
.......
I believe it will likely be a Wabco unit likely  like this link below.(the fourth down)for bus and motorhome

It is the Wabco unit. The ABS light has been on for a while. I didn't know there was a process to bleeding the brakes with that ABS unit. I hope that is the case for me. There was hardly any fluid coming out of the RR side and the LR was essentially dry. The brake lines were all good. I hope that's the case since a new unit is $3000.00

Thanks,
Greg

[Eric Maclean]

Greg
If the coach hd an abs light on prior to the brake issues it may have have more than one issue for instance there may be a wheel speed sensor with too much air gap which allows the signal to drop out.
The best way to know is to retrieve any codes from the system.
This is a common problem and can be easily fixed by taping the sensor back in untill it touches the sensor ring.
For the mean time let's try and get the system bleed out and working to do this you can try using a bleeder ball at the master cylinder to help push the fuild through the system or you can try sucking the fluid through the system from the rear calipers using a vacuum pump .