2002 Monterey Seaclif brake frustrations

[Christopher Clark]

During the last few weeks I have preformed a bit of and over haul to my brake system. I have a 2002 Monterey Seaclif with Cummins 350 isc on a Roadmaster chassis and Allison Transmission. The brakes are air assist-hydraulic. My rig has been in storage a few years with regular starts and maintenance. I had decided for a number of reasons to replace all 4 calipers, all brake pads, all flex lines from frame to calipers, and the hard lines from each master cylinder(2) to the ABS box and both front brake lines from ABS to frame where flex lines attach. I then drained and flushed all brake fluid, replaced with DOT 3 as specified on reservoir. I have bled the brakes twice and find no air. The brakes feel fine, responsive, with hard pedal.
 The problem, I have a dragging and heating front left brake. That brake, as all others, has a brand new, lubricated caliper pins and slides. This is one of the reason why I decided to preform the overhaul, overheating brakes! I have read about the historical issues with these brakes, and know the issues are many. Can anyone suggest what I might try to remedy this issue???

[Gerald Farris]

Chris,
The secret to any coach repair is to first diagnose the cause. If you know the cause, it is always easier and cheaper to repair the problem than it is to through parts at it in the hopes that you hit the problem.

To locate your problem, you need to determine the cause of the dragging (overheated) brake. First, never assume that just because a part is new, that it is not the cause. To determine the reason for the dragging brake, you need to narrow the problem down to mechanical or hydraulic. If you can jack the wheel up and apply the brake and it does not fully release when you release the brake pedal, it will be easy. If not you will need to duplicate the condition to properly diagnose it. If the brake is dragging, open the bleeder, and if pressure is released and the dragging stops, your problem is hydraulic. If there is no pressure the problem is mechanical from resistance in the caliper slides, internal caliper resistance, or a binding in the caliper mounting caused by a bent or misaligned mounting part. If your problem is hydraulic and it can be duplicated, just start venting the pressure back up the circuit until you locate the source. It might be in one of the parts that you have replaced or in the ABS valve block, but locate the problem and repeat the condition to be certain before replacing any parts.

Gerald     

[Christopher Clark]

Gerald thanks, from your description I will check for a mechanical issue. Another question about this style of brakes. The master cylinders receive brake fluid from a reservoir supplied by one green line and one red line. I “assume” these two masters were, front and rear. After some thought about red and green, could the cylinders be port/starboard as in left/right? And have you ever seen or heard of some sort of remaining air pressure causing brake drag?

[Gerald Farris]

Chris,
There are two types of split master cylinders used on hydraulic brake systems. The original design (oldest and most common) split master cylinder separated the front and rear brakes. However, some of the later models (most with ABS systems), split the system with the LF and RR for one circuit and the RF and LR for the other circuit. I am not sure how your coach brake system is split, but it is very easy to determine by having someone apply the brake pedal and then go around and open the brake bleeder at each wheel to see which wheels remain pressurized after opening the bleeder on one wheel. 

Anything that causes pressure to remain in a brake system could be problematic, but I have never seen a brake drag issue caused by residual air pressure. Residual air pressure in a master cylinder reservoir is almost impossible, and any residual air in the brake fluid will cause a low pedal/spongy brakes condition.

Gerald