Part 20: Brake Repair


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The Trip

As fate would have it, our brake failure happened on the 4th of July.  I had been in contact with Rob, but he was out of the state and was not planning on returning until the 6th and had customers scheduled on the 7th.  But he stated that he would be available to assist us on the 8th.  So, we cooled our heels in Golden for a few days and then prepared for his arrival.  Our friends Bob and Kitty from Tennessee happened to be in Denver, so they came to assist us.  But, to no avail.  Nothing that we tried helped the situation, but we did have several nice meals together.

Based on my diagnostic information and our collective knowledge of the failed system, Rob, Bob and I agreed that the issue was likely in the air booster.  But, since the master cylinder had just been serviced, we could not rule out an in issue with it either.  So, Rob brought a whole assembly from another 1017A that he had at his shop.

The Photos

The photos below are what we saw.

In preparation for his arrival, he requested that we removed our cargo basket and the batteries from the battery box.  When the basket is removed, there is reasonably good access to the brake compartment.

The top view of the brake compartment shows the actuator cable on the left (with the rubber boot) connected to the actuator lever.  The air booster is in the center of the photo with a piston that hooks the actuator lever to the control point of the booster.  At the right of the booster cylinder is the hydraulic master cylinder and two reservoirs for the two brake circuits.  The various wire looms supply current to the tire crane, winch and the cab of the truck.

The top of the booster controller has a snap ring port that allows inspection of a portion of the mechanism.  We also discovered that it will vent air pressure allowing clearing of any debris that is in the system.  Bob assisted me and operated the brake pedal.  With the snap ring and port cover removed, he cycled the brakes and my hand was sand blasted with rust chunks.  We cycled the system a number of times and while the amount of particles reduced with each cycle, it never went to zero.  This seemed to point to a piece of rust blocking an exhaust port preventing the hydraulic portion of the assembly from moving past the reservoir port.  But nothing we tried allowed us to build hydraulic pressure.  Little did we know that the pistons were stuck in the master cylinder!

Rob arrived as planned with spare parts in hand.  He went right to work removing brake lines and reservoirs in anticipation of removing the whole assembly.

This show shows the size of the booster assembly. Once it was unbolted, it was slid rearward and then rotated to allow access to the air lines.  The exact configuration of the air lines is a bit mysterious, but we surmise that there are 2 feed lines (one from each tank) and 2 exit lines for trailer brake control.

The whole assembly was out in only a few minutes leaving a huge cavity at the side of the truck.

The old assembly was put into Rob's truck for a trip back to the shop.

The "new" brake assembly was brought from Rob's 1017A at his shop in La Junta.

The installation of the new assembly was reasonably straightforward and was accomplished in short order.  Next, the power bleeder was used to eliminate air from the brake lines.  Note the power bleeder line on the front fluid reservoir.

As it turns out, the front reservoir is actually the rear circuit. After the rear circuit was bled, the front circuit got the treatment.

Once we demonstrated that the brake system was functional, we broke camp and headed directly back to Rob's shop in La Junta.  We stayed in Thor inside his shop.  Next morning, we attacked the air tanks.  Since we had seen rust during the flushing operation, we decided to remove, wash and rust treat the inside of the tanks to prevent further issues.  When the tanks were removed, we found a large pile of rust in the small (outboard) tank.  Fittings were removed and plugs installed.  Then the tanks were filled with hot detergent solution and left to soak for about 15 minutes.  Then they were rinsed with hot water until all the rust particles were removed and left to dry in the sun.

While the tanks were drying, Rob dismantled the master cylinder.  It did not come apart as expected.  I, personally, expected that one of the rubber seals was twisted and preventing the pistons from moving, but that was not the case.

We discovered the culprit: a washer was jammed in the bore of the cylinder preventing movement of the pistons.  The question was how did that happen?  A new rebuild kit was installed just days before.

The flat washer was deformed into a cone and the cone had become press-fit into the bore of the cylinder.

The washer on the left was the original washer from the cylinder prior to the rebuild.  The one on the right is the new washer (after being deformed).

Note the base of the piston inside the bore of the booster.  The base is a cone and the shape matches the deformation of the washer.  The root-cause of the issues were that the incorrect rebuild kit was used.  As it turns out, there are THREE kits specified for my truck; only one is right, but the MB electronic catalog gave no clear indication of which was correct.  Last year, I purchased a master cylinder rebuild kit, but it was incorrect as well (but that mismatch was obvious -- the bore of the cylinder did not match the piston.  This mismatch was more insidious in that the piston fit the bore and only the washer was different.  Thor has the "heavy duty" brakes which have the conical base on the booster to improve the robustness of the booster piston.  The inside diameter of the rebuild washer fit over the piston but was too small to fit over the cone, causing an interference.  Delivering about 6,000 pounds of force, the booster won that battle and deformed the washer.  After several hundred cycles on the service brakes, the washer bound up in the bore of the master cylinder and the game was over.  No amount of action on our part could have resolved this failure once it happened.  We were, as they say, "well and truly screwed".

The air tanks were treated with Red-Kote polymer liner.  This is poured into the tanks and then sloshed around and poured out.  The solution is the viscosity of maple syrup.  Once it dries, it leaves a polymer coating on the inside of the tanks.  Oh, the fumes from the drying are very noxious.

Once the tanks were dry, they were reinstalled back in place under the battery box.

Once we were done in La Junta, we headed north to Limon then continued on to Brush, CO.  Along the route we passed some large corn fields with a substantial wind farm.

The wind farm stretched for miles and spanned both corn and wheat fields.

These are huge turbines that are perhaps 100' tall.

Further north we came upon some wheat fields being harvested by large combines.

The combines process a huge swath of grain and expel the harvest out the spout on the rear into the open hopper trailers for transport to the grain elevator.

We made it to Brush, CO and then headed west to Jackson Lake State Park on the Platte River.  We managed to find an open spot and settled in for the night.  After we set up, Kathleen noticed that there was a fluid splash present on the tool boxes and underside of the camper.  The following morning, we pulled onto some asphalt and I got underneath to see what had happened.  It appeared that the fluid was vented from the transfer case.  Why is not clear, but I pulled the vent plug and discovered that it was clogged with particles of black paint used on the frame.  I am guessing that the blockage was removed by force and when it opened up, it resulted in a gush of synthetic oil from the vent.  I checked the fluid level and it was down an amount that seemed consistent with splash area.  I filled up the fluid and sealed up the fill port.  We inspected the area repeatedly during our drive from Jackson to Longmont and there was no further spillage.

While driving, we did notice that during the hottest part of the day we were getting 230 degree F temperatures on the transfer case.  The transmission was about 150 degrees.  Later in the day, we saw 185 on the transfer case and 150 on the transmission.  This will merit some careful monitoring in the days to come.

We traveled through Longmont and Fort Collins and then went up Poudre Canyon looking for a campsite.  But, being close to civilization, on a blacktop road and a Friday evening, we had to travel many miles before we found a camping spot.

Tomorrow, we head over the mountains toward Laramie, WY.

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Photos and Text Copyright Bill Caid 2014, all rights reserved.
For your enjoyment only, not for commercial use.