[HiFlite]

My car has been in service for 5 1/4 years with only 37,000 miles. About 1/2 of these miles have been in town. My work commute is all of 4 miles each way, with 13 stop signs or lights each way. It's quite common to have rear brakes issues in Michigan; we have lots of winter which comes with lots of salt. Spray from the front wheels tends to keep the rears drenched in salt water. The rear brakes are only lightly used, especially in town, so they seldom get warm. Every car I've had up here with rear disk brakes has had issues (and none with rear drums have had issues). The most common one is that the floating pins bind, resulting in uneven wear. But my issue this time was a bit strange.

The LR disc was not getting swept as evidenced by rust build up. Removed wheel to lubricate pins and discovered that the pads were worn out with ~0.70” of pad remaining. It looks like there is a “stop” that prevents metal to metal contact when worn. Both sides were nearly even with each other indicating a caliper problem rather than a stuck pin, plus the pins did not seem to be stuck. Lubed pins and replaced with Autozone Duralast Gold DG1468. (Retracting the piston requires a spanner tool with 1 5/8” pin separation which can be rented for free from Autozone). The new pads have a thickness of 0.370” (9.4 mm). Also, even though they were still good, I replaced the pads on the RR for balance. The old RR inner pad measured 0.320” or 50/300 = 17% worn. Extrapolating from the present 38k miles gives a projected lifetime of 229k miles. The old outer RR pad measured 0.370” thick which is essentially zero wear. Unknown is why the left side wore out and why the right side is wearing unevenly.

I'll run it for a while this way and see what develops. Both sides seemed to have the same amount of drag and there was no significant difference in disk heat when measured with a pyrometer.

 

[freshcut]

First thought that comes to mind comes with a question. Do you regularly use your parking brake? I'm thinking perhaps the cable for the culprit caliper is binding and not allowing it to fully release?

 

[FI Spyder]

The rear brakes should be little used (even less than front brakes). In rust belt areas, this is a problem. I looked into the availability of the replacement bolt that hold the caliper brackets from Raybestos. There where none in stock in Canada for front but some for the rear brakes as the rear discs rust and have to be replaced sometimes. Besides the floating pins, a piston could freeze (rust), parking brake mechanism freeze. Use it or lose it. Flushing the rear wheels from salt not usually an option when it's 20 below. Only thing I can suggest is greasing pins every fall, using parking brake when parked, if there is any hills near home put into neutral when going down periodically to use the friction brakes briskly rather than regen to prevent them from rusting in place.

 

[HiFlite]

Good observations. Yes, I always use the parking brake when parking and it's also been my observation that doing so reduces the chances for it seizing up. Implying "our time is up" for salt water brake operation, with another take on the cause is here:

https://gm-volt.com/forum/showthread.php?325339-Dragging-Rear-Brake-FIXED

Yet the subject of parking brake led me into a deep dive into the FSM. Guess what? There's a cable release and retensioning procedure which is supposed to set the cable tension properly. Though not discussed much, it seems to me that this should be done periodically as pads wear or when pads are replaced. Procedure for both attached below.

 

[jbakerjonathan]

Thanks for the efforts, HiFlite. It is good to know how to re-adjust the EHB.

I religiously use the EHB but have noticed an odd wear pattern on the rear rotors. When the car was new, the wear pattern extended in the normal way across the rotor. After three years on the road, the wear pattern has shrunk to the middle of the rotor wear area. In my mind I have tried to envision in what way a mal-functioning caliper could cause such wear. I have no idea the condition of the inside wear surface, nor of the pads themselves. Any ideas?

I took my car to the dealer for its annual state inspection, thinking that the problem would be noticed and a recommendation for service made. I purposely did not flag the problem before hand. I assume that I received the "cursory" inspection and no look-see of the brakes was done by the mechanic. Any quick look through the wheel shows the abnormal wear pattern., so, I'm rather disappointed. The rooky mechanic probably was given the task.

I'll be taking the Volt to a local mechanic whom I trust to see if he will work on the car. My days of doing brake jobs is in the past.

 

[FI Spyder]

Something else comes to mind (from another post I think). Apparently the pads can get jammed with dirt/rust so they don't "float" in their holders. Taking the pads out and cleaning around the edges and where they fit in the brackets will help as well if that is an issue.

 

[jbakerjonathan]

Following up, I had the rear brakes checked. The calipers, pins and pads are functioning correctly. No remedial work needed to correct any deficiencies as there were none. It is puzzling that the rotors are being worn in the center, not evenly across the disk surface (both inside and outside surfaces). The pads themselves are wearing evenly (inside pads and outside pads are the same thickness), the guide pins are operating smoothly and the pads are not sticking in the guides. This is after 80,000 miles on the odometer.