TL;DR at the bottom.
So, I had a caliper lock up earlier this year in the rear and decided to replace both rear calipers. They were very old and worn out and both had seized parking brake mechanisms (of course). So, I managed to source both sides rebuilt and had new parking brake cables. Bolted everything up and it all looked great at first. I finally had the parking brakes back, which is amazing, but after driving for a while I started noticing an issue with the right rear caliper. When the brakes were not under load I could here it "tapping." Its hard to describe, but essentially, as I went faster it got more frequent, applying the brakes stopped it all together. Though I couldn't see it, I pictured the pad bouncing off of the rotor.
When I first got both calipers, I wanted to make sure they were lubricated since I have heard a lot of stories of the boots being dry and causing premature wear. So, when I grabbed the right rear and pulled the bracket out to expose as much of the guide pins as possible it was really easy. I thought this was due to the lubrication that was already there. I added a little more, worked the bracket on the slides and figured that was a bracket that was good to go. I grabbed the left rear and tried to move the bracket and it would not budge. Gently peeled back the boot and saw there was almost no grease, so i got a little in there and gently pried it open to expose more of the guide. I added grease and worked it in, eventually being able to get that caliper to slide back and forth with quite a bit of force. I thought that was the caliper that would give me hell, and it still may down the road, but its performed great so far.
Back to the right rear issue, I got the car back on the lift removed the wheel and upon inspection I didn't really notice anything wrong. I thought maybe the slide pin bolt (the exposed one) was loose and tightened it, but it persisted after that. So, off with the wheel again, and this time I grabbed everything that could be loose and tried to move it. What I found was that the rear bracket could be moved with diagonal force: Youtube Link to Moving the Caliper. So, it seems that the bracket was moving and bouncing off of the rotor. I checked the left rotor to try and create the same movement and it absolutely does not move in that way. It does open and close properly, but there is no shifting the bracket on that caliper, which I am assuming is correct performance.
I removed the caliper and inspected the guide pins since that appears to be the source of the movement. The lower slide pin and bolt (pink box) sits in a rubber guide pin boot and seems to be specifically designed to not be tight in its bore because it has a boot between it and the metal it slides through. The upper guide pin (red circle) goes into a hole in the body of the caliper (orange boxes).
The one I removed from this caliper had wear marks on it from just 60 miles of driving, pictured here:
This appears to be the problem, the upper guide sits loosely in the caliper body's hole, allowing for this movement. Searching around I was able to find some threads on the DSM forums mentioning a similar issue with the rebuilt rear calipers. Some speculated that during the rebuilding process too much material is taken out of the hole by the rebuilders who are wire-wheeling rust out of the hole. Unfortunately the solution for most at that time was to buy a new caliper instead, but that was years ago when you could still get them. In a desperate attempt o use this caliper I first decided to try a few different guide pins, hoping they are different diameters. Measuring with calipers I found that they do vary by brand, ranging from 13.76mm to 13.89mm (worn one was 13.81mm). I tried the biggest one I had with a bunch of fresh grease, but alas, it was only a minor improvement on the range of movement.
So, I tried to get another caliper, hoping this was rampant across all brands, and spent hours calling and scouring the net to get rebuilds. I found a few and ordered them up, some got cancelled for not being in stock, but I have managed to source 2 more of them. Both of them have the same issue, one is worse than the other, but they all have the same movement. Contacted a few places about sleeving the whole, but concerns about removing too much caliper material (causing cracks over time) and metals with varying expansion rates under heat have scuttled that idea.
At this point, the best idea that I can come up with, to avoid junking these rebuilds, is an oversized guide pin. I can't seem to find any info on that though. Its a fairly simple piece of metal that I think any machine shop could replicate, but I'm not sure the material and coatings on the guides and I can't find any info on the internet. Does anyone have any info on that or know where I should look?
Or, am I missing a different solution?
Got a rebuilt rear caliper that has too much movement, causing the pad to bounce off the rotor.
Tried 2 more rebuilt calipers and found the same issue with the caliper body hole for the upper guide pin being oversize.
Has anyone found a solution for rebuilt calipers that have the bore worn out for the upper guide (slide) pin (besides throwing them out)? Oversize slide pin, sleeving the hole, etc. Or, am I totally overlooking another solution?