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- - Caliper guide pin rubber sleeve (https://www.ft86club.com/forums/showthread.php?t=134192)

Caliper guide pin rubber sleeve

Hi all - I rarely post but I figured this was too good to pass up given the relative lack of information available about this particular issue on the internet.

The brakes on this car use asymmetrical caliper guide pins. The lower guide pin for each caliper has a rubber sleeve (in addition to the accordion-style boot that retains the grease) that sits in a groove along the lower aspect of the pin (fully retained within the caliper bracket bore). The red arrow points to this rubber sleeve on this Subaru parts fiche diagram I edited and attached.

Despite the caliper guide pins moving well in their bores, it turns out that even the most minor swelling of this boot is catastrophic. This swelling can be impossible to see with the naked eye (as was the case for me) and can variably allow the guide pin to be reinserted into the bore without issue. Indeed, the left and right sleeves on the two lower pins on my front brakes appeared identical, but my right sleeve variably wouldn't re-insert into either bore while my left did. This was true before cleaning, after cleaning, and after greasing with a high-temp silicone grease. This sleeve, if left untouched, can cause the caliper guide pins to fail to fully re-seat after piston compression, essentially binding the guide pins and causing the brakes to drag. What is so annoying about this is that the pins will still move freely and the loss of pin travel in the bore is so minor it a) doesn't affect replacing the caliper on the bracket or aligning the rotor and pads within the assembly and b) can even still allow the wheel to spin relatively freely after reassembly. This makes it really hard to diagnose as there are many more obvious and common issues to consider, including a stuck/misaligned caliper piston, faulty replacement parts (e.g. warped rotor surface, unevenly milled rotor hat, brake pad misalignment, and even brake hose failure).

This rubber sleeve, according to a 2007 patent filing (see: https://patents.google.com/patent/US20080093181 ), has three purported design goals. As speculated in various forums and blogs (see: https://forums.anandtech.com/threads...his-is.259493/ and https://blog.1aauto.com/what-does-th...t-actually-do/ ), the primary goal is to reduce caliper vibration, presumably by dampening the rate of return along the guide pin and/or compensating for upper guide pin wear. The secondary/tertiary goals as described in the patent filing are to possibly improve guide pin alignment/centering and even improve lubricant distribution, although it is unclear in my brief search if there is actually any data behind these claims.

Anyway, I wanted to provide a sample size of one (1) to state that removing these sleeves doesn't appear to degrade brake performance in any noticeable way. I did apply a little extra grease in order to compensate for the loss of volume after sleeve removal. I'll update if I notice any issues, including increased noise or wear.

Hope this helps some of you if and when you encounter overheating calipers with no readily apparent cause.

:popcorn:

They keep the pins from seizing.

Quote:

Originally Posted by Ultramaroon (Post 3209397)

:popcorn:

They keep the pins from seizing.

I could definitely see how that could work that but why wouldn't they be used on all the pins? The "top" pin in each bracket is honed to the bore diameter and then a strip of metal is milled off in two places presumably to allow better flow of grease and possibly reduce the likelihood of seizure. Further, the top pins seem to be made from a carbonized metal of some form that I would imagine has anti-seizure properties. In my particular case, none of my pins was seized across all four calipers; in fact, the pins with rubber sleeves seemed to be moving more slowly and even sticking slightly more than the non-sleeved. I admit I haven't looked up the patents for this particular variant of guide pin nor do I have any professional expertise in this field. Mostly just curious and definitely wanted to share this with others since I spent a couple hours trying to sort this out myself this week.

Quote:

Originally Posted by theadmiral976 (Post 3209407)

I could definitely see how that could work that but why wouldn't they be used on all the pins?

Oh, wait. Now I think I get it. Are you talking about a spacer in the bottom one? I thought you were only referring to the outer boots. It's not a boot. It's a damper. (Wow, my reading comprehension is for shit tonight.)

Lube it. Leave it. If it's damaged, replace it. If it's swollen, hmmm... replace it and make sure the specified grease is used.

Will the brakes fail without? I'll pop a fresh bowl of popcorn next year.

I'll do you one better. It's a single-use item.

https://demos.starbase7.net/t3Portal...00CIF02EX.html

Quote:

Originally Posted by Ultramaroon (Post 3209413)

Yeah, I was referring to the bottom rubber piece as a sleeve just so I didn't confuse people with the boots found on all of the pins. The parts guy at the Subaru dealer didn't know what they were called, so I just used "sleeve." (He also couldn't order it as a separate piece - as is typical with Toyota and Subaru in their quest to make DIY repair as difficult as humanly possible. I much, much, much prefer Honda's approach to parts.)

Looks like they are called bushings as you found in the shop manual which makes sense given how they are positioned in the bracket. I definitely didn't leave off any of the boots - that would be very sad, indeed!

I'm hoping they are just there to dampen vibrations and aren't critical for active brake function. At this point with nearly 100k on the car, I could care less if there is ultimately damage in the bore or whatever from not using them. Next time I pull the brakes, I'm replacing most all of the parts and fully rebuilding everything that isn't damaged. Or better yet, I'll just get an AP Racing Sprint kit so I can continue to use my two sets of OEM wheels (one summer, one winter).

I probably should have rebuilt the calipers and slide pins this time around but everything was in very good shape and it requires a ton of patience to deal with my dealer and their complete inability to stock anything related to any Subaru other than the Forester and Outback. And I forgot to add rebuild kits into my last online parts order because I'm dumb.

Quote:

Originally Posted by theadmiral976 (Post 3209427)

Forgive me. I skimmed and jumped to the worst conclusion. :(

The top pin takes the majority of the shear load. The bottom one is more of a follower but the damping effect is real. I see your point. It will be interesting to see if there are eventual consequences for omitting them.

It is the same way for my 20 year old Toyota and I know as a fact that Toyota sells them separately. So if it is not available for 86, the fault is with Subaru. Toyota is actually very particular with this and for the same car, V6 version got a different bushing from an I4 version.

I also drove 10k+ miles without this bushing and nothing went wrong with it. I installed a new one eventually because I want to. It is very sensitive to the lube we use. I lubed it with CRC caliper pin lube and it swelled. It worked fine with 3M silicon paste. So the bottom line is to stay away from CRC junk. Using a good product from a reputable manufacturer you will be fine.

Quote:

Originally Posted by theadmiral976 (Post 3209386)

Quote:

Originally Posted by qqzj (Post 3210994)

Go with the best: OEM Toyota Rubber Grease (08887-01206), about $20 for the real thing on eBay.

A little pricey just for a tube of grease, but man is it a big tube of good grease.

Quote:

Originally Posted by qqzj (Post 3210994)

Thank you for the information - this is very helpful. So far things are okay without the four pin bushings and I doubt it'll become an issue anytime soon. I normally replace everything per OEM instructions; however, I didn't see the actual brake job instructions until it was too late (the ones on the 1k page service guide, not the oversimplified "instructions" on the "service" manual). The dealer was wholly unhelpful in all of this because, as I now understand, at least in my area (Indiana, Michigan), when dealers do brakes, they don't even mess with calipers, guide pins, or even support brackets. They literally purchase entire remanufactured assemblies, pre-lubed, and bolt them in with some pads. Which explains why three different dealers quoted me over $800 to do the brake job as they are essentially replacing calipers, pads, rotors, and support brackets. I suppose this is not the worst idea in the northern Midwest; however, I garage my car (but do drive it throughout the year) and I didn't have any issue with nearly any aspect of this job (other than the rotors mildly rust-welded to the hubs - easily solved with a couple 12 mm bolts).

Live and learn - I will plan ahead and obtain all of the bushings and boots to properly redo the job when these pads die.

Quote:

Originally Posted by qqzj (Post 3210994)

I lubed it with CRC caliper pin lube and it swelled. It worked fine with 3M silicon paste. So the bottom line is to stay away from CRC junk. Using a good product from a reputable manufacturer you will be fine.

Can it be that the CRC lube is petroleum based hydrocarbons that easily gets ingested into the rubber, while silicone is... silicone, without hydrocarbons?

Quote:

Originally Posted by chipmunk (Post 3213339)

Can it be that the CRC lube is petroleum based hydrocarbons that easily gets ingested into the rubber, while silicone is... silicone, without hydrocarbons?

I am not a chemical engineer. Don't know the details. It will be nice if someone with the knowledge can answer your question.

Sent from my Pixel 3 XL using Tapatalk

Quote:

Originally Posted by chipmunk (Post 3213339)

Can it be that the CRC lube is petroleum based hydrocarbons that easily gets ingested into the rubber, while silicone is... silicone, without hydrocarbons?

Eric the car guy said he uses silicone lube on these, because petroleum degrades rubber.
Did a quick search, and petroleum is a main solvent for *natural rubber.

Per the service manual, lithium soap base glycol grease is specified.