Couple questions on a '08 brake job

[krock12]

First I want to thank all the active posters of the forum. I am a member of a couple forums, but no automotive forums because I'm just not a car guy. I know how tiresome it can get having new one-time posters like myself come in, ask their question, get their info, never to be heard from again. For every person that posts, their are probably 100 if not 1000 people that never post that are helped by the info you guys put out there. So THANKS!!

That said, I have a couple questions that I couldn't find the answers to in a search.

I am changing the pads on an '08 4runner. Pulled the front drivers side tire and saw the outer pad worn down to about 2mm while the inner pad was at about 5mm. I immediately think I must have a stuck piston as is apparently common on these. Pulled the passenger tire, and pads are worn, but even. Since I had already ordered new Akebono pads I figured I would just wait until they came before checking for a stuck piston.

Got the pads, started with the Drivers side, and to my surprise, no stuck piston. So I button everything up after dropping in the new pads and move on to the passenger side. What do I find? A stuck lower inside piston. So I put back the old pads and button that side up. So here are my questions.

1) Am I ok driving (I can keep it light if I need to) with new pads on the drivers side and old on the passengers side for a week until I get the parts to replace the piston?

2) Should I be looking for or doing anything else on the drivers side that would have caused such an uneven wear in the pads or am I good to go?

3) The new Akebono pads came with a shim already on the back of the pads, but different from the 2 part OEM shim. Manufacturers instructions say to take the protective film off the shim before applying Moly-lube between the shim and back of pad. I dont see anything on the shim. Question is, does this shim replace the 2 part OEM anti-squeal shim, do I put the 2 part OEM anti-squeal shim on top of the new shim, or is this shim in fact the protective piece they were describing, and I should pull it off, discard it and put on the 2 part OEM anti-squeal shim? (Drivers side currently has all 3 shims stacked. Rotor still turned fine without contact, so I figured there shouldn't be any harm)

4) After replacing everything and going inside to pump the brakes, after a few pumps I got an audible tone along with the ABS, traction control, and one other light. Tone and lights went away after about 3 seconds. At no point did I open the master cylinder or bleed screws, so there shouldn't be any issue. Was the constant pumping just triggering some sensor, or is there something I should look for?

Sorry for the long read. Thanks again for all your help. This site helps countless people that never join or post.

Scott

 

[bob3dsf]

Well I can't say a whole lot about the stuck pistons. I haven't had that problem. Most everyone who did changed out their calipers. If you're still waiting for parts to fix that, I'd guess your alright since you had been driving with it in that condition before you identified it. Maybe someone else will have different advice about that. I have 107k on mine with original brake fluid [I think] (haven't had the time yet to change) and they use salt brine in the winter here if Canada gets snow. Don't know why some get stuck pistons and some don't. I check mine every time I rotate my tires. So far so good (knock on wood)...

The Akebono pads and shims: You do not need to reuse your OEM 2-part shims. Just take all of the old stuff out and pop in your new pads. I replaced mine with Akebobo ProAct pads. I called Akebono to ask about the shim. They are "integrated."

Don't know about your "tone" after pumping your brakes. I've never had that happen. Make sure you bed-in your new pads. Do a google search, or the search function on T4R. It's easy.

FYI: If you are doing your rear pads. I highly recommend getting a brake piston compressor.

This:

They are cheap (especially if you are near a Harbor Freight store) and make pushing the rear piston back in to make room for the new pads super easy. There is a write up on the toyota120 forum about doing the rear pads, but he used a big wrench the push those pistons back. I forgot I had the tool at first and tried the method in the post but it didn't work. Then, I remembered I had the compressor tool. EASY.

Sorry for not being able to answer all your questions...

 

[krock12]

Thanks for the help Bob. I have a garage full of clamps, so luckily the rear was no problem.

I'm not terribly concerned about the locked up piston, since like you said, it's presumably been that way for a while. I'm just wondering about the harm/risk of driving with new pads on the drivers side and the old ones on the passenger side for a week. Unbalanced braking is the only thing I could come up with. A weeks worth of wear on the new ones before changing the other side shouldn't be a big deal I wouldn't think.

 

[krock12]

Bump. Any other input? Everybody on a long weekend working on their rides?

 

[zopperman]

4) After replacing everything and going inside to pump the brakes, after a few pumps I got an audible tone along with the ABS, traction control, and one other light. Tone and lights went away after about 3 seconds. At no point did I open the master cylinder or bleed screws, so there shouldn't be any issue. Was the constant pumping just triggering some sensor, or is there something I should look for?

its just ABS yelling at you because it doesnt like to be pumped - mine has always done that since the day i had it, my dad's does it too. First time I did the brakes I was like oh shit what did I royally screw up, but seems normal.

 

[DC runner]

Never had this happen. Are you pumping with car on? Normally, when talking about seating,or pressure building, you pump with car off. Usually takes 10-20 pumps until the brake becomes rock hard and you have built up pressure. Doing it with the car on seems odd, since the master cylinder intentionally bleeds pressure and maintans a status quo.

When I do brake jobs,I always open the brake resevior. You need a way for air pressure to escape as you push the pistons back in. If you don't, the force of the fluid compressing backwards without release can damage your system.

 

[anotherrunner83]

I wouldn't worry about the mismatch in the pads for any amount of time. It's a hydraulic system so it will balance itself. You will have the same amount of force, independent of the pad thickness.

I had to replace my driver side caliper last time. I didn't mess with trying to fix the piston, just replaced the whole thing and went on my way.

As far as doing anything differently to change the wear pattern, I wouldn't worry about it. If you had one full pad and one pad to the metal, I may be a bit concerned. I've worked on several braking systems and 4 4runner braking systems (which have only changed slightly since the late 80's). From what I've seen, it's fairly normal to have one pad worn a little more than the other.

Hope this helps to ease your mind a little. Kudos to you for doing the work yourself and asking the questions.

 

[anotherrunner83]

Oh, and as far as damaging your system from not opening the cap, I wouldn't worry about that one, either. There is no difference in you pushing the piston back or the system releasing the piston; the end result is that the fluid moves in and out of the reservoir. The piston started at the "full pad" position and has eventually traveled to the "worn pad" position without any interaction from you, other than your input on the pedal. The extra fluid used to fill the piston to make up for this added displacement is simply pushed back into the reservoir.

 

[krock12]

Thanks guys. New piston and seals should be here tomorrow.

I didn't describe that very well. I pumped the brakes with the car off until firm and then turned the car on to see how it felt. It was then (after a number of pumps) that I got the alarm. I didn't think it was serious, it would stop when I stopped.

As far as not opening the cap, like was mentioned, I figured since I hadn't added any fluid to the system, there was enough space to allow for compression.

 

[DC runner]

The brake system uses the booster pressurize the system. The whole principle behind a power brake system is force multiplication from a pump that pressurizes the system to maginfy the power of a pedal pump.

As a result, the brake booster incorporates pressure as the pad wears down. When you push a piston back in your pushing against this negative space and can absolutely do damage.

 

[krock12]

So then would you suspect that damage has been done from a single brake job or would multiple occurrences be required? What would you recommend I do/look/feel for to inspect for damage?

 

[Sungod]

Don't waste your time replacing the pistons (and I hope you are not just replacing the one stuck one). Just buy rebuilt calipers from a local parts supplier that carry a lifetime warranty. You should also not be just replacing one side. You need to do both.

 

[nevada]

Never had this happen. Are you pumping with car on? Normally, when talking about seating,or pressure building, you pump with car off. Usually takes 10-20 pumps until the brake becomes rock hard and you have built up pressure. Doing it with the car on seems odd, since the master cylinder intentionally bleeds pressure and maintans a status quo.

When I do brake jobs,I always open the brake resevior. You need a way for air pressure to escape as you push the pistons back in. If you don't, the force of the fluid compressing backwards without release can damage your system.

no, that's not true. In fact leaving the cap off is a very bad idea. brake fluid is hygroscopic, it absorbs moisture out of the air. the less time its exposed to the air, the better.

Oh, and as far as damaging your system from not opening the cap, I wouldn't worry about that one, either. There is no difference in you pushing the piston back or the system releasing the piston; the end result is that the fluid moves in and out of the reservoir. The piston started at the "full pad" position and has eventually traveled to the "worn pad" position without any interaction from you, other than your input on the pedal. The extra fluid used to fill the piston to make up for this added displacement is simply pushed back into the reservoir.

this.

The brake system uses the booster pressurize the system. The whole principle behind a power brake system is force multiplication from a pump that pressurizes the system to maginfy the power of a pedal pump.

As a result, the brake booster incorporates pressure as the pad wears down. When you push a piston back in your pushing against this negative space and can absolutely do damage.

nope.

depending on the system, the cap is either vented, or has an expanding bellows. I think Toyota typically uses the bellows.
as the brakes wear, and the fluid level drops, there is a vacuum developed in the reservoir, this will draw the bellows in, or expand it. when the pistons are compressed, the fluid pushes into the res creating pressure. this pressure collapses the bellows.

unless you are adding/removing fluid from the system, you should never remove the cap.

Don't waste your time replacing the pistons (and I hope you are not just replacing the one stuck one). Just buy rebuilt calipers from a local parts supplier that carry a lifetime warranty. You should also not be just replacing one side. You need to do both.

agreed.

 

[krock12]

Sungod, do you have an explanation behind that? Since plenty of people are reporting stuck pistons with the remanufactured calipers as well, I'll take the $16 fix vs the $170 replacement. I plan on cleaning up and inspecting all the pistons, lubing and replacing all the boots, and replacing the stuck piston.

 

[Sungod]

Sungod, do you have an explanation behind that? Since plenty of people are reporting stuck pistons with the remanufactured calipers as well, I'll take the $16 fix vs the $170 replacement. I plan on cleaning up and inspecting all the pistons, lubing and replacing all the boots, and replacing the stuck piston.

It is based on best practice. Brakes are something that you don't want to go cheap with. You have two independent calipers and 8 individual pistons that all need to work exactly in tandem to insure you stop straight and as expected. You have one piston that has failed. Your other 7 have been exposed to the exact same environmental conditions as the one that has failed. This means that the others could be right behind. Replacing a single piston is no easy task, and it isn't something that you will notice right away when one fails. Also replacing a piston isn't something DIY guy is necessarily adept at doing. You need to be able to properly inspect and hone the bore. It is a fairly precise fit that could be easily over looked by someone without the proper training.

Over all there are a lot of 'what ifs?' that may not happen, but if they do, they could be pretty nasty considering the low cost following best practice. You can get remanufactured calipers from Advance for $120 or so for the pair that have a lifetime warranty. They won't last a lifetime and there will undoubtedly be more issues since this seems to be a common problem with these calipers, but it won't cost you anything to swap them out. I am in my 3rd set of calipers. I have pretty much resigned myself to replacing them every other set of pads.

As the saying goes, an ounce of prevention is worth a pound of cure.