Brake Caliper Noise????

[crios]

Hi all,
My right rear brake caliper is apparently very dirty and is doing something that cause a clunk…cluck….cluck noise which increases with speed. When I engage the clutch or cruise without accelerating, the noise stops.

This first started happening about a year ago. I took it to the dealer ($400 later) and they said the caliper was really dirty, they cleaned it and three months later it was doing the same thing. Since then it has happened on and off, usually goes away on its own, but for the last week it has stayed. I even took the tire off and caliper off and cleaned the outside of it the best I could. The noise went away for a day, but now it’s back.

Has anyone else experienced this? I’m thinking of rebuilding the caliper and cleaning the inside of it. Is this hard to do? What will I need to replace once I take everything apart? What should I use to clean the caliper?

Thanks,
Cesar

[jhandy]

same type of thing happened to me and it turned out to be the caliper bolts. They are one time use only. They have some kind of antiseze threadlock coating and if you dont screw them in tight or use the same bolts, they work thier way loose and the caliper clunks.

Mine was most notiable when, driving a little. stopping. then reverse a little stop and clunk. forward again, stop, and clunk. driving along at speed, on a small bump, then clunk.

Replaced the bolts, tightened to tourqe and has not returned.

Just a thought.

[RandallNeighbour]

Caliper bolts are really one time use only?

Are you sure about that?

My front brakes are clunking a little too. I might pull my wheels on Saturday and have a look at them.

[jhandy]

I am 110% positive that the caliper bolts are one time use only. When I did my brakes the dealer told me to buy new bolts. I did not listen. Then suncoast told me to buy new bolts, I did not listen. Then i had the issue, tightened them a few times only to have them shake loose. Got new bolts, cost of about 20$, looked at them, they are covered with a green coating.
put the new ones in, tightened to specs, and never had another issue.

part number 999.067.041.09

just from an educational standpoint, Google "replace caliper bolts boxster"
and see what comes up.

James

[RandallNeighbour]

How about that!

I gotta check all four corners now. I replaced the front bolts because the stinking things rusted out and totally reamed out my wheel carrier (well, the top one anyway), but I've removed one a second time because the rotor warped.

[crios]

You know, that could be it, the noise goes away when I tighten to spec, 63lbs, for a day or so...intresting. Thanks, I'll order some new ones today...$2.60 each at Suncoast.

http://www.e-partssales.com/miva/merchant.mvc?Screen=PROD&Store_Code=P&Product_Code=99907340201&Category_Code=98625brakes

[Lil bastard]

ALL Caliper bolts are one-time use! The same goes for cylinder head and conrod bolts.

These bolts use inherent elasticity to keep from working loose. Once that bolt has been torqued once, it's been stretched beyond the point of regaining this elasticity and if reused, could work it's way loose.

Does it happen all the time? Well it probably does eventually, but many have reused them and not yet discovered a failure. But, that's what these people who've had noisey caliper issues are experiencing, albeit short of a total failure... at least to-date.

The question is: For the simple cost of a couple bolts, do you wanna take that chance on your beloved car? I certainly do not.

[RandallNeighbour]

LB, in my case I must say I was under a cloud of total ignorance about replacing caliper bolts after a single use. I'm ordering six right now.... one corner has two new ones on it and I'm not worried about it.

Not changing them out had nothing to do with cost for me. I just didn't know

Moreover, I'm going to read up on it tonight in my Bentley manual but I can't remember seeing where Bentley says to discard them and use new ones, but I could be all wrong on that.

I love this forum. I learn something valuable with each and every visit. :dance:

[manolo]

The Bentley manual has you scrap them, positive on that. I went ahead and re-used all of mine after installing H&R springs, but added medium strength hi temp loctite. It's not the best idea, but I pull the car apart often and check on them and they've been fine so far. I considered safety wiring them, but I'm just too lazy.

[jmatta]

I wonder how many other autos this applies to? I have removed the calipers countless times on my track Porsche, only to re-use the bolts time and again.

[Lil bastard]

Originally Posted by jmatta

I wonder how many other autos this applies to? I have removed the calipers countless times on my track Porsche, only to re-use the bolts time and again.

It's inevitable that someone will chime in with unique anecdotal information whenever an absolute is proferred. As I mentioned, untold numbers of people who are either too cheap or unknowing will reuse the bolts. That doesn't mean they were not engineered for single use.

Any threaded metal-to-metal fastener works by actually stretching and it is this stretch which actually holds the fastener in place - the tension between the threads. Simply screwing it together does not put the fastener under tension, but torqueing it does. It is this tension, not the thread-to-thread friction, which keeps the fastener in place.

Combined with the torque spec, these are not merely threaded fasteners, they are engineered ones. They rely on the torque spec to do their jobs. Think about it - a typical caliper bolt torque spec is around 70 ft.lbs. This torque stretches the fastener and allows a bolt threaded to 70 '/" to withstand the force of a 3,000 lb. car (+momentum) being exerted on them. Well, 4 calipers/3,000lbs = 750 lbs/caliper (actually more since the front calipers do 70% of the braking). Without the tension gained from torqueing them, a 70'/" bolt simply cannot withstand this force - eventually, they will work loose. Similarly, a caliper bolt under-torqued will also eventually work loose for the same reason.

In the 30+ years I have been wrenching on cars, I have never seen a caliper bolt which wasn't recommended as a one-time bolt. That doesn't mean people aren't always aware, or heed the advice.

[vath2001]

What about adding Lock-tight, or thread locker instead of buying new bolts?
You discuss the fact the bolts are "stretched" when applied to the torque spec, but are we exceeding the tensile strength of the bolt design... or even reaching the yeild strength?

Don't get me wrong, caliper bolts are a safety item and critical to the operation of the braking system. But I don't always have extras available.

[Cloudsurfer]

Originally Posted by vath2001

What about adding Lock-tight, or thread locker instead of buying new bolts?
You discuss the fact the bolts are "stretched" when applied to the torque spec, but are we exceeding the tensile strength of the bolt design... or even reaching the yeild strength?

Don't get me wrong, caliper bolts are a safety item and critical to the operation of the braking system. But I don't always have extras available.

Not the same thing. Once a stretch bolt stretches, it is stretched. Using your idea, you are relying on the loctite to pickup where the tension between the threads left off, as the bolt you are re-using is already stretched.

For a few added bucks during a brake job, is it really a big deal to just do it the right way?

[sd_boxster]

Just got done replacing mine. I ordered them a couple of months back when I picked up my new rotors, but I didn't have the bit I needed. The OEM bolts (at least on an '03 non-S) require a hex bit, while the Suncoast replacement bolts require a star driver bit... so I got to spend my $20 AutoZone reward on a new bit and a 1/2" drive 19mm socket for the impact wrench.

[vath2001]

Originally Posted by Cloudsurfer

Not the same thing. Once a stretch bolt stretches, it is stretched. Using your idea, you are relying on the loctite to pickup where the tension between the threads left off, as the bolt you are re-using is already stretched.

For a few added bucks during a brake job, is it really a big deal to just do it the right way?

But we aren't stretching the bolts beyond the tensile or up to the yeild strength? By the same arguement, I would need to replace my lug nuts and studs everytime I take a tire off.

Is the requred torque (I thing its 63 ft-lbs for the M12 x 1.5) exceeding the tensile strength of the bolt? If it is, I would step up to a Grade 8 bolt or higher. And should we be worried about bracket failure? If the bolt is stretching, then the bracket is also deforming and the threads in the bracket under tension. And the caliper itself is under a compression load. All potential failure conditions.

[sd_boxster]

My layman's understanding - with a Google assist - is that the reusable bolts undergo elastic deformation - they deform under load but return to the original shape when the load is removed. A bolt formulated to undergo plastic deformation when torqued to spec preloads the joint to ensure that the bolt doesn't work loose due to vibration, but it makes the bolt non-reusable.

[vath2001]

This is the not the forum for the discussion of the design of the mechanical elements of the Boxster brake system.

I will agree that it is good practice to replace the caliper bolts, along with the retaining spring and pin... per the Porsche Technical manual. Then again, the Porsche owner's manual allows oil changes up to 15,000 miles.

I will choose to be selective about the maintenance of my car.

[sd_boxster]

"Technical Chat" seems like a pretty good choice of forum...

Originally Posted by vath2001

This is the not the forum for the discussion of the design of the mechanical elements of the Boxster brake system.