gunderwood

I noticed that there was a weird, but minor "vibration" or pulsing on the way to work, but it was intermittent. Car drove fine most of the time, but for a minute or two there would be a "vibration," didn't seem to pull and didn't seem to be speed dependent for frequency. It felt almost like a tire had lost a weight, but obviously wasn't that since it was intermittent and not speed dependent. I checked and the front driver side wheel was warm, much warmer than the other wheels. I was fairly sure the brake was dragging. Otherwise the car drove fine and the brakes worked fine too. However, on the way home I noticed that while the pulsing was less, at least when it was present, the car now pulled slightly to the right upon braking. When I got home the same wheel was warm again.

I've looked at the caliper slider pins and they appear to be greased and fine. However, the brake was obviously still clamping the rotor a bit and it took some effort to get it off. Upon inspection, it appears that the piston is stuck/not releasing consistently. There are no ABS warning lights or any other indications that something is wrong so probably not electronics? In my mind that could be:

1. Something contaminating the brake fluid and getting stuck in a valve. I bring this up because there was some funny "growth" in the brake fluid when I changed it last spring. Kind of greenish in color and suspended (i.e. it didn't discolor the whole fluid), but I hadn't had any problems before or after the fluid change till now. I've changed brake fluid enough and know what fluid that has absorbed water looks like, that wasn't it. It was mostly clear with a weird suspension in the reservoir. I figured something had gotten in there, sucked out the old fluid, put new in and proceeded to bleed the brakes with a vacuum bleeder. Also, the fluid has been changed regularly and I typically use the Valvoline DOT 3/4 Synthetic because I can find it locally and always a fresh bottle.

2. Something is wrong with the caliper. Could do a rebuild.

3. Master cylinder? I've never had to replace one so I'm not really sure what the failure modes are, their indicators, or how to test one.

I'm leaning towards #3, but would love some help. I'm thinking of opening the bleeder valve to see if there is pressure in the line and if so how much. I think that if there is, then it's likely something is driving the brake when it's not suppose too. If there is only a little or none, then probably the caliper?

Thoughts?

Edit: There is no noise or indication that it's a wheel bearing either. I'm certain it's the brake.

gunderwood

Think I may try this procedure first and see if it helps.

http://www.dianasmercedes.com/Techni...tuckPiston.htm

Bugsy

If both front brakes were dragging hard, I'd say you had a clogged compensating port in the master cylinder.
If it's just the one, probably caliper piston corrosion.

downloader

push in the piston, if its hard going in its time to change the caliper. If its the caliper flush out the fluid at the same time you are changing it.

gunderwood

No, it is just the one side.

Billman250

I have seen brake hoses hold pressure, but not yet on the s2k. The test is simple. Hold the brake pedal tight, and release. Go try to turn your rotor by hand. It should turn free, but you say yours is sticking.

Just open the bleeder. If the rotor suddenly turns free, it is the hose or something hydraulic holding the caliper in the on position. If it remainds stuck, it is 100% the caliper.

In my experience, it is always the caliper. Rust builds up over time due to not changing the fluid, and locks up the piston. you can pump the pedal till the piston pops out of the caliper, I'm sure you'll find tons of rust.

Once the piston comes out, disconnect the steel line from the brake hose and put a rubber cap on it (use the cap from the bleeder screw) this will keep the system from running dry.

Now, change your fluid, reconnect your steel line to your hose, and gravity bleed till clean fluid (super blue work great) runs out of your brake hoses. This way, when you re-attach to your new or build calipers, only clean new fluid will enter. Any other way will run old fluid into the caliper first, and you dont want that.

NOTE! I have removed pistons on the s2k and fixed calipers this way by cleaning them out, but re-installing the piston can be very challenging. you will need to use an air hose and blower to inflate the outer dust seal over the piston before you start pushing it in. you may be best off getting a new caliper.

gunderwood

Thanks for all the insight. I've ordered a re-manufactured caliber and it should be here on Wednesday. Guess I'm stuck riding my motorcycles till then...hope the weather holds.

Edit: I'm thinking of replacing the fluid with Motul RBF600 and am switching over to stainless lines while I'm at it. I've searched, but didn't see any advice on change intervals when using that specific fluid. In the past I've changed it every two years, but the bikes recommend every year so I'll probably change it at least that often from now on. I drive the S2000 year round and they do use salt around here so I suspect that isn't helping.

Should I change the Motul RBF600 more often than 1 year for street use? Thanks.