Ongoing Brake Issues

[DocWalt]

Polygon, I had assumed my issue was the HPS pads, but it may not have been.

Max, great post. I had always wondered if the slightly rubber first bit of travel was normal.

[R/T93]

Polygon,

on the 'other' forum, you mentioned something about SCE caliper bolts. What are these exactly? And did you have these when you were experiencing problems with the old setup (btw, HPS pads suck a fat one. They aren't great to start with but they really start sucking when they're a little older)


Max

Damn you never heard of these? They are a really nice upgrade to the stock calipers. They give a better feel during braking.

http://supercar-engineering.com/sc2/...roducts_id=136

[Polygon]

Polygon,

on the 'other' forum, you mentioned something about SCE caliper bolts. What are these exactly? And did you have these when you were experiencing problems with the old setup (btw, HPS pads suck a fat one. They aren't great to start with but they really start sucking when they're a little older).

The bolts I'm talking about are these.



They're the bolts in between the rotors. Super Car Engineering makes them and they're for the fixed calipers. They're supposed to reduce flex in the caliper. I assume you can tell but they go where the old pins are that go through the caliper. I did not have them before. They were installed this weekend.

About the HPS pads, I found that out after I had installed them. It's one of the reasons I got rid of them.

Pedal travel under maximal braking should be minimal, i.e. the pedal should never get close to the floor. The pedal in general (with the engine running and a properly functioning booster) should feel like you're stepping on one of those rubber gym mats (not the kind people do Pilates on, but the kind they use to stop dropped weights from cracking the floor) covered with about 1/2" - 1" inch of medium density foam (I've noticed that unlike some platforms, 3/S brake pedals have some travel before the brakes fully engage). In other words, when you stomp on the pedal, you should get 1/2" to 1" max of softer travel before you feel a whole lot of resistance (like trying to crush a rubber gym mat with your foot, i.e. your foot isn't going to move more than 1/4"). If you're getting more than 2-3" of pedal travel, you either have air in the system, or a leak.

If the pedal travel is fine, then the problem is either internal in the MC or something else.

Pedal travel feels substantial to me. More than a 1/4 of an inch after I start to feel resistance. That's for sure. I wouldn't doubt air in the system. However, I've checked all the hard lines and can find no leaks. Also, the fluid level is constant. What other ways can you get air in the system besides letting the fluid get low in the MC or a leak?

Outline your exact rotor installation and bedding-in procedure?

Carbotech Bobcats are fairly easy to bed-in. With zinc coated rotors, generally the first couple of stops is enough to wear off the zinc coating from the swept area.

Things to keep in mind when bedding in pads:
- You need to generate enough heat in the system to create and bond the pad layer to the rotors
- Done properly, brake torque WILL reduce significantly in the middle of the bedding procedure
- Full brake torque should be achieved by the last few deceleration events of the bedding procedure without really needing to let the brakes sit and cool (especially for street pads like Bobcats), UNLESS you've overdone things and have exceeded the pads' MOT.

To street bed Bobcats, I would find a clear stretch of road, accelerate up to 60-65mph and then brake at 60 - 70% of maximum pedal effort down to 15-20 mph (don't stop the car while bedding pads), accelerate hard, back up to 60-65 mph and repeat about 8 times. Don't drag the brakes with light/moderate pressure. Medium high pressure is essential to the bedding process. You need to alternate medium high pressure (to generate enough heat in the pads to transfer material to the rotors), with zero pressure as the cooling between braking events, while you're accelerating back up to 65mph, helps the deposit layer bond properly to the rotors. Dragging the brakes with light pedal pressure doesn't allow the cyclic cooling and the lower pressures can produce uneven pad material deposits.

Usually, with street pads like Bobcats (and even AX6's) by about the 3rd-4th (and potentially even up to the 6th) braking event, the pads will start smoking, you'll smell the brakes and you'll notice that for the same (or more) pressure on the pedal, the car is taking significantly longer distances to slow down to 15-20mph. This is normal with most pads. The heat is burning off the excess binder (even with newer compound pads, there will still be some excess binder burnt off during bed-in) and this excess binder reduces mu and brake torque while it bleeds out and is burnt off.

By the 7th to 8th braking events though, with the same pedal effort as the 1st through last, you should notice the brake torque getting significantly higher and the rate of deceleration increasing dramatically. At this point, you SHOULD (barring problems with the brake system) be able to lockup wheels or trigger the ABS (if still active) with maximum pedal pressure. The brake torque for similar pedal pressure should feel (in relative terms from a scale of 1 - 10 for a given set of pads), like this for bedding in:
- Braking events (BE's) 1-3 = Brake Torque (BT) ~6
- BE 3, 4, 5 maybe 6 = BT ~2-4
- BE 7, 8, 9, 10 = BT 9-10

Max

I pretty much did it like you have said except I was pushing more than 70% - 80%. Also, it all happened just like you said it would. The brakes effectiveness got worse as I did the bedding process. I never saw smoke, but I could smell them. Also, the braking never got better. Here's the instructions I got with the Bobcats:

1. Brake from 60mph down to 30mph about 4-6 times.
2. Then let your brakes cool for about 2-3 minutes while driving.
3. Repeat step # 1.
4. Allow the brake pads and discs to cool down to ambient temperature (about 30 minutes or more).

Now, if I got them too hot, what can I do? I can definitely see an even layer of pad material on all the rotors. There is even some in the slots.

[bluemax_1]

Wasn't aware of those bolts. Been running the Stoptech kit for a few years. I wonder how much difference they would make for the stock rears. Might get a set to check out the difference.

Polygon, air can enter from the master cylinder but it can also enter anywhere there might be a leak in the seals. It's also possible for air to enter while bleeding the brakes depending on how they were bled. If the air gets ingested from the MC or through the lines and makes it to the ABS unit it's quite a pain to get the air out. If the replacement MC doesn't do the trick, one thing you could potentially try is to have a Mitsu dealership flush the brakes. The proper procedure to flush the brakes involves hooking up to the OBD port and triggering/cycling the ABS unit while flushing the brakes to ensure that ALL the old fluid (and any entrained air or moisture) is flushed from the system.

As for overheating the brakes, I don't think that's it. If you maintained medium high pressure on the pedal while bedding in the brakes, it would prevent an uneven deposit layer from forming. Your car however, doesn't appear to exhibit the shuddering that is symptomatic of that. You're just not inducing enough brake torque. You could of course, try turning the rotors and deglazing the pads (although that really shouldn't be a problem with slotted rotors). My recommended systematic approach would be
1) replace MC with the unit you just bought and flush the brakes, if the problem still exists,
2) have the brakes properly flushed by a shop that cycles the ABS unit while the system is being flushed and then, if that still fails,
3) try turning the rotors and deglazing the pads before rebedding them.

When deglazing the pads, I personally advocate avoiding sandpaper. Regular sandpaper uses aluminum oxide particles or even silicon carbide, these can embed themselves in the pad surface and cause problems down the line (although you will find folks that do it). It's safest to use a metal file. BTW, when you first installed the pads and rotors, the first thing you should have done was wash them with Dawn Blue dish soap. Some companies occasionally pack their components using a corrosion inhibitor (no one wants to see their brand new parts come out of the box with rust on them). The corrosion inhibitor might not be seen or felt, but if it is not completely cleaned off, it can interfere with the brake's performance (and proper bedding in). Because the rotors are usually cast iron, they rust easily when the rotors are cleaned off the corrosion inhibitor. In fact IIRC, after washing the Stoptech rotors before I first installed them, after a few hours, by the time I was done with the installation and bleeding the system with the brand new calipers (installed SS lines at the same time), I could already see some light surface rust on the rotors.


Max

[Polygon]

That, in all honesty could be my problem. When I bled the system after flushing, we had the car running for that reason. That damn ABS pump. If the prop valve weren't so hard to get to I would do the ABS delete right now and be done with it, but it will have to wait until I pull the engine.

That sounds like a good plan. A bench bleed will prove if the MC I just bought is still good, correct? That way I can test it before putting it in. Then, have a Mitsu dealer bleed the system. I have a ton of ATE sitting around anyhow. I think I'm going to get some SS flex lines as well, just for good measure. I wouldn't trust them at a track day anyhow.

As for the pads and rotors. Deceleration is definitely smooth, no judder. I didn't wash the pads or rotors. I never heard of having to do it with pads, I have with rotors though. However, I called R1 and they told me that since they are Zinc plated they don't put any other rust inhibitors on them. So, I simply wiped them down with brake cleaner. From now on I'll just take the dish soap to them. It's cheap insurance.

[MR2]

since I've just done the same, let me know how you go with the ABS stuff

I'm just going to beat the shit out of my car till it hits abs.

[TUFFTR]

Funny you mention this Polygon....I purchased your old HPS's......I'm basically scared to stop the car as it....well doesnt really stop. I'm just running factory blanks with these pads and it is SCARY putting the foot down. My M/C was on it's way out anyway so I'm putting another one in this week, the week after I'm putting in QFM HPX's (Australian brand of pad)

These pads are just utter crap (no offense to you :P) and yeah....coming out ASAP and being binned.
Strange to see you used these and had next to no brake feel too.
hell I'm NON-ABS and can't lock the brakes! no-where near being able to lock them. My old single piston calipers felt better!

Hope you sort it out dude.

[IPD]

since when are speed-bleeders bad? i love mine.

[Caswell239]

Did you ever get this figured? Do you have any rubber line anywhere? A friend of mine had a rubber line that would bubble when applied and retract when released so the level never looked low.