9

Background

I drive a 1989 BMW 325i, and a few months ago I got a brake lining warning light. I gladly took the opportunity to upgrade from OEM rotors and pads to nice, shiny, new cross-drilled and slotted rotors with street performance pads that came highly recommended from Turner Motorsports, a well-respected online retailer of BMW parts. I didn't replace the calipers.

I installed the rotors and pads myself, then brought the car into a local shop that's very well known in the area for their work, to put on some shiny, new stainless steel lines and to bleed the system.

All well and good.

Symptoms

However, ever since I put on the new pads (and did all the other stuff), my brake pedal now goes down to the floor, and stopping distance is, well, scary.

To put things in perspective, I can be moving forty miles per hour, then floor the brake pedal to be nearly flush with the clutch (as far down as it can physically go), then the car will stop after a second or two.

I don't have any numbers off the top of my head of what comparisons in stopping distance may be between OEM and what I'm facing now, but as someone with experience in the car, something's not right.

But that's where it gets interesting. We brought it back to the shop and asked about why it might not be performing as well, and they bled it again and found no air in the system. But on top of that, they said that it feels fine to them.

Just a few days ago, I took it to a dealer (this was their first time seeing the car) and they bled it again, and said that it felt fine, too. They also said that they found no air in the system.

So I'm confused. I respect and trust the opinions of each of these places independently (we've been working with each of them for probably fifteen or twenty years), but I also know that I don't feel comfortable driving my car because it just doesn't stop.

One thing that both mechanics had mentioned is that it could just be that my brakes aren't hot enough to be operating well, particularly since they're apparently very hard material, as I might expect of track pads.

Question

My question is three-fold:

  1. I understand that track driving isn't like street driving (obviously), but shouldn't "street performance" pads generally, you know, perform well on the street? If I had gone for straight-up track pads, I'd get that they'd need to be hot. But for one, these aren't "straight-up track pads," and for two, I've had these ones smoking (literally) and still not been able to stop.
  2. Does it make sense that my pads being hard and not heated enough could lead to the pedal going to the floor? I totally get that this could lead to the car not stopping as well, but I'm confused about why the pedal would go further just because the pads aren't getting as much traction.
  3. I've tried following bedding procedures, but is it possible that I just didn't do that well? Could that lead to these symptoms?

Other information

The thought had crossed my mind that this could be a master cylinder problem, but this has been going on for months, and I can't imagine something like that continuing for so long.

My brake lining warning light is still on, and has been since I did the rotors and pads. I'm assuming this is coincidence and that the sensors are just not connected properly, but they are new sensors and I have checked them with a multimeter and they check out.

I bought new front OEM pads and they arrived today, so I haven't gotten a chance to install them, but even if they do work, I'm still curious about how that would lead to these symptoms.

One weird, and probably irrelevant thing, I popped off the caliper on one side the other day with one of my friends, and the brakes felt noticeably worse after that. They were bad before, but they were more consistently bad afterwards. I can't imagine what would have changed, so I'm going with coincidence, but that's another thing to note.

Update

I put on OEM pads, and I am now able to get ABS to engage (one thing that was sorely lacking with the old pads). But it still really just doesn't feel right, and my pedal is going down just as far as before.

I'm surprised, since now the only things I've changed are the rotors and lines, neither of which has anything to do with being track-prepped. But I'm also not surprised, since I can't imagine how pads would make much of a difference with pedal travel.

  • Does the pedal get firmer if you pump the brakes (while braking, quickly let off of the brake pedal and then press it again)? – Pᴀᴜʟsᴛᴇʀ2 Jan 16 '15 at 22:35
  • @Paulster2 Oops, I meant to mention that. Nope, pumping has no effect. – Matthew Haugen Jan 16 '15 at 22:52
  • Double check to ensure the stainless brake lines are good ... no bulges. I know, there shouldn't be any, but have someone pump down hard and hold the brakes while you check them. – Pᴀᴜʟsᴛᴇʀ2 Jan 16 '15 at 22:58
  • @Paulster2 Interesting. I thought of that early on, but I forgot to try it since so many professionals were dealing with it. I'll try that this evening when I'm putting on my new OEM pads, and perhaps they did miss something there. – Matthew Haugen Jan 16 '15 at 23:14
  • 1
    You said your brakes have been smoking at some point. Are they consistently hot? Maybe you have a stuck caliper creating a lot of heat that then boils the brake fluid causing your pedal to sink to the floor? – Becuzz Feb 10 '15 at 15:48
4

It sounds to me like you either don't have enough brake fluid in the system, or that the pedal travel is different now for whatever reason.

But I'm also skeptical of drilled and slotted rotors. They have less surface area that actually comes in contact with the brake pad, so the net effect is that your brake pads are "smaller".

I think you might have two separate issues here

  1. there's something wrong with the hydraulics. Specifically with how far the pedal travels.
  2. your rotors aren't the best choice for street driving. Slotting and drilling is really only for race conditions where the holes and grooves improve heat dissipation. They actually work against you in normal operating conditions because your contact area is smaller (brake pads don't grip on the air in the slots and holes).

Or maybe the rotors are constructed of material that is simply too hard and slippery.

  • 1
    Drilled and slotted rotors do not negatively impact performance for street use. Drilling and slotting is done to prevent overheating. The stopping grip difference is negligible. They also tend to work better in the rain, as the openings allow water to evacuate the rotor surface faster when the brakes are applied. The only real downside for street use is increased pad wear. – cscracker Dec 4 '18 at 3:57
1

If the pedal is going to the floor, you either have air in the system that needs to be bled out, not enough fluid in the system, or a leak. This has nothing to do with the pads or rotors. Regardless of how well or poorly the pads grip the rotors to stop it, they will hit it, and the pedal will harden up if the hydraulic system is working properly. Check for leaks first, if there are none, fill up the system with fresh fluid and bleed them again. If the pedal still doesn't firm up, you may have a failed master cylinder. You may also have a failed brake pedal bracket. It's less common but it does happen.

As for brake grip, you probably don't have enough brake pressure due to the hydraulic problem. That said, you also never bedded in the brake pads, which makes a big difference in stopping power. Once you have fixed the issues with the hydraulic system and have a firm pedal, you should bed in the brakes.

This is done by taking the car to a safe, long, straight stretch of road, accelerating to 60mph as fast as you can, then braking as hard as you can without locking up the tires to 10mph, accelerating as fast as you can back up to 60mph, braking hard again to 10mph, and so on, five times in a row. After the last hard slowdown, accelerate to normal driving speed and allow the brakes to cool for a few miles. During this entire process, do not come to a complete stop, as that will cause the pad material to stick on the rotor unevenly.

Slotted rotors will not negatively impact braking force in any noticeable way, and they actually help quite a bit in the rain, as the water can evacuate from the surface of the rotor faster. I prefer to use them on the street for this reason, and for the reason that I have overheated stock brakes on several cars with hard stops from high speeds, ruining the brakes ("warped" rotors and reduced braking effectiveness).

The BMW e30 is known to have undersized brakes by modern standards for track use, but they're more than adequate for street use. You should have a firm pedal and good feel, the main weakness is their small size allowing them to overheat with heavy use.

0

Several things can contribute to poor braking.

  1. Pads not heated - as u stated.
  2. Fluid on the rotor - unlikely
  3. brakes not bedded in - happened to me once. The contact path on the pads were not optimal.

Also, how are you doing the brake test? I have hawk street pads and if i speed off in the mornings from my cold start, and THEN hold my brake, i better not be heading towards a wall as i won't be able to stop! The brake is very tough and won't go down to the floor. This is a brake booster issue. After the first few pumps it worked fine.

  • This isn't a very helpful answer - please elaborate further as to why you think those might be happening in this instance, and how they would cause a problem. The OP has stated that he knows the pad temperature might be a problem, and there is nothing in the question to suggest the other two might be... – Nick C Feb 10 '15 at 14:43

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.