Calling big brains brakes replaced/upgraded, front rotors drag, rears get hotter

[pbonsalb]

Any of the “high carbon steel” rotors should be fine. Brembo, Zimmerman, Centric, etc.

[trading10]

I have found on a couple of Brass Bushing/SS Guide Pin installations that the tolerance of the distance between the center lines of the threaded fastener holes in the caliper attach bracket and the fastener bores of the caliper are quite loose. Meaning that there is little chance the Guide Pins match perfectly in the bores of the Brass Bushings. Once the bushings are installed the caliper no longer ‘floats’ on the (supplied) Guide Pins. I have had to ‘fit’ the Brass Bushings until the calipers easily slide upon the Guide Pins.

I use a large cotter pin with a strip of 150 grit crocus cloth paper strip to create a flapper wheel to sand the bores of the brass bushings to open the bores till the caliper easily glides on the Guide Pins

I chuck the cotter pin in a drill motor and spin it in the bushing bores, test fitting till I get the gliding fit I am happy with.

If the front caliper brass guide pins are too tight of a fit they most likely bind and apply no clamping force causing the rear brakes to do all the braking.

These brass bushings need lubrication and at least annual cleaning.


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Bluptgm3

One question for you, when you sand these out for more clearance, do they then make noise when you tap the brakes in 1st gear/slow speed? ie. Metal to metal clank when the calipers shift around on the pins. My 2007 335i does that - for different reasons, but it's an audible noise that sounds like a bolt is snapping off.

[trading10]

Any of the “high carbon steel” rotors should be fine. Brembo, Zimmerman, Centric, etc.

What about having these powerslops turned down a bit so they don't have as much runout? Is that even possible with a cross drilled slotted rotor?

[bluptgm3]

Bluptgm3

One question for you, when you sand these out for more clearance, do they then make noise when you tap the brakes in 1st gear/slow speed? ie. Metal to metal clank when the calipers shift around on the pins. My 2007 335i does that - for different reasons, but it's an audible noise that sounds like a bolt is snapping off.

No, I have no additional noise, just instant response and great modulation even with stock street Pagid pads


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[trading10]

No, I have no additional noise, just instant response and great modulation even with stock street Pagid pads


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Sure sounds exactly like what I want for this braking system. Better modulation using stock calipers and upgraded pads. Have you tried other pads before landing on the Pagid ones? I ask because as part of this brake project, I'm trying out the Akebono ceramic pads.

Edit. Blutgm3, stupid question on my part. Of course you've tried other pads. I think what I was really trying to ask is, why Pagid now in your case?

[trading10]

https://www.bimmerforums.com/forum/s...=asc%2Bt+bleed

This is a thread I found here in bimmerforums that I haven't found anywhere else. Part of the problem I'm facing as mentioned earlier in this thread was a soft mushy pedal after switching to the powerslop rotors and their ceramic pads. I'm already aware of the usual methods, including stomping the brakes to activate the ABS or shorting out pins in the fuse box to activate it. Others who have done these steps and still have a soft pedal might find this information useful. The thread was from 2018 and ended with the guys who came up with the idea of routing a hard line from the ABS nipple up the strut tower for easy bleeding not selling their kit due to possible legal liability. There is a parts list to do it yourself for $80. Has anyone solved their mushy pedal by bleeding the ABS pump this way?

[bluptgm3]

As for the o-ring design, it seems to work well. It keeps the insides clean. What are your concerns?

I am concerned that the caliper pads do not get knocked back enough when the pedal pressure is released.


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[trading10]

I am concerned that the caliper pads do not get knocked back enough when the pedal pressure is released.


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I am leaning toward the master cylinder at this point. I took the o-rings out, sanded the bushing bores out on one corner, re-greased it, and made no difference. So, I put the old pads back in, which are 1mm thinner. As soon as I press the brake pedal, the calipers clamped down, but would not release enough to allow the rotor to spin freely. In fact, it was very difficult to spin at all. The reason I'm suspicious of the master cylinder is because during previous attempts to bleed the brakes, I pushed the pedal as far as it would go. Based on what I've read so far, this was a mistake, and could have damaged one or both seals in the master cylinder. I was reading this in a Jaguar forum. Calipers clamp down, but are not seized internally from corrosion, blocked brake lines, sticking guide pins or thickness of the pads. All four calipers behave the same way.

I have a new master cylinder arriving in a couple days, and a racer friend of mine coming over tomorrow to have a look over my shoulder. I'm still interested in your point of view though.

[importbanana]

If the master cylinder is causing pressure to stay in the system when the pedal isn't pressed, then if you crack open a bleed nipple all pressure is released, no matter where it comes from and the wheel should turn freely. Is that the case?

[trading10]

If the master cylinder is causing pressure to stay in the system when the pedal isn't pressed, then if you crack open a bleed nipple all pressure is released, no matter where it comes from and the wheel should turn freely. Is that the case?

I started this test by pumping the brake pedal. Then when I removed the nipple, fluid started to leak out slowly over about 3 mins, and the rotor goes from totally unmovable to movable. I did press on the caliper slightly to compress the piston and force more fluid out. After doing that, with moderate effort, I could spin the rotor about 1 rotation, and I can hear the pads touching the surface. A wisp. I then put the nipple back in snug, and without pressing the pedal, it still spun about the same amount. Did I ruin this test by pushing on the caliper vs just letting it sit and drain longer than 3 mins? I could redo this test without touching the caliper if that would tell you more.

[importbanana]

Why do you let it drip for 3 minutes? Did you check the level in the reservoir? If there's pressure then it's gone within 1 second. It will drip until the reservoir is empty. Why is it necessary to pump the pedal? The way I read your problem it happens under normal circumstances, therefore simply braking as in pressing the pedal once normally.

The way I understand it your brakes drag for some reason and you think it's the master. That would mean after releasing the brake pedal the master leaves pressure in the system. Is that your theory and the reason why you want to replace the master? If yes:

Go to your car, turn the wheel --> turns freely? all good. Doesn't turn freely --> no good, get in car, press brake pedal, check wheel again, turns freely --> all good. doesn't turn freely --> no good, open bleed nipple, now turns freely--> yes means you had pressure in the system, no means it's not pressure related and the problem is within the caliper.

[trading10]

That is my theory, yes. (edit) I did not mention that I had to push and pull on the caliper to get the rotor to move free enough for 1 full rotation. I redid this test, and only pressed the pedal once - the rotor would not spin easily until I pushed/pulled on the caliper. Does this mean a sticking piston?

I only let it stay open that long because I wanted to see if the rotor would spin more easily than it did initially after removing the nipple to let any pressure out to in case the caliper was binding on the pins. I pressed the pedal three times before doing this because that is when the caliper stays clamped, and I was trying to simulate what it would do if I drove the car. The pedal got firmer with each press, and then the roto would not turn without muscling it. Open the nipple, it spins 1 rotation. By the way, I'm doing this test on the front left. I have the front end of the car jacked up so I can try to rotate the right front rotor as well - it is still difficult to move regardless of what I do to the front left. Does that mean anything as far as the master cylinder is concerned? Should both calipers release by doing this test to the front left?

I'm at the point of isolating the master cylinder based on what I read elsewhere from a Jag owner who had what appeared to be the same problem. He had already replaced lines, rebuilt the calipers, tested the booster, but could not determine the cause. He swapped out the master cylinder and the problem was solved. So, I am not doing my own troubleshooting of the MC at the moment other than what you have suggested, and want to do this exactly as you're saying so we have meaningful results. In my original post, I mentioned a soft/low pedal and whooshing sound with the engine running - when off, the pedal firms up with a few presses, so because of that, I ruled out the booster. Maybe that was wrong thinking? I don't know enough about master cylinders to say.

Last paragraph - after that first test of removing the nipple, the rotor spins as I mentioned earlier. If I press the pedal now, the rotor stops turning freely. If I read that correctly, there must be pressure left in the system after pressing the pedal indicating this is not the caliper piston sticking or it binding on the pins. Maybe there is a combination of all three here, and I'm chasing only one?

Sorry for such a long reply. It's hard for me to know what info is important to share when several things are happening at the same time.

[ScotcH]

The rotor will always drag on the brakes, even with no pressure. There is no "spring" or anything to retract the piston after the pressure is released. But you should be able to rotate it easily by hand. If it's not able to rotate, that's an issue. If you crack the nipple does that change? If it becomes easier (but still drags), then I would agree with you, it's the pressure not being released. If cracking the nipple does nothing, or very little, then I would suspect the piston sticking.

[trading10]

The rotor will always drag on the brakes, even with no pressure. There is no "spring" or anything to retract the piston after the pressure is released. But you should be able to rotate it easily by hand. If it's not able to rotate, that's an issue. If you crack the nipple does that change? If it becomes easier (but still drags), then I would agree with you, it's the pressure not being released. If cracking the nipple does nothing, or very little, then I would suspect the piston sticking.

Cracking the nipple lets fluid out, but doesn't immediately allow the rotor to spin easily by hand. I have to push and pull on the caliper to get it to open up enough to spin the way you describe. I still have the bronze bushings in, but hollowed them out a little with a steel wire brush bit in a drill, as well as removed the rubber o-ring (just mentioning this in case you didn't already see it above). Those two extra steps seem to make the caliper move more easily than before. Before, they were very tight, and the caliper would only move freely if I loosened the pins slightly. Soon as I tightened them up, the caliper would not move nearly as well. For those above that have commented on these bronze or brass guides, I think they have been correct about them binding or being out of alignment with each other. I want them to work as described for better pedal feel, but will abandon them for BMW OE if that proves to be the better way to go.

Sounds like I should rebuild the caliper and see if it solves this binding issue. In anticipation of this possibility, I have a replacement piston/gasket/seal kit in-hand now. Not sure if the piston is exactly the same as BMW OE until I get it out of the caliper though. I would assume that there is no negative consequence with replacing these parts, but maybe you or anyone else could correct me on that.

Just for some positive feedback to everyone who has been contributing expertise here in this thread - thank you - I'm following the 'trust but verify' approach to this because while I'm trying to learn as much as I can, I still fit that old saying you may have heard before, which is my 'ambition exceeds my skill' on this project. When the binding and soft/low pedal issues are finally resolved, this thread should be a good resource for others in the future that find themselves in the same jam. That's my hope anyway.

[importbanana]

Cracking the nipple lets fluid out, but doesn't immediately allow the rotor to spin easily by hand

Then how do you expect the master to solve your problems?

I want them to work as described for better pedal feel, but will abandon them for BMW OE if that proves to be the better way to go.

Throw that crap out and go OEM if they're confirmed to be the cause of your problems!

[trading10]

Then how do you expect the master to solve your problems?



Throw that crap out and go OEM if they're confirmed to be the cause of your problems!

I expect a new master cylinder to resolve the soft/low pedal since no amount of bleeding the system including the abs by my bmw indy shop has made a bit of difference or any of the many attempts I've made to bleed the system. My indy shop said the mushy pedal would improve over time using the powerslop pads. They were right about that, but the pedal was never firm as it had been before. Back to the drawing board. I'm changing pads to akebono for better bite on short trips vs the powerslop ceramic pads that require more heat to develop good bite. The powerslops allow more modulation, which is good thing for more aggressive driving, but the cost, driving around town, isn't practical to me. The questions I've had about the calipers and the master cylinder are whether or not the two issues are related.

Can do on going back to OEM. I have the OEM parts on order. I just need confirmation that these bronze bushings are causing a problem. So far, I haven't been able to confirm either way. Only suspicion.

As an aside, that is why I want to learn the details, not just guess. I'm trying hard to learn and sort things out, and that's why I have consistently thanked everyone here for contributing their knowledge and insight, including yours. Thank you for that. I sincerely appreciate what you're trying to do to help, and am in no way opposed to scrapping my own conclusions if any are proven incorrect.

[importbanana]

Did your brakes drag before you installed these aftermarket pins?

I don't know what to tell you. I think you're on your own now. Is all this trouble worth it? Maybe you can isolate the cause, but it wouldn't be worth my time, but I understand that you have a different connection to it by now. If I were you I'd remove all aftermarket products and go back to a working OEM system and upgrade from there, one thing at a time, so that when you have a problem you'll know what caused it. I'd throw everything out and go OEM and ATE rotors & pads and go watch ice hockey instead.

[trading10]

I accept that going back 100% OEM may be the simplest solution, even though it would feel like total failure.

The long term problem was the soft low pedal that no one else had been able to solve. I was living with that in disgust because in my field of expertise, I'm used to dealing with complex problems that others fail to solve. The short term problem was the left rear rotor overheating, and stinking pads. It was dragging, but not for the reasons I suspected. I thought - sticking piston, or maybe an internal issue with the brake line -the check ball effect. Once I started looking closer, I discovered other issues, and then decided that after 120k miles and 22 years, it was time to refresh with new parts. After reading so much about a that issue as well as a soft/low pedal, repeatedly bleeding, trapped air in the ABS, BMW software, and the lengths guys have gone to in their efforts to resolve those problems, my head was spinning with incomplete and copy/paste answers going back decades. So, I decided to dive in on my own and work through it, at least until hitting the limit of my knowledge and ability to troubleshoot. That is why I started this thread. I don't need this car for daily driving as I have other cars available. This is a project car that I'm fond of, and view it as a chance to challenge myself by learning new things. I've pushed through upgrade challenges like this before by applying myself, which has been very satisfying. So, that is my connection as you put it.

I racing buddy of mine is coming over tomorrow to have a look at it with fresh eyes. Right now, I can tell you that those bushings are still suspect even though they seem to have less friction than the OEM ones I took out. Alignment I think is the underlying issue, and sanding them out more might resolve the the problem or destroy their purpose. They were a pita to get in, and for all I know might be just as difficult to get out. If I could tell whether they are the problem or the piston isn't retracting, that would help. Seems to me, it has to be one or both. We'll see if the master cylinder fixes the soft/low pedal as the Bentley manual recommends.

[ScotcH]

Sounds like you have different issues for sure ... low soft pedal could very well be MC. The sticking/ binding ... they sell super cheap rebuilt calipers (like $50) ... almost not worth the hassle to rebuild yourself, but if you already have the stuff, fine. It migh end up that your piston is damaged, so the rebuild not not do anything.

New rotors and pads should not be an issues, regardless of manufacturer ... unless they are incorrect parts. Of course feel/performance will vary, but they should at least all function the same way in terms of mechanics. Now the brass bushings, that is a different engineered solution, and I would agree ... remove those because it adds a non-standard variable.

[trading10]

MC received today - Centric was the only one I could get, so I hope it's worth the effort to put in. If that does in fact solve the low soft pedal, I'll be very happy. I haven't found cheap rebuilt calipers in that price range - I think maybe $230 or somewhere around there - possibly ATE's. Since I already have the rebuild kit for front and rear, I might as well use them. Seems like there is no downside, but if there is, please chime in. I bought the Akebono ceramic pads from buybrakes.com, the 'brake experts'. I did a live chat with them to ask if the pads are the correct models, thickness, etc, and they assured me that they are. My racer buddy suggested taking the anti-squeal plate off and then remount them to see if they still dragged. They do, so cross that possibility off the list. New OEM bushings, pins, and bleeder screws (removing the speedbleeders) are due here in a few days, so if rebuilding the calipers doesn't solve the dragging, then I can go back to original BMW bushings. Not looking forward to doing that, but will if necessary.

[bluptgm3]

Be prepared to by new caliper pistons
Centric front
p/n 146.60009
Centric rear
p/n 146.40032

Or go to BimmerWorld for Stainless caliper pistons


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[trading10]

Be prepared to by new caliper pistons
Centric front
p/n 146.60009
Centric rear
p/n 146.40032

Or go to BimmerWorld for Stainless caliper pistons


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Thanks. I will check those out. The rear replacement pistons I have now are ebay, but appear to be stainless. The fronts are from bimmerworld if I recall correctly. Also appear to be stainless. I just need to see if what I bought is the same design as the oem. When I was shopping around, sorting by model number, different shapes kept coming up. Rears have a beveled edge. Fronts not so much.

[bluptgm3]

BimmerWorld stainless steel pistons are not an exact duplication of OE pistons, however they work.
Not sure how close the Centric pistons are to OE.


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[trading10]

BimmerWorld stainless steel pistons are not an exact duplication of OE pistons, however they work.
Not sure how close the Centric pistons are to OE.


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I need to correct myself. I said earlier that the rears came from ebay, but they in fact came from bimmerworld, same as the fronts. So, both are for sure stainless.

I have a caliper cylinder honing bit for a drill. Do you or anyone else know if honing is needed or advisable?

[ScotcH]

I need to correct myself. I said earlier that the rears came from ebay, but they in fact came from bimmerworld, same as the fronts. So, both are for sure stainless.

I have a caliper cylinder honing bit for a drill. Do you or anyone else know if honing is needed or advisable?

Never done it, but if it's rusty in there it won't hurt to clean it up ... But just make sure the seal goove is nice and clean. The seal is what is the important part as the piston rides on that.