Brake Caliper Stiffening

piloto · 07-29-2011, 04:44 PM

Does anyone know if the stock brakes use a rubber bushing for the caliper slide (guide) pins? I haven't yet had a chance to take mine apart to look, and if so, does anyone make a steel replacement, similar to the Tyrolsport ones for VWs? I had the Tyrolsports on my GTI, and it really helped the pad/rotor combo to wear more evenly. Thanks.

JAJ · 07-29-2011, 05:36 PM

Yes, the brakes have rubber bushings, and yes, there are brass bushings available to replace them. Personally I wouldn't bother - all of my stock BMW "M" brakes wore very evenly with both stock and track pads.

Radiation Joe · 07-29-2011, 06:03 PM

First of all I ran those on my e46 and loved them.

Second, I believe the link is incorrect. Those won't fit our calipers. If someone will correct me I'll call up Bimmerworld today for a set.

r53s65e90 · 07-29-2011, 06:23 PM

I think the bushings are rubber for a good reason: the guide pins are bolted on the caliper with only 30nm (22lbft) of torque. Any little caliper flexing is absorbed by the rubber and does not put too much load on the pin. Pads are supposed to be held in place by the pad carrier. Brass bushings would definitely put more load on the pins. The pins have not been tested using brass bushings. I cannot speak about the feel as I haven't driven anything with brass bushings, but I believe it is more subjective feeling than fact. So IMHO not a terribly good idea with at best minimal returns. My stock brakes wear pads very evenly without them.

elh0102 · 07-29-2011, 06:34 PM

Sometimes the factory engineers actually know more about building the car than we do.

JAJ · 07-29-2011, 11:55 PM

I don't know about the VW design, but the BMW caliper has the pads "captured" and held in place by the fixed bracket that's bolted solidly to the knuckle. They slide in and out on machined abutments, and the design makes sure that they can't move any direction other than in or out (toward or away from the rotor).

The piston assembly floats on rubber bushings, but it doesn't have anything to do with positioning the pads. All it does is clamp the pads together against the rotor or release them. The rubber bushings do not bear any of the load when braking - that load is transmitted directly to the fixed bracket by the pad pushing on the abutment plate.

If the bushings didn't keep the piston assembly in the center of the fixed bracket, then there's a chance that the pads would wear unevenly. But if the design is sound and the rubber is in good shape, all should be well for hundreds of thousands of miles.

piloto · 07-30-2011, 01:09 PM

^ Thanks for the info. I'll be taking mine apart soon and will see if first hand. But what you're saying makes sense, and no, the VW's wasn't quite like that. In fact, a small difference in friction (or resistance, caused by excess debris, design tolerance, etc.) in the slide pins/rubber bushing assembly would cause one side of the caliper slide to clamp faster than the other, thus causing the outboard pad to be tweaked when making contact with the rotor.

From what you're describing, the M3's caliper doesn't quite have this issue. You almost need a method of allowing the pad to slightly swivel in the sliding protion of caliper so that it can account for any slop due to the two pins sliding at different rates.

^^ to the poster above referring to brass bushings loading the pins in bending, you are correct. However, the amount of force and the duration over which it is applied is relatively little given the strength of the solid pin, and wasn't a problem, even given the VW's amount of flex in the sliding caliper.

But anyway, the bottom line is most everyone that's replied seems to agree that the pads wear very evenly, and a solid bushing would add little or no value.

Radiation Joe · 08-07-2011, 10:23 AM

Quote:

Originally Posted by r53s65e90

I think the bushings are rubber for a good reason: the guide pins are bolted on the caliper with only 30nm (22lbft) of torque. Any little caliper flexing is absorbed by the rubber and does not put too much load on the pin. Pads are supposed to be held in place by the pad carrier. Brass bushings would definitely put more load on the pins. The pins have not been tested using brass bushings. I cannot speak about the feel as I haven't driven anything with brass bushings, but I believe it is more subjective feeling than fact. So IMHO not a terribly good idea with at best minimal returns. My stock brakes wear pads very evenly without them.

This is incorrect.

The rubber bushing can put a higher load on the guide pins. The solid bushing keep the pins in shear, where the rubber can't. The pins are stressed LESS with the solid guides.

What the rubber guides do is eliminate noise. The rubber guides don't wear out in a year of use. The solid guides require maintenance and periodic replacement. This is the reason the factory uses rubber.

The solid guides keep the calipers aligned so that the pads don't wear unevenly or compromise braking.

07-29-2011, 04:44 PM	#1
piloto Captain 29 Rep 843 Posts Drives: 2011 E90 M3 - AW/FR Join Date: Jun 2010 Location: Orange County, CA iTrader: (0)	Brake Caliper Stiffening Does anyone know if the stock brakes use a rubber bushing for the caliper slide (guide) pins? I haven't yet had a chance to take mine apart to look, and if so, does anyone make a steel replacement, similar to the Tyrolsport ones for VWs? I had the Tyrolsports on my GTI, and it really helped the pad/rotor combo to wear more evenly. Thanks.
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07-29-2011, 05:36 PM	#2
JAJ Captain 80 Rep 961 Posts Drives: 2014 Shelby GT500 Join Date: Apr 2008 Location: Vancouver, BC iTrader: (4)	Yes, the brakes have rubber bushings, and yes, there are brass bushings available to replace them. Personally I wouldn't bother - all of my stock BMW "M" brakes wore very evenly with both stock and track pads. Last edited by JAJ; 07-29-2011 at 11:33 PM.. Reason: If the link was incorrect, let's remove it!
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07-29-2011, 06:03 PM	#3
Radiation Joe Veni Vidi Vici 89 Rep 2,750 Posts Drives: '11 JB/BBe-6sp-e90 Join Date: Jul 2008 Location: Macungie PA iTrader: (0) Garage List 2011 e90 M3-Sold [8.50] 2003 RS6 - Sold [0.00] 2009 e90 M3 - Gone [0.00] 2003 M3 SOLD [0.00] old 2002 [10.00]	First of all I ran those on my e46 and loved them. Second, I believe the link is incorrect. Those won't fit our calipers. If someone will correct me I'll call up Bimmerworld today for a set. __________________ Dinan compliment of stuff plus PF rotors and RG63s. Enough for now. Why, yes. I am an abrasive bastard.
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07-29-2011, 06:23 PM	#4
r53s65e90 8300 19 Rep 573 Posts Drives: r53 s65e90 Join Date: Mar 2009 Location: San Jose, CA iTrader: (0)	I think the bushings are rubber for a good reason: the guide pins are bolted on the caliper with only 30nm (22lbft) of torque. Any little caliper flexing is absorbed by the rubber and does not put too much load on the pin. Pads are supposed to be held in place by the pad carrier. Brass bushings would definitely put more load on the pins. The pins have not been tested using brass bushings. I cannot speak about the feel as I haven't driven anything with brass bushings, but I believe it is more subjective feeling than fact. So IMHO not a terribly good idea with at best minimal returns. My stock brakes wear pads very evenly without them.
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07-29-2011, 06:34 PM	#5
elh0102 Captain 15 Rep 751 Posts Drives: 2009 335i coupe Join Date: Apr 2010 Location: USA iTrader: (0)	Sometimes the factory engineers actually know more about building the car than we do.
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07-29-2011, 11:55 PM	#6
JAJ Captain 80 Rep 961 Posts Drives: 2014 Shelby GT500 Join Date: Apr 2008 Location: Vancouver, BC iTrader: (4)	I don't know about the VW design, but the BMW caliper has the pads "captured" and held in place by the fixed bracket that's bolted solidly to the knuckle. They slide in and out on machined abutments, and the design makes sure that they can't move any direction other than in or out (toward or away from the rotor). The piston assembly floats on rubber bushings, but it doesn't have anything to do with positioning the pads. All it does is clamp the pads together against the rotor or release them. The rubber bushings do not bear any of the load when braking - that load is transmitted directly to the fixed bracket by the pad pushing on the abutment plate. If the bushings didn't keep the piston assembly in the center of the fixed bracket, then there's a chance that the pads would wear unevenly. But if the design is sound and the rubber is in good shape, all should be well for hundreds of thousands of miles.
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07-30-2011, 01:09 PM	#7
piloto Captain 29 Rep 843 Posts Drives: 2011 E90 M3 - AW/FR Join Date: Jun 2010 Location: Orange County, CA iTrader: (0)	^ Thanks for the info. I'll be taking mine apart soon and will see if first hand. But what you're saying makes sense, and no, the VW's wasn't quite like that. In fact, a small difference in friction (or resistance, caused by excess debris, design tolerance, etc.) in the slide pins/rubber bushing assembly would cause one side of the caliper slide to clamp faster than the other, thus causing the outboard pad to be tweaked when making contact with the rotor. From what you're describing, the M3's caliper doesn't quite have this issue. You almost need a method of allowing the pad to slightly swivel in the sliding protion of caliper so that it can account for any slop due to the two pins sliding at different rates. ^^ to the poster above referring to brass bushings loading the pins in bending, you are correct. However, the amount of force and the duration over which it is applied is relatively little given the strength of the solid pin, and wasn't a problem, even given the VW's amount of flex in the sliding caliper. But anyway, the bottom line is most everyone that's replied seems to agree that the pads wear very evenly, and a solid bushing would add little or no value.
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