A calipers in M struts....

[MMBRAZIL]

Will A calipers fit my front M strut?

[Joe Bob]

Nope....one has a 3.5" spread on the mounting ears and the other is 3".....

But the struts are interchangeable. Use the same strut you got the calipers from.

[Oldporsche]

Someone out there has a modified set of boxter calipers that will fit on an "m" strut.

Good luck,
David Duffield

[MMBRAZIL]

what if I made wider holes on the mounting years? I would need .25" in each to the sides. Do you think the resistance of the material would suffer?

[SRT356/911]

You can put 77BMW 320i calipers onto the M strut with no modification to the strut or caliper.



Buy stock SC pads and cut the outside corners of 2 of them off with a hacksaw or file them off with a bench grinder. Put these two on the inside. They clear the bolts. The pads will ride a little high on the rotor, but it is not a problem, and you will not experience any brake fade if you have a Cool Brake kit. Should you want to go to Carrera rotors, have a machune shop shave the mounting ears enough to center the caliper and then file the inner space open a bit to clear everything.

Be real careful in your work. You have to know brakes to assure all is done on a quality level. Brakes stop your car. I have Time Trialed the car all year this way.

My experience and what I have seen at the track is that you should not need to do anything to a street or AX car with the M calipers if the car is only used on the street. Only the upper limits of Time Trialing begin to stress the stock M caliper brake system. And there are people that still run on M calipers and have no problem.



Steve

[zotman72]

Cool! Finally someone tells me which year BMW and model I can scab some calipers for my 72T. Why can you not use BMW pads rather than SC pads?

Bill
72T with an 2.4S engine. needs better brakes

[Joe Bob]

Dunno....I plan on using those calipers and BMW style Pagid pads on my 914/6 install. The /6 uses the same struts as you do....

I will also be using cross drilled Zimmerman rotors, I will no be doing any track use, so the cracking issues should not arise.

BTW....the vented BMW rotors can be found rebuilt with pads for 100-150 each including core charge....

[SRT356/911]

Bill

You can use the BMW pads. Right out of the box.

The SC pads are a little deeper, giving you slightly more surface area.

The BMW calipers can be had from any wrecking yard for about $30 each. I recommend buying a rebuild kit for about $13 and rebuilding the caliper before putting it on. I personally only remove the pistons and blow out the caliper. I do not unbolt the halves. Too much room for leakage and finding a full rebuild kit to get all the seals in. If you have the entire kit, follow the factory guidlines and go for it.

A hint on getting the pistons out if they do not readily come out with air or if one or both are stuck. Use the cars brake system. Loosely put the caliper on the car. (If it is mounted, do this before you remove the caliper.) Take the pads out and then step on the brake pedal until the pistons hit the rotor. Remove the caliper and block the pistons with creative items while you continue to apply pedal pressure. If one piston comes out before the other, put it back in and block it so that the pressure will push the other piston out. Done! And you have not ruined the pistons by prying on them. Now you can clean out the bores and clean up the pistons and rebuild the caliper.

Good luck

Steve

[zotman72]

Thanks for the info. Tomorrow morning, I am heading to the local junkyards and see what I can find. Last week, MikeZ I believe mentioned GPR as a source for these ATE calipers. I call them and they would not give any details as to which/what BMW the calipers came from. $300+ plus seemed somewhat reasonable but I would rather rebuild some used ones instead.

However, I am kind of in a jam as I am the PCA/RMR Chief Tech Inspector and putting non Porsche brakes on my car throws me way out of my current class(2.4S and 944S2 etc.) and into a heavily modified class. Oh well, I do need better brakes at a reasonable price. Maybe no one will notice......

Bill

[Joe Bob]

Well...I'm the SB PCA Safety weenie...and I can't tell one ATE caliper from another....they don't say BMW on the side. They look like an A caliper.

Been to more than a few tech sessions and have never heard a tech inspector say...."caught some guy using BMW calipers.... "

[SRT356/911]

If you are running in the 2.4S class, and have the BMW calipers you are at a disadvantage by weight from the true 2.4S. The BMW calipers are heavier.

The pads are the same size as the S.

The calipers are all ATE. Like Mikez, I also do tech and I would never call anyone on the calipers.

Steve

[zotman72]

Back from a junkyard today with a set of BMW calipers off a '77 320i. Cost me $40 and change. Yep they are heavier than S calipers and the pad size is about .5 inch less than S pads. I am not too worried about the Class change as I do not intend to advertise it. I am in the S class because of my engine (2.4S MFI) but could not swing ($) the strut change with A or S calipers. Our challenge series rules are somewhat inflexible about non Porsche components on modified stock classes.
http://vista.pca.org//rmr/Training/ChallengeSeriesRules2000.htm

Again thanks for the tip, you have saved me some serious cash and hopefully I will have better brakes in place soon.

Bill

[911pcars]

Just to recap. The objective is to install vented rotors on an early 911 with M Sruts.

The 77 BMW 3201 front calipers have a 3" bolt pattern and will fit on the early 911 vented rotor.

The brake pad is smaller in area than the "S" pad; about the same size as M pads.

Have I got that right?

BTW, some early Alfa's. MB and Ferrari's use the ATE caliper. Don't know if these calipers are 3" or 3.5" or will fit vented rotors.

Sherwood Lee

[zotman72]

That was the recap, however there are some twists and I went down one blind alley. The BMW ATE calipers that I pulled today from what I believed was a '77 320i DO NOT fit a vented disc of 911 M strut. The rotor gap is too tight, ie. they are made for a non vented rotor. I should have noticed this before I pulled/bought them. I was on mission today and missed the obvious until I got to cleaning them up in the garage. It was only $42 bucks though.

So the BMW calipers NOT to use are BMW# 66R, ATE# 54.
My 911T M ATE calipers have an ATE# of 252.

WHAT are the right BMW/ATE number calipers fellas? As there are more BMW 320is at this junkyard....

On a side bar, the lip inside of the caliper might lend itself to grinding down to fit my vented ATE slotted rotors. I will give that a go tomorrow. The saga continues

Bill

[Joe Bob]

On the plus side...you can sell those to the 914 guys...they bolt onto the pre 73 front ends and will work with a little machining on the 73 and up....

[SRT356/911]

Hearing that the calipers you got from a 77 320i were not made to fit vented rotors was a first. I personally know of 4 sets- including my own- that came from 77 320i's and they bolted right up to Porsche vented rotors. And they were made to fit BMW vented rotors.

I do not know what is going on there, but if anyone goes to get them it is one question to assure is asked before pulling the parts.

Bill. I am not sure that you want to grind down that much metal. There may not be room to fit the pads if you take too much off.

Could the car have been a 76 or maybe a 320? I just looked at my calipers and the only number was on the left caliper on the 'hat'. It was 115R.

Steve

[ChrisL]

FWIW, the Bentley BMW 3 Series Enthusiast's Companion notes that for the 1977-1979 320i (E21)- US Model, the front 255 mm disks were vented in 1977 only.

Chris.

[SRT356/911]

Chris

Thanks or the info. on the vented rotors. That was great.

Sherwood

The BMW and SC pads are considerably larger in surface area than an M pad. That is the reason to switch to the BMW caliper with the 3" mounting ear spacers.

If you are time trialing be cautious of changing pad brands. I went from Performance Friction 90's to Pagid orange. The PO's in my opinion were not as rotor friendly as the PF 90's and I thought they did not give me the braking that I desired. Plus they wore much faster than the PF 90's. I went back to the PF90's and had to grind all of the PO 'debris' from the rotors to stop the vibration when the brakes got super hot.

Rotors today all seem to have some warpage no matter what your source or brand. This goes for dealer supplied rotors too.

The dealer rotors are a notch better though. Porsche I am told inspects random samples of shipments and if the samples are not up to their standard, they reject the entire lot. This of course pisses off the supplier and prices climb at the dealer. Places like SSF buy more volume than PCNA, and SSF can get better pricing than PCNA.

So choose your brand and your source and stay with it.

Steve

[rvanderpyl]

Now does anyone have a replacement caliper for the rear of 68 and prior cars?

Robert

[Joe Bob]

I would bet that 914 calipers would work....been a while since I seen a 68. Does it have an internal brake shoe for the e-brake or does it have a cable trigger like the 914s....

What is the distance on the rear mounts? If they are three inches, the BMW one will fit also....it just depends if an e-brake is important to you or not....