3" ear brake upgrade

[trak ratt]

Has anyone tried using the Carrera’s rear M calipers on the front of early cars equipped with 3” struts? Even though the pad size is the same, as the smaller Ms it seems that the larger 2 x 42mm. pistons and 4mm wider rotor would be a nice cost effective upgrade for the early cars. Since the stock early car’s calipers have the same size pistons front and rear would the Carrera’s 2 x 42mm calipers mounted front and rear on early cars retain the stock braking balance. This would allow the use of the 24mm wide Carrera rotors front and rear and still fit the whole setup inside 15” wheels. Netting a substantial increase in clamping power and a nice increase in thermo capacity. I suspect this setup would be optimized using a 19mm master cylinder too. Hard brake lines would likely need to be changes though.

[RallyJon]

48mm (narrow M front) is larger than 42mm (wide M rear).

But if you use wide M (rear) spacers and bolts in an M front (w/48mm pistons) caliper, you could use 24mm Carrera front rotors. Maybe. If it all bolts up.

[johnsjmc]

Why not leave the stock calipers on it and fabricate spacers to fit between the 1/2s to fit the thicker rotors.The larger pistons will mean lower pedal pressure for a given stop but also may produce a longer pedal travel to pump enough fluid to the bigger pistons. Isn,t there a BMW (320?) caliper that will allow an upgrade to the fronts? (ie larger pad?)

[trak ratt]

Thanks for the replies. Except for the Carrera rears I believe all M calipers had the smaller pistons. The primary reason for my post was how best to use the wider by 4mm rotors all around on an M equipped car to increase their thermal capacity. The basic idea of using a wider spacer between the two halves of the stock Ms is what started me thinking. From other postings and my own experience the O ring seals and bolts can be hard to source and are pricy. I understand that the spacers themselves are made from unattainium, so I would have to cutup 4 rear Carrera calipers to “harvest” the spacers anyway. The BMW caliper does have a larger pad but uses the stock rotor and may require additional machining (per PP tech article). I thought the upgraded 19mm MC would easily handle the larger brake fluid requirement.
I was just wondering about the larger piston Ms front/rear balance. Anybody ever try or hear of anyone who may have tried this set up?

[}{arlequin]

interesting idea Dave. Not sure about what it'll do to the bias though.

At one point I was looking to cannibalize rear Carrera calipers to stick the spacers into my narrow M calipers to fit the 24mm rear rotor.

As for the difficulty of finding seals, I believe someone has solved this problem, complete w/ part #'s:
Oh No, I split my Carrera Calipers

[trak ratt]

Hi Dave! I saw that also but noted the c$$t and that availability in the past has been sketchy. Any idea why ATE would use “special bolts” for the calipers? Why would you worry about the bias if both ends were the same size, just like the stock ones only larger? Which takes me back to my original question. I still really like your car (even the color)!

[jpnovak]

Dave, the method you have outlined would work, but only if you added a rear proportioning valve to rebalance the bias. The front M and A calipers have a 2x48mm pistons. The narrow rear M have 2x38mm and Carrera M have 2x42mm pistons (info from Bill V.'s site).

the combination of 42mm piston diameter up front and 42mm in the rear creates an imbalanced brake bias. The bias is specifically setup to have more clamping force up front. You do not want a strong forward brake bias. When the weight transfer occurs during hard braking the rear of the car can lock up causing some interesting turn-in points.

[}{arlequin]

Jamie, I think Dave wanted to simply widen the front narrow M's to fit the Carrera rotors, and maybe even do the same to the rears, thus keeping the pistons/ratio same. I think.....

Dave,
With my approach, I wouldn't be seeing a bias problem b/c I was going to go w/ true Carrera front calipers and only widen the rear M's (and not put true Carrera rears) which should allow me to retain the same ratio as any other SC.

I must've misunderstood you, b/c I thought you just wanted the complete Carrera rear caliper installed on the front of your car. If you did that, you'd be ditching the front narrow M's 48mm pistons and replacing them w/ Carrera's rear 42mm pistons, hence the bias change.

[mjmoran]

Just to make sure all are on the same page...ALL front M calipers have 48mm pistons...So, there are three different types of M calipers: Carrera rears (42mm) All other rears 69-83 (36mm) and T fronts (48mm). So, Dave Riley there would be no more clamping force by changing to Carrera rears...you would have less. Although IF you added the Carrera spacer as }{arlequin mentions to a T front M caliper you would retain the good brakes and get a higher thermal capacity. If you add the Carrera M to the rear, you will need the Carrera Proportioning valve to retain the bias. Otherwise you will have rear lock up...bad!

Good L:uck

[trak ratt]

Thanks, I had forgotten that the M fronts were 48mm, couldn’t find the reference either. My idea was to increase the thermal potential not increase clamping force. I’m just not comfortable splitting the calipers even though I’ve heard that the O rings are available again.