Move front 'M' Calipers to the rear?

[joeblow]

Guys I have an early car with F & R 'M' calipers on it. The front is getting later BOGE/Bilsteins with Alloy 'S' calipers.

So I am sitting here looking at the removed front 'M' calipers thinking it might be a nice upgrade to mount them in the rear. I know the 'balance' will be off but a proportioning valve could fix that. They will need new lines but everything else is bolt on it looks like. Thoughts?

[djpateman]

I don't think it is worth the aggravation. 48mm pistons vs 38mm pistons is a huge difference to compensate for. I've only seen race cars with pistons that big on the back, and few enough of them. It also adds a lot more unsprung weight.

[Grady Clay]

Is my memory failing or are they different bolt spacing on SWB?
Same F&R on 'M' caliper LWB.
Different on 'S' caliper LWB.

Best,
Grady

[Bill Verburg]

Originally Posted by joeblow

Guys I have an early car with F & R 'M' calipers on it. The front is getting later BOGE/Bilsteins with Alloy 'S' calipers.

So I am sitting here looking at the removed front 'M' calipers thinking it might be a nice upgrade to mount them in the rear. I know the 'balance' will be off but a proportioning valve could fix that. They will need new lines but everything else is bolt on it looks like. Thoughts?

don't do it

no, a p/v will not correctly compensate

you want ~1.6+/- bias, moving front to rear will give you 1

[Trackrash]

don't do it

no, a p/v will not correctly compensate

you want ~1.6+/- bias, moving front to rear will give you 1

+1

You don't want to increase the rear braking on your car. You will find that with the S calipers in the front the brake balance will be great with your original rear calipers.

[joeblow]

They do bolt on as I test mounted them.

Originally Posted by Grady Clay

Is my memory failing or are they different bolt spacing on SWB?
Same F&R on 'M' caliper LWB.
Different on 'S' caliper LWB.

Best,
Grady

[joeblow]

OK it seems the consensus is that they are too much unless I go much bigger in the front which I do not intend to do.

I would think that if a four piston caliper was used with larger piston area it would be a nice easy way to add some rear brake without a lot of $$$ investment.

By the way the weight difference between the front M and rear M is not very much.

[chris_seven]

Originally Posted by joeblow

They do bolt on as I test mounted them.

Seems a bit odd.

The Rear M should be a 3" spacing

Early Front M had the same spacing.

All Alloy S Calipers had a 3.5" spacing so you may have an issue with your struts.

[Bill Verburg]

Originally Posted by joeblow

OK it seems the consensus is that they are too much unless I go much bigger in the front which I do not intend to do.

I would think that if a four piston caliper was used with larger piston area it would be a nice easy way to add some rear brake without a lot of $$$ investment.

By the way the weight difference between the front M and rear M is not very much.

nope,
common choices for the front and resulting hyd bias ratio w/ front M used in back
964 or Boxster 2
993 or 993tt 2.2
930 2

remember you want ~1.6

the bigger rotors used on all of the above further move bias to the front

when the car is set up right you can take advantage of more rear bias down into the 1.475 + area, but no further

[jpnovak]

Originally Posted by Bill Verburg

when the car is set up right you can take advantage of more rear bias down into the 1.475 + area, but no further

Bill, Can you elaborate on this statement? What setup changes need to be in place? I would assume a much stiffer suspension would not weight transfer as much to the front. This could take advantage of increased rear bias and therefore more braking force from the rear tires before rear lockup.

[Walt Fricke]

Anti-dive (as the 930s had) front suspension might reduce weight transfer.

[Flieger]

Anti-dive does not reduce weight transfer, it actually speeds it up. The main way to reduce weight transfer is to lower the center of mass or lengthen the wheelbase.

[Bill Verburg]

Originally Posted by jpnovak

Bill, Can you elaborate on this statement? What setup changes need to be in place? I would assume a much stiffer suspension would not weight transfer as much to the front. This could take advantage of increased rear bias and therefore more braking force from the rear tires before rear lockup.

the car needs to be very low and stiff, you will also want a p/v and an effective lsd, if you do that then you can get f/r pad/rotor temps to be almost equal, the braking decel rate is just awesome

[Green 912]

Originally Posted by Trackrash

+1

You don't want to increase the rear braking on your car. You will find that with the S calipers in the front the brake balance will be great with your original rear calipers.

I did just this to make a full set of four on the 912 after the rears were found to have been damaged by an old ham-fisted rebuild. I just so happened to have a later set of stuts and some S binders in hand and threw it all on the car.


Don't do it. the results are not an improvement. S fronts and M rears are well set up together. I even run this set on the 911. Think about it. IIRC the pad size is the same and you will need to reduce the pressure to make them work with the fronts. You are now right back where you started.

[joeblow]

You forgot downforce! Big wings go up in angle of attack during high speed braking which adds downforce during the nose down giving further ability to efectivly add rear braking.

Ask me how I know

Originally Posted by Flieger

Anti-dive does not reduce weight transfer, it actually speeds it up. The main way to reduce weight transfer is to lower the center of mass or lengthen the wheelbase.

[joeblow]

Sorry if I confused anybody I have six calipers, two front M, two rear M and two front S. I changed struts and front calipers, swaping in the S calipers in front which left me with two front M calipers I was thinking about putting on the back. I think that I will hold off though now that I am hearing all this.

I do have some 944 Turbo calipers I was once thinking of putting on the front but I am leaning more toward period parts for this car, even if they are not 'original'. I figure the guys in the day were mixing things up that they had access to for race cars so I will do the same

Originally Posted by chris_seven

Seems a bit odd.

The Rear M should be a 3" spacing

Early Front M had the same spacing.

All Alloy S Calipers had a 3.5" spacing so you may have an issue with your struts.