Brake Caliper Question, Front Calipers Out Back? Options

[Seventyfive914]

Hey All. First off,...I did do a search on this topic and there's a load of information on brakes all-right, but I didn't find where swapping front calipers to the rear is discussed. It seems that I have read about it somewhere, and I mocked up one of my spare trailing arms with a core front caliper and it looks like it will work. I don't want/need the parking brake function and the front calipers are lighter without that mechanism. Is there anything I should know before I proceed with the swap? Thanks for any advice. Regards, -K-

[DanT]

Not suggested unless you are using a very large vented type front caliper.
I was going to do this with M calipers on the front and the stock fronts on the rear with a T fitting in place of the proportioning valve.
The stock fronts have a very large piston diameter which does not match up well with most of the older front calipers. There are at least one or two threads about this topic specifically.

You would need to go the a 911 front strut (5 lug) setup with a front caliper from a Boxster or a 944 turbo.
Overkill unless you are going to be using some very big horsepower on the race track.

[hmeeder]

Well, I'd have to disagree with you on a couple points, Dan.

I went to BMW front calipers, moved fronts to the rear (you lose the p-brake and do need to shim the caliper with one wavy-type washer per bolt) and swapped to a 19mm MC. I also ditched the Prop valve in favor of a "T"

I find my brakes to be very well balanced (the fronts lock up just a hair before the rears) and the total brake package is vastly better.

Now, I'm not saying that the swap to Ms with a vented front disk wouldn't be an improvement. It most certainly would be. However, the BMW brakes increase the front pad area by some 40 percent and the move of fronts to the rear about 35 percent and the larger MC accounts for the increase in piston volume. The brakes are extremely firm and ease to modulate. For a 2000 pound car, the braking is entirely adequate. All these mods can be accomplished for a very thin dime and won't require converting the entire suspension to a 5 lug, a much more expensive proposition.

After all, once your brakes lock up, you have exceeded the friction of the tires. More brakes will not stop you faster unless you have a sophisticated system like ABS to monitor, control and inhibit lock up. Bigger brakes doesn't always mean more stop, you just get to lock up quicker.

My $.02 YMMV

OPAF

[DanT]

Actually I think you just agreed with me (IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif)
The M calipers have the same size pad as the 914-4 fronts the only difference is in the piston diameter. The 914-4 front piston is considerably larger than the 91-4 rear piston. Ask Eric Shea, one of our resident brake gurus. That is why they are not suggested to be used together. Your solution with the larger piston and pad size more than off sets the increased size of the 914-4 fronts on the rear. I am sure that is why you are having good braking results.

[Dr. Roger]

dan, on mine i've noticed that my pedal feel is way soft (please note that they're old pads on all calipers but they have not been seated yet in their new locations) and the brakes ahve been bled 3 times over and the p valve bled also.

could it be that the stock master cylinder is too small now that the "A" calipers are installed and i'm just running out of pump throw distance???

sorry for the hijack.. (IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif) but i thought it would be helpful to all concerned. (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)

[hmeeder]

QUOTE

Actually I think you just agreed with me

Well, OK then (IMG:http://www.914world.com/bbs2/html/emoticons/laugh.gif)

You're right. I just reread seventyfive's post and I hadn't realized that he was doing nothing to improve the front to offset the increase in the rear.

I agree that merely putting fronts on the rear without doing anything to the front is to be avoided. It appears that it would create significantly worse pedal feel, longer pedal travel to create the same braking pressure, and worst of all, the rears would lock up before the fronts and result in some extremely dangerous braking conditions. The trick with brakes is balance and just putting the fronts on the rear dicks that up.

Roger, the stock 17 MC may well be the culprit. Think of it this way; the mc moves a given volume of fluid for a given pedal travel. When you increased the volume of the front brakes (large calipers require more volume movement to create the same braking pressure.) you will have to press the brake pedal that much further to move that extra volume. That may very well feel to you like a softer or mushy pedal feel.

Compound this with the p-valve which is designed to balance the stock fronts and rears and you may very well be feeling that your brakes aren't what you were hoping for.

I would suggest ditching the p-valve for a "T" and if that doesn't improve things (I believe you will notice an immediate improvement) after that, the move to a 19mm may be warranted.

you may have your hijack back!

[Seventyfive914]

Thanks for all your replies and valuable information/advice. I have been considering the BMW calipers up front and will most likely go with that set-up. Just for grins though, how do you suppose a 19mm M/C pushing stock front calipers up front and out back with an adjustable proportioning valve would work out? -K-

PS - hmeeder,...What's the thickness of the "wavy-washer" (and what stock application do you source 'em from) for shimming? I had a feeling there would need to be a little tweak to keep the correct clearance back there. -K-

[Powerman]

M fronts on the back work well on a FP car with new porportioning valve.

[davep]

I'd guess that if you don't want the parking/emergency brake then you will be tracking the car. Stock front rotors, I found, were no use on the track due to overheating. BMW calipers will help make overheating occur sooner.

Balance is it. The 911 went to the 914/4 front caliper as a rear caliper at the same time as they went from 20mm vented rears to 24mm vented rears and huge calipers at the front.

BTW, front and rear calipers weigh the same. I'm not sure I'd want to run without an emergency brake. It is not legal for the street, and I don't know about the track.