911 Caliper Upgrade Question

[crashr]

Ever since I got my 911 back on the road a couple years ago, I have never been very happy with the quality of the braking on the car. In fact I think it is worse now than when I started my restoration. During the restoration, I have changed multiple things on the car which may have led to poorer braking quality so it has been a challenge to figure out exactly what is causing the issue.

I rebuilt all 4 M-type calipers and am using a high quality brake fluid. I have bled the lines countless times, and more recently replaced the master cylinder.

After all this, the pedal feels semi-firm, however I struggle to lockup the brakes. Which leaves me with a less than safe feeling while driving the car in traffic.

In terms of changes to the car,

1) I did replace the engine with a 3.2 which I know is heavier than the 2.7, so the weight of the car is probably sitting too far back, as I have not updated the suspension, however I wasn't sure how much of an issue this would cause for braking.

2)The other big upgrade is the car has 17x9 and 17x11 wheels on it now, so there is obviously a lot more rubber on the road.

Would either of these be the main culprit for the poor braking?

Becasue the car is only street driven, I am currently considering either moving to a wide-A type caliper (which would be costly because I would need to replace my Strut assembly for the proper spacing), or I more recently found the Brembo AM-caliper on the PMB site.

Has anyone had any experience with this AM-caliper and would it provide the improved stopping performance I am looking for over the current M-caliper?

[gtc]

I'd suggest you email Eric at PMB directly. He is very helpful, and will give you honest advice about his products. I don't think he would try to sell you something you don't need.

Also, in order to get some meaninful advice, I think you may need to be more clear about what has changed with regards to how your brakes work and how your car stops.

[Madsimilius]

Hmm sounds weird to me, unless your brakes are hot i don't think it should be a problem locking up the brakes even on older 911 cars.

[Bob Kontak]

Originally Posted by crashr

Would either of these be the main culprit for the poor braking?

Just talking here and beer is in play.

No. You have air in your lines and/or your master cylinder and I feel your pain.

12 years I owned my car before getting the air out properly. Finally bought a Motive bleeder, Mini-Vac, one way bleeders, etc.

Not until I flushed it, drove it for few days and bled it again (maybe again) did the pedal tighten up. I mean the pedal tightened up to where 1" of pedal movement hit a brick wall. That little step you feel now as the pedal goes down two inches is gone. It never gets that far.

I honestly think the one way bleeders did the trick (um, aggressive bleeding) associated with at least one repetition after a few days of driving.

Tell us about bleeding the MC? Were the caliper piston bores as smooth as a baby's behind?

[combatic]

I second the notion to talk with Eric at PMB.

As understand brakes. Your M calipers should be able to provide adequate stopping power. The 'bigger brakes' such as wide A's, S and later model SC brakes and the corresponding rotors all have the same diameter pistons. Where they perform better is in heat dissipation during aggressive, repetitive braking. This is accomplished by vented rotors and mass in the caliper itself. (there are other factors such as flex, gas dissipation etc). That being said running modern sticky rubber on yoru 7/9's might be gripping beyond the brakes ability during hard stops?? I would be curious how others weigh in on this for my own understanding.

I didn't read that you changed pads out. Pads can get soaked with oils and will never be the same. Upgrading pads (like tires) are also one of the single biggest performance upgrades you can do to your car.

It does sound like you have air in the lines. I use a MityVac 7400 with the brake bleed kit. (i cursed everyday I had a Motive ...but others love them. The difference is pulling fluid at the brake with a mityvac or pushing from the reservoir with a motive).

Either way, AFTER 'power bleeding', I found that I still needed a helper to pump the brakes at EACH corner to to get the rest of the air out on my lines on my 1969 with M calipers b/c I was getting some squishy pedal feel. That seemed to sort it for me.

I assume you are also starting your bleeding at the furthest brake from the master cylinder (passengers rear brake) and working to the nearest (drivers front).

[Charles Freeborn]

Talk to Eric, but I can say with out a doubt that my '74 brakes feel much better after switching to front calipers from an SC. And I had the fancy pants aluminum S units to begin with.
Bleeding is key. For some reason Porsche cars are fussy in this area.

-C

[Flojo]

Originally Posted by crashr

I rebuilt all 4 M-type calipers and am using a high quality brake fluid. I have bled the lines countless times, and more recently replaced the master cylinder.

did you change the discs and pads too????????????????

when I got my 79 SC, the brake system was unrefurbished stock with first well loocking discs and ca. 5mm thick pads. no signs of unusual wear to each discs and pads.

but: breaking performance felt somewhat weak (even though it had fresh fluid).

nontheless, the car did pass the german TÜV aprovement.

but I didnt like the idea of an old brake system on a sports car, a car that can well be driven up to and above 200kmh.

so I changed it all!

new M-calipers (ate), new dics (textar) and pads (EBC red stuff), new lines, new hoses, new cylinder, new fluid (regular DOT 4).

WOW

since then, I whish this SC hat ABS ;-)

so as you've done the calipers and the cylinder, I recommend you change the discs and pads.
doesnt cost much, is done in 2 hrs and gives you confidence.

[dfhtrhjn]

I switched from stock to hawk performance pads on my '77S and I liked the extra grip. I also have the S calipers in front on both my cars.

I've got the same hawks on my '74S (no brake booster on '74) and they feel better than stock.

Our host carries them and they're very well priced.

Porsche 911 & Carrera Brake Pads & Rotors - Page 2

I use a power bleeder to get the firm pedal feel; our host carries that too.

Porsche 911 & Carrera Brake Hydraulics - Page 2

Since you've already done so much, like the previous post suggested, you may wanna do the pads and/or rotors next.

[Tidybuoy]

I had rebuilt my "M" calipers on my '74 but I never felt that they gripped like they should. It was also difficult to get used to non-boosted brakes. After watching the rebuild video from PMB, I concluded that although I did a good job rebuilding my brakes, they would never be as good as what I would get from PMB. I eventually found a set of struts with 3.5" spacing and I bought rebuily "A" calipers from PMB. The price per pair for front "A" and rear "M" is really not super expensive (I think $375 per set). My brakes have been very nice ever since and I never worry about being able to stop.

Here's a video from PMB that shows how they do it:

[911pcars]

Porsche brakes aren't normally borderline, even with a 3.2. Something isn't working to spec.

Got to ask. Is this for a DIY repair, a guide to possible causes or a to do list for your tech?

From your symptoms, I would inspect/repair/replace in this order. All relatively DIY and stuff a shop might replace in the course of their inspection and diagnosis.

1) Brake pads and rotors - worn, glazed?

2) Brake fluid. Black or contain bits of debris?? Could indicate either neglect or some issue inside the system. Flush and refill, then test drive after the following inspections.

3) Flex brake lines bulging or any other signs of deterioration? Not easy to spot a worn internal fluid passage restricting fluid flow, but if fluid doesn't easily pass through.........

4) The last two items are the master cylinder and the calipers. Is the pedal firm? Does each caliper work (clamp the rotor)?

Or throw money at it. Eventually, that always seems to work.... to the benefit of the repair shop.

Got an honest tech? If so, ask for an inspection.

Sherwood