Front BMW brakes locking front wheels all the time, why...please guys can i have your advice? Options

[budman5201]

I recently bought new rear calipers, redid the front BMW brakes up front and installed HAWK race pads up front. The braking has significantly improved! YES! but now i have one dilema......The front brakes lock up EASILY and the rears never at all..........I wish i could make all them lock up in emergency situations or at least more Braking in the rear.


Did i just significantly make the front brakes better by installing new race pads and BMW brakes? Can i adjust anything with the stock rear system to get more pressure to the back so i dont lock up the front VERY EASILY???

thanks guys i appreciate your help.....

Stock 1.7 liter GOING SUBARU 2.5 200 hp N/A soon!! Trying to make everything else PERFECT before i get my third Subaru done.....The braking was lacking on my last conversion......

thanks!

[horizontally-opposed]

I used to recommend it but that was before...

Blah, blah, blah....

Zing-zing-zingahed! (IMG:style_emoticons/default/w00t.gif)

pete

[Eric_Shea]

Go write something... (IMG:style_emoticons/default/biggrin.gif)

[davesprinkle]

Kyle,

Do you have a firm pedal issue? If so I would look to the shut-off valve and measures to make sure air is out of it.

Regarding the locking - Dave Sprinkle had this same problem and his pads weren't bedded in yet.

For his street car I recommended the Ceramic pads which he eventually thought were "good" (once they bedded) but not great. He ended up not liking them because they were very dusty. I have the same situation on my wife's Mercedes wagon. I "really" liked the ceramics but they are dusty. I think they're the best in-expensive pad solution at around $35.00

Back on target, you should have great pads, I would be concerned that they've yet to bed in as P4S's are one of the best pads out there. The only other person I heard of with a similar problem was Dave and he reported back as mentioned above.

Regarding the bench bleed and the pedal. You mention bleeding so I mention pedal. I don't think the master cylinder would be an issue. I have a theory on 914 brake bleeding that I want to look into this weekend. If I'm correct and I can come up with a solution this could solve the spongey pedal thing. It involves the shut-off valve.

Work on getting the rears bled and bed in the pads and you should be good to go.

I'm gonna weigh in here with my brake experience. I recently went through my entire braking system -- rebuilt all 4 calipers, new 19mm master cylinder, new lines, new rotors, new pads. Post-rebuild, the braking sucked -- soft pedal and poor decceleration. I'll spare you the interminable details, but the end result was this:
A : You must ensure that all the air is out of your system. This will be less a problem when you are simply replacing the fluid, but if you've evacuated the system of hydraulic fluid (as would be the case if you've rebuilt the caliper, or replaced the mc), you're going to struggle to get all the air out. Conventional wisdom is that the air predominantly gets hung up in the proportioning valve. This may be true, but you shouldn't disregard your front calipers. I recently rebled my system and got air out of the FRONT, not the rear. Bleed, bleed, bleed. Use the McMark long-tube method so you can keep your wife out of the garage and save your marriage. Drive, bleed, drive, bleed. PITA.
B : You must ensure that your new pads are bedded into the rotors. This has a big impact on braking effectiveness and the bedding might not happen readily if you're just cruising around town. Find an empty straight road. Get up to highway speed and then stop as aggressively as you can without locking the wheels. Do this over and over. At the end of this exercise, I could smell my brake pads, but damn they worked better.
C : Pad choice is a big deal. Refer to Eric's recommendations. I'm currently running the PBR organics. I'm pleased. Low dust, good stopping performance.

[budman5201]

OKay guys I will ring back into here next week when my rear pads are in and i put 100 miles on them......Proportioning valve is STAYING due to safety....catch u guys later THANKYOU FOR YOUR HELP!!....

[budman5201]

OKay guys I will ring back into here next week when my rear pads are in and i put 100 miles on them......Proportioning valve is STAYING due to safety....catch u guys later THANKYOU FOR YOUR HELP!!....

Pads almost seated, brakes already better! give ya more updates in 80 or so miles

[ChrisFoley]

The reason for matching your pads front to rear is due to the coefficient of friction of the pad material. High performance pads such as Hawk have a much higher c/f than cheap street pads. Using high c/f pads will improve braking immensely as long as the rest of the system is functioning properly. I used stock brake calipers front and rear on my FP race car for years with no stopping problems from up to 120mph. You should not need any enhanced cooling such as the AJ setup unless you track the car. One thing to watch out for with high performance pads is squealing. I have a set of KFP race pads on my street car right now that squeal badly at 30mph or less.
I have to slightly disagree with Eric on the rear pad clearance. IMO .008" is correct and proper per the factory manual. I have always used this with no problems. Some aftermarket manuals specify .040" which is way off. Excessive clearance will lower the brake pedal, not reduce the force applied, except under light braking circumstances. The primary reason for adjusting the venting clearance is so the parking brake will work. There is enough play in the wheel bearing for the rotor to move 8 thou when you set the p-brake. Too little clearance will cause drag and overheat the caliper.

[Dave_Darling]

Remember, though:

Brakes stop the wheels. Tires stop the car!

If you want to cut down on your stopping distances, get grippier tires!

(That assumes you can lock the brakes by standing on the pedal; if you cannot then your brakes are broken and must be fixed!)

--DD

[Eric_Shea]

You should not need any enhanced cooling such as the AJ setup unless you track the car. One thing to watch out for with high performance pads is squealing. I have a set of KFP race pads on my street car right now that squeal badly at 30mph or less.
I have to slightly disagree with Eric on the rear pad clearance. IMO .008" is correct and proper per the factory manual.

Except he has BMW calipers now with about 40% more pad up front on the same rotor. I agree however, probably not needed for regular street duty even with the BMW calipers.

.008" was the original spec. in the manual but they (Porsche) sent out a TSB revising that number after the manual was printed. All of the Haynes and Clymer folks picked up the .008" as well. Later the factory revised to .004" -or- basically the thickness of a business card vs. two business cards. I doubt there would be much difference as the mechanism in the piston allows for much more travel but, as the pads wear you may eventually have handbrake issues.

.008 - .004. Either one is better than where 80% of them are set right now. (IMG:style_emoticons/default/biggrin.gif)

[ConeDodger]

You should not need any enhanced cooling such as the AJ setup unless you track the car. One thing to watch out for with high performance pads is squealing. I have a set of KFP race pads on my street car right now that squeal badly at 30mph or less.
I have to slightly disagree with Eric on the rear pad clearance. IMO .008" is correct and proper per the factory manual.

Except he has BMW calipers now with about 40% more pad up front on the same rotor. I agree however, probably not needed for regular street duty even with the BMW calipers.

.008" was the original spec. in the manual but they (Porsche) sent out a TSB revising that number after the manual was printed. All of the Haynes and Clymer folks picked up the .008" as well. Later the factory revised to .004" -or- basically the thickness of a business card vs. two business cards. I doubt there would be much difference as the mechanism in the piston allows for much more travel but, as the pads wear you may eventually have handbrake issues.

.008 - .004. Either one is better than where 80% of them are set right now. (IMG:style_emoticons/default/biggrin.gif)

E,
I would add to your advice that since he has the BMW calipers he should never have his rotors turned. They should be replaced as he needs all the mass he can get. His rotors were engineered with the 914 calipers in mind. They are getting lots more heat to dissipate with the BMW calipers...

As usual, my opinion is of no relevence and I bow to your superior number of wives. (IMG:style_emoticons/default/biggrin.gif)

[Eric_Shea]

I don't know jack but... it sure is fun pretending online. (IMG:style_emoticons/default/biggrin.gif)

[ConeDodger]

I don't know jack but... it sure is fun pretending online. (IMG:style_emoticons/default/biggrin.gif)

Still, I bow to your superior wife count... I am in awe!

[PeeGreen 914]

I don't know jack but... it sure is fun pretending online. (IMG:style_emoticons/default/biggrin.gif)

(IMG:style_emoticons/default/blink.gif) Then why did I spend so much money with you if you know nothing? (IMG:style_emoticons/default/headbang.gif)

Eric is the man, heed his words and you too may have many wives of your own (IMG:style_emoticons/default/av-943.gif)

On second thought, I can only handle the one I have (IMG:style_emoticons/default/laugh.gif)

I have talked with Eric over the phone about brake combinations for a few hours and this guy knows what he is talking about. Not only that but he has the goods to get you what you really want and he will try to SAVE you money. (IMG:style_emoticons/default/pray.gif)

[Eric_Shea]

Still, I bow to your superior wife count... I am in awe!

TIP: Sisters. (one mother-in-law)

Jon Von B. Your check is in the mail. (IMG:style_emoticons/default/biggrin.gif)

Did you get everything hooked up yet?

[PeeGreen 914]

Not yet... getting it started though. Just got my car up on stands last night.

[horizontally-opposed]

I don't know jack but... it sure is fun pretending online. (IMG:style_emoticons/default/biggrin.gif)

(IMG:style_emoticons/default/blink.gif) Then why did I spend so much money with you if you know nothing? (IMG:style_emoticons/default/headbang.gif)

Eric is the man, heed his words and you too may have many wives of your own (IMG:style_emoticons/default/av-943.gif)

Never really thought about this before, but:

1. Get into Porsche brake rebuilding business
2. Acquire more wives

Potential connection? You decide (IMG:style_emoticons/default/biggrin.gif)

pete

[davesprinkle]

... he has BMW calipers now with about 40% more pad up front on the same rotor.

Eric, you mentioned the increase in pad area. My understanding is that the fundamental contributor is the increase in piston area. Am I wrong? Can you comment further?

[budman5201]

WOO HOO!!! The verdict is in! My brakes are Sweet now. PADS BROKEN In........

Now the only limit are exactly as someone put it, my tires. My tires look brand new, but are obviously very old. Build date 2002. They are hard as heck when i try to bend the tread with my fingernail. NO give. So fresh tires all the way around soon, I bet i'll see even better than my stopping distance i already have...

Current setup. BMW calipers up front, hawk pads. New rubber lines all the way around. NEW calipers in back with Portofield Orange pads (now broken in fully). Patrick motorsports Brake fluid inside lines.

Stops on a dime, rears never lock up during emergency situations. Fronts Lock up easily, but probably a little too easily to once again NEEDED new rubber up front first.
Solution today or next weekend. Sticky nice quality tires.

COOL thanks guys for your help. My first 914 with Killer stopping.

[Eric_Shea]

Eric, you mentioned the increase in pad area. My understanding is that the fundamental contributor is the increase in piston area. Am I wrong? Can you comment further?

Both but, I'd say the pad area is causing the fronts to lock. Front pistons are 48mm which has thrown things off a bit as well which is why I recommend the 19mm MC.

Chris... curious as to why you mismatched the pads. Glad you're stopping better.

[budman5201]

Eric, you mentioned the increase in pad area. My understanding is that the fundamental contributor is the increase in piston area. Am I wrong? Can you comment further?

Both but, I'd say the pad area is causing the fronts to lock. Front pistons are 48mm which has thrown things off a bit as well which is why I recommend the 19mm MC.

Chris... curious as to why you mismatched the pads. Glad you're stopping better.

i tried my best to find rear Hawks brand for the back, but couldnt locate a reseller so i chose the next best i though...portofields (the oranges is the one they sent me)

Wouldnt a 19mm MC increase my foot pressure needed for the same pressure to the pads?

[PeeGreen 914]

I'm thinking of doing a Portofield group buy through Eric in the next month or two. Maybe wait until then? Or maybe you want to start it earlier. I will jump on it whenever.