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!

[Mike Gilbert]

i would try adjusting the rear brake proportional valve(see your repair manual) or just remove it completely with an inline tee....about $15.00 but be carefull on wet roads untill you get it right

[Eric_Shea]

Sorry Mike, the "remove the proportioning valve" thing is really bad advice that could cost someone their life. The rear brakes lock up on a mountain ridge in the rain and his car can go spinning off the edge like a top... real things can go real wrong, real fast.

The valve is a rear caliper saftey shut-off valve, made to disengage the rear calipers in a panic stop. I wish that brake "T" thing would go away.

Yes Budman, you significantly goofed up your brake bias. You now have 40% more pad material upfront "and" you have Hawk race pads up front (but not on the rear?).

Mike had it right in the first part. You'll want to adjust your shut-off valve but, not before you match the pads in the rear.

If you've yet to adjust your venting clearance your rears may not be working at all.

Sorry Budman... I see this as a problem all around. This is why I don't recommend the BMW calipers as an "upgrade".

The best upgrade for your situation would be to get M-Calipers and vented rotors. This will give you the same pad size you upgraded to now but the "MUCH NEEDED" venting to cool the rotor. Your new calipers will add heat to your solid rotors. You may be able to get by with an AJ Racing venting kit.

You won't want to hear it and, I've said it so many times that I'm a broken record but; my advice is to put the stock fronts back on and get the awesome Hawk pads all around. You will have a MUCH better matched and biased brake system and it will still stop like crazy.

[ConeDodger]

As much as anyone would hate to admit it (IMG:style_emoticons/default/biggrin.gif) , I have to agree with Eric on this... I think anytime you hear yourself about to say the word "upgrade" you should ask yourself if you think you are smarter than a Porsche engineer. In some cases new technology has come along but this is not an upgrade. It would be much better to get the heat out of the rotor than a bigger clamper... Venting - Gud! Cooling - Gud! Better pads - Gud! Bigger calipers without the other three - Not Gud!

[markb]

(IMG:style_emoticons/default/agree.gif) Listen to Eric, he knows what he's talking about.

[jaxdream]

Hi , I was wondering if any of you more experienced guys have tryed using the " proportioning " valve from the 944 ( turbo ?? ) setup which was mounted on the master cylinder BEFORE the line or is the thing I am referencing something else entirely??? I've read all about the pitfalls of the Tee fiting , heck I even got some with the same ideaology as others in the replacing with part , haven't done it yet , probably won't as I understand more of what the 914 prop. valve really does , slick as hell those Germans, looking to do 911 M rear , maybe A front or if I get the courage up to refurb the S set I have , like I stated just curious if the 944 part was a possibility .

Jack

[budman5201]

okay so....get hawk pads for the rear, then adjust rear proportioning valve? i love my brakes, just want them a little more in rear. i havent bought hawk pads for the rear yet, but when i do how many turns would i have to turn incrementally each time to slowly get to where i want to in the rear brakes. I turned a half turn then 3/4 turn OUT and still lock the fronts.......guess i am still WAY over biased in the front since i have correct venting (checked perfect) with stock cheap pads in the rear......


i dont do any racing, or plan on it. Just some spirted driving. Mainly looking for emergency stopping power only when i need it. I dont overwork my brakes on a constant basis, just LOVE knowing that they are perfect when i need them.......

This is my STARBUCKS run car or short trip car...no high speed canyon driving....

And wow, i never knew the difference HAWKS pads can make....amazing!

[budman5201]

okay so....get hawk pads for the rear, then adjust rear proportioning valve? i love my brakes, just want them a little more in rear. i havent bought hawk pads for the rear yet, but when i do how many turns would i have to turn incrementally each time to slowly get to where i want to in the rear brakes. I turned a half turn then 3/4 turn OUT and still lock the fronts.......guess i am still WAY over biased in the front since i have correct venting (checked perfect) with stock cheap pads in the rear......


i dont do any racing, or plan on it. Just some spirted driving. Mainly looking for emergency stopping power only when i need it. I dont overwork my brakes on a constant basis, just LOVE knowing that they are perfect when i need them.......

This is my STARBUCKS run car or short trip car...no high speed canyon driving....

And wow, i never knew the difference HAWKS pads can make....amazing!

just bought rs-4 s for the rear .....lets see how much better they will do than stock!

[Dr. Roger]

blue, black, or orange?

okay so....get hawk pads for the rear, then adjust rear proportioning valve? i love my brakes, just want them a little more in rear. i havent bought hawk pads for the rear yet, but when i do how many turns would i have to turn incrementally each time to slowly get to where i want to in the rear brakes. I turned a half turn then 3/4 turn OUT and still lock the fronts.......guess i am still WAY over biased in the front since i have correct venting (checked perfect) with stock cheap pads in the rear......


i dont do any racing, or plan on it. Just some spirted driving. Mainly looking for emergency stopping power only when i need it. I dont overwork my brakes on a constant basis, just LOVE knowing that they are perfect when i need them.......

This is my STARBUCKS run car or short trip car...no high speed canyon driving....

And wow, i never knew the difference HAWKS pads can make....amazing!

just bought rs-4 s for the rear .....lets see how much better they will do than stock!

[Brett W]

Toss the stock rear calipers and put the stock front calipers on the rear. Then add the T. That setup worked really well with PBR metal master pads all the way around. The fronts would lock up nicely and the rears would lock up shortly after that. Very controllable and predictable. What master are you running?

[Cap'n Krusty]

Toss the stock rear calipers and put the stock front calipers on the rear. Then add the T. That setup worked really well with PBR metal master pads all the way around. The fronts would lock up nicely and the rears would lock up shortly after that. Very controllable and predictable. What master are you running?

But then you have no hand brake, which is not only illegal, but many would call it dumb. The Cap'n

[Root_Werks]

This is some good reading. I need to go through my brakes (All stock) and this has given me some good tips on what to not even bother with and a couple of good things to do.

[Eric_Shea]

QUOTE(Brett W @ Nov 14 2008, 06:22 AM)

Toss the stock rear calipers and put the stock front calipers on the rear. Then add the T. That setup worked really well with PBR metal master pads all the way around. The fronts would lock up nicely and the rears would lock up shortly after that. Very controllable and predictable. What master are you running?



But then you have no hand brake, which is not only illegal, but many would call it dumb. The Cap'n

Couple things in there I would call dumb... especially for a Starbucks car. Sorry Brett.

* Fronts in the back - now you have a 43mm piston where a 33 used to be. Porsche didn't do this until 1984 with the 3.2 Carerra and they installed a P-valve in the 911 for the first time to compensate for this. 911 track guys have complained of squirrely handling when attempting to remove this as well. This is a narrow bodied, solid rotor street car.

* T Fitting - As explained. Saftey feature that prevents the rears from locking. Your statement that the "rears would lock up shortly after that" should scare the living hell out of anyone reading it. If the rears lock in any angle off dead center in a 914 you risk spinning like a top in a mid-engine car.

* Metal Masters - Those are the worst pads I know of. No noise, no dust, no stop.

Since many have made this "upgrade" (cause I guess Pelican isn't about to take that stupid article down anytime soon), I'll offer my recommendations of what I would do if I inherited this misbalanced setup:

1. Start looking for a nice 911T front strut solution and start saving lots of money for a proper rear solution.

**now that I got that outta the way** (IMG:style_emoticons/default/smile.gif)
2. Ensure that my rear calipers are working properly. Not just the venting clearance, make sure they're operating as many have stuck pistons etc.
3. Get the same pads all around.
4. Make sure the venting clearance is set to .004" not .008"
5. Get a 19mm Master Cylinder. Don't get the Chinese copies just yet because I hear there are problems still.
6. Get a cooling kit from AJ Racing/Alan Johnson Porsche. Very simple and very effective.
7. Finally - if you determine that your rear shut-off valve is coming on too early and shutting down your rears I would then attempt to adjust it.

In Budman's situation I doubt that's the case. I think he'll be in a different place once he gets the proper pads on the back and has them vented and bedded in.

I like the thread because it spells out a LOT of things:

1. BMW Calipers have 40% more pad area and will heat up your solid rotors and cause a mis-bias in the rear. This is not as crucial as it seems in this thread because Budman has good pads up front and old glazed bad pads in the back. Which leads me to my next reason I like this thread... (IMG:style_emoticons/default/biggrin.gif)

2. If you "really" want to upgrade your 914 brakes, GET REALLY AWESOME PADS... like our Buddy Budman did. This really goes to show how an awesome pad will make your car stand on it's nose. If you think $100 is too much to pay for pads, especially when you have $25.00 pads waved under your nose all day; think again.

Again gang, our 914's can lock up their brakes again and again and again with little or no fade. That being the case, you don't have a caliper problem. If you're not getting the braking performance you think you should be getting, check your pads and your tires.

[Solo914]

QUOTE(Brett W @ Nov 14 2008, 06:22 AM)

Toss the stock rear calipers and put the stock front calipers on the rear. Then add the T. That setup worked really well with PBR metal master pads all the way around. The fronts would lock up nicely and the rears would lock up shortly after that. Very controllable and predictable. What master are you running?



But then you have no hand brake, which is not only illegal, but many would call it dumb. The Cap'n

Couple things in there I would call dumb... especially for a Starbucks car. Sorry Brett.

* Fronts in the back - now you have a 43mm piston where a 33 used to be. Porsche didn't do this until 1984 with the 3.2 Carerra and they installed a P-valve in the 911 for the first time to compensate for this. 911 track guys have complained of squirrely handling when attempting to remove this as well. This is a narrow bodied, solid rotor street car.

* T Fitting - As explained. Saftey feature that prevents the rears from locking. Your statement that the "rears would lock up shortly after that" should scare the living hell out of anyone reading it. If the rears lock in any angle off dead center in a 914 you risk spinning like a top in a mid-engine car.

* Metal Masters - Those are the worst pads I know of. No noise, no dust, no stop.

Since many have made this "upgrade" (cause I guess Pelican isn't about to take that stupid article down anytime soon), I'll offer my recommendations of what I would do if I inherited this misbalanced setup:

1. Start looking for a nice 911T front strut solution and start saving lots of money for a proper rear solution.

**now that I got that outta the way** (IMG:style_emoticons/default/smile.gif)
2. Ensure that my rear calipers are working properly. Not just the venting clearance, make sure they're operating as many have stuck pistons etc.
3. Get the same pads all around.
4. Make sure the venting clearance is set to .004" not .008"
5. Get a 19mm Master Cylinder. Don't get the Chinese copies just yet because I hear there are problems still.
6. Get a cooling kit from AJ Racing/Alan Johnson Porsche. Very simple and very effective.
7. Finally - if you determine that your rear shut-off valve is coming on too early and shutting down your rears I would then attempt to adjust it.

In Budman's situation I doubt that's the case. I think he'll be in a different place once he gets the proper pads on the back and has them vented and bedded in.

I like the thread because it spells out a LOT of things:

1. BMW Calipers have 40% more pad area and will heat up your solid rotors and cause a mis-bias in the rear. This is not as crucial as it seems in this thread because Budman has good pads up front and old glazed bad pads in the back. Which leads me to my next reason I like this thread... (IMG:style_emoticons/default/biggrin.gif)

2. If you "really" want to upgrade your 914 brakes, GET REALLY AWESOME PADS... like our Buddy Budman did. This really goes to show how an awesome pad will make your car stand on it's nose. If you think $100 is too much to pay for pads, especially when you have $25.00 pads waved under your nose all day; think again.

Again gang, our 914's can lock up their brakes again and again and again with little or no fade. That being the case, you don't have a caliper problem. If you're not getting the braking performance you think you should be getting, check your pads and your tires.

Eric,
Since we are on the topic, and you have recommended the exact solution I have but I am still having problems maybe you can help.

I have rebuilt front calipers from you, rears that I have tested and seem to be in good working condition(adjusted), a new 19mm Master Cylinder, SS brake lines and Portfield R4S pads and I still can't lock em up. I have autocrossed and roadraced(specmiata) so I am familiar with brakes and typical bedding procedures but I have tried almost everything, checking for pad glaze, readjusting the rears, standard rebleed then tried bleeding with a vacuum bleeder etc. Could it be the proportioning valve? Could I not have bench bleed the new master cylinder well enough? I have the whole brake system apart right now(5lug swap, redrilled rotors and hubs) so I would like to get this taken care of. Any thoughts.

Kyle

[Eric_Shea]

turned a half turn then 3/4 turn OUT and still lock the fronts.......guess i am still WAY over biased in the front since i have correct venting (checked perfect) with stock cheap pads in the rear......

I want to clarify this comment.

The rear valve is not a brake bias valve. It is a saftey shut-off valve. You're generally not going to turn it in or out to get more rear brakes. It will simply shut them off sooner or later.

In Chris' case he'll need to get real pads in the back before even attempting this.

Also, Chris, you mentioned the venting was perfect. Keep in mind most manuals are wrong at .008". Set the venting clearance to .004" on your new pads.

Hope that helps.

[Eric_Shea]

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 R4-S'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.

[Solo914]

Eric,
I would say that I have a firmer pedal than when I had the old master cylinder and rubber brake lines. I think what it is that I press harder and harder to try to get them lock up and the floor is flexing (IMG:style_emoticons/default/smile.gif) So that may be the little bit of spongy feel I am getting. So, maybe I should go with one of those mastercylinder reinforcement kits. Also, seeing as I am going to bed these in again, should i do anything to the pads or rotors(hit em with sand paper etc?).

Kyle

[horizontally-opposed]

Too many variables left out of the mix.

The following are my opinions based upon engineered systems:

M-Caliper and Boge Strut - Good for stock 914's through 150hp. Replace the P-valve with a T-Fitting -or- replace the 914-4 rear caliper with a 914-6 rear caliper (t-fitting is $9.00 and 914-6 calipers are more like $900) This works for 914-6 applications and basic 911's up to 140hp.

S-Caliper/A-Caliper (SC) and Related Strut - Good for stock 914's through 240hp. Replace the P-Valve with a T-Fitting and possibly use a vented rear rotor. Stock rear brakes are marginal at this point. Consider using a rear M-Caliper and a different handbrake assembly. Works for 911S, 911RS and the first 930 Turbo (240hp).

Carrera 3.2 and Related Strut - As above but I would definitly use a larger rear and vented rotor.

Early 930 (meaning the specific 930 caliper which is noted as the 917-style) - Go with the entire system and find a handbrake alternative.

Beyond those... as above for the 930 (917-style).

Weight in with your other caliper choices (but he did say 911). I think Mueller has a formula for piston size. That's what I would go with if you wanted to do a mix and match.

Gee, sure am glad I never got around to taking THIS clown's advice... (IMG:style_emoticons/default/happy11.gif)

pete

[Eric_Shea]

Yup... that was me. (IMG:style_emoticons/default/clown.gif)

I knew someone was going to dredge up one of those old posts... had to be a pickup truck driving Porsche hat wearing editor type. (IMG:style_emoticons/default/tongue.gif) I used to recommend it but that was before I tore into a couple of them and found out the real answer.

Do as I do... not as I once said! (IMG:style_emoticons/default/lol3.gif)

The reason I used to recommend it was because the 911 never had it. I like engineering "systems" based on what Porsche had offered.

After looking into the feature and understanding the spin dynamics from Mr. Elford's book, I have REALLY become an advocate for keeping the rear shut-off valve.

The main thing I came to understand is, the valve won't be any different from a T. It does not restrict the flow to the rears until it shuts them down.

So, yup... over the years I've learned and now I'm trying to help others learn from my mistakes. (where's my merit badge damnit?) (IMG:style_emoticons/default/biggrin.gif)

[Eric_Shea]

So, maybe I should go with one of those mastercylinder reinforcement kits. Also, seeing as I am going to bed these in again, should i do anything to the pads or rotors(hit em with sand paper etc?).

I just ordered one from Uncle Chris Foley. I like his design.

Check the pads, if they seem glazed then you might want to dress them. If not, have at it.