Brakes / Spring Rates - Brad? Racers? Options

[Evill Ed]

tesserra, I am using 320i calipers at all 4 corners and the front and rear lock just about the same time if I make it lock. Normally the braking is really even and smooth so don't worry about it as it is really worth the $$$ and time to convert. I use the 23mm m/c too so I don't have a lot of pedal travel. I am also using Goodyear slicks so I get LOTS of road traction with the tire. I also the small spot caliper that Wilwood sells as a parking brake, one for each side and I had to get custom cables as the stock ones were too short. I still leave the car in gear if I park it just to be safe. Ed, have you tried a residual valve in the rear lines? My brake system smoothed out some when I installed one for the rear brakes. Good luck.

What is a residual valave? What does it do? I have a Titlton proprtioning valve at the rear just in front of the T fitting.

Ed

[Evill Ed]

-Ben

ps - Ed, how much advance are you running under boost? I'm just looking for some benchmarks. (I'm getting closer)

Ben, I set the stock d-jet dual canister dizzy to retard to 24 degrees BTDC at 8-psi boost. The inital winds up being 34-35 degrees BTDC @3500 rpm.

This works well for 8-psi w/out any intercooling on 93 octane.

Ed

[john rogers]

Ed, a residual valve maintains a small amount of pressure in the brake system where it is installed which will keep the calipers pushed out slightly. Works well if you have a large mismatch in caliper piston size or a mismatched brake system. The pads don't actually drag anymore than normal so there is no problem with heat build up. Give Chuck at CNC Brakes in san Diego a call as he was the person who helped me out with brake questions (great guy). Good luck.

[ChrisReale]

Kellezy,
Here is the thread about the trosion bars vs spring weight
http://www.914world.com/bbs2/index.php?act...&hl=torsion+bar

[Brad Roberts]

Ed,

How much negative camber is in the right front ?? I run more on the right front than I do in the left front. My point: how much tire is on the ground with reguard to the right front ?


B

[airsix]

Ed, thanks for the turbo info. Back to your brakes....

Not having any experience with the particular calipers you are using... Do they line up perfectly centered over the rotor? If they are off-center and you have worn pads one piston may be overextending and while not being out far enough to cause leakage, it could be getting jammed up. If exented enough the piston will wiggle in the bore. Under heavy braking it can 'cam forward' (go cock-eyed in it's bore) wedging the pad into the rotor.

Just more brainstorming.

-Ben M.

[Jeroen]

I don't understand why you are concerned about locking the front wheels.
You don't wan't any locking of the rears (unless you like to view traffic behind you through your windshield)

The left/right pulling under braking is most likely a suspension problem.
Check the cornerbalance first, but unless it is off by a lot, that shouldn't be the problem.
Most likely it's the shocks...

cheers,

Jeroen

[Evill Ed]

I don't understand why you are concerned about locking the front wheels.
You don't wan't any locking of the rears (unless you like to view traffic behind you through your windshield)

The left/right pulling under braking is most likely a suspension problem.
Check the cornerbalance first, but unless it is off by a lot, that shouldn't be the problem.
Most likely it's the shocks...

cheers,

Jeroen

The problem with the locking fronts is when they lock. If I brake hard, like I do at the track, and the front(s) lock, I start to loose control of the front end and the car is not really slowing down anymore. I also wind up flat spotting my expensive street and track tires.

I may be desribing the problem wrong.

I know I want the fronts to be able to lock before the rears. I'm having trouble finding balance right now. Either I get too much or not enough rear braking. It seems to me that I should be able to slow down at a much more aggressive rate before the fronts lock.

I will check out the suspension components tonight. If I don't find any problems, i will put some more miles on the rears to be sure that the pads are fully bedded in.

Once I assure myself that the brakes are not the problem, I will realign the car and have it corner balanced. Does this seem like a reasonable approach?

I never checked the center line of the front calipers to the rotors, I bought the set up from Rich Johnson, and just assumed that all was right. But I will double check it tonight. Ben has a good point about the piston extending too far and rocking. Could be worn pads too. This problem only started last year, so something seems to have changed. Or maybe I just drive alot faster now ;^)


Ed

[Evill Ed]

Duh!!!! I just remembered that before I stopped driving the 914 last fall, that the steering wheel was pulling hard to the right every time I slowed down. Sure seems like there may be an issue with the right front caliper or suspension huh? I'm gonna rip that bitch apart as soon as I get home tonight.

This is the problem with living on the East coast and not driving your 914 regularly, you forget shit. Maybe my highschool years are catching up to me.

Jeezzzzzzzzz

Ed

[Evill Ed]

Okay, found the problem, fixed it, learned a few things.

The pads on the BMW calipers overhang the edge of the 911 rotors a bit. This caused a step at the edge of the pad that was rubbing on the outer edge of the rotor. The edge of the rotor was polished smooth. This was causing the lock up on the right wheel. The left side had the same ridge, but it was just starting to contact the edge of the rotor.

I took a grinder and cut down the ridge and put a slight bevel on it to prevent it happening again as quickly.

Now both front brakes lock evenly.

I have the proportioning valve set in position 6 out of 7. The braking is very strong and agressive. The fronts will lock first in an all out panic stop.

I need to double check the 320 calipers on the rear for pad overhang.

If anyone is using BMW calipers, be sure to check the pads often and correct any lips that form on the edges to prevent uneven braking.

Ed