Wilwood big brakes, 914-4 brakes Options

[Freezin 914]

I figure some here will have more info on this, but Wilwood is advertising it has a big brake available for 914-4s. Just in case anyone would be interested. I haven’t even looked it up yet, but seen the ad in Excellence.

[technicalninja]

I had BMW front calipers and the front brakes were doing 90% of the braking. The rear pads were hardly worn while the front pads were shot. I switched back to stock front calipers with Porterfield R4-S pads and pad wear is even all around. Greg Amy uses BMW calipers up front, but installed a brake proportion valve with heavy bias towards the rear for even braking.

That is the exact opposite to what I would have believed would happen!
With a 3/4" master and the BMW caliper the bias should move rearward anyways.

I HATE the original pressure regulator. In stock form it does not even see the front circuit and is merely an accumulator that starts to fill beyond an adjustable limit.
The stock pressure for actuation is 525 psi from what I remember.
It just "snubs" the pressure at 525...
For a stock car that's fine but I'm betting both you and Greg Amy are using non/stock tires and that threshold needs to be adjusted.

I'll be interested in how the 75 narrow body brakes work when I am finished.

[GregAmy]

That is the exact opposite to what I would have believed would happen!

Maybe not. I can't offer that I noticed, but bigger pistons would offer more piston force up front, ergo a lighter pedal pressure required for the same amount of deceleration. With a lighter pedal pressure you're less likely to hit the "knee point" on the rear bias regulator, thus less line pressure in the rear and less pad wear.

Just a WAG, though.

I HATE the original pressure regulator.

I adjusted my pressure regulator on the stock/street 914 with a washer under the screw to increase the spring pressure to initially bias more pressure toward the rear.

Manual Tilton bias lever on the race car, also typically turned favoring more rear bias.

I think Porsche/VW intentionally biased brakes more toward the front to keep the masses from locking up the rears and spinning the car in slick conditions.

Recall that the BMW calipers with the bigger pistons won't give you any more front pad friction (ignoring pad differences) or tire grip (ignoring weight transfer differences). The bigger pistons give you more piston force (not PSI) for the same line pressure with the compromise of increased pedal travel due to larger diameter/volume swpet area (adding the bigger 19mm MC helps on that last point).

Honestly, I didn't notice a significant difference on the street in braking other than a slightly different pedal feel, mostly because I don't drive on the street like a maniac... (IMG:style_emoticons/default/wink.gif) Changing pads would likely make a lot more difference. - GA

[Superhawk996]

That is the exact opposite to what I would have believed would happen!

Maybe not. I can't offer that I noticed, but bigger pistons would offer more piston force up front, ergo a lighter pedal pressure required for the same amount of deceleration. With a lighter pedal pressure you're less likely to hit the "knee point" on the rear bias regulator, thus less line pressure in the rear and less pad wear.

Just a WAG, though.

I HATE the original pressure regulator.

I adjusted my pressure regulator on the stock/street 914 with a washer under the screw to increase the spring pressure to initially bias more pressure toward the rear.

Manual Tilton bias lever on the race car, also typically turned favoring more rear bias.

I think Porsche/VW intentionally biased brakes more toward the front to keep the masses from locking up the rears and spinning the car in slick conditions.

Recall that the BMW calipers with the bigger pistons won't give you any more front pad friction (ignoring pad differences) or tire grip (ignoring weight transfer differences). The bigger pistons give you more piston force (not PSI) for the same line pressure with the compromise of increased pedal travel due to larger diameter/volume swpet area (adding the bigger 19mm MC helps on that last point).

Honestly, I didn't notice a significant difference on the street in braking other than a slightly different pedal feel, mostly because I don't drive on the street like a maniac... (IMG:style_emoticons/default/wink.gif) Changing pads would likely make a lot more difference. - GA

Pretty much agreeing with all this

It is most definitely standard practice to bias toward front brakes to avoid rear lockup and inherent instability that comes with it. It would be considered negligent in a court of law to allow rear brake lock before fronts on any modern vehicle.


Good summary GA. (IMG:style_emoticons/default/beerchug.gif)

Edit: GA’s bias for race car is distinctly different that what’s suitable for street use.

[GregAmy]

It would be considered negligent in a court of law to allow rear brake lock before fronts on any modern vehicle.

Which suddenly reminds me of the Chevy Citation debacle. As I recall, the Citation didn't have a rear brake bias adjuster, or maybe it was tuned bad, and there was a rash of crashes where the drivers were locking the rear wheels when the brakes were applied hard, which would cause a skid/spin right into what they were trying to avoid. I think it even killed a few people.

Couple recalls didn't work (don't remember what they tried) and eventually NHTSA sued alleging Chevrolet knew and sold 'em anyway and it ended the car entirely.

The X11 was a good Showroom Stock B car for the times, though (let that sink in...)

I do agree that I'd not suggest anyone dink around with their rear brake bias unless they were very very comfy with what they're doing. The change I made with a thin washer to pinch the spring a tad is not much, but I'd remove it prior to selling the car. - GA

Edit Found an article on the Citation thing:

https://www.washingtonpost.com/archive/poli...6-c4cef1d6d390/