Front wheels locking up under braking

[SkinnyG]

I had a similar issue of the fronts locking on my Locost when I was autocrossing it. I tried all sorts of solutions, but the best fix, hands-down, was switching to dual (dissimilar bore) master cylinders and a balance bar.

 

Still keeping a proportioning valve on the rears, the brakes are now beautifully adjustable and I can dial the brakes to do whatever I need them to do.

 

Dual masters and a balance bar were probably the best improvement I made to my Locost.

[degoetz]

Autocrossed this weekend and set up brake bias. Ended up with the frt valve 3/4 turn from full open. Most control and confidence in braking since I got the car.

At a full turn the back end wanted to start to drift under full braking.

With no bias adjustment the frt would lock up at maximum force

Never had the brakes lock up the rest of the two days after the adjustment

[xcarguy]

Autocrossed this weekend and set up brake bias. Ended up with the frt valve 3/4 turn from full open. Most control and confidence in braking since I got the car.

At a full turn the back end wanted to start to drift under full braking.

With no bias adjustment the frt would lock up at maximum force

Never had the brakes lock up the rest of the two days after the adjustment

 

Great news, Don! Sounds like another resolve for the next-gen Storker crowd . . . . . . :hurray:

[subtlez28]

Congrats Degoetz! I'm glad to hear you have confident braking.

 

I'm tempted to do the same to get me through the rest of the season.

 

On my end though, I feel if you need to restrict front brake pressure, the master cylinder is improperly sized. Additionally, I think the power assist is unneeded.

 

So... I have contacted Wilwood directly to seek their recommendations.

 

I sent the following:

"I have a component car Lotus Seven replica (Brunton Stalker M-spec), it weighs 1,500-1,600 pounds.

 

It uses 99 Miata brakes and suspension uprights.

 

I have upgraded Wilwood 4 piston calipers on the front, with stock size rotors (Wilwood 150-9413K pads).

 

On the rear I have stock 99 miata brakes (rotors and calipers) - EBC yellow pads.

 

I have a stock, 99 Miata master cylinder, and a Wilwood proportioning valve inline to the rear brakes.

 

The proportioning valve is set fully open, with no restriction to the rear.

 

I am experiencing front lock up. I suspect the factory miata master is improperly sized for my application.

 

I would like to run a manual, Wilwood master cylinder. I have Wilwood floor mount pedals (340-1289).

 

I would like to know:

-Would a different combination of pads eliminate this front lock up issue?

 

-Do you offer a better sized master that will resolve the front lock up?

 

-Is there an upgraded rear caliper that will provide better braking?

 

-I'm told I should run a "split master, with balance bar". Is this a product you offer?

 

Thank you in advance

-Shaun-"

 

I will pass along any feedback I receive.

[degoetz]

I feel this is not restricting the front braking as much as I am proportioning the proper balance between the front and rear braking. This is what the the properly designed M/C for the car would do anyhow. I have talked to Scott, the designer, and builder of the car. He is building the exact car for himself and will use the same set up I have now (including the frt proportioning valve) . I feel the foot applied pressure to the braking system is about the same as I had on my C5 ZO6. He has used and doesn't recommend the 2 master cylinder with adjusting bar system. He has had many complaints about too much foot pressure and fatigue, especially for street drivers. I am used to the feel of this system.

I would recommend you try this first and maybe save yourself a lot of work and money.

Edited September 24, 2014 by degoetz

[xcarguy]

. . . . I have talked to Chris, the designer, and builder of the car. He is building the exact car for himself and . . . . .

 

 

I thought Scott Mineheart built your car . . . . :rofl:

[degoetz]

I thought Scott Mineheart built your car . . . . :rofl:

Yes, he was, My mistake

[subtlez28]

As promised, here is Wilwood had to say so far:

 

You may have too much piston area in the front (or pad compound is too

aggressive), but it is never recommended in plumbing a proportioning valve

to your front brakes. You never want to reduce pressure to your primary

brakes(fronts). If you are looking in going with a manual brake system, a

15/16" bore size master or a 1" would be recommended. A 15/16" master

cylinder will have slightly more pedal travel than the 1" but will require

less leg effort to make the same amount of psi.

 

 

 

Regards,

Wilwood Disc Brakes

 

and then:

 

The Balance bar will need to be custom mounted to your pedal assembly

(minimum 6:1 pedal ratio is recommended).

 

Below is a link to the balance bar information:

 

http://www.wilwood.com/PDF/DataSheets/ds252.pdf

 

Regards,

Wilwood Disc Brakes