Brake Servo Options

[anonymous-user]

Running a pedal box with brake bias and separate cylinders and reservoirs front and back (on a road car and a racer).

Both light cars with big brakes.

I don't want a sensitive pedal, but wouldn't mind some servo assistance.

Anyone know if there is a nice compact unit that will do the job?

[GreenV8S]

Would you be prepared to increase pedal travel? If so, consider increasing the pedal leverage, or fitting smaller bore m/cs.

[anonymous-user]

Hi Peter,
Have reduced cylinder sizes on the race car from what they are, and it should help improve feel.

Expecting the road car to need a servo, just looking around upfront.

[phillpot]

TVRMs said:

Running a pedal box with brake bias and separate cylinders and reservoirs front and back

Would this require two remote servo's?


Just answered my own question, odd looking thing.

[GreenV8S]

Do you actually need to adjust the static brake balance on a road going car? I mean, do you realistically expect that the driver will move the brake balance when his mates get in the back, or whatever? It would IMO make more sense to design the brake hardware so that the front and rear circuits run on the same line pressure and then use a conventional tandem master cylinder with a single servo.

[anonymous-user]

GreenV8S said:

Do you actually need to adjust the static brake balance on a road going car? I mean, do you realistically expect that the driver will move the brake balance when his mates get in the back, or whatever? It would IMO make more sense to design the brake hardware so that the front and rear circuits run on the same line pressure and then use a conventional tandem master cylinder with a single servo.

LOL, lots to be said for thinking first and buying second Peter.

I replicated the arrangement I have on the race car when building the road car as they both run very similar brakes, albeit the road car is 25% heavier and 30% more powerful...

So I have separate cylinders 3/4" front and 5/8" rear with balance bar in a floor mounted pedal box, which I like, but its not plumbed yet.

May look at the options to plumb it up to a single remote servo...if that's doable?

Its a TVR that will carry a cockapoo in the back from time to time, but he's not big enough to make a difference to brake balance..

Edited by anonymous-user on Tuesday 6th June 12:07

Edited by anonymous-user on Tuesday 6th June 12:11

[GreenV8S]

TVRMs said:

I have separate cylinders 3/4" front and 5/8" rear with balance bar in a floor mounted pedal box

It would be possible to estimate the front and rear lines pressures given enough information about the dimensions of the car and brakes, although there's no substitute for actually trying it. Ideally you would design the brakes so that the front and rear circuits ran at the same pressure - then you can use the tandem m/c I mentioned earlier. This would correspond to the balance bar adjuster being in the middle position. I assume you will only have one of each type of car so the extra cost/hassle of the balance bar and separate brake servos is probably not a big deal.

Once you have got the static balance right (i.e. by sizing the brakes and/or m/c and/or balance bar) you still need to set the dynamic brake balance i.e. so that the brake balance varies under heavy braking to match the weight transfer. You would normally achieve that using a bias valve in series with the rear circuit, and there are plenty of adjustable aftermarket ones available. This is something else you can set from a rough estimate to get the car driving and then fine tune it to accommodate the handling characteristics of the car.

Edited by GreenV8S on Tuesday 6th June 20:18

[anonymous-user]

Thanks Peter, it's a TVR 3000m. Cylinder sizes were recommended by AP but guess it's a guide. I'll have a play servo free and tweak from there,

I'll let you know how it works out.