Brake servo on Marina based cars

[greyV8pete]

Re: Brake servo on Marina based cars

I believe some proportioning valves were linked to the rear suspension thereby increasing/reducing effort to the rear brakes depending on load

The Sierra P100 L pickup truck had one. Peter.

[dogoncrazy]

Re: Brake servo on Marina based cars

I believe some proportioning valves were linked to the rear suspension thereby increasing/reducing effort to the rear brakes depending on load

[cameronfurnival]

Re: Brake servo on Marina based cars

I know this thread isnt about the iva, but the rules now are that any proportioning valve must be locked and inaccessible from the cockpit and that once the required balance has been found the bar should be welded to prevent "future tampering". For cars not going to the iva the issue is moot. I would suggest that if there is an imbalance that the first thing that is checked is the size of the rear pistons as the marina ones were a common looking design and may have been inadvertently swapped for something off a different BL car. Also, you can use a brake bias compensation valve - like on sierras - its a ball bearing in a tube which reduces rear brake effort as the car pitches forward under braking. Also used on early lotuses iirc.

[chris_cussen]

Re: Brake servo on Marina based cars

IVA requires that any brake proportioning value is not adjustable.
Of course what happens after IVA......

[andyf]

Re: Brake servo on Marina based cars

Just noticed a RAW Siker on ebay with a proportioning valve in the engine bay.

[stevejgreen]

Re: Brake servo on Marina based cars

I've read elsewhere that balance bars are ok so long as they are fixed in position. IMHO you could use one to optimise the bias in a safe environment and then leave it alone.

It would be fair to argue that if you can't reach it whilst driving then it meets the requirement, even more so if it's forward of the bulkhead.

[andyf]

Re: Brake servo on Marina based cars

I've read elsewhere that balance bars are ok so long as they are fixed in position. IMHO you could use one to optimise the bias in a safe environment and then leave it alone.

[scott h]

Re: Brake servo on Marina based cars

^ ok, accepted so what should they be set at/to? I have one fitted to my Berly , the valve being installed to better balance the lsd/ disc brake configuration mods up the back!

During the rebuild of my Berlinetta I changed from rear drums to discs. I thought it would be a good idea to fit a limiter in the rear brake line as it would be very dangerous to have the rear wheels lock before the fronts. So far in short testing with a driving chassis the valve is set to have no effect and the front still locks first. I have standard brakes from an XR 4x4 Sierra all round with Mintex pads. See Berlinetta build and restoration for the full story.

[stevejgreen]

Re: Brake servo on Marina based cars

By definition a Brake Bias Adjuster, is adjustable. But if it cannot be adjusted from the cockpit of the car, then it could be viewed as permissible in a road car, it's a matter of interpretation.
As for settings, there are too many variables and even comparing to a donor car with different weight disribution, no comparisons can be drawn.
Vehicle designers spend a long time setting up suspension and brakes depending on the feel that they want on the finished car, it's close to being mathematically calculated, but variables like road surface and conditions cannot be ruled out of the equation.
Race drivers are constantly adjusting the bias on a circuit but they are skilled drivers and generally have a lot off run off areas and the budget to repair their cars, and no insurance to worry about.

[milliemarlin]

Re: Brake servo on Marina based cars

Brake bias adjustment is illegal to use in a road car! It does not however make them illegal to fit.

My understanding is that you can fit a device to change front to rear brake bias to a road car but it must not be adjustable. Unlike a racing car where the trained driver can adjust the bias as conditions change.

I could well be wrong though, so check before fitting.
Paul

[Tony Stott]

Re: Brake servo on Marina based cars

^ ok, accepted so what should they be set at/to? I have one fitted to my Berly , the valve being installed to better balance the lsd/ disc brake configuration mods up the back!

[stevejgreen]

Re: Brake servo on Marina based cars

Brake bias adjustment is illegal to use in a road car! It does not however make them illegal to fit.

[jhaines]

Re: Brake servo on Marina based cars

My old Marina Roadster Q621CGY had a brake bias valve to adjust the pressure front and rear, you can still get them from the likes of Demon Tweaks and the like. Current Vitesse roadster doesn't have a servo and seems to stop ok despite the considerable lump of cast iron up front.

[FranklinLeicester]

Re: Brake servo on Marina based cars

Thanks for all those comments. Steve, you are quite right about the servo not making any difference to the brake balance but my thought was that if there wasn't a servo, it would get rid of the sudden (panic) braking that the servo tends to give rise to. This is just a layman's thought, not a scientific thesis. My main reason for getting rid of it would be to give more room for lowering the column to give a better (in my opinion) steering wheel angle.
Ben, I take your point about softening the front suspension, maybe I ought to look at my shockers, I think they are adjustable but couldn't say sitting here what setting they are on.
Franklin.

[andyf]

Re: Brake servo on Marina based cars

I have also considered fitting one of the peddle boxes with a balance bar to be able to adjust the bias... I had a proportioning valve on the rally car and it made it easy to fine tune the balance based on the conditions. So long as you brake in a straight line you're ok ;-)