Brake Bias Valves

[cunning plan]

Number 14 on the diagram below:

My Bus is a '68 and had drums all around, however, it has been years since I took it all apart and I cannot find a Bias Valve in my parts box which came from the Bus, but I cannot remember it having one on there anyway.

Incase it changes your answers to the questions below:
When the Bus is back on the road, I am planning to use the drum setup for a little bit, with the intention of upgrading to front discs using a remote servo in the future.

Questions:

1. What does the Bias Value do?

2. Is it required?

Thanks.

arty0021:

 

[vinvan]

Hi
The bias valve was only fitted to late bays so you won't have one from your early, but if you intend to fit front discs you will need one, you can't buy a new one so it's the second hand guys you need try
The Gate Keeper (Dessie) he may have one, be sure to fit it correctly, it fits under the front chassis member at an angle, take a look in Bentley think there is some info there

Hope this helps
Vinvan

 

[Bluesnailman]

as far as I could tell when researching this...... the bias valve is more or a pressure regulator when the vehicle does a real nose dive under braking. In this situation its intended purpose is to limit pressure to the rear wheels (stop them locking prematurely) it has a large ball bearing inside that rocks forward to do this. Like all mechanical pressure limiting devices its a bit of a compromise, but it seemed the best compromise out there. So i went on latebay forum and picked one up.

Just watch - it has a odd plumbing arrangement... (back hose connects to the front port)

 

[cunning plan]

Thanks for the reply guys.

I also contacted VWJim (http://www.vwjim.co.uk/" onclick="window.open(this.href);return false as I am intending to use one of their remote servos as an upgrade at some point when the Bus is back on the road.

Jim being a helpful guy, sent me this reply:

I never fit a Bay valve, as they're not necessary on Splits.

If you're Bay is lowered / stiffer suspension then I probably wouldn't fit one on a Bay. If the Bay is stock height and still has boat like body roll in the braking, then I possible would fit one so the rear brakes don't lock up as the weight shifts to the front.

Along with this segment of information, which I presume is from a workshop manual (possibly the Bentley manual, but I have not got mine with me to check):

My bus is lowered (not slammed, a useable height instead) using dropped spindles and rear adjustable spring-plates. From VWJim's reply and reading that segment of information, it seems that the Bias Valve will not operate unless the vehicle is at an angle as a result of heavy breaking and the front is lower than the rear.

With a lowered Bus using upgraded suspension, the ride height is more level and stiffer, which means it is unlikely that the vehicle under braking will ever be at an angle where the Bias Valve would operate. Also, if the vehicle is more ridged, the requirement to reduce braking on rear wheels which have been lifted as a result of the front dipping is also negated.

So, even with front discs, it seems that the Bias Valve is not required, which is great as it is one less thing to buy and from the research I have done, they are only available second-hand and often leak or seize up.

It seems if you have a Bias Valve in good condition and want to fit it, especially on a stock-height Bus and even more so on one with front disc brakes, then it is a good idea which should help in extreme circumstances. Otherwise, it seems less essential for lowered vehicles with harder suspension, including ones with front discs, as it was a device to alleviate the condition created by a high vehicle using soft suspension and more modern disc brakes with greater braking power.

This may help someone else when researching Brake Bias Valves, as I could not find that much information on them.

 

[snow_pikey]

Thanks for the info!

Funny I was just under my bus (cross over bay) and I hadn't ever noticed this valve before on any of my earlier buses, guess it's good mine works as it's higher than stock with discs on the front.

Cheers - Matt