I don't really see how they could, or if they did, how they could work
effectively. Proportioning valves are basically a pressure reducer
that works dynamically, as you increase the pressure on the input side
you get a proportionate increase on the output side, but it's still
lower. That works okay in a single circuit, but it seems to me that it
wouldn't work well in a two-mc system. You'd have to press like hell
on the brakes, and a little mis-adjustment would give you no brakes at
all--not what I'd be shooting for. I don't like proportioning valves
at all.
You can make a balance bar by simply building a set of brackets with
different ratios for the attachment points. Peyote had a setup like
that which worked fine for many years. I added an adjustable bar and
gained nothing from it--the bracket approach works just as well if the
car is not super-sensitive to brake bias.
On May 20, 2008, at 10:41 AM, Robert MacKenzie wrote:
> Bill;
>
> Thanx for the help! I am equally confused.
>
> I think the valves were intended to take the place of a balance bar
> as the pistons are actuated be a single straight bracket attached to
> the brake pedal. The fabrication of the mounting bracket is very
> good and I assumed it would all work together. I looked at balance
> bars but cant find one that will work on a 2 inch center I now
> have. Tilton sells a 2.5 inch balance bar and said it can be
> trimmed but I then loose most of the adjustment range. I may have
> to go that route.
>
> Robert
>
>
> From: Bill Babcock [mailto:Billb@bnj.com]
> Sent: Tuesday, May 20, 2008 11:57 AM
> To: dodo@texas.net
> Cc: fot@autox.team.net
> Subject: Re: [Fot] Dual Tilton Brake Masters on MK1 Spitfire
>
> You've got me pretty confused here. You've set up a two-MC system
> and you have proportioning valves on it? What are they proportioning?
> Most folks that do two MC brakes do the proportioning with a balance
> bar. A proportioning valve reduces downstream pressure. In a single
> MC system so you can put it between the front and rear systems to
> have less pressure applied to the rear cylinder than the front. I
> don't know what they would be used for in a two mc system, and I
> assume that's your problem.
>
> Placing a proportioning valve in the rear circuit only generally
> does work since it reduces the pressure at the rear brakes, but it
> gives a hard pedal. You'd be better off getting rid of the
> proportioning valves entirely and using a balance bar. I'm assuming
> you feed the front from one MC and the rear from the other. If this
> isn't the case, then do.
> On May 20, 2008, at 9:02 AM, Robert D. MacKenzie wrote:
>
>
> I have having some issues with a Tilton dual brake master cyl
> installation I singley
> started over the weekend on my Spitfire Racer
>
> I bought two used 1 inch Tilton masters with all the correct
> brackets/mounts
> with remote reservoirs plus two Wilwood proportioning valves to be
> installed
> on my Mk1 spitfire, replacing the original single circuit master.
>
> The cylinders were rebuilt using the correct Tilton kits. I made up
> new
> lines from the master outlets to the valves and then into the
> existing brake
> lines.
> Everything went well until the final bleeding process began.
>
> The 1st time I tried to bleed the front first then the back. The
> front
> brakes felt fine with good travel and pedal feel. But when I tried
> to bleed
> the backs the system would bind and I had a very high pedal effort.
> When I
> blend the backs with the fronts open they worked fine by
> themselves. When
> everything was closed the system will bind with very high pedal
> effort but
> no brakes. Not good.
>
> I then tried bleeding both systems at the same time, and that seemed
> to work
> until I closed off all the speed bleeders and the system would bind
> again.
>
> I believe that the master cyl providing pressure to the front brakes
> caused
> the pistons to press the calipers closed before the rear ones can
> apply the
> rear brakes. Making adjustments to the proportioning valves does
> not seem
> to make any changes. I also tried adjusting the bracket connecting
> the two
> pistons to the pedal to push one in earlier than the other but that
> did not
> make a difference. Swapping the cylinders or the valves side to side
> made no
> difference. I believe each individual component is working right,
> just not
> together.
>
> Before I go much further I have some basic questions:
>
> Are two 1 inch masters the way to go? Do I need to run a smaller
> cylinder
> on one side or the other? Do I need two valves or will one suffice
> as the
> other will always be open?
>
> Any help/advice will be appreciated.
>
> Thanks
> _______________________________________________
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> Bill Babcock
> Babcock & Jenkins
> Billb@bnj.com
> 503.936.7660
> www.bnj.com
>
>
>
Bill Babcock
Babcock & Jenkins
Billb@bnj.com
503.936.7660
www.bnj.com
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