disc brake conversion proportioning valve

I don't believe it's necessary on a Speedster, I think the master/caliper piston ratios/pad sizes are good. Even with the aftermarket 4 wheel EMPI discs that Greg uses.

On a Bus, I do know that the later Vanagon had a proportioning valve from the factory, so there's that. My Vanagon had disc front and drum rear(I think). Mine was a 1991. I do not know what they used on Buses or on ones that had a brake conversion.

Very good question though, Julie.

I’ve always assumed that OEM VW master had built in proportioning via the rear circuit being slightly shorter bore than the front. Is that not correct?

Umm, bore is bore, as in bore of master to bore of caliper piston=braking power. We're not going to go into pedal ratio, disc size etc.

The length of the bore will not change the braking power/hydraulic ratio.

There is no proportioning valve on my Spyder, with Airkewld discs all around. Solid, drilled rotors. 4 piston Wilwood front and stock VW/Varga single piston e-brake caliper in the back. Front I use Wilwood street/track pads and stock rears. My brakes are sublime, and don't fade even with lap after lap of heavy track use.

That makes sense, I guess it would have to have a smaller bore to move less fluid.

Almost nobody uses proportioning valves, or finds the EMPI setup to be unsatisfactory for cruising, or driving briskly - but the rear caliper bore on the EMPI brake sets is bigger than ideal. You wouldn’t find this out unless you were hooning on a public roadway (perish the thought) at 9.5/10s or above, but your back brakes will likely lock before your front.

Henry at IM found this out when building a car for an automotive engineer, and began installing a BMW rear caliper with a slightly smaller bore around 2006 or so (if memory serves). This modification required a custom caliper bracket, so it wasn’t anything “off the rack”.

My car was built with CB Wide-5 brakes prior to this, and I notice the over-braking when I’m "obeying every speed limit and observing all of the rules of the road" in the mountains with other law-abiding citizens, but I doubt anybody with even more love and respect for their fellow man would ever notice.

I’m fixing my issue by going the other way and installing 4 piston Wilwood front calipers on a custom bracket with some CB brakes.

Give your brakes a try. If you don’t like it, you’re a $20 valve away from true love.

Yup, install it in the rear line in the cockpit where you can adjusticate it. Not a hard job, and probably won't need a lot of adjustment either. But if you dislike good enough and LOVE perfect, you'll do it.

Nobody would hoon on public roads, would they?

(Lets out maniacal Doctor Evil laugh)

Let me remind you gentlemen that there are laws against hooning, and as a former law enforcement officer I demand that you hoon not!

There, that should fix it!

I feel much safer now. Bob.

I put my foot down with you in mind Lane.

I believe that's called "lettin' 'm off with a warnin'."

And that is the only one they will get!

Next time it's free room and board at the Grey Bar Hotel.

I have the 911 front end and a proportioning valve, I do not remember any discussion on if it should be done or not ... just saying.

I installed one on the Spyder fwiw.

Remember that when stepping on the brake your life is in you foot's hands!*

I went with the same Airkewld brakes as Danny. Neither AirKewld nor Greg felt a valve was going to be necessary. You're more likely to have seen my car lately than I am if you picked yours up from VMC (and assuming mine wasn't still at A-1 getting its exhaust). Can't give you a report yet...

* George Carlin - Album liner notes from "The Seven Words You Can Never Say On Television"

Just to clarify, the speedsters brakes are fine thus far (have not had occasion for any Oh Sh*t moments)

The VW in question is a 66 23 window bus, the front calipers are Wilwood and it looks like the best? setup for the calipers out back (for the IRS suspension conversion with parking brake) are Empi.

Folks doing the work believe it should have a valve and I'm not disagreeing with them; with regenerative braking already a thing on very the nose-light bus, we're keen not to add any undo excitement by virtue of the brake pedal. 

@DannyP in the cockpit sounds good, not sure how to do that with the bus as most everything is literally under the driver

Now that I think about it, I don't know if the bus was already converted to dual circuit or not - something I should check into!

Julie - almost all the rear disc brake kits use the same caliper. If that's what you've got, and you've got Wilwood Dyna-Lite 4-pot front calipers - that's the same setup Pete at AirKewld uses on his kits without a proportioning valve.

Regarding the MC - you'll need not only a dual circuit, but also the one with the larger bore.

I thought the EV bus was done?

@Stan Galat posted:

Julie - almost all the rear disc brake kits use the same caliper. If that's what you've got, and you've got Wilwood Dyna-Lite 4-pot front calipers - that's the same setup Pete at AirKewld uses on his kits without a proportioning valve.

Regarding the MC - you'll need not only a dual circuit, but also the one with the larger bore.

I thought the EV bus was done?

I'll check on that kit, thanks

As for being done - it's always 2 weeks out!  Tiny things keep getting in the way like the above sudden question, TBH I would have hoped they would have thought of these things earlier but they are so bloody apologetic on delays...  we remain civil. Soon though I suspect my tone will get more energized

I wasn't talking so much about the specific kit, Julie, as I was about the fact that AirKewld is using the same calipers as your bus, and is successfully doing it without a valve. I know a bus isn't a Spyder, but my experience with the 4-piston Wilwood/rear e-brake caliper kits has been pretty illuminating (Danny P's Spyder, running the Rattler backward). I've never experienced harder braking. Ever.

Regarding the endless delays - you've really got my sympathy there. Custom stuff is generally lousy for the shop doing the custom work as well as the customer paying for it. Nobody ever wins in that situation. Hopefully, they're doing a good job, which would ultimately soften the blow (a bit) of being very late on delivery.

What's inexcusable is late delivery and disappointing workmanship in the same transaction. I really hope you get what you're after.

Usually custom stuff has the builder wanting to add to his offering and some of the R&D is absorbed for that reason but Upgrades usually means UP Prices.

@IaM-Ray posted:

I have the 911 front end and a proportioning valve, I do not remember any discussion on if it should be done or not ... just saying.

Just to clarify all this, the suspension used has absolutely ZERO to do with whether a proportioning valve is needed. It has to do with braking power front versus rear.

I don't know what the preferred ratio is, but front to rear sizing is important to get right. It doesn't matter if you're all drum, all disc, or front disc/rear drum. It is wheel cylinder size and/or caliper piston sizing.

Master cylinder sizing doesn't matter, unless you're using TWO and they are connected by a balance bar(which usually negates the need for the valve).

All the proportioning valve does on a VW is REDUCE the line pressure in the line it is located in. This can help reduce rear brake lockup when the rear brakes are simply too large for the braking load that's required of them.

For an example, my old car had solid CSP discs in front and stock VW drums in back. In extreme braking, the front tended to lock. So I learned how to threshold brake.

If the rear locks up, the back end can come around which is VERY disconcerting and alarming!

My point was I have larger 911 disks that was all I was saying on the other hand I thought the valve also kept a residual pressure in the rear to balance braking as it kept a residual force thereby reducing the amount of pedal pressure you needed to apply but do correct me if I am wrong.

That's a residual valve, Ray. A proportioning valve is different.

Ah, there you go as they say learning keeps going forever.