TheSamba.com :: View topic - Dual Circuit Master Cylinder: Why NOT a 67?

Sun Mar 21, 2010 1:29 pm

BarryL wrote: Don't the WW ones actually say FTE on them?

the '67 bus only master cylinder and reservoir we installed on jimmy4's bus were shipped to our shop from WW and both parts were ATE and made in germany.

Sun Mar 21, 2010 8:19 pm

so I gather from here http://www.type2.com/library/brakes/dualmas.htm that I can buy this master cylinder from Ronnie http://www.bustoration.com/Master-Cylinder-fits-1973-1979-Buses_p_874.html and this reservoir from WW http://www.wolfsburgwest.com/cart/DetailsList.cfm?ID=211611301E&AD=Wired_05_08 that they will mate up and with some hard brake line work and longer bolts and a 1/2" spacer that this is the most cost efficient way to step up to a dual circuit system?(aside from finding the elusive volvo or rabbit reservoir) can anyone share their ideas on this? my main concern is that the reservoir will fit that m/c.

Mon Mar 22, 2010 6:55 am

bherder wrote: cdennisg wrote: jimmy4 wrote: i switched my 64 crew cab to dual circuit as soon as i got it....

i bought the complete 67 dual circuit M/C and the reservoir for it... from wolfsburg.... and yes, it came with two new brake light switch...

yes... 300 bucks for the parts....

but i value my time too.... and it fits perfect

(needed a longer push rod according to my VW guru Scott at germansupply.com)

i have to decide if i want to put wide 5 front disc brakes next....

for sure the new wiring harness... it's sitting on the floor right now.

Will that 67 MC work with a disc brake setup, or will you have to change to a bay window MC (or something similar)?

From what I read, if you upgrade to disc brakes, you need to upgrade to a bay window MC.

Read: http://www2.cip1.com/ProductDetails.asp?ProductCode=C31-611-015-267

Eric&Barb wrote: 67 MC does not have the fluid capacity for disc brakes.
Also if/when you do go to disc brakes you have to have a pressure regulator for the rear drum brakes. Drum brakes take less pressure than disc. Having the rear brakes lock up first will result in sudden 180 degree spin of the vehicle when braking hard, especially in wet/icy weather.

This is not true. I'm still running a '67 master cylinder on my bus with 944 discs.

The only thing you need to do when switching to discs is disable the residual pressure valve for the front circuit. It's easy to do. On the master cylinder, you'll notice that the brake lines thread into two larger pieces that both thread into the master cylinder. Those are the residual pressure valves. Just pull out the one for the front circuit, pull out all the guts with a pair of pliers, and then put it back in.

As for the pressure regulator, on most cars, yes, you do need to have a pressure regulator; but in cases where the front brakes are a great deal stronger the fronts by design, the fronts are going to inherently lock up first. Putting discs on the front of a bus that still has rear drums is one of those cases. The pressure regulator is redundant.

Mon Mar 22, 2010 10:42 am

Good to know that info about the residual pressure valve on the 67 MC.

About the pressure regulator. If what you say is true, why would VW have installed them on late bay buses that had front discs, and rear drums? Not trying to start an argument, I just want to know as much information as possible.

Mon Mar 22, 2010 10:51 am

http://www.thesamba.com/vw/classifieds/detail.php?id=906802

:D 8)

Mon Mar 22, 2010 10:54 am

my65vert wrote:
http://www.thesamba.com/vw/classifieds/detail.php?id=906802

:D 8)

Caught caught shameless plug caught :lol:

Mon Mar 22, 2010 2:10 pm

Talked to a guy at WW today and the "new" 67 only master cylinder reservoir will fit the 71-79 m/c just fine but he told me that if you are running drum brakes that you will need check valves that the m/c doesn't come with.

Mon Mar 22, 2010 3:33 pm

cdennisg wrote: About the pressure regulator. If what you say is true, why would VW have installed them on late bay buses that had front discs, and rear drums? Not trying to start an argument, I just want to know as much information as possible.

Manufacturers are always going to put in a proportioning valve in a front disc/rear drum application just for liability reasons.

Drum brakes take less force to apply than disc brakes because drum brakes will actually use the rotation of the drum to force the trailing edge of the brake pad into the brake drum, increasing the braking pressure. This works great in a car with 4 wheel drums. However, when you've got a car with rear drums and front discs, it could potentially pose a problem, because the driver is applying the same amount of force throughout the braking system. BUT, when you've got the front discs sized so that they take less force to lock up than the rear dums in all situations, even taking into account that they inherently take more force to lock up, the proportioning valve becomes redundant.

There are, of course, a number of factors that will increase/decrease how easy it is to lock up the front brakes in comparison to the rears besides just the braking system itself. Anything you do to decrease the traction on the front end will make the front lock up easier (like switching from 195 tires to 165's or maybe your wife is driving the car instead of you so the front end doesn't have as much weight on it). Anything that increases the traction on the rear end will make the rear harder to lock up, causing the same effect of the front being more prone to locking up first (like putting a wider tire on the back or hauling stuff in the back of the bus, for example).

Mon Mar 22, 2010 3:52 pm

Andrew wrote: maybe your wife is driving the car instead of you so the front end doesn't have as much weight on it).

disclaimer; this one may not apply to everyone.

Mon Mar 22, 2010 7:03 pm

sventinker wrote: ...but he told me that if you are running drum brakes that you will need check valves that the m/c doesn't come with.

Every ATE '67 master I've bought came with the residual pressure valves installed. The reservoir doesn't use check valves if that is what he meant.

Mon Mar 22, 2010 8:25 pm

BarryL wrote: sventinker wrote: ...but he told me that if you are running drum brakes that you will need check valves that the m/c doesn't come with.

Every ATE '67 master I've bought came with the residual pressure valves installed. The reservoir doesn't use check valves if that is what he meant.

he said that the 73-79 m/c doesn't have check calves because that year bus has disc brakes in the front.

So far the limiting factor has been finding a reservoir that will fit. now it appears to be check valves? do drum brakes use check valves?

Tue Mar 23, 2010 11:22 am

my65vert wrote: Andrew wrote: maybe your wife is driving the car instead of you so the front end doesn't have as much weight on it).

disclaimer; this one may not apply to everyone.

:lol: True...

Tue Mar 23, 2010 4:45 pm

Explain check valves because the '67 residual valves are on front and rear circuits and they are all drums. The theory is that they keep a miniscule amount of pressure against the springs in the drums. That way when you tromp, both front and rear shoes get hit at the same time.

Tue Mar 23, 2010 4:53 pm

I think what he meant by check valves is the residual valves you speak of. The 71 through 79 master sold at WW or cip! or Ronnie does not have these valves because thos buses had discs. so the big question when running drum brakes will I need them and if so how do I source them?

Tue Mar 23, 2010 8:44 pm

There's some misconception here regarding the need of proportioning valves/check valves.

Check valves:On 67 (and older) master cylinders, the check valve is built into the cylinder. On bays (at least bays with discs) it's inline with the rear brakes. The brakes will still function 'fine' without it, but the proper adjustment will be imperitive, and a nice consistent 'high' pedal height will be impossible. If you run discs with a check valve, they will slowly drag, hurting gas mileage and wearing pads quickly.

Proportioning valves: The reason it's not necessary with the 944 brakes or the original split setup is because the front to rear pistons and the swept areas were calculated "just right" so everything works without needing equalization. Often this is not the case, I'll give an example from the watercooled world. An early Audi 5000 uses the same front brakes as a late rabbit, but different rear brakes and a totally different weight distribution. In order to reuse parts VW style, they had to make things "match up" with a proportioning valve specific to the car. Even if the parts are designed for one car, it's pretty hard to get the proportioning 'just right.' We're just lucky with the 944 stuff.

Tue Mar 23, 2010 9:15 pm

bagpipe goatee wrote: There's some misconception here regarding the need of proportioning valves/check valves.

Check valves:On 67 (and older) master cylinders, the check valve is built into the cylinder. On bays (at least bays with discs) it's inline with the rear brakes. The brakes will still function 'fine' without it, but the proper adjustment will be imperitive, and a nice consistent 'high' pedal height will be impossible. If you run discs with a check valve, they will slowly drag, hurting gas mileage and wearing pads quickly.

so If I want my DRUM brakes to function correctly with a dual circuit master cylinder I need check valves? I want a high pedal. And quick responding brakes.

are these the check valves?

Tue Mar 23, 2010 9:35 pm

Well.

Here's my experience:
I used the '71-'79 MC and spacer kit, and adjusted the pedal free play at the pushrod.
Otherwise stock '62 drum brakes on all corners. Actually, I have a big-nut trans so the back brakes might be a bit bigger than the stock '62 rears.
I haven't even heard about check valves before this.
I adjust my brakes every oil change. I have a nice, high pedal, brakes are nice and firm and I can lock 'em up if I want to. Thankfully, I haven't had many emergency situations, but I know that it will stop fast if I need it to.
I have heard that the later model MC has a bigger piston, so it requires a bit more pedal force than the original single-circuit MC. But I never ran single-circuit, so I have nothing to compare it to.

So there you have it.

Tue Mar 23, 2010 9:43 pm

sventinker wrote: bagpipe goatee wrote: There's some misconception here regarding the need of proportioning valves/check valves.

Check valves:On 67 (and older) master cylinders, the check valve is built into the cylinder. On bays (at least bays with discs) it's inline with the rear brakes. The brakes will still function 'fine' without it, but the proper adjustment will be imperitive, and a nice consistent 'high' pedal height will be impossible. If you run discs with a check valve, they will slowly drag, hurting gas mileage and wearing pads quickly.

so If I want my DRUM brakes to function correctly with a dual circuit master cylinder I need check valves? I want a high pedal. And quick responding brakes.

are these the check valves?

Those are the check valves. And yes, for drum brakes, you do need them. Drum brake applications need about a check valve that maintains about 10 psi of residual pressure on the system because wheel cylinders will only correctly seal when there is some pressure on the system. Otherwise when you rapidly let off the brakes, the seals will relax and the vacuum created by rapidly letting off will suck in a little bit of air. Over time, your brakes will get spongy. And for anybody wondering, it takes around 75 psi to overcome the return springs.

If you left in the check valve and changed to discs, it would be like lightly stepping on the brakes all the time since discs brakes don't need 10psi of residual pressure. A 2lb valve can be a good idea if the calipers are higher than the reservoir because in that case fluid will siphon back into the reservoir over time; but otherwise, no check valve is needed.

Tue Mar 23, 2010 10:30 pm

okay one more question. where are the check valves on my stock single circuit brake system?

Wed Mar 24, 2010 7:21 am

Here's my opinion on this here discussion.

I've never seen a "check valve" on any pre '67 master cylinder or in-line. "Check valve", to me, is an unrelenting valve that would keep the brakes locked up. "Residual pressure" means that most of the fluid returns to the master after you let up but with a dual circuit system a tad stays against the spring tension so the front and rear circuits don't do a ba-dump or out of sync two-step. If your wheel cylinders need pressure against them to not suck air then something is haywire. The spring pressure pushes the fluid rather than the piston sucking in.

Look at a disc brake and you'll see how the bore fills with fluid and pushes the piston into the pad into the disc. When you let off there is no need for a spring as the pad only needs to relax against the 90 degree surface its against. Whereas a drum the lining pad needs to withdraw with a spring to keep from the entire circumference's surface dragging.

I like those numbers of 10 psi and 75 psi but I've never measured them.

Your single circuit system should have come just basic with no residual valves anywhere.