Do I need a residual pressure valve for Front disk/rear drum???

[xHOBOPHOBIAx]

I am looking to use this disk brake kit for the front and leave drum brakes on the back for now. Do I need to get any inline residual pressure valves when using the following parts?

Front Disk Kit:
https://socalautoparts.com/product/wide-5-lowered-...-for-1967/

Master Cylinder:
https://www2.cip1.com/ProductDetails.asp?ProductCode=C13-16-9554

Rear STOCK

[wheel607]

No.

[stevebaz]

in the instructions, additional parts needed, list doesnt show it.

[xHOBOPHOBIAx]

[HBRag]

Disk in the front, Type III in the rear and the 20.5mm master cylinder from CB (which I believe is the same). The pedal is low for me, without a 10 lbs rear residual valve and the parking brake adjusted up for three clicks with light drag. Some master cylinders have integrated pressure valves, so your mileage may vary.

[toxicavenger70]

If you want a good pedal then get one.

[viiking]

Most if not the vast majority of disc brake MC’s do not use residual pressure valves. They are fitted with small orifices internally that do the work for you. This is how VW did it with their standard disc brake master cylinders for overseas beetles and US Ghias.

However you need to understand EXACTLY what your replacement MC has to make sure it is safe. What someone does successfully on their combination of MC and discs may not be safe on your setup.

The general rule is that if your MC is above the callipers (which on a VW they are) then you don’t need a residual pressure valve. Pedal travel to me is a red flag indicating some other issue.

Google disc brake residual pressure valve and look at those discussions. Here is just one interesting discussion

https://www.onallcylinders.com/2020/07/27/mailbag-what-does-a-residual-pressure-valve-do/
_________________
1968 1500 RHD Lotus White Beetle since birth. In the hospital for major surgery
1966 Lancia Flavia Pininfarina Coupe - in the waiting room
Discharged: 1983 Vanagon, 1974 1800 Microbus,1968 Low Light,1968 Type 3

[viiking]

Most if not the vast majority of disc brake MC’s do not use residual pressure valves. They are fitted with small orifices internally that do the work for you. This is how VW did it with their standard disc brake master cylinders for overseas beetles and US Ghias.

However you need to understand EXACTLY what your replacement MC has to make sure it is safe. What someone does successfully on their combination of MC and discs may not be safe on your setup.

The general rule is that if your MC is above the callipers (which on a VW they are) then you don’t need a residual pressure valve. Pedal travel to me is a red flag indicating some other issue.

Google disc brake residual pressure valve and look at those discussions. Here is just one interesting discussion

https://www.onallcylinders.com/2020/07/27/mailbag-what-does-a-residual-pressure-valve-do/
_________________
1968 1500 RHD Lotus White Beetle since birth. In the hospital for major surgery
1966 Lancia Flavia Pininfarina Coupe - in the waiting room
Discharged: 1983 Vanagon, 1974 1800 Microbus,1968 Low Light,1968 Type 3

[xHOBOPHOBIAx]

[viiking]

As I said you need to find out perhaps from the manufacturer of your MC if it is needed. The original VW MC for discs up front and drums at the back did not need them.

I would say no you don’t need the RPV. See the comment in that link.

“Notes

When converting from drum to disc brakes, you should remove the 10-psi valve.
The constant line pressure causes the brakes to drag.
This will cause overheating and premature wear.”

Looking specifically at the MC you are talking about it says it is suitable for discs all round! But you are leaving drums at the rear. The larger bore diameter of this MC actually INCREASES the pedal pressure required to get the same result!

Then look at what Willwood says noting again the first sentence.

A residual pressure valve is used when a master cylinder is mounted equal to or below the horizontal plane of the calipers or drum brake wheel cylinders. This valve prevents fluid flow-back to the master cylinder reservoir which can cause excessive brake travel or “pumping” of the pedal to engage brakes.
Install the valve as close as possible to the master cylinder and position the end marked “M.C.” toward the master cylinder and the end marked “OUT” toward the brakes. Ports in the valve are 1/8-27 NPT threads and will accept standard inverted flare tube nut adapters.
A 2 lb. valve is designed for disc brakes and a 10 lb. valve for drum brakes. If the vehicle has a single outlet master cylinder and a disc/disc system, only one 2 lb. valve is required. If the vehicle has a single outlet master cylinder and a disc/drum system, a 2 lb. valve is required in the disc brake line and a 10 lb. valve in the drum brake line (after the tee fitting). Balance bar systems require the appropriate valve just outside the master cylinder”

Using a RPV means that there will be a pressure of 2 or 10 psi dragging on your brakes when the pedal is released.
_________________
1968 1500 RHD Lotus White Beetle since birth. In the hospital for major surgery
1966 Lancia Flavia Pininfarina Coupe - in the waiting room
Discharged: 1983 Vanagon, 1974 1800 Microbus,1968 Low Light,1968 Type 3

[mukluk]

If the master being used specifies it's for front and rear discs, then you will need to install a residual pressure valve in the master cylinder port for the rear drums to prevent excessive pedal travel when the brakes are first applied. Original VW drum master cylinders had an internal check valve installed to maintain residual pressure for a reason -- see paragraph 2/70 below.

_________________
1960 Ragtop w/Semaphores "Inga"

[[email protected]]

The 67 Beetle I have has had a standard style OEM 19mm TRW/Varga dual circuit master on it with CB’s drop spindle discs, and stock 19.5mm rear wheel cylinders going on about 16 years. I actually had to shorten the pushrod to allow the pedal to go down further for clearance to get my knee under the steering wheel. If people are having trouble getting a firm/high pedal with disc front/standard drum rear vehicles, there are issues with the rear components like the adjusters/shoe arc to the drum. Ghias, with dual piston calipers that require a lot more fluid movement than the single piston CB calipers, used a standard 19mm master. You shouldn’t need any residual valve/larger master for a stock Type 1 rear drum wheel cylinder.

[toxicavenger70]

I have that same brake kit without the lowered spindles. I ran it 6 months without a residual valve. It did okay, but not great. My local VW shop told me to add a 2psi valve from Empi. I did and and it made it even better. Without out the valve the fronts brakes would also lock up to fast. Not the case anymore.

One thing is the brake pads on this kit sucked imo. I got some better pads from a local parts store and they worked great.

Last thing. My after service with SoCal was not so great. I would recommend these guys before them http://vwparts.aircooled.net/VW-Front-Disc-Brake-Kits-s/61.htm

[xHOBOPHOBIAx]

[toxicavenger70]