A while back I answered a post about someone upgrading their 55 Olds drum brakes. I said that my booster/master cylinder assembly was rebuilt by Fusick and the car stopped on a dime. Well, now I have to regroup. The brakes began to drag and as time went on they began to lock up after about 20 to 30 miles. I changed every line, both metal and rubber (even replaced some that were less than 6 years old), then replaced all 4 wheel cylinders and shoes and turned the drums. The brakes still locked up, so that left only the rebuilt assembly to be causing the problem. Now I've ordered a 7" dual booster and remote master cylinder from Master Power Brakes and a disc conversion kit from Auto Classic City. Now my question is: is the proportioning valve necessary, or will the brakes work without it in place? Replumbing will be one of the major jobs to be done anyway, but if the valve is necessary the job will be even more difficult. Thanks fellas, I know there is some great advice on this site!

 

Your four wheel DRUM brake system does not use a prop valve.

 

I know that drum brakes don't require the valve. My question is, will the valve be necessary once my front disc conversion is installed? I'll have disc on front with the original drums on rear.

 

It's appropriate to employ the correct nomenclature when discussing/addressing your choices. This will make it much simpler/easier to discuss.
(1) An adjustable proportioning valve is NOT a combination valve. Adjustable proportioning valves are available for vehicles. An adjustable proportioning valve is used ONLY on rear brakes it is NEVER used on front brakes. An adjustable proportioning valve is used if you want to gain better control of the rear brakes ONLY. You can use an adjustable proportioning valve by itself in a disc/disc brake system or use it in combination with a metering valve (#3 below) in a disc/drum application.
(2) A combination valve contains three valves: (a) Metering Valve, (b) Pressure Differential Valve & (c) Proportioning Valve. Albeit the term combination valve. They are employed for either disc/disc or disc/drum braking systems.
(3) A metering valve can be used (by itself) on the front (disc) brakes in a disc/drum brake system; or, the metering valve can be used in combination with an adjustable proportioning valve (rear brakes) if you're after more control in tuning your own brake system.

Your '55 did not use a combination valve. I'm assuming you're installing a FRONT disc conversion kit & you will be operating under a disc/drum braking system?

The combination valve contains a Pressure Differential Switch located above the Pressure Differential Valve (piston). This Pressure Differential Switch notifies the driver of a brake condition (warning lamp on dash). Since your '55 does not have such a dash warning lamp, you would not need to hook up the Pressure Differential Switch itself; yet, the combination valve would still operate as designed.

I am not positive about this, but I believe they manufacture and sell all three types of valves based upon vehicle application. That is to say, I believe they are rated/designed based upon nominal brake pressure, weight class of the vehicle, & vehicle manufacturer e.g. Ford, GM, International, etc. Again, that's just my basic understanding since they do employ these valves on very large commercial applications until you get to the point where air brakes are mandatory.

Addressing your question (others will provide more guidance), I'm not clear if any of these valves are "necessary" as you asked. They certainly provide (as in the case of the combination valve in particular) a margin of safety in your brake system, and allow you to fine-tune your braking system.

If you elect to install a combination valve, you can mount the combination valve on the side of the MC. Since you are purchasing brake booster & MC from Master Power Brakes, I'd probably call them and get their opinion, as well.

 

Thanks! This helps a great deal. I will be converting the front drums to disc using a kit supplied by Auto City Classic. The photo of the kit components showed a proportioning (I think) valve, but that may just be a generic photo. I read a blog some time back by a fellow who had done the front conversion who said that he did not use the valve and got good results. Trevor at Master PB said that he is available for questions, so I'll probably be taking him up on the offer. Maybe I can take some photos of the process and post them on here.

 

Factory disc brake A-body cars from Olds did not use a proportioning valve in the 1967-70 model years. The item next to the M/C on those cars is a metering valve, not a prop valve, and serves a different purpose. Olds controlled the front/rear brake balance on these cars by using different (smaller) wheel cylinders on the disc brake cars, which does the same thing. The 1971-up cars used a combination valve that combined (get it?) the distribution block, differential pressure switch, metering valve, and prop valve all in one housing. Unless you plan to mimic the factory sizes of the wheel cylinders, use a combo valve. The factory doesn't waste money on parts it doesn't need.

I still don't understand the desire to do things half-fast, especially with something like brakes. The fact that some nameless person on the interwebs has been lucky (so far) is no reason to copy him. The factory brake system was designed and tested to operate correctly under the full range of vehicle loading cases, speeds, surface conditions (wet and dry), and linings at the limit of wear. If all you plan to do is creep the car to and from the weekend cruise night, then do whatever you want. If you plan to actually drive the car, don't take short cuts.

 

I don't like half fast either. That's the reason I asked for info on here and it has all helped. Thanks for your input too! I'll be taking my time on this job because no matter if I only drove the car once a year, I'll want it to stop like it should.

 

I hope you’ll stop back and post a follow up once completed. I enjoy hearing how a ‘55 drum/drum conversion to an upgraded disc/drum works out. Good luck w/ your project.

 

Gonna sell the treadle-vac?Could be interested....Tedd

 

I'm going to check with Fusick once more to make sure warranty is out. If not I'll send it in for repair. Whether it is under warranty or not I'll let you know ASAP.

 

The warranty is one year on the booster rebuild, so my warranty is out. I would like to get $300 for the assembly (including a new master cylinder) including shipping. There is also a new hose with it that I replaced just to make sure that was not the problem. At the vacuum inlet from the engine I get about 19 bars of vacuum, but at the nipple that goes to the reservoir there is only about 5 -6 bars. I don't know if that tells you anything about the problem with it. Let me know if you're still interested in buying the unit. Thanks, Eddie

 

I'm still working on my new booster/master cylinder upgrade from Master Power Brakes. Plumbing is a real problem since I ordered the master cylinder with left side outlets when it should have them on the right side. There's way more room between the assembly and the engine than there is between the assembly and frame. I had to have a special hose made up to supply the rear brakes and found a great place to get it. If you need a hose that you can't find anywhere, call Nick Christman at Brake Hoses Unlimited - 616-836-7885. Great folks to deal with and they can make up what you need.