Ok, let me start by saying I've been a mechanic (professionally) for almost 20 years now. 99% of my experience however, is diesels and computer run vehicles. These classics are a totally different animal. With that said, I picked this 70 Cutlass with the 455 last week and immediately ordered the front disc conversion for it. I read the "Low Cost A-Body Conversion" thread (which was an absolutely phenomenal write up btw). I've got factory power drums all the way around. My booster and current M/C works great.

First question: Do I still have to get the Raybestos MC36306 that was in the write up or will the one I currently have work?

I found the proportional valve on the frame rail. Mine doesn't have the little metering block at the end of the MC that the write up said the 70 uses.

Second question: Do I still need to get a PV2 proportional valve to replace the one that's there and regardless, do I need to get the metering block as well?

My conversion kit has come in. Just trying to get everything ordered so the car isn't down for an extended period of time, seeing as how I daily it.
Any part numbers of exactly what's needed would also be greatly appreciated!

Thanks in advance guys!

 

Yes, you need the correct M/C. Yes, you need a combo valve because your drum brake car does not have one. The thing on the frame rail is a simple distribution block with a differential pressure switch. There is no valving inside it.

 

So I'll need the PV2 proportional valve or something different?

 

You'll need some type of combo valve (which is more than just a proportioning valve). The Chinesium PV2 is a one-size-fits-none and has had quality issues, but it's the most easily available. The factory used a range of combo valves calibrated for different car weights and weight distributions.

 

You can call Master Power Brakes & discuss if you questions. Beware they only speak English.

 

Just be aware that they also only sell the one-size-fits-none "universal" combo valve. Theirs is coated black. Wanna bet it's exactly the same inside?
Sorry but I am underwhelmed at these disc brake companies. Some of them confuse metering valves with prop valves. None of them really understand what it takes to properly size and balance a braking system. Their recommended solution will always be exactly the parts that they sell.

 

Ok, so what valve should I get?

 

A factory 1971 442 valve. Just as an example of why the "universal" valves aren't really the right ones, for the 1971-72 A-body cars Olds used four different part numbers.

5472140 for wagons
5472141 for all others with power disc (this is the one you need)
1237944 for W31s with manual disc
5472359 for W30s with manual disc

Unfortunately I doubt you'll be able to find a correct 5472141 valve. The PV2 is unfortunately the closest you can come unless you use an adjustable valve and take the time to dial it in. You will still need a metering valve for the front brakes if you do this.

 

Maybe I'm alone, but I'm struggling to find logic in your statements:

If you don't want to recommend a universal Combination Valve because you suspect they don't fit anything (i.e. one size fits none), why not begin saying:

What did I miss?

 

It's possible that the OP can find a used 5472141 valve. And yeah, I'm whining a little at how poorly the aftermarket gets this.

 

 

Man I appreciate it. Do you happen to have a part number of a metering valve that will work? Or a picture so at least I know what exactly I'm looking for?

And will the plumbing go M/C--> Metering Valve-->PV2?

 

If he uses a Combination Valve.....doesn't that obviate the need for a 1970-style metering valve (the valve hanging off the booster stud {if power brakes}/master stud from firewall {non-power brakes})??

I believe that's what happened on the factory system when they started using the Combination Valve.

Pics below showing the original Bendix Combination Valve from a '72 Cutlass w/factory power disc front brakes.

 

Great, so the combination valve looks just like the PV2 which is, from what I'm gathering, junk lol.

I appreciate the photo bud. I swear, they're research I do on this, the further out in left field I get. Gonna see if there's a resto shop anywhere near me that I can swing by and see how they do them.

Not taking anything away from y'alls help. I'm just at the end of my budget for now and don't want to be buying a bunch of parts that are either wrong, or not needed.


Edit: That valve looks identical to the one on my frame rail. I'll get pictures tomorrow.

 

The valve I show in the pic (a Combination Valve) was not used on 1970 Olds Cutlass's or 442's. They started using it on the 1971 model year cars.

 

Correct that the metering valve is incorporated into the Combination valve, as shown in the diagram I posted above. Since the OP is converting a drum brake car, his easiest solution is to use the 1971 style combo valve since the 67-70 cars that did not use a proportioning valve instead used rear wheel cylinders with a smaller bore to achieve the required front/rear brake balance.

 

Ok, so MC to the Combo Valve then to the brakes. Sounds easy enough.

 

You'll need the bracket that attaches to the frame rail down there (where the Combination Valve goes).....bracket held to frame w/two bolts/screws and then the valve is attached to the bracket w/two much longer bolts.

This frame mounting bracket is repro'd as well.

 

This appears to be a disc brake car and possible source for the parts you need though they would likely need going through. https://classicoldsmobile.com/forums...-price-177861/ White Post or others could rebuild them. Get the spindles too.

Scott

 

Preciate it. I've got the spindles and everything. Just need to order the MC and valve.

 

Would I not mount it directly underneath the MC? Or are you saying frame rail because that's where the factory valve was?

 

Thats why when i did my Chevelle I just got all factory replacement parts. You can use the drum brake spindles. You just have to grind the boss down where the big anchor plate bolts on. All of the other parts are still available new in the aftermarket. Most of the repo suppliers have the backing plates.

 

Unfortunately the repro parts aren't necessarily the same as OEM. Witness the PV2 combo valve discussion above.

 

.............and the repro front caliper mounting brackets that scrape on the inside of the factory rims....LOL

I don't know what your "plan" is....going for a "restoration" where everything looks factory original? Or....slight variations are fine? I just mentioned the bracket in case you were trying for a factory type setup/look. Yes, I've seen where folks mount the Combination Valve directly under the master cylinder.

 

When I changed my 70 from drum to disc I used as many factory parts as possible. I used the 70 metering valve mounted by the master cylinder instead of the 71/72 proportional valve. The brake line running from the distribution block to the rear brakes is different on the 71/72 cars with a proportional valve.

Do lots of homework and test fit everything. Good luck with your conversion.

Don W

 

Not to hijack this tread at all i just want to add this years ago i added factory disc setup on a 68 Malibu wagon that was factory power drums.No prop valve added it stopped normally except the rears would tend to want to lock up on gravel moderate to hard braking.

 

Which is EXACTLY why the factory used a prop valve. I'll also wager that you never actually had a panic braking situation. Locking the rear wheels is a great way to cause the car to swap ends. Keep in mind that the factory designed and tested these systems to operate safely under all worst-cast operating conditions, including empty and fully loaded, wet and dry, etc, etc. You don't want to find out that you actually needed that valve when it's too late.

 

As Joe said, if the rears lock up in a panic situation it's likely that the car will spin and you will be driving backwards at speed trying to stop. GM did not make 5 different combo/proportioning valves for a single car model 1971-1972 A bodies, because it wasn't necessary. They spent the money because is was necessary for safety. Just because someone sells a disk brake kit doesn't mean it works as well or better than the factory setup. Especially because they sell one combo valve for every single car and model (full size, mid size, Buick, Olds, Cadillac, Pontiac etc..)