1950s Proportioning Valve for Disc Break conversion

[Patrick Fant]

Ready to convert to disc breaks - front only - in my 1956 Series 62.  Looking for the conversion kit now.  Question - is there a need or necessity to add in a proportioning valve to the set up to get the right fluid/pressure to the discs? pat fant #31723

[The Tassie Devil(le)]

Pat,

In a word, Yes.   If you aren't going to do any adjustments to the rear wheel cylinders, you will need an adjustable proportioning valve to get the brake balance right.   Leave one out, or use the wrong one, you will end up with the rear brakes locking up well before the fronts on a hard stop.   This will cause an uncontrollable sliding of the rear end.

All vehicle makers have spent millions of dollars designing the correct wheel cylinder to Proportioning valve ratio to stop rear wheel lock up so that they can make a fixed proportioning valve.

Us Modifiers don't have the wherewithal to do such calculations, so adjustable ones are ideal.

When I put Disc Brakes on my '37 Chev Hot Rod I had to sleeve the rear wheel cylinders from 1" to 5/8", (a 1968 Chev 12 Bolt Diff) with different size wheels and tyres back to front, and still ran a small fixed proportioning valve in the rear line.

You have to remember that when hitting the brakes hard, the front end drops down, and the rear rises, taking weight off the rear tyres, making locking up even easier, and dangerous.   The rears maintain straight-line control by retarding, and not locking.

Bruce.      

[MY 59]

Hi patrick
I bought my conversion kit from ABS power brake over there in the US, as luckily I had a contact with a shipping container who brought it over to Western Australia for free
Their kit and booster bolted straight in, I was surprised at that and highly recommend.
I see kits for 57-58, and 59-61 only though

[Cadman-iac]

Ready to convert to disc breaks - front only - in my 1956 Series 62.  Looking for the conversion kit now.  Question - is there a need or necessity to add in a proportioning valve to the set up to get the right fluid/pressure to the discs? pat fant #31723

 Pat,

 When you look for your conversion kit, I've found that the 56 is not listed for whatever reason. I believe it's because of the booster/master cylinder location.
 However the 55 is identical in every way to the 56, except for one thing that doesn't matter. And that's in how the bottom of the shock mounts to the lower control arm.
 The spindles, upper and lower control arms, steering arms and linkages, are all identical.
 So if you can't locate a kit that is specifically listed for the 56, the 55 will fit with no problem.
 I have the catalogs from OPGI since 2010 or earlier, (gotta look again to be sure) and they used to include the 56 in the listing for their kit. Not sure why they dropped that year.
 But I have both years, 55 and 56, and I can tell you that they are the same.
 The shock on 55 is bolted to a small bracket that then is bolted to the lower arm, and for 56 they just modified the shock to bolt directly to the control arm.
 Just thought you should know that going in just in case they haven't changed the listing since I last looked.

 You do know that your wheels will not work with the disc brakes, and the original hubcaps will not work with a newer wheel, unless that wheel has a reversed center section on it.

 Good luck with your car.

 Rick

[Patrick Fant]

Thanks for these great answers - really appreciate the input very much. I believe before I do any of this I am going to a drum brake expert here in Houston and have him just look at brake conditions and adjustment options with springs etcetera and see what I am dealing with.  Keeping the disc break idea in mind and getting ready to shop if the old drums are a no go... thanks very much! pat

[Cadman-iac]

Pat,

Here's a link to a thread I did on converting to roller bearings on the older Cadillacs and keeping the drum brakes.
https://forums.cadillaclasalle.club/index.php?topic=172548.0

I showed using newer model drums for better cooling, but there is a modification necessary. The backing plate needs the outer lip removed so the drum doesn't contact it.

I did another thread on this particular modification, but I haven't found it yet, gotta do some more searching.
I upgraded the brakes with self adjusters, return springs from a newer year, 1963 to be exact, and the hubs with roller bearings as well,  with the help of a spacer I figured out so that the wheel seal has a place to ride.

There's an article in the Self Starter on the roller bearing conversion in the November issue I believe.

Wish you the best with your car. Hope this helps in some way.

Rick

[Cadman-iac]

 Pat,
 Here's the link to the drum brake upgrade I posted earlier.


https://forums.cadillaclasalle.club/index.php?topic=158478.0


  Rick

[klinebau]

OEMs also introduce a delay valve because the disc brakes take less time to apply than drum brakes.  Does this need to be accounted for or do the adjustable proportioning valves address that also?

[Cadman-iac]

OEMs also introduce a delay valve because the disc brakes take less time to apply than drum brakes.  Does this need to be accounted for or do the adjustable proportioning valves address that also?

That's something that you would have to check with the manufacturer of the valve about.
I know that there's a residual pressure valve on the disc brake side of the factory proportioning valve to prevent the pads from being backed off by the natural warp of the rotors. It's only something like 2 psi, but without it the pads can be "slapped" away from the rotor causing a longer reaction time before they begin to clamp down.
  Rick

[TJ Hopland]

I don't think Cadillac did it but on other GM's in the drum to disc era there was an inline device that hung below the MC in one of the lines.  I would have to pull out a manual and refresh my memory on which line it was in and what it did.  It was only used in the 67-70 before disc were standard so maybe useful for swaps?

Here is an example:  https://www.fusickautomotiveproducts.com/prodinfo.asp?number=BPV70

Looking at their other parts it seems like 71 they maybe put what ever this was doing in the main valve which implies that at least these drum cars didn't have any sort of valve at all?   Maybe the reason Cad didn't do this was because discs became standard sooner so they built it into the main valve right away vs just added the extra device if they got the disc option?  Dunno just throwing it out there. 

[Patrick Fant]

Thanks for all the GREAT info here.  Very good overview of what needs to happen in order to successfully (you hope) change a 58 year old car from the original way it worked to the new and improved way we want it to work. First, I guess I just can't give up my coveted Sombrero hubcaps to accommodate the new set up.  I have a really good mechanic here in Houston at SouthWest Alignment who has the experience to make sure my drums are in like new  condition.  I think I am going to stick with original and just stay 4 car links back from the guy in front.  will report back, Thanks again!! pat

[TJ Hopland]

Hubcaps is I think what keeps a lot of us from doing a swap like this.  We seem to be one of the few demographics that prefers the stock hubcap look vs aftermarket usually larger wheels.  With all the custom wheel options seems odd that there isn't an option for a new wheel made to fit the hubcaps.   

[Cadman-iac]

  That's because nobody makes a better looking hubcap than Cadillac does, or did anyway. And no one with any sense of style would put Donk wheels on a classic Cadillac just to clear a disc brake system.
As I've mentioned before, if you could get a later model wheel rim, (outer portion), and get a reversed center section, that would allow for the original hubcaps, then I'm sure they'll sell like hotcakes, as long as they're not made in China.

  Rick