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dual circuit brake conversion issue

Started by David Greenburg, August 13, 2009, 02:33:44 AM

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David Greenburg

I had my '59 converted to dual circuit brakes.  The work was done by a respected old car specialist, who installed a dual circuit master cylinder on the existing (fairly new) power brake booster.  Generally, the brakes work ok, but during a fairly hard (not panic) stop, during the last 10% or so of  the stop, the pedal feels hard and like the brakes aren't grabbing as hard as they should; it is hard to get the brakes to lock up (not that I try that often).  The overall feeling can be disconcerting; you roll up behind someone at a light and feel like you might not be able to stop in time.  The drums, shoes and wheel cylinder all appear ok; checked by me and 2 professionals.  The only thing I can think of is that the dual circuit setup is too much for the power brake booster.  But before I shell out for a new one, I wanted to see if anyone else had experience with this.

Dave
'59 60S
David Greenburg
'60 Eldorado Seville
'61 Fleetwood Sixty Special

Dave and Deb

What diameter is the bore of the new dual circuit master cylinder? 
1958 series 75 9 passenger sedan
1959 series 62 six window sedan
1960 series 62 convertible
Hunter Valley NSW Australia

Dave Shepherd

Can we assume a proportioning valve for a disc brake set up was not installed and the dual cylinder is for a drum/drum set up?

Sweede64

Quote from: David Greenburg on August 13, 2009, 02:33:44 AM
I had my '59 converted to dual circuit brakes.  The work was done by a respected old car specialist, who installed a dual circuit master cylinder on the existing (fairly new) power brake booster.  Generally, the brakes work ok, but during a fairly hard (not panic) stop, during the last 10% or so of  the stop, the pedal feels hard and like the brakes aren't grabbing as hard as they should; it is hard to get the brakes to lock up (not that I try that often).  The overall feeling can be disconcerting; you roll up behind someone at a light and feel like you might not be able to stop in time.  The drums, shoes and wheel cylinder all appear ok; checked by me and 2 professionals.  The only thing I can think of is that the dual circuit setup is too much for the power brake booster.  But before I shell out for a new one, I wanted to see if anyone else had experience with this.

Dave
'59 60S

Dave

Is the new mastercylinder bult for discbrakes? I had a simular problem with a Chrysler -68, it turned out sombody had changed the mastecyinder and got one made for discbrakes instead. Once the cylinder was changed everything worked fine.
Thomas Karlström

35-709

I had the exact same problem on my '71 Sedan deVille, even changed out the brake booster for a rebuilt one, no help.  Finally discovered that the original vacuum hose was collapsing on the inside severely restricting the vacuum going to the booster,  New hose, no problem.
Geoff N.
1935 Cadillac Sedan resto-mod "Big Red"
1973 Cadillac Caribou - Sold - but still in the family
1950 Jaguar Mark V Saloon resto-mod - Sold
1942 Cadillac 6269 - Sold
1968 Pontiac Bonneville Convertible - Sold
1950 Packard 2dr. Club Sedan
1935 Glenn Pray - Auburn Boattail Speedster, Gen. 2

David Greenburg

Thanks for the input.  Glad to know I'm not alone with this problem.  There is no proportioning valve; the new master is for a drum/drum setup.  I don't know the bore of the new master cyl., but will check it out.  Anyone have the correct bore for the master?  Also will check the booster hose.  A friend aslso suggested checking the vacuum reservoir in the fender.
David Greenburg
'60 Eldorado Seville
'61 Fleetwood Sixty Special

The Tassie Devil(le)

David,

The Bore of the Original M/C is 1".

If you are using a M/C with a smaller Diameter, then you will not be delivering the correct amount of Fluid to the Wheel Cylinders for them to work properly.

If the Pedal is going to the floor, with a smaller M/C, you will be losing pressure at the Wheels.   Therefore poor braking.

The Rear Wheel Cylinders are 1" each, and the Fronts are 1 1/8", and it will take a lot of fluid from the M/C when trying to expand the brakes.    Plus, the Rears will be filling up faster than the fronts, and if the Shoes aren't properly set up, using the correct factory method, things could get worse.

With the Single Circuit, the Braking is automatically balanced between the front and the back, so that the extra diameter of the Front Wheel Cylinders will apply increased pressure to the Shoes, whereas the Rears will not work as efficiently, as all they are designed to do is retard the Rear Wheels without locking them up.   This in itself keeps the rear of the vehicle from sliding and trying to pass the front.

The original Piston Stroke is only 1 1/8", so by the time you transfer that to the pedal, say 4" of pushing, there isn't much left as the piston will be near the end of its' travel.   And, as the Brake Drums heat up and expand, things get worse.

Bruce. >:D
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
'02 VX Series II Holden Commodore SS Sedan
(Past President Modified Chapter)

Past Cars of significance - to me
1935 Ford 3 Window Coupe
1936 Ford 5 Window Coupe
1937 Chevrolet Sports Coupe
1955 Chevrolet Convertible
1959 Ford Fairlane Ranch Wagon
1960 Cadillac CDV
1972 Cadillac Eldorado Coupe

Dan Marinola

Go to www.photopaige.com/edscars/ and click on the 1960 cadillac restoration and the on dual MC brake conversion. This WORKS and works great. The power brake booster and MC are from a 1968 Cadillac and practically bolt up to your car.It's available at AutoZone and the part number is 50-1117. Several club members have done this conversion and are very pleased with the results. Hope thi helps. Dan
Daniel P. Marinola

David Greenburg

Thanks, Dan and Bruce for the info.  Considering my symptoms in light of Bruce's explanation, I'm guessing that more of the fluid is going to the rears and causing the sensation of losing braking power at the end of the stop.  And the fix by Ed Mobley described in Dan's link sounds like the way to go.  I corresponded with Ed a few years ago here about the pitman arm recall and driveshaft vibration issues; he had a wealth of info.  I like the idea of using a matched Cadillac booster and mc. 
David Greenburg
'60 Eldorado Seville
'61 Fleetwood Sixty Special

walt chomosh #23510

David,
  I installed an adjustable proportioning valve to the rear brakes on my 1955CDV in order to tune the brakes(with dual MC)....75-80% to the front and 20-25% to the rear.....walt...tulsa,ok

David Greenburg

Walt:

That is an interesting approach.  I had been told back when looking into the original conversion that I should not  use a MC w/ proportioning valve (although no one mentioned an adjustable valve). 
David Greenburg
'60 Eldorado Seville
'61 Fleetwood Sixty Special

Dave Shepherd

There is no real reason to use a prop valve in these systems assuming the use of a 4 drum m/c.  The brake bias should not be 75x25, this overloads the ft brakes and under utilizes the rear, the balance should be close to 50/50 as designed.

walt chomosh #23510

Yeh,I had assumed that we were talking about a disc brake conversion which I did to mine.....sorry....walt...tulsa,ok

David Greenburg

Based on the above, I've picked up the Autozone booster/master cyl. assembly.  Installation looks pretty straightforward, with the exception of the barke lines clearing the windshield washer jar.  I note that the picture in Ed Mobley's blog about doing this conversion on his '60 shows the washer jar removed, perhaps for clarity in the picture.  I'm just wondering if any of you who have done this conversion were able to clear the washer jar.  I could do without the washer jar if need be (washer doesn't work), but it does add a sense of completeness under the hood, so I'd prefer to retain it if possible. 
David Greenburg
'60 Eldorado Seville
'61 Fleetwood Sixty Special

The Tassie Devil(le)

G'day David,

Shouldn't take much to bend the lines to clear the Jar and its' mounting.

One can really bend these 3/16" lines into some extremely short radii's with a bit of inginuity.

Place a spring of 3/16" Inside Diameter around the tube, and bend it around a mandrel which could be as small as a 1/2" rod.

Bruce. >:D

PS.   Make sure you do the Flare BEFORE trying to bend the tubing.
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
'02 VX Series II Holden Commodore SS Sedan
(Past President Modified Chapter)

Past Cars of significance - to me
1935 Ford 3 Window Coupe
1936 Ford 5 Window Coupe
1937 Chevrolet Sports Coupe
1955 Chevrolet Convertible
1959 Ford Fairlane Ranch Wagon
1960 Cadillac CDV
1972 Cadillac Eldorado Coupe