Disc brake conversion

[rwchatham CLC 21892]

A friend of mine wants to put disc brakes on the front of his 59 with a dual resovoir master cylinder , Im more of an original guy so I’ve never done one so has anybody out there put disc brakes on their 59 and if so which kit did you use and are you happy with the outcome ?

[Glen]

One thing people forget to do when going disc on front, drum on back, is adding residual pressure valves to the line servicing the drums. Without these the shoes will fully retract from the drum leaving a lot of travel when you push the brakes effectively making them inoperable till you achieve enough pedal to force them back out. Doesn't really hurt anything except it puts all your stopping power on the front since the discs are in contact all the time, and the pedal may feel soft for a split second when brakes are applied.

This and some other things seem strange to me. 
1.   All drum brakes cylinders retracted completely when the brakes were released.  To prevent too much pedal travel the brakes had to be kept adjusted to keep the shoes near the drum.  Automatic adjusters should take care of that. Why does having disc on the front change that? 
2.   My 68 ELDO came with a device that delayed the disc brakes.  It is a piston in cylinder that move back when the pedal was pressed, in theory delaying the disc from moving until the piston bottomed out.  But pressure can not build up until the shoes come into contact with the drums.  In the early 70s the piston blew out on my car and I could find a replacement.  I eliminated it and have not had any problems without it.   
3.   Proportioning valves, why?  The pressure in the brake lines are the same, front and back.  In the past designers selected the brake cylinder size to provide the required force.  Larger cylinders in front and smaller in the rear.  What has changed?

[76eldo]

I’m interested in converting my 60 to s dual reservoir master cylinder but keeping the drum brakes. I find them to be excellent for stopping such a large car.

Was it the 1962 booster and master cylinder that was basically a bolt on?

Thanks
Brian

[marty55cdv]

I’m interested in converting my 60 to s dual reservoir master cylinder but keeping the drum brakes. I find them to be excellent for stopping such a large car.

Was it the 1962 booster and master cylinder that was basically a bolt on?

Thanks
Brian

Brian ,  I used the 68 master and booster combination on my 59 it works great but when I recently went to buy another set for my 60 Flattop I couldn't find one.  I just completed the conversion to dual master on the 60 over the weekend leaving the drums . I got the dual master from https://www.performanceonline.com/power-brake-conversions-57-68-cadillac/.  They have a ebay store which is where I purchased mine.  The good thing about this set up is the lines can be installed from either side. It bolts right in no opening the firewall holes and it stops like a modern car now.  You will need a line and a union and a plug to connect the master to the rear at the junction block at the frame

[rwchatham CLC 21892]

Marty does that master cylinder you installed have a proportioning valve on it or was that not necessary since you kept drums all the way around ? Thanks

[Dave Shepherd]

No prop valve for drum/drum.

[marty55cdv]

   As Dave said not needed for drum / drum , they do sell complete kits for going to front disc but after driving mine yesterday I can't imagine it could stop any better with disc.

[rwchatham CLC 21892]

Marty so is it setup so one line from the master feeds the front brakes and another line feeds the block to supply the rear brakes ? Thanks

[marty55cdv]

     If you follow the line from the original master it goes to a junction block on top of the frame rail , from there it splits, 1 line goes to the rear, one line for the left front and one for the right front you remove the line that goes to the rear put a plug in the block and then use a union to connect a new line and extend it up to the new master.  All the fittings, lines etc can be had at Oreilly or Napa

[rwchatham CLC 21892]

Marty thanks ,that is what I figured that way you still get the benefit of dual resovoir Incase you develop a leak .  Besides the safety aspect  is there an actual difference in the feel of the brakes driving it now compared to the old master cylinder ?

[marty55cdv]

Marty thanks ,that is what I figured that way you still get the benefit of dual resovoir Incase you develop a leak .  Besides the safety aspect  is there an actual difference in the feel of the brakes driving it now compared to the old master cylinder ?

The difference is night and day as far as the light pressure from your foot required to bring the car to a stop. It stops like a modern car

[The Tassie Devil(le)]

The use of the proportioning valve in the rear line is there to stop the rear brake from locking up first, especially as the weight is lifted off the rear axle, as the front dives down.

This transfer of momentum combined with the locking up of the rear wheels can cause the vehicle to slide out of control, as the rear end follows the downward movement of the camber of the road.

When fitting "odd" brakes and parts, one needs an adjustable proportioning valve as one doesn't have the millions of dollars to test like the factories have.

When I fitted Disc Brakes to the front of my Hot Rod, which had a '68 Chev 12 Bolt rear end, I had to sleeve the rear wheel cylinders down to 5/8" from the factory 1".   Plus, I had bigger wheels on the rear which also threw a spanner into the works.

Bruce.

[bcroe]

   As Dave said not needed for drum / drum , they do sell complete kits for going to front disc but after driving mine yesterday I can't imagine it could stop any better with disc.   

The dual circuit on my 68 gave me the confidence that a single
fault would not leave me with zero brakes.  But the discs on later
cars worked much better (yes I have been up Pikes Peak a few
times), and were entirely predictable in the rain.  Bruce Roe

[fishnjim]

I had a "classic disc brake" conversion done on the '58 and kept the drums because the disc conversion requires different rims to fit over the calipers.   There's some spindle kits that can off-set that but it's not original appearing.   
I agree the big GM drum brakes stop plenty well.   I wish they had self adjusters back then or a conversion kit.
The main item is the pedal linkage and mounting bracket to convert the original vertical booster/pedal to the modern horizontal style booster/master.   They're using an OEM 9" GM booster, not sure what P/N or year to fit in the space.   A couple other '58 guys I know did there own from scratch.  It makes it a little tight for maintenance on that side but not any worse than the original.
When it comes to brakes, since this is a non-factory replacement, I think from a liability standpoint, should a problem arise, dictates professional installation.  That takes the onus off the owner.  I'm sure there's plenty of competent owners, but it's a risk management situation.   Even though it's a much safer braking system from a failure mode stand point(dual vs one) to the original and better reliability, if you don't match the pressure, flow, and proportions on a split system (half disc half drum )you can have a complete loss of fluid failure - no brakes.   Someone has already figured that out in a kit - usually.