Disc Brakes-1950 Desoto

[James_Douglas]

I have a kit on the front from ECI and the rear*** I built myself.  I use a Midland-Ross remote power brake booster with a stock MC with linkage and pedal from a 1952 Chrysler that came from the factory with power steering. The Pedal ratio and the linkage are different.

 

***The big issue of rear disc's is getting the disc to run true on the tapper.  The only way I have found, other than dumb luck, is to pull the axle and have the disc-hub trued on a long lathe using the axle shaft centers.  Even then, you have to make them left-right and if you change the disc you have to do it again.  If you true the face of the hub first with the axle, you get 90% of the way there.

 

The rear uses Cad calipers with the mechanical parking brake that acts directly on the disc pads.  Since this is a fluid drive car one must always use the parking brake.  So the Cad caliper issues of going out of adjustment never happens as every time you stop you pull on the cable.

 

The system works really well.  Stopping power is almost scary. The only problem is that the mechanical ratio of the stock parking brake handle and the Cad Calipers is too low.  On an extreme hill here in San Francisco the parking brake will not hold.  The car mushes down the hill at 5 MPH.  If I press on the brakes, with the power assist hard, then set the parking brake it holds fine.  An indication that the mechanical advantage is not enough.  I will build this winter a double link pivot under the frame that will increase the mechanical advantage and that should take care of the issue.

 

I use all DOT Russell racing stainless lines and all new hard lines since I am using the stock MC.

 

James

Edited October 16, 2013 by James_Douglas

[50desotocoupe]

Well, I finished up the disc brake upgrade this last weekend. I can't wait to get it on the ground and see how it stops.  The whole process was pretty straightforward.  The most difficult part of the job was tapping the spindle for the 5/8 18 bolts.  That took awhile and I went through 5 taps...  I also had to have the passenger side bracket holes machined out just a slight amount to get everything to line up.  I am going to use the stock master cylinder for now as it is brand new and I have all new rubber lines.  I had to adjust the brake pedal pushrod a little bit but now the pedal is great.   The dual pot mc might be on the calendar for a winter project this fall.    I know they aren't for the purists but for me it was the perfect thing to do.  Next is to take the car in for the interior to be installed in March. 

[40desoto]

50desotocoupe  if this car was lowered would the brake caliber clear your frame?  I heard of people having such issues with similar setups and lowering their cars

[50desotocoupe]

Hello.  Well, that is a very good question as I haven't taken the car off the jackstands yet.  Visually it looks like both the front and rear calipers will clear.  I guess I will have to see when I take it down this weekend.  Thanks for that thought...hmmmm

[50desotocoupe]

Another quick question for the experts.  I went out last night (car still on jackstands) and the pedal went to the floor.  After 1 pump it was back up but then I couldn't easily turn the front rotor.  I originally thought I had a leak because of no pedal..but then woke up in the night and remembered something about having to install a residual valve with less pressure after removing the stock valve from the stock master cylinder. 

 

I have read lots of posts and realized that the factory residual valve is too much for the new disc brakes on all 4 corners....so can someone confirm my thoughts.

 

remove factory residual valve in master cylinder and plumb in a 2lb residual valve for both front and rears.

 

Thanks in advance!!

Matt

[50desotocoupe]

Or do I remove the internal residual valve and wait and see if I need to install the 2lb in the lines?  I don't mind having to pump the pedal after letting it sit for awhile as I do that in all my old cars...kind of like making sure you zipper is up on your jeans...lol  Guess I should probably be more awake before posting. 

[Don Coatney]

You should not have to pump your pedal even after sitting for a while. If you do have to pump it you most likely still have air in the system or a master cylinder issue.

[pipebomb]

i had to take out the valve at the end of my m/c to get it to work properly. been working fine for 3 years.

[50desotocoupe]

thanks for that information.  once you took that out of the master cylinder did you put the 2lb residual valves in the lines or did you have enough pedal and pressure?