[ALDEEM]

Hello everyone,

My 68 mustang failed the yearly inspection due to the difference in braking power and the parking brake which is about 82% on the rear axle. From the numbers I have on the inspection sheet, RR brake 0.43 KN, RR parking brake 0.24 KN, RL brake 2.33 KN, RL parking brake 1.84 KN.

So there is an issue with the rear right drum brake. 2 months ago I had a problem with my brakes not bleeding properly so I have replaced most of the hydraulic parts of the braking system parts, One year ago I have installed front disk conversion kit and on the rear brakes I have replaced every single part except for the backing plates.
When I couldn't bleed the system 2 months ago, I have replaced the rear wheel cylinders and when I removed the drums I have noticed that the right brake is very clean and looks like the brakes never applied on that side, but on the left side there was a lot of brake dust which indicates it was working. with the drums removed I asked a friend to apply the brakes and noticed that the shoes on the right side barely move and on the left side they were moving as expected. Also, when I removed all the brake parts to replace the wheel cylinders, the springs on the right side brake were much more stiffer than the other side and took me much more effort to remove and re-install.

Could it be because of the stiffness of the springs, or are they stiff because they haven't been moving a lot like the other side?

What else could cause this problem? and the problem is with both the normal braking and parking brake.

 

[stlwagon]

So if it weren't also happening with the parking brake, I might have suspected the proportioning valve.

 

[paul289]

The difference is springs is most likely the culprit. I'd recommend a new spring kit for both sides just to make sure that they're the same.

 

[rex1965]

I agree with paul289 about getting some new springs that match, however you must realize that hydraulic braking pressure is around 800-1200 psi, so those springs no matter how stiff they are are no match for the pressure applied. Some things to consider is whether the self-adjusters are working, which keeps the shoes close to the drum. I usually adjust the shoes out with a brake spoon (brake adjusting tool), until the shoes just barely drag on the wheel, with the wheel raised off the ground. Also if the finish of the drum surface on one drum is more polished than the other, I would take some 220 grit sandpaper and sand then in a diagonal pattern then reverse so it looks like a crosshatch pattern, just to bust the glaze on them. Plus there are points where the shoes meet the backing plates that are supposed to be greased slightly with a high temp brake lubricant, as well as the cable, cable guide, and the self-adjusters. I would also look at the shoes, the longer lining is the secondary shoe it goes on the rear most position in the brake assembly, as the shorter lining shoe is the primary shoe and goes on the foremost position in the brake assembly, which if they are reversed on one side or if both primary shoes were on one side and both secondary shoes on the other will cause your problem also. My 2 cts. Good luck.

 

[Ironhorse302]

Rex just touched on the easiest (and most often made) drum brake error. It is critical to lay out the parts thus...Primary ("short") shoe and short upper return spring is installed towards the front of the car. "Long" (secondary) shoe and longer upper return spring is placed facing the rear of the car. Again, this is sooo easy to get wrong, but also sooo easy to fix.
I can see where this would also affect parking brake holding...if there is 1/3 more braking surface available on one side, it would sure hold better!





Disclaimer: this my opinion only; there may be other, better informed members to reply to your post.

 

[ALDEEM]

Thank you so much guys, I will place an order for a new set of springs and when I install them I will check if the primary and secondary shoes are installed properly. They will take some time to arrive since I am not in the US. I will report back when everything is installed and inspected. :wink:

 

[Ivy66GT]

You will never get the parking brake to be as effective as the regular brakes on one of these cars. I hope that isn't how your inspector thinks it should work.

As Rex indicated those springs are return springs and pretty wimpy compared to the hydraulic pressure from the foot pedal. I highly doubt that new springs will make any difference as long as the brakes aren't dragging without pedal pressure.

 

[Charles Reeves]

This reminded me of an episode of "Wheeler Dealers" where Ed China took a car (perhaps even a Mustang) to the local MOT station in the UK to check the brakes. One of the standard tests is to check that both sides apply equal pressure, within a certain tolerance. He was checking the hydraulics, but I suspect they also check the parking brake.