Datsun Roadster Forum-311s.org

I agree with Phil, best to make them yourself. Not sure if anybody sells them due to the ability of a lot of roadster owners to make them instead, hence they wouldn't sell for much.

Solex68 wrote:I would go with the above recommendations (you are getting some experts responding BTW) but if all that fails…

You may want to check where the brake pedal rod connects into the master cylinder. In your first photo, from the interior side of the vehicle, slide the rubber cover that covers the rod so you can see the situation from that angle. Press the pedal with your hand to verify that there is no physical binding between the brake rod and the master’s piston.
That is where I was having issues. You can remove the pin that holds the rod to the pedal arm as well, but don’t go that far unless you believe there is an issue with the rod or if you suspect the rod does not come out far enough due to linkage or if the washer on the backside of the master is so thick that is doesn’t allow the master’s piston to retract all the way (that was an issue I encountered when I installed a Different model Datsun mater in my roadster)

There is no adjustment within the rod (unfortunately). I know some people do the math based on the throw needed and re-drill the hole where the rod connects to the brake pedal lever. It may be above or below the current hole depending on the master cylinder installed, original or other Datsun model.

I worked on my brakes today. The engine isn't in it yet so I had plenty of time to ponder. I remembered that one of the master cylinders (brake or clutch?) I bought earlier had an adjustable rod? I didn't use it originally because it was way to long, but if I cut the adjustment rod down it work perfect. I dug through my spare parts box and found it and that is how I solved my issue.

Going to revive this thread as it is similar to my current problem.Alot of threads on soft brake pedal issues but not many on hard/ no travel brake pedal.67 1/2 1600 dual reservoir master. New rear cylinders and shoes, new frt caliper assemblies and pads. After replacing all of these parts I took the car for a drive. About 20 miles to a marina with no problems, good smooth braking and no brake pull. After about thirty minutes at the marina, started back. About 5 miles down the road, I start smelling overheating brake material. Brake pedal becomes progressively stiffer to apply and eventually has no travel at all. Pull over, frt brakes are hot and obviously not retracting fully.I let the car sit until the brakes have cooled, jack the front and the tires rotate freely. Drove the car this morning with almost the exact results. Since the calipers are new its not likely they are the problem. Seems likely that its a master cylinder problem but the m/c was rebuilt shortly before I purchased the car about 6 months ago. been reading threads for a couple hours and it sounds like a m/c piston travel issue but the timing is confusing me. No issues before replacing the frt and rear brakes. I see no shims on the m/c mounting hardware and am assuming installing shims will increase rod travel and possibly allow for the return of brake fluid to the master from the front brakes?

Did you replace the calipers or just the wheel cylinders? If you replaced the caliper did the new one center on the disc? Sometimes they need to be adjusted by shimming. I put new fronts on mine two years ago and one side took two shims and the other none. I replaced just the cylinders there was no need to replace the calipers. There is the possibility of the fluid expanding as it becomes hot resulting in more pressure and more heat, and progressively stiffer pedal.

Make sure the pads slide freely on the calipers. The pads may need to be filed or ground a little on the sides. Check for binding

Did you check the condition of the front brake hoses? The hoses may have deteriorated internally and are not allowing the brake fluid to return to the master cylinder when you release the brake pedal. Over a short drive, the the disc brake pads do not retract and continue to apply pressure to the brake rotors.

This happened on the front brakes on my motorcycle. I had to replace the hoses.

Hi Adam,
The first thing I noticed is you don’t have a firewall/brake brace. Most dual master cylinder cars already have one but your does not and might be adding to what I think is your other problem. When putting in the new brake pads they need to be fitted by sanding the top and bottom of the pads so that they install smoothly. If you don’t sand the pads to fit they are so tight they are great difficultly moving and also tend to not release after presser is taken of the pedal. Which can lead to another problem, the ads can glaze and not have any friction effect as the resins in the pads have no ability to “light off’ so no heat is generated when you apply the brake pedal.
Good luck Adam.

C.Costine I replaced the wheel cylinders and the entire caliper assemblies. I did not replace the brake hoses as they appear fairly new.( no cracking or discoloration) As far sanding the pads, Im not sure if that was done as I had a local shop do the frt brake work. I can tell you that after the brakes have cooled down, the tires spin freely when the frt end is jacked up. No friction from pads at all. During both test drives the frt brake calipers would not return after being applied. This happened progressively until they were applied to the point that the car could no longer move. After a cool down period the tire/wheel spins freely.

Are the rears locking up also when this happens? Certainly sounds like fluid is expanding in the heat but still seems very odd. Like it's in a positive feedback loop...the warmer it gets, the more the pressure builds, which makes it get warmer, etc.

MattC rear brakes are not locking, which brings up the question in my mind, if this is a master cylinder problem, could it only affect the frt brakes and not the rear? I suppose so since it is a two resevior system. I have contacted the PO to find out if he replaced the frt brake hoses. Waiting on a reply. Also, it looks as if the M/C rod that attaches to the brake pedal on my car IS threaded but adjusted all the way out. Am I correct in thinking that I need to shorten the length of the rod to get the piston to return further to allow the brake fluid to return to the master? Forgive my limited mechanical knowledge. I enjoy working on my car but am learning as I go.

I had the exact same problem on my 67.5 as you are. Mine has a 510 MC. After driving for a while the pedal would get harder and harder and eventually the front brakes locked up. A quick check would be for free play in the pedal rod. I found it easiest to take the spring off the pedal and see if there was any free play. Mine had none, which was not allowing the piston to fully open. I ended up grinding the rod down a bit and installed a couple more shims. There has to be a small gap between the rod and the end of the piston. I suspect your piston is not returning all the way back and is allowing pressure to build up and by the time the brakes cool down the pressure has bled off. You may just need a few shims. And of course it may be different on your car.
Mike

dads311, thanks Mike. Sounds like an easy possible solution to try. I have done a visual inspection of the master and can see no shims.Am I correct that the shims would be installed between the firewall and the master cylinder base? I have read that most members have made their own shims out of thin sheet metal. Any reason a flat washer would not work? I don't have the tools to fabricate my own shims. Also, how much play did you find to be correct to solve the problem on your car? (thickness of shims used)

bajaroadster wrote: Fri Mar 27, 2020 1:00 pm dads311, thanks Mike. Sounds like an easy possible solution to try. I have done a visual inspection of the master and can see no shims.Am I correct that the shims would be installed between the firewall and the master cylinder base? I have read that most members have made their own shims out of thin sheet metal. Any reason a flat washer would not work? I don't have the tools to fabricate my own shims. Also, how much play did you find to be correct to solve the problem on your car? (thickness of shims used)

Yes the shims would be between the MC and firewall. The washers would cause uneven pressure on the MC mount and firewall. The firewalls have a tendency to crack already. No need to help that along. I have seen people make their own shims with different gauge sheet metal.

Like Zippy said the shims are between the MC and firewall. Washers might work for a quick test but not a permanent solution. If you have a hardware store near, buy some tin snips and a small piece of thin sheet metal, you can make your own shims. Some one posted dimensions on page one of this post. Homemade shims may not be perfect but is a better solution than washers. A small gap between the rod and piston is all that is required maybe 1/16".

Thanks Zippy, Mike, et all. Was able to fabricate some shims and install them. Just got back from a test drive. No change in symptoms at all. Still have increasing hardness of brake pedal as I continue to drive. After about 5 miles, frt brakes are on continuously and brake pedal has no travel. Stayed close to home and returned as soon as symptoms started. Frustration level ever increasing. These are such simple cars, there has to be a simple solution.