Datsun Roadster Forum-311s.org

Very nice looking, and well worth stopping..haha
Linda

The saga continues. Frt brake symptoms returned on a second trip into town. I thought adjusting the piston rod length on the master had cured the problem (and it did temporarily) but on my next drive, the frt brakes slowly locked up again. Im out of ideas. Im out of patience. Im almost out of hair as I continue to slowly pull it all out! A quick recap of the process so far. Replaced caliper assembles with new. New brake pads. Re-installed caliper assembly shims in same position as removed. No friction when the front wheels are off the ground, the tire/wheel assembly rotates freely, so im assuming the calipers are centered over the rotors correctly. Brake hoses not replaced but seem to be new. No cracking or dis-coloration. Disassembled the master to install a rebuild kit only to discover the master is an aftermarket part number of some sort so the kit I had ordered was slightly different and not useable. The P.O. told me the master had recently been rebuilt and an inspection of the housing and seals seems to confirm this as all looked good.Shimmed the master cylinder at the firewall and adjusted the throw on the push rod to gain more return . As stated, that seem to solve the issue on several ever longer test drives. And now, here I am again. Any thoughts? All I can think of to do next is replace the master. Unfortunately, I cant get parts across the border currently. Id gladly pay the price of a new master at this point if it would solve this problem.

Do you have a spring on the brake pedal to pull it back when not applied?

Maybe try rebleeding everything, including the master ( clear hose on bleeder and looped back into the cylinder) Do you have speed bleeders? Very helpful for this job.

Linda

Notoptoy, yes there is a return spring. Linda, its worth a try. At this point, I'll try a witch doctor and a sage cleansing. Don't have a speed bleeder but do have a lovely volunteer in the form of my ever patient wife. (Who , by the way is starting to seriously question my mechanical abilities.)

Haha. Her efforts are better spent making you a sandwich.
Get the speed bleeders, info in WIKi, at least for the future.
Good info here:

viewtopic.php?f=3&t=19730

Linda

Hey Baja sorry you are still having problems. One more quick check and I am out of suggestions. Take the spring off the brake pedal and hold the pedal about where it normally rests, Move it slowly toward the floor. It should have a slight amount of free travel before it hits the back of the piston. So it should move very easily and then have some resistance. You brake rod may still be just a tiny bit too long. It got better after you shortened the rod some, maybe it just needs a bit more.There has to be some space between the rod and the piston to allow the piston to return completely.
When mine did the same thing yours is doing I had to open the bleeder while right in the middle of an intersection to get it to move, I used the hand brake to get it home. It was only a couple of blocks so I lucked out. Good luck I know it will get figured out so don't pull your hair out... you need it to protect your brain from that hot tropical sun.
Mike

This is why some people swap out the aftermarket push rod to the OEM Roadster brake master pushrod, because it IS the right size. Maybe someone has a measurement of that rod for you so that you can see if you are close. Or if you have one, swap it in and go for a drive.
Don’t overcut the aftermarket push rod though

Linda

I actually was going to pose that question Linda. Can someone tell me the length of the OE pushrod? As to Dads question, I do not seem to have any free play before the piston engages when the return spring is removed. Possibly an indication that I need more travel as you have suggested. But , I also noticed no freeplay when I removed the rod from the brake pedal completely and manually checked for the small amount of play that you described. Also, I conducted an experiment this afternoon in an attempt to better understand what might be causing the overheating problem. There is a loop very near my home that has almost zero traffic which allowed me to drive the car without applying the brake pedal, with the exception of using the brake pedal once when backing out of my garage. I drove the loop multiple times for several miles and then checked to see if the rotors were getting hot. Lets just say several of my finger tips now have blisters from reaching past the wheels to test the rotors. Not totally conclusive because I DID apply the brake pedal once but a possible indication that the pads are constantly rubbing. I will try the experiment again tomorrow without using the brake pedal AT ALL to see if I have the same results. If so, perhaps it is a caliper assembly centering problem and the pads are constantly causing friction? This has been suggested by several members but as stated before, I jacked the front end up and spun the tires by hand, and they seemed to turn freely, so I mentally eliminated that possibility as the problem. Perhaps some shims for the caliper assemblies? The adventure continues.

I seem to recall that there were some shims involved with the front brakes. Usually you put back what was in there but if one fell out you might not have known. Perhaps check the online parts manual to see if they are shown.
If someone can loan you a spare push rod to try and/or measure I think that would help. Or the slow way is to take off 1/8” at a time and test
You are sure that the pads have been sanded enough to not bind?

Linda

My bet is that the pushrod is still too long. The spring should be able to do some "work" by holding the pedal back into the free travel area. If there is no slack, then there is constant pressure on the system, no matter how slight.

How old are the flex hoses?

Using a pair of pliers, twist the pushrod in a clockwise direction to increase the height of the brake pedal. If you need to lower the brake pedal you can do so by twisting the push rod counterclockwise.

The pads dragging could easily be caused by them sticking in the caliper, a know problem.
Remove you pads and sand the edges so the slide in easily.

The stock cylinder has a "captive" push-rod. I have seen them get dirt or crap in them that can cause a problem.
If you are careful not to let the piston come out, you can remove the clip and clean the end of the piston, rod retaining washer and clip and re-install with the master cylinder in the car. Otherwise you need to remove the cylinder. Use lots of towels.

Linda, on the subject of someone loaning me a stock pushrod, that would be great, but since I am 800 miles south of the Mexico border in Baja I don't have any fellow members within easy driving distance. If anybody feels like a nice Mexican getaway, free lodging and i'm buying the tequila. FJ20SPL311, I did take the new pads back out and sand them in one of my first attempts to resolve this problem. They definetly were a bit tight, but now move freely.Also, I did remove , dis-assemble, and inspect the master cylinder Everything looked good. The bore looked clean and all seals looked new. SPL310, I cant be sure how old the flex hoses are, but an inspection shows no indication of extreme age. There is no cracking or discoloration. BUENAVIDOS1, My M/C is one that has the threaded pushrod. It is currently adjusted as far as the threads will allow for maximum return.