O.K. guys sorry in advance for the long post. My '71 was in storage for approx 23 years. At some point the master cylinder was removed so the system was basically "open" for lack of a better term. I've replaced everything with new except hard lines(cleaned out) and the factory proportioning valve. Everything has been bled properly including the master. My problem is that after bleeding, I get a firm pedal which apparently is only activating the rear brakes. I'm getting good clear fluid out of the calipers, but no braking action. I'm wondering if it's possible there may be something gummed up in the proportioning valve??? The master and rear wheel cylinders are Nissan OEM and the Calipers are from NAPA. Has anybody had a similar problem? BTW, the rears work well........

So you have a new:

master cylinder

cleaned lines

new calipers

new wheel cylinders

humm

Did the fronts bleed okay? Did the front calipers move freely when you put in the pads in?

The proportioning valve may be iffy, I would try to find one.

Correct on all of the above new, replaced, cleaned. I didn't really check the calipers for movement when I put the pads in because they were new. They seem to bleed ok. I'm just wondering why I'm not getting any front braking action. Maybe I should take the prop valve off and give it a good cleaning? I did flush all the lines through the prop valve with brake clean and air though. Maybe there's some junk in it somewhere. It's a mystery to me.

Are you getting full stroke on the master Cylinder piston?

Very important that you adjust the length of the pushrod between the vacuum booster and the master cylinder such that there is a small gap (forgot manual rec but think it is about .060) in the free state. Pain to measure accurately but it is critical to system performance. You may have mixed configurations which may not be compatible.

Edited December 8, 201014 yr by kinfish
clarification

Ron, I'll check that, but the car was not "messed with" according to the PO when it was in storage. No reason to think things weren't as they were prior to the original master being removed.

You should clean up the Proportioning Valve anyway. I am thinking that Ron is right on the money though. Make sure that the Master Cyl is installed properly and that the Rod is correctly adjusted.

Question. Are you Sure that the hardlines were cleaned properly? Just asking. Sometimes when you clean everything up and put on a new Master Cyl. the pressure blows some crap loose that was way up in the line.

Good luck

Okay, does this thing you all continue to call a proportioning valve have a wire the comes off of it?

I'm suggesting you still have air in the front circuit of your MC. That's why you aren't getting movement in the calipers..... Once I had a situation where when I put the brakes on I'd get a light come on on the dash. That's a "circuit fail" indicator light which comes from the thing everyone continues to call the proportioning valve. I pulled the new MC and opened it up and sure enough one of the seals had been installed with a pucker in it so it would not supply pressure to that system front or rear.

If you end up pulling the MC and looking inside to see if you can see anything amiss, go ahead and flush the bore out really well. I've have found shavings and all manner of grit inside new units. Can only serve to shorten the life.

Also as a general rule a complete flushing of a brake system annually will go a long way toward extending the life of brakes.

Andrew- I'm pretty sure the lines were clean. I had lots of good clean brake kleen coming out after sitting for awhile when i blew them out with compressed air.

Bruce- Yes, the "proportioning valve" is what I'm referring to where the hard lines come out of the master, to it, and then out of it to the respective calipers/wheel cylinders.

I will re bleed the front section on the car and see how it goes again......

You said you get a firm pedal but this might still be worth checking. It happens occasionally and is easy to do. Is the bleed screw on the top of the caliper? On some (many) model years, 76 for sure, the calipers will bolt up perfectly on the wrong sides, putting the bleed screw at the bottom. This leaves an air pocket above the bleed screw which is impossible to remove completely.

Brakleen is a strong solvent and will swell rubber, I believe. Maybe you gummed up the caliper seals or the master, if they were exposed to it? Hopefully you had everything disconnected when you were flushing the lines.

As the M/C has been removed, have you checked to see if the rubber reaction disc is in place inside the booster ?

Okay, does this thing you all continue to call a proportioning valve have a wire the comes off of it?

I'm suggesting you still have air in the front circuit of your MC. That's why you aren't getting movement in the calipers..... Once I had a situation where when I put the brakes on I'd get a light come on on the dash. That's a "circuit fail" indicator light which comes from the thing everyone continues to call the proportioning valve. I pulled the new MC and opened it up and sure enough one of the seals had been installed with a pucker in it so it would not supply pressure to that system front or rear.

If you end up pulling the MC and looking inside to see if you can see anything amiss, go ahead and flush the bore out really well. I've have found shavings and all manner of grit inside new units. Can only serve to shorten the life.

Also as a general rule a complete flushing of a brake system annually will go a long way toward extending the life of brakes.

Bruce, FYI the Proportioning Valve is the manifold that all of the Hard Lines go to right after the MC. It is bolted to the firewall, lower left of the Master Vac. There are no wires attached to it (at least on later S30's). Your MC suggestion is correct and good advice!

When the system was cleaned out, there were no components attached. The calipers are oriented correctly with bleeders @ the top. I'll check the rod and bleed the front M/C resevoir again. Thanks for all the suggestions guys. I know I'll get this figured out. It's not rocket science.

Edited December 10, 201014 yr by 5150 will
left something out