BC

Thanks guys.

The early master was replaced with the s4 master and this is when the problems started.

As I stated abive, I removed the bias valves completely and T-d the line for the rear after a wilwood or Tilton bias adjuster into two lines as the early cars do have two rear lines to each caliper.

I am tempted to cap off the early master down to two outputs - front and rear and bench bleed and install that.

The original reason I did all this was that the original booster was clamping the brakes

BC

That did not work. With booster on it still goes down the floor on the first pump and near the floor on the second.

The s4 master was bench bled and then capped off and careful installed. Before installing I even capped off the ports and tested if the piston could be pushed in and it could not.

Im out of ideas so I’m just going to have to start changing parts now. It should not be this difficult.

dr bob

BC --

Just re-read and saw that you mentioned using copper tubing in the system. Don't. Copper isn't strong enough on its own for the service. Plus it flexes and work-hardens, eventually fracturing. Copper is good for wiring and antique radiators. Steel brake line tubing is readily available. The CuNiFer stuff used originally is also available but not quite so easily.

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I chased air entrained in my system for a while. Finally ended up bleeding the system section by section, from low end (wheels) towards the master cylinder. There were some challenges with the ABS unit that you don't have. Still, air bubbles in the lines would rather go up than down, and they will camp out in local high spots given half a chance. Rear llines and connections on my later car were harboring fugitive air bubbles. You don't have the T on the rear bulkhead that the later cars have, and in turn you undoubtedly have substitute high spots in similar places. The later 4-piston calipers enjoy a little manipulation as they fill with fluid too, so that the air ends up only at the tops of the fluid cavities. Think like a bubble on the rise.

BC

The copper I meant was the original (but now nearly 40 years old) hard lines.

I guess I have two options at this point.

1- there is entrapped air after the master, way down lines that I never let drain (only have replaced the master and booster and some lines near it)

2- the master whilemit bench tested okay with capped (bent) lines after being bench bled, may be allowing cross- flow past the seals when installed.

BC

I suppose if I bench bleed and install the other original (known good) master and it still acts this way is is entrained air somewhere else.

dr bob

My air-in-the-ABS ordeal ended with vacuum from the MC end to pull the air out, then push fluid from the calipers to refill the voids. This --should-- work if you have tight thread sealing at the bleeders, or sub in a couple short sections of hard line with a valve at the caliper ends. I started off vacuuming with an air eductor setup that would tolerate liquid, but moved to my multi-stage vacuum pump with a little catch bottle when I couldn't get enough vacuum from the eductor. Remember that you can't draw vacuum on the master cylinder (fluid bleeds forward...), so it gets a bench bleed and is then reconnected wet.

The factories use this kind of vacuum-fill method when the cars are originally built. there are pseudo-vacuum systems that draw fluid and theoretically any air, usually with some kind of hand pump.

Start by reverse bleeding with the power bleeder pushing from the connection where the flex lines connect to the hard pipes. That will push the bubbles uphill towards the master cylinder end. Connect to the bench-bled MC. Then reconnect the calipers and do a normal bleed out the caliper ports. If that method doesn't work, try the vacuum method; it's tedious but it ALWAYS works.

BC

The early, previously working and now bench bled master now results in the same soft or non existent pedal.

Taking off each wheel and caliper and doing whatever the hell dr bob is talking about sounds like the next step which is fvcking rediculous and why so many old cars are in fields rotting and people look at “car people” like we are nuts.

BC

Something like this?

BC

I’ll try the mittyvac at the bleeder screws and see what happens.

Fishah

Bob,

I'm not sure I'm smart enough to understand your first paragraph completely, but I did recently install a new Booster and MC on a 79'. I used a power-bleeder, but did not bench-bleed the MC.

Haven't driven the car yet, but the pedal feel seems very good. Am I missing something here? Do you feel I should go back and bench bleed the MC?

Thank you sir!

BC

I think it either works or it doesn’t with traditional installations and then if it is unsuccessful we have to go through this much more expanded process.

Lloyd

Just MY experience..for what its worth...I put a s4 master on my race car with Bigger GTS calipers on the front. Also had the 10" booster. Never could eliminate the mushy pedal. It did not ever give me a good feeling of confidence. Switched out the whole system with a 3 pedal Tilton system running individual cylinders for the clutch, front brake and rear brake. There is also a manual proportional adjustment. The brake feel is stiff, but a very confident feel and they work very well. Of course the size of each master cylinder does have an effect on the pedal stiffness.

dr bob

That would get the job done, but remember you have a Motiv or similar unit that will do the same thing. Just connect it at the caliper end of the lines and push the fluid uphill. No hand-pumping and you save $60.

My pre-Motiv tool is adapted from a garden sprayer, and uses common plumbing/tubing connections that make it easy to push fluid from bottom to top. Disconnect each hose at the chassis, and use a piece of hard line and a F-F connector to connect to your bleeder. You are pushing through the lines and NOT through the caliper, so you are pushing fluid and air uphill only. The caliper has air in it that will try to stay in the caliper; if you want to "bleed" the caliper as part of this process you'll need to be able to articulate the position of the caliper to get the air out through the port for the line. The caliper normally sits bleeder-port-up, and it will need to be inlet-port-up if you want to leave it in-circuit and push any air out.

Things to think about:
-- Be sure to seal the bleeder screw threads with a little silicone grease, some TFE thread sealing paste, or even some teflon thread tape on the threads only. Keep it away from the tip of the bleeder and the mating seat in the caliper.

-- Know that you can substitute a piece of hard line for the bleeder screw, as the seat in the caliper is able to seal on a bubble-flared end of the tubing.

-- This is a very low-pressure procedure. The total height of the system is less than two feet, so 1 PSI is all that's needed to move the fluid up to the master cylinder.

-- Monitor the fluid level in the reservoir, using a turkey-baster or similar to suction out fluid to keep it from overflowing as you fill from the bottom.

-- Know that there can still be local "high spots" where air will tend to accumulate. On later cars there's a high spot at the T fitting on the rear bulkhead forward of the battery box. ABS cars have the ABS unit to contend with. With calipers mounted, the caliper itself is a high spot, hence the need to unbolt and articulate to allow a continuous uphill path from the bleed screw to the hard line to the reservoir.

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Drawing a hard vacuum on the system with a real vacuum pump means you can "bleed" fluid back into the very empty system and leave virtually no air. The fluid fills any voids "automatically". You can't pull a vacuum on the master cylinder, as it will draw air around the piston cups. If you are using a mechanical vacuum pump as I did (my trusty multi-stage lab pump) you MUST prevent liquid from passing into the pump. Add an isolation valve you can close after drawing the vacuum but before allowing fluid in. Or use a "trap" similar to what's used in a typical hand vacuum-bleeding pump kit. In my quest to purge air from my ABS unit, I managed to gather a Craftsman vacuum test/bleeder kit with fittings and a plastic fluid trap included. It's identical to this kit that Harbor Freight sells. This kit is often on sale for less than $20, and doubles as a vacuum system tester for HVAC and flappy actuator testing on the 928. Better than the plastic Genuine MitiVac that has no tolerance for organic solvents, IMHO.

BC

I am going outside now to figure out how the motive can push fluid back up.

BC

Thanks BTW