'72 Wagon: Bueiz

[bueiz]

just a quickie....

[bueiz]

Okay, maybe two...

[JordanTr]

Yumm. That looks great.

Please do let us know how the car drives with the Megan coils. Are you still running the 8k springs or have you downgraded them?

[Byron510]

So, I've been jacking around with the brakes for a few weeks now. I can't get the system to tighten up. If I pump 10-20 times I can get some pressure, but the brake pedal is spongy and the pressure won't hold.

I've bled all four corners all sorts of different ways, finally using the method described in the book "How to Keep Your Datsun Alive".

I tried bench bleeding the master cylinder but that was stupid because I didn't have plugs for the output valves. So, I bled the MC on the car and everything looked good, solid stream of fluid, no bubbles.

But, I still can't build up pressure. I'm thinking the MC that I have is bad. It's an NOS 280ZX MC, but I have read in the forums that the seals in the NOS MC's could be bad. Maybe that's what I'm dealing with here.

Anyone have any suggestions?

Just a thought here - the rear brakes are not a mile out of adjustment are they?

It would seem to me that if the M/C can build pressure eventually, then it is likely OK. Certainly starting to bleed at the master is always a must. And never, ever at any point run out of fluid when bleeding the system. The tiniest air bubble taken in will cause havoc. Next is making sure that all the fittings are good - every joint in the car. However if one of the fittings was wrong - you'd likely see a puddle by now.
If you are still going nowhere - pull off the rear drums - make sure the wheel cylinders back there are ok. I'm suspecting there is an issue with the rear half of your system. But hard to tell through the monitor from 4400 kms away. I have had on occasion over the years a stubborn M/C that just didn’t want to get going. But once it did – all was good.

Keep us posted.

Byron

[okayfine]

Yeah, if it builds pressure (good pressure?) eventually, 99% of the time there's air in the system. I had the never-ending-bleed-procedure once when I R&Red a master, and it's frustrating.

[bueiz]

Jordan. I'm still running the same springs that Kamodo put on his coilover setup. We'll see how smooth it does or doesn't roll. I'll report back here if I don't die from whip lash first.

Yumm. That looks great.

Please do let us know how the car drives with the Megan coils. Are you still running the 8k springs or have you downgraded them?

[bueiz]

As for the brakes...

I did adjust the brake drums per the manual, so there is a little rub.

Do you guys think I should keep on working on the Master that I have? I did buy some new rear wheel cyclinders so I'll be replacing those before I try again.

When you guys bleed the MC, do you run a hose from the nipple back into the reservoir or run the hoses out from the nipples into a container? Do you bleed the fwd (furthest away from the driver) resovoir first, then the rear reservoir? What about pedal work; do you stroke the entire reservoir when your bleeding it and keep the pedal down on the last pump, then close the nipple?

[okayfine]

Bleeding IS a PITA. IMO the only way to do it is with two people. I've used Speedbleeders and found they'd sometimes let in air around the threads. Similarly, when bleeding a BMC I'd only recommend opening and closing the nipple every time, 'cause I've had problems with air seeping in past the threads when leaving the bleeders open enough to pass fluid.

Stroke entire travel, keep the pedal down, then crack the bleeder, allow the pedal to fall to the floor, then tighten, let off the pedal, repeat.

I also prefer to direct all bled fluid to a container and not back into the reservoir. Reason being is that you're aerating the fluid, and you don't want that to get back into the system. Some guys in mountain bike circles will degas brake fluid before bleeding their disc brake systems.

[Three B's Racing]

Not really, bleeding is simple. All you need is a tank that holds a qt or more of fluid that will seal over the master cylinder that you can pressurize with a small amount of air. Then you simply open the bleeder and let the bubbles out. I built one back in the 70's I've been using since. Sorry no pics but I imagine you already have it pictured in your head.

Now back to Nuclear work aka: Hurry up and wait

[Byron510]

If the system is totally dry - bled out from the master all the way to each wheel cylinder/caliper, I do find it rough to just get some fluid moving through the system at first.

For starters
- Definitely a 2 person job moving forward
- If you are using a one person fancy bleeder, well I haven’t found one I like, I prefer a person on the pedal

First up, you need to get fluid in the system at all four corners. From this point on, you need a pedal lackie - someone who can listen to you when you say pump, down, and again! It just takes one time where the person at the pedal brings the pedal up while the bleeder is still open and all your efforts are for not.
Secondly - never run out of fluid! Again, you'll be starting all over again. So 6 or 8 good bleeds (once the fluid is rolling) and you have to get back up off the floor and check that reservoir. It’s a pain in the ass, but even more of a pain to start again – not to mention a waste of fluid.
Also, a little hint here. The caps will be off the reservoirs throughout the process, make sure the (clean) screens are in the reservoir. These help diffuse the splash as the piston moves back and forth uncovering and recovering the port to the reservoir. Without the screen in place, little shots of paint eating brake fluid shoot pretty high out of the M/C though the process.
Step 1) Starting at the master - obviously full at all times - open one of the bleeders 1/4 turn - that's all it takes. Place your finger with slight pressure over the bleeder (and a rag underneath held with the other hand) and get your pedal person to slowly cycle the pedal to the floor and back again - note slowly - 2 second cycles each direction. (Don’t hit the pedal with your foot – this agitates the fluid, possibly causing air bubbles and uses a lot of energy. You may feel little puffs of air at the bleeder as the pedal goes down, until you get fluid. As the pedal cycles back up, you just need enough pressure so that the piston doesn't draw air back into the reservoir. Once you have fluid, stop, close the bleeder nipple and repeat for the other circuit on the master.
Step 2) Now, you are going to do the same method at the wheel cylinders/calipers just to get fluid in the lines. Start at the furthest point from the master for each front and rear circuit. Which circuit you do first really doesn't matter – they are completely partitioned from one another. But the pass front and drivers rear are the furthest away due to the line routing. Again, crack one bleeder at a time (1/4 turn), with very slight pressure over the bleeder nipple, get your pedal guy to slowly cycle again until you get fluid. Close the bleeder. Repeat on the opposite side of that same circuit. On the rear brakes you'll really notice the little puffs of air in a dry system for a number of cycles. ***Watch that fluid level!*** 6 cycles and it could be empty depending on your bore sizes of the M/C and wheel cylinders. Repeat for the front and rear circuits until you have fluid at all four corners.
Step 3) You should be able to get some sort of pedal - likely spongy, but it will pump up with a few pumps. Now you pressure bleed the system, starting at the M/C again. Which circuit doesn't matter. What is really important here is that your pedal lackie listens and follows your directions. The bleeder person is always in control of the routine at all times. The routine is;

1) "Pump up" ( pedal person shouldn't usually need more than 3 pumps on the pedal)
2) "Hold" (pedal guy says holding the pedal down, placing a moderate pressure on the pedal - at first it will hardly be anything, but will get better as the air is bled out)
3) Crack the bleeder ¼ turn (catching fluid in either a rag or into a hose and then into a bottle)
4) Pedal guy says "Floor" when the pedal hits the floor (DO NOT LIFT PEDAL UNDER ANY CIRCUMSTANCE!)
5) Close bleeder nipple and then say "Closed", signaling that the circuit is sealed
6) Pedal person can now release pedal to its natural up position
7) Bleeder says "Again" to start the cycle over. Repeat back to #1

I use a piece of 3/16 clear vinyl tubing, this way I can visibly see the air bubbles coming out. Bleed until there is absolutely no air bubbles visible.

I do not recycle the fluid that has been bled through the system, mostly because contamination is very easy. When bleeding the M/C, it usually doesn't take many cycles to get the fluid moving, and again rigging up a recycle system isn't worthwhile. New, fresh fluid is vital to good brakes. And your brakes are just something you don't cut corners on. If you need a few more ounces of fluid, just buy it is my advice.

Hopefully it works out for you, and hopeful this explanation helped if you didn’t already complete the steps above.

Keep us posted, good luck.

Byron

[bueiz]

Thanks for the responses guys. This gives me the confidence to go and try bleeding again with the MC that I have.

The new rear wheel cylinders get in today so I'll replace those before trying again.

Byron, thanks for the step-by-step. I really appreciate it. I did get fluid to all for corners in my previous attempts at bleeding the brakes, but I haven't tried the "Pump Up" method. I'll re-bleed all for corners and try the pump up method.

If that works, it would be amazing.

[bueiz]

Byron, using the "Pump-up Method", could it potentially take a while to get the system up to par?

When we started it would probably take 15-20 pumps to get any feedback from the brake pedal. After going thru and bleeding all four corners using the pump-up method it would take about 3-5 pumps to start getting feeback (firmness) from the pedal.

THEN, I realized I cross-threaded one of the rear wheel cylinders. But, I have another cylinder ready to install so I'm going to give it another go.

1) "Pump up" ( pedal person shouldn't usually need more than 3 pumps on the pedal)

Byron

[okayfine]

I think Byron's comment you quoted was just for bleeding purposes. That's just been the accepted technique prior to cracking the bleed valve. Creates pressure in the system to move air along to the bleeder.

Relative to your question about braking performance outside of bleeding, you should have a firm pedal with a single press. You likely still have air in the system, as evidenced by the improvement in pedal firmness after bleeding it again.

Cross-threaded wheel cylinder probably isn't an issue unless you also have fluid leaking from the threads.

[bueiz]

Yea, I was referring, particularly, to the bleeding process. I definitely know that brakes are working best when they're firm with a single press.

I did have fluid leaking from the wheel cylinder which is how I confirmed that I had cross-threaded it. I do have a good feel that the "pump-up" method was working so I'm hoping to have 100% success this week! I'm itching to get this thing on the road.

I think Byron's comment you quoted was just for bleeding purposes. That's just been the accepted technique prior to cracking the bleed valve. Creates pressure in the system to move air along to the bleeder.

Relative to your question about braking performance outside of bleeding, you should have a firm pedal with a single press. You likely still have air in the system, as evidenced by the improvement in pedal firmness after bleeding it again.

Cross-threaded wheel cylinder probably isn't an issue unless you also have fluid leaking from the threads.

[okayfine]

Gotcha. Bleeding can be a long process, especially if you have air in the fluid already (as opposed to a pocket of air at the high point in the system, which will bleed out fairly quickly).

That you've gained pedal in 3-5 strokes compared to 15-20 shows you're making progress.