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This may end up being a long post because I want to highlight all of the things I've tried to get the brake pedal to not depress all the way to the floor.

 

1. I believe the brake booster is a 280zx booster. I had to widen the holes in the fire wall to get it to fit. I purchased the booster from O'Reilys.

2. I did the maxima caliper swap on the rear.

3. All brake lines to calipers are steel braided.

4. I removed the stock proportioning valve insides and converted it to a pass through splitter.

5. I first tried a 7/8" master cylinder and bleed the brake using several methods includ8.ing a pressure bleeder, traditional bleeding, and even an electric pump.

6. I thought that maybe the booster push rod wasn't quite long enough so I put a spacer in the end of the master cylinder. The brakes then worked well enough to stop the car, but only at the last 0.5" of travel.

7. I then removed the spacer and adjusted the push rod to almost touch the master cylinder plunger. The brake pedal still went to the floor with no stopping power.

8. I then removed the booster and checked that the reaction disc was still on the push rod. It was. I epoxied it to the push rod just in case. I reassembled the booster. I set the push rod clearance to 0.3mm.

9. I bench bled a 1" Wilwood master cylinder until there were no bubbles. I removed the check valve from the rear brake outlet.

9. I installed the 1" Wilwood master cylinder.

10. I installed a Willwood proportioning valve/switch in place of the stock brake switch/valve.

11. I bleed the brakes using the pressure/pump bleeder. It's basically a round-up sprayer with a cap you place on each reservoir and pump it up to 15 psi or so. I started at the furthest away wheel, then the rear left, the front right, the front left, and finally the MC itself. No bubbles come out of the calipers unless I loosen the bleeder a lot, at which point I think it's sucking in air from around the bleeder screw so several small bubbles show up at that point. After bleeding the pedal still depressed to the floor.

12. I then got a helper to pump the brakes and I bled each caliper the traditional way. The pedal STILL went to the floor.

 

I'm out of ideas and at a loss. Especially after dripping brake fluid on the fresh paint and melting it.

 

Does anyone have any ideas that might help out? Could the calipers themselves be screwed up? Is there a second bleeder on the calipers that I need to bleed?

 

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I have used both the Maxima and 240SX rear calipers on my Z cars. The problem is that the bleeders do not point straight up such that air remains trapped in the cylinder. Wasted lots of time and fluid.

 

Remove caliper with flex line  connected method:

 

You can remove the caliper while leaving the flex line connected.  Block the piston so it can not move otherwise when you pump the brakes you will just blow the piston out of the  cylinder and you will be very very sad.

 

Hold the caliper so the bleeder points up and shake the caliper while your accomplice pumps the brakes. Repeat. Repeat etc.

 

Speed bleeders (type with spring and plug inside or check ball inside) make this job easier.

 

Bench bleed caliper method:

You can try what I came up with this week: bench bleed the calipers before installing them. While prepping the new calipers I noticed my MC bench bleeding kit on the bench. The fittings used for the MC will also fit the caliper. I used the fittings/hoses  from my MC bench bleeding kit (O'reilley's)  plus a huge syringe I found at a grocery store. Connect the syringe with hose to the speed bleeder. Screw in  a plastic push-on hose fitting (from a bench bleeding kit) into the inlet of the caliper with a hose to a bottle to catch the fluid. Push fluid into the caliper with the syringe being careful not to push any bubbles in the hose into the caliper. Once the caliper is full, and no bubbles are seen, close the speed bleeder and plug the inlet with a M10 x 1.0 bolt. I was amazed at how much air flowed out of the caliper. It took about three full syringes of fluid to get all of the fine bubbles out. After installing the calipers (see procedure below), and doing one side at a time, it only took three pumps to get a firm  pedal for each caliper.

 

Steps:

  • Bench bleed calipers being sure to tighten the speed bleeder and install a M10x1.0 bolt in the  caliper inlet when done  to keep the caliper sealed.
  • Fill MC reservoir with fluid.
  • Push brake pedal with your hand and block it in place with a stick between the seat  and the pedal. This blocks the fluid return port in the MC so fluid will not flow out of the MC.
  • Remove old caliper leaving the flex line attached and hang it from the spring with some wire. This keeps the brake line sealed and prevents any fluid loss while installing the new caliper.
  • Install new caliper and pads.
  • Move the flex line from the old caliper to the new caliper. Since you blocked the return port in the MC there should be almost no fluid drips from the open flex line.
  • Attach hose and catch bottle to the speed bleeder. Open the speed bleeder and pump. The first pump will go to the floor because the piston will move out taking up the slack between the piston and the brake pad/rotor. The second and third pump will firm up the pedal.

I just did this this week. It was the quickest brake bleed I have done with Maxima/240SX calipers. No wasted fluid too.

 

MC bleeder kits are available from O'reilley's. They contain a variety of plastic MC outlet fittings, but for some reason only one M10 x 1.0 fitting so I buy two.

 

With your brake set up your brake pedal should feel about stock.

 

I will post some pictures later today.

Caliper Bleed Syringe Hoses.jpg

Caliper Bleed Connections.jpg

ear-280022erl_ml.jpg

Edited by Miles
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This may be your problem:

 

You wrote:

 

7. I then removed the spacer and adjusted the push rod to almost touch the master cylinder plunger. The brake pedal still went to the floor with no stopping power.

 

So you adjusted the plunger with the spacer removed?  And then you put the spacer back on? That would move the MC away from the push rod by about .75 inch which would increase the gap between the push rod and the MC piston such that the piston would move a small amount if at all.

 

If I recall correctly, for my 280ZX and Wilwood MC  I adjusted the tip of the plunger about 14mm/15mm as measured from the face of the spacer. You can also fine tune the push rod once the car is on the road for testing. Just be aware that if you adjust the pushrod out too far you will lock your brakes up because the MC piston gets pushed past the return port in the piston preventing fluid from returning back into the MC from the calipers - kind of like a line lock. Opening the MC bleeders will relieve the pressure.

 

Picture is for using a 280ZX  MC, but the math is fairly close for a Wilwood 1 inch MC

 

Push Rod Adjustment.jpg

Edited by Miles
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9 hours ago, jkelly said:

6. I thought that maybe the booster push rod wasn't quite long enough so I put a spacer in the end of the master cylinder. The brakes then worked well enough to stop the car, but only at the last 0.5" of travel.

 

To Miles's point - #6 is the only step you showed that suggests pushing the pedal actually moves any fluid.  Your pressure bleeder doesn't do that, it can move fluid with out any of the mechanical parts even connected.

 

Focus on the pedal linkage, brake booster, and master cylinder hard parts before worrying about the hydraulics.

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33 minutes ago, NewZed said:

 

To Miles's point - #6 is the only step you showed that suggests pushing the pedal actually moves any fluid.  Your pressure bleeder doesn't do that, it can move fluid with out any of the mechanical parts even connected.

 

Focus on the pedal linkage, brake booster, and master cylinder hard parts before worrying about the hydraulics.

 

Agree with Newzed.

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1 hour ago, Miles said:

This may be your problem:

 

You wrote:

 

7. I then removed the spacer and adjusted the push rod to almost touch the master cylinder plunger.

 

I was actually referring to a cylindrical spacer I made to lengthen the push rod. I removed that and didn't put it back. Your advice reminds me, though, that I didn't take my measurements with the flange/spacer installed between the booster and the MC, so everything is off by about 0.5" (thickness of the flange).

 

Here are the measurements and adjustment I made to the push-rod last night., but again I forgot to take into account the aluminum 4-hole flange/spacer between the booster and MC. This would add approximately +0.5" to the push-rod adjustment.

 

 

image.png.cbdad854a62d276c692b1a17bd0a6278.png

 

I took a measurement of the 4-hole flange/spacer and it should change my adjustment by:

image.png.f48db95d728a5b22b15c325a80128cb0.png

 

Can you confirm my approach? I'm not sure how you went from 0.39" measurement to a 0.53" adjustment.

 

Also, thank you for the caliper bleeding tips. My bleed screws are not at the top of the caliper at all, so I will try the bench bleed technique you recommended after correctly adjusting the push-rod.

 

EDIT: @Miles Disregard my comment on how you got from 0.39" to 0.53". I didn't catch that it was illustrating the adjustment to a 240z stock push-rod position to accommodate a 280zx MC. Thanks.

Edited by jkelly
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8 minutes ago, jkelly said:

I unbolted each caliper and bleed them with the bleeder facing up at the highest point. Some air came out and the brakes are a lot better now and the car can actually stop. They're still quite squishy so I'm missing something.

 

There is still air in the system. Could be the MC. Have to get all of the small bubbles out and be sure you are pushing the piston full stroke. Take your time so the bubbles can form up between bleeds. Speed bleeders installed on the MC  help insure that bubbles don't get suck back  into the MC. Plug the outlet ports when transferring the MC to the car to prevent fluid leaking out and air getting in.  Could be some air in the caliper still. 

 

You are very organized and methodical.  Just keep at it in a logical step by step way.

 

Don't mean to scare you, but I have stopped using the Wilwood 1 in. MC.  I got three bad ones right out of the box. Two leaked internally and the other one had the bleeder screws smashed.

 

That is bad quality control. I am now using a 79 280zx 15/16 MC that I bought from Dave at  Arizona Z Cars.

 

Now back to your push rod. If I recall correctly, the push rods came in two lengths.  As I mentioned before, measuring from the tip of the push rod to the face of the spacer should be around 14mm to 15mm  as a starting place. Too short = long pedal.  Too long = brake lock up after 2 or 3 applications due to blocked return port. You mentioned that you added a spacer to the push rod to get the length you need.  Not sure what you did, but adding  a spacer to the push rod may not be a good idea.

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You could just use some plumbers compound on the bleeder threads but Speed Bleeders take care of that and allow you to work by yourself. Sometimes a light rap on the caliper with a small hammer just before cracking the bleeder open will dislodge the little bubbles and allow them to be bled away.

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On 7/26/2020 at 2:31 PM, grannyknot said:

You could just use some plumbers compound on the bleeder threads but Speed Bleeders take care of that and allow you to work by yourself. Sometimes a light rap on the caliper with a small hammer just before cracking the bleeder open will dislodge the little bubbles and allow them to be bled away.

 

What does plumbers compound on the bleeder threads do? Yeah, I've been using the tapping method with the back end of a screw driver. I'm hoping to get back at it this weekend and get this rest of the air out, although, the pedal did seem a little stiffer yesterday than the day before.

 

On 7/25/2020 at 3:11 PM, Miles said:

Don't mean to scare you, but I have stopped using the Wilwood 1 in. MC.  I got three bad ones right out of the box. Two leaked internally and the other one had the bleeder screws smashed.

 

That is bad quality control. I am now using a 79 280zx 15/16 MC that I bought from Dave at  Arizona Z Cars.

 

Now back to your push rod. If I recall correctly, the push rods came in two lengths.  As I mentioned before, measuring from the tip of the push rod to the face of the spacer should be around 14mm to 15mm  as a starting place. Too short = long pedal.  Too long = brake lock up after 2 or 3 applications due to blocked return port. You mentioned that you added a spacer to the push rod to get the length you need.  Not sure what you did, but adding  a spacer to the push rod may not be a good idea.

 

Interesting regarding the Wilwood quality. That's disappointing to hear. It seems like half the tools and parts I come across are poor quality. For example, I had an OTC double flare die split in half when making my final double flare just the other day. I'm going to give the Mastercool hydraulic tool a shot.

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