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Brake bleed/brake pedal pressure question with engine On or Off

MvM

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This weekend I removed my front brake calipers for painting.
I had wrapped my brake fluid reservoir and both the front brake lines with plastic to minimize brake fluid loss, but the lines still leaked a bit.

Today, I put the calipers back on the car and connected the brake lines according to spec. Because I had leaked some brake fluid, I dediced to do a full brake bleed again.

I filled up the reservoir with fresh fluid. Then, with my fathers help, I did a brake bleed, using the Rear Right, Left Front, Left Rear, Right Front procecure. Rears were done about 25 times, fronts about 15. in total
My new fluid is a different color, so it was easy to see when I was bleeding new fluid. There were some air bubbles in the beginning, but I did not see any at the end.
When I was finished, I redid every corner with another 5 bleeds to make sure everything was fine.

When this was done I had firm brake pressure, no issues.

Then I started up the engine and immediately, my pedal pressure is gone with my brakes only activating at the near end of the pedal stroke.

Checked the fluid level and it is OK. It drops a little when I push the pedal, but not much.
Checked for leaks on all corners but no leaks to be found.

Switch engine off and the brake pedal is hard again.
Turn the engine on and it is soft again.

When for a short test-drive in the pouring rain, found an empty spot and did three emergency stops from about 25 mph. ABS kicks in fine, car steers true and straight and no difference in brake pressure at all. But still the pedal engages very late, much later than before.

Did I miss anything?
Why is my brake pedal fine with the engine off but not when it's on.
What can I do next to solve this issue?
 
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bleed more... looks like you still have air in the system sometime.

one thing I would check, is how tight you tight the brakeline bolt to the calipers? make sure there's no trace of fluid lost there... (I found out aftermarket brake line bolt is not as stiff as the factory one, yet they must be tight from letting air in.

and also, when you have your calipers off your lines, here's a good tip someone gave me... grab some of those rubber valve stems, and then push hard into the brake lines, and then turn that line facing up, this will eliminate the air getting into system.
 
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Since you had a helper, what was your method? How far was the brake pedal depressed during your bleed process?

Regards,
LarryB
 
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Now this sounds kind of crazy, but did you get the calipers put back in the same position as before? Is the bleeder at the top of the caliper?

Did you use new crush washers under the banjo bolt at the hose attachment to the calipers? Did you torque the banjo bolt to the value in the manual, 25 ft/lbs, page 19-26.

You can over torque the bolt and possibly have a bolt failure with a rapid heavy brake application. Sure don't want that to happen!

Brad
 

MvM

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Since you had a helper, what was your method? How far was the brake pedal depressed during your bleed process?

Regards,
LarryB

My helper would press down the brake pedal all the way at my command 'Down'.
Then he would hold the pedal down until I had closed the bleed nipple and only release the pedal on my command 'Up'.

OLDMNSX said:
Now this sounds kind of crazy, but did you get the calipers put back in the same position as before? Is the bleeder at the top of the caliper?

Did you use new crush washers under the banjo bolt at the hose attachment to the calipers? Did you torque the banjo bolt to the value in the manual, 25 ft/lbs, page 19-26.

You can over torque the bolt and possibly have a bolt failure with a rapid heavy brake application. Sure don't want that to happen!

Brad

Yes, the calipers are in the same position as before. I used new crush washers and I torqued the banjo bolts at the corrects spec.
Even used new banjo bolts too.

Checked the pedal pressure this morning before going off to work.
With the engine off, pedal is hard, but as soon as I start the engine, the pedal feels very mushy again. Turn it off, and it feels ok again after 1-2 pedal pumps.

Also checked for leaks by moving the car to a different spot. No leaks as far as I can tell.
 

MvM

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You have a small amount of air left somewhere in the system. The power assist on the brakes makes a great difference in the pedal effort.

That is what I am thinking now (even though I washed through almost a full liter of fluid through the system).

Am thinking of getting a set of speedbleeders so I can do this all by myself.
Can anyone tell me if you can savely keep the speedbleeders installed on the car afterwards or is it better to put the original bleed-nipples back on again after you are finished?
 

goldNSX

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I just wanted to suggest using the Speed bleeders. If you get them there's one for the clutch hydraulic also. Yes, they stay in place. Otherwise there surely gets air in the system. One could raise the question when the bleeder was closed, before or after releasing the brake pedal.

I'm not sure about your problem. If the engine is running the brake booster is storing pressure. So you have enough assistance for one of two brake pedal strokes until the brake pedal gets hard AFTER the engine is shot off.

I don't see any problem with your car, this is normal. You can flush again and the best thing to do is a comparison to another NSX.
 

MvM

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Speed bleeders stay in. They are same as the regular bleeders accept for the check valve.

goldNSX said:
I just wanted to suggest using the Speed bleeders. If you get them there's one for the clutch hydraulic also. Yes, they stay in place. Otherwise there surely gets air in the system. One could raise the question when the bleeder was closed, before or after releasing the brake pedal.

I'm not sure about your problem. If the engine is running the brake booster is storing pressure. So you have enough assistance for one of two brake pedal strokes until the brake pedal gets hard AFTER the engine is shot off.

I don't see any problem with your car, this is normal. You can flush again and the best thing to do is a comparison to another NSX.

Brian & Thomas,

Thanks for the information. I think I will order a Speedbleeder set so I won't have to call upon someone else for assistance every time.

I don't think I have a real problem either. I just thought that after pumping out so much fluid I would have gotten all the air out of the system by now.
I know I am not leaking any fluid anywhere because the pressure stays the same even after four hard stops, so that part of the system is OK.

Will redo the bleeding somewhere next week and post my results here :smile:
 

MJK

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I've rebuilt my calipers a couple times now. In my experience:

1. Speedbleeders rock
2. Ignition off
3. Takes me more than a liter. 2 liters last time, IIRC.
4. Takes forever unless you tap the caliper sharply (box wrench, hammer) between bleedings to get all the air to the top where it will go out the bleeder valve
5. Even teeeeeeeny little bubbles make a difference in feel
 
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My helper would press down the brake pedal all the way at my command 'Down'. Then he would hold the pedal down until I had closed the bleed nipple and only release the pedal on my command 'Up'.

Unfortunately, this is not very good. I suspect you will need to purchase a Brake Master Cylinder. You should NEVER depress the brake pedal further then it would travel if the system is fully bled and working properly.

I would bleed it again. If after the second bleed it is still soft, you will need to replace the master. This is why I do not use this method any more. I use a power bleeder.

The thing you want to do, is when the system is fully functional, depress the brake pedal and when it stops, place an object under the pedal so you know where you must stop when bleeding.

I have ruined a few master cylinders over the last 30 years, before I understood my method was the cause.

HTH,
LarryB
 

MvM

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MJK - thanks for the input :smile

Unfortunately, this is not very good. I suspect you will need to purchase a Brake Master Cylinder. You should NEVER depress the brake pedal further then it would travel if the system is fully bled and working properly.

I would bleed it again. If after the second bleed it is still soft, you will need to replace the master. This is why I do not use this method any more. I use a power bleeder.

The thing you want to do, is when the system is fully functional, depress the brake pedal and when it stops, place an object under the pedal so you know where you must stop when bleeding.

I have ruined a few master cylinders over the last 30 years, before I understood my method was the cause.

Larry,

Thanks very much for the input.
If I understand you correctly, pressing the pedal down to the floor damages the master cilinder? This would then also apply for someone who is using speedbleeders as well?

I'll take note of that. I am going to buy a set of those speedbleeders but for now, a helper with better instruction will have to do.
Will post how it will all end.
 
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Yes, you understand my comment correctly.

Speedbleeders eliminate the need for a "helper", however the pedal issue is the same.

Regards,
LarryB
 
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goldNSX

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If I understand you correctly, pressing the pedal down to the floor damages the master cilinder? This would then also apply for someone who is using speedbleeders as well?

An older brake master cylinder won't like it. Having this in mind I only pressed the pedal about 1/2 to 2/3 while bleeding. You can also follow Larry's method.

Another hint: The last pedal pump (means when the bleeding bolt is closed) is the trickiest one. Before the speedbleeders I always told my assistant to press the pedal slowly enough for me to close the bleeding bolt WHILE he still was moving the pedal down AND BEFORE he reached the floor. If there is only the slight movement upwards you surely get air in the system with the OEM bleeders.
 
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An older brake master cylinder won't like it. Having this in mind I only pressed the pedal about 1/2 to 2/3 while bleeding. You can also follow Larry's method.

It's funny... Larry was saying this exact same thing late Friday night at Est Fest, about how pushing the pedal too far will cause the seals to possibly encounter very rough master cylinder surfaces and then ruin the seals.

Another hint: The last pedal pump (means when the bleeding bolt is closed) is the trickiest one. Before the speedbleeders I always told my assistant to press the pedal slowly enough for me to close the bleeding bolt WHILE he still was moving the pedal down AND BEFORE he reached the floor. If there is only the slight movement upwards you surely get air in the system with the OEM bleeders.

I dunno... if you have a long hose attached to the bleed screw that is full of fluid with no air bubbles, and the hose itself ends in a pail of fluid, you won't suck any air back up, just a little fluid.
 

goldNSX

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I dunno... if you have a long hose attached to the bleed screw that is full of fluid with no air bubbles, and the hose itself ends in a pail of fluid, you won't suck any air back up, just a little fluid.

This is not correct. The air will most likely find its way along the threads of the bleeding bolt. That's why the Speedbleeders are sealed. :wink: In addition: Most of the small air bubbles you see in the hose attachted are from the threads.

@MvM: If you order the speedbleeders, get some thread sealant too ($10). :wink:
 

MvM

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UPDATE !!

Today I again put up the car on stands, took all the wheels off and redid the brake bleed.
This time, I instructed my helper to press slowly and not too deep.

I also used the method of tapping the calipers prior to bleeding to give bubbles a chance to rise to the surface.

Took me about an hour and a half to do everything, but the brakes are fine again. Just went for a drive and the pedal is hard both with the engine off or running. No leaks anywhere as far as I can tell at this moment.

So, to all you guys, thanks again for all the good advice :smile:
 

MJK

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Good news! Glad to hear it worked out.
 

MvM

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Glad it worked out..
MvM, have you installed your new ABS?

Hi Spooler,

No, I have not yet upgraded my ABS although I keep thinking about it.

I had some problem with my ABS system which would let my left rear wheel lock-up under heavy braking which made the car very unstable. Because of that I though my ABS was really having big-time problems.

I did an ABS brake flush using the www.danoland.com -method about three weeks ago and spent a lot of time alternating between the left-rear solenoid switch and the ABS-pump before it would finally open up and pump the old fluid out. Ever since, the ABS is working fine again, car tracking straight and braking hard (also replaced my front RB rotors - worn out in just 8500 miles)

From Chris at SOS I more or less understood that as long as your old ABS is in good working order, the upgrade should not be neccessary. However, when I have some funds available, I might still do it. For now I would rather do a engine upgrade of some sort first.
But the idea remains tempting - loose some weight AND improve the car can never be a bad idea of course.
 
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Then, with my fathers help, I did a brake bleed, using the Rear Right, Left Front, Left Rear, Right Front procedure.

Now, that's curious. This statement sent me to the NSX shop manual to confirm what MvM wrote.

I always thought the sequence is:
- furthest from the master cylinder
- next furthest from the master
- next
- closest to the master.

Which I would have thought was:
RR
LR
RF
LF

Anyone know why it's not per what I thought was conventional wisdom?

Also, glad I read this thread. I hadn't heard about Larry's concern, although whenever I bleed I don't force the pedal down, just enough to pressurize it using three slow, steady pumps then a hold.

All KINDS of things to learn here on Prime! :smile:
 

goldNSX

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I don't think the sequence matters much as long as you're only refreshing a filled system. Bubbles most likely are at the calipers whenever. The sequence is important if the system was empty for some reason (master).
 
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