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Brakes Hard When Car Off, Soft When On

FLUID
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FLUID Enthusiast

FLUID

Posted
Posted

I've upgraded the brakes on my R34 Gt(NA) to R33 GTST 4 pots. I have bled the full system with new fluid. When the car is off you can pump the brake and the pedal gets hard, when you turn the car on the pedal goes soft and there is minimal pressure.

Could there be air in the abs?

Sinista32 Grand Master

Sinista32

Posted
Posted (edited)

When the car is off the pedal should be hard.

When the car is on the brakes will be soft/softer due to power assist (Brake booster)

one way valve from the plenum? to the booster.

There may still be an issue but hard when off /softer when on is the way it should be.

Edited by Sinista32
Daleo Grand Master

Daleo

Posted
Posted

Is the pedal sinking to the floor?

Have you actually road tested; the amount of pressure that you are applying may well be in excess of what it takes to lock the brakes in normal running.

As Sinista32 says; booster makes the pedal softer when engine is running, perfectly normal.

SMOKEYV35 Mentor

SMOKEYV35

Posted
Posted

Yep - but with the car on, and stationary, repeated pumps of the pedal should stiffen it up. Do that, then hold the pedal firm - if it starts to sink towards to floor......you've got air in the system.

This happened to me with my stagea when I bled the system completely dry painting my calipers. The ABS needs to be 'pressure bled' because the ABS manifold sits up so high and there is no bleed nipple on it.

At least that's the diagnosis I got from Holfords.

I hate bleeding brakes. Bought a Motive Power Bleeder and never looked back.

MBS206 Grand Master

MBS206

Posted
Posted

I've never yet managed to get a car to get firm brake pedal by repeatedly pumping the pedal while the engine is running.

Reason... The motor keeps sucking the master cylinder into vacuum.

If you're braking and then do a big down shift so you go from low RPM to high RPM you'll actually feel the pedal sink a little as the engine sucks into a deeper vacuum.

Sinista32 Grand Master

Sinista32

Posted
Posted (edited)

All true.

The pressure bleed worked fine on the Stag? (Edit: to bleed the ABS?)

WIth the R32 GTR you need to use correct Nissan consult with engine running as there is solenoids that open/shut to push the old oil/air out and the new oil in.

But the other way to activate this is stop really suddenly and hard (so that the ABS works) then complete the bleed.

Plus it has nipples on the ABS unit

Edited by Sinista32
SMOKEYV35 Mentor

SMOKEYV35

Posted
Posted

I suspect this ABS tomfoolery will be your issue, OP.

Might be a job for the professionals.

I didn't use the power bleeder on the stagea (it actually sold a week later) but I used it on my V35 (which you'd think would have a more advanced ABS but maybe not) and it worked a treat.

Firm pedal after only once around the car.

FLUID Enthusiast

FLUID

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  • Author
Posted

Okay yes, while the car is on and stationery I pump the brake a few times, then hold, and it becomes stiff, then sinks almost to the floor.

I haven't road tested as yet, but I am almost positive it doesn't feel right.

Will try to take it to a shop tomorrow or I will purchase a motive power bleeder.

Thanks for the help guys.

Sinista32 Grand Master

Sinista32

Posted
Posted (edited)

A shop with the right nissan consult is best. But not always possible.

No - don't bleed with engine on. Some shops do as the bleed process takes time and you need healthy power/battery so they prefer to have car running. Nissan say NO.

and my earlier post I should have said ignition to on and not engine running (sorry).

As per earlier comment. also

You could try (in a safe place).

1. Put the 2 wheels on the passenger side in the dirt and stopping relatively hard to engage the ABS at 80 to 100kms - You should feel a shudder through the brake peddle (hold/release of the pads) - Checks ABS working.

and this will move the Air and/or old brake fluid through the ABS unit. Do this a few times.

or

2. All 4 on the bitchaman and just HARD braking to achieve the same effect. (You'll feel a shudder through the brake pedal or you should !)

Then finish your bleed (or power bleed) of all 4 as per

Edited by Sinista32
Daleo Grand Master

Daleo

Posted
Posted

Not being a smartarse, & I'm sure you've got it sussed, but the rookie error I've seen a few people make is having the calipers on the wrong side, with bleed nipples facing down.

All good in your case?

SMOKEYV35 Mentor

SMOKEYV35

Posted
Posted

Tried your method Sinister, but not luck. Brakes are functional but not where near ideal.

I'm going to try and source the Motive power bleeder and try that, I will do some research but any ideas of a stockist in Sydney of the Motive products?

In just grabbed mine off eBay. The Ford specific one suits nissans, but I just got the universal one - it's a bit more fiddly but it means you can use it for any car. Loan it etc.

Under $100 - don't bother with those 'one man bleeder' check valves from Repco etc - they're shit.

Sinista32 Grand Master

Sinista32

Posted
Posted

Depending on how often you intend on DIY brake bleeding it may be worth paying a good shop to do this for you.

They'll have a power bleeder and the experience to identify and resolve the issue/s.

and even your own time is worth something. (Let alone the frustrations - I know :( )

SMOKEYV35 Mentor

SMOKEYV35

Posted
Posted

Yeah - I agree - if it were a daily driver I would just get the job done by the pros.

I had my car off the road for 6 weeks and it's a weekend car only so for me the power bleeder made sense, plus I'm

a bit OCD about other people working on my cars - especially when I had just spent two weeks repainting and rebuilding the calipers and didn't want anyone reckless spilling corrosive brake fluid on the finish but me!

But. You don't want to take chances when it comes to your braking system.

FLUID Enthusiast

FLUID

Posted
  • Author
Posted

I too am a bit OCD about others working on my car (I also recently painted the calipers). A friend from Holden suggested (and says they do this at work) to bleed from the ABS lines?

Basically disconnect the ABS, pump as per usual, crack a line on the ABS and tighten back up. I'll try that and see if I incur any positive results.

If that method doesn't work, I'll take it to a shop (when I've actually acquired enough funds)

Thanks for the help guys

Sinista32 Grand Master

Sinista32

Posted
Posted

ABS is the highest point and can/does require bleeding.

Otherwise they would not have Nipples (said nipples again :P)

It's always best to use the proper equipment as the ABS is semi complex and has little places that need opening and closing to allow brake fluid to travel through (or air).

That said it's not always possible. If you've attempted engaging the ABS then it is likely any air has shifted...

Let us know how you go :yes:

After several attempts at multiple brake places I finally found a shop who did it right.

They bled the ABS unit

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