Pump Brake - Revs go up

[CMF_evade]

Just wondering how many people this happens to.

Basically you sit there pumping the brake pedal and the revs will climb about 500rpm..then drop again.

I want to know if its just a micra thing..or maybe an actual problem?

 

[CMF_Yom]

My super s does it.

Every super s I test drove did it.

:S

 

[CMF_Yom]

And the brake pedal is really soft, has to be pressed pretty hard to do anything significant and can be a real pain the ass with the ABS activating too early (or when you don't expect it to)???

Basically just overall crappy feeling brakes?

 

[CMF_Yom]

Haha curse this, just went out and tried it and repeated pumping, the brake pedal gets stiffer (normal, afaik) and my revs drop HEAPS (like from idle at just above 650rpm to 500rpm).

 

[cisco]

My car definately does it.

I also have removed ABS, and it still does it. I'll go and have a test right now because I kinda forgot.

I think the white Super S does it too, but nowhere near as bad as the blue one seemed to. Will go and do two quick tests to confirm right now..

When my intercooler piping was all removed, I noticed when pumping the brakes that air was pushing out quite swiftly into the plenum, I could feel a fair bit of air whooshing out. Should be the booster's one way valve allowing air to escape out of the booster (to create a vacumm in it).

Going to test both cars right now..

 

[CMF_evade]

My brake pedal feels fine, as you pump it though you feel the pressure building up and you can hear sorta like an air pumping sound..

but my actual brake performance is great..i like the pedal feel and everything..abs never kicks in too early for me...so thats a bit weird for you.

 

[CMF_Yom]

I think our Super S boosters just plain suck.

THey might be larger than the LX/SLX boosters but heck, what use is the larger size if they feel crappy.

AlexB replaced his booster with an SLX item and his brakes feel awesome - so much better than mine and you have much greater control over the ABS as well. I think i'll have to do it one day because I really hate my brakes. They make the car feel so old...

 

[cisco]

Ok results..

Blue Monster (Aftermarket simple throttle body, no AAC valve or bypass valve, just a simple mechanical throttle body): Idling at 800rpm, with fast pumping of the brake pedal, revs climed to 1400rpm and you could keep them there.

White Super S (Full factory setup, apart from extractors): Idling at around 1000 (was still half cold), with fast pumping of the brake pedal, revs dropped to about 600rpm and you could keep them there.

My thoughts: The pumping is pushing air into the plenum / intake manifold. The monster has nothing so the extra air just makes the car rev more, like a mini turbo giving it more air.

The factory super s knows that this would happen, and perhaps its bypass valve or something tries to compensate by dropping the revs, but perhaps its overcompensating and hence they drop to around 600rpm..

Hmm!!

Blue Monster has the larger ABS booster, but now with no ABS. And seriously, the brake pedal is truly more powerful. Pumping through the ABS introduces a loss. But weird re:your ABS Yom, my old ABS and also shortcake like evade's never does that, always kicks in only pretty well when you need it.

 

[CMF_evade]

hrmm...

interesting to see that it drops hey, matty was just telling me thats what his does as well..

i wish i had a consult tool so I could test all the little bits and pieces as per the workshop manual.

 

[CMF_evade]

also when mine was dropping back to idle..usually it would go past the idle (pretty low..sometimes nearly stall) and then rise up again...ive put the idle up a tad to get around this though.

mine idles around 800-900 as well. with all lights and stuff on it might be about 750.

when i start cold its something stupid like 1500-2000rpm.

 

[CMF_1300supers]

same happens to me, its the hidraulic fromthe brakes getting extra power from the engine... its a normal thing... at least my mechanic says so!!!

 

[CMF_Yom]

That is random.

I just went out and tried it (after it had been warmed up to around 75deg C according to the consult) and the revs stayed put. Nothing changed. Idle is currently set to factory 650rpm.

Usually the revs drop down.

No sensors/valve changes were picked up by my consult computer either.

 

[cisco]

Yom,

Just checking the ABS trouble shooting section in the nissan workshop manual and it says to check:
- gunk and crap around each of the 4 sensors (I'm sure you thought of that)
- Check wheel bearing play
- Check sensor clearance, should be between 0.2 and 1.0mm
- Check the resistance of each sensor wire, all should be between 1.2-1.8kohms - if not, replace sensor.
- Of course check pads and check booster for air tight seal, can check this by: Start engine, and stop it after 1-2 mins. Depress brake pedal several times slowly. If pedal goes further down the first time and gradually rises after second or third time, booster is FINE. AND by: Depress brake pedal while engine is running, and stop engine with pedal depressed. If there is no change in pedal stroke after holding down 30 seconds, booster is airtight.
- Check continuity between control unit connector terminal and ground.
- Check continuity between actuator connector (vehicle side) and body ground
- Check ABS motor continuity to body ground.

Far out, then it goes on with HEAPS more stuff. Check resistance of actuator relay circuit. Check harness, check control unit. bah bah bah. Can't be anything too tricky. Surely there's just some gunk in your sensor wheels or something, who knows?? Or perhaps a wheel bearing. Perhaps the actuator is playing up? Hey, is your ABS the different brand one to ours?? I think our 1995 models is Lucas.

 

[cisco]

Yeah I was thinking, such a small amount of air, would effect a tiny engine like ours so much more than it would a large engine.

MUST be normal. And the computer and valves and stuff just try to correct it as best they can..

 

[CMF_jaxx]

my rev's drop slightley when i put the hazord warning lights on. with all my lights and gadgets on you can feel it more. but nothing different with the brake being pressed. hmm, interesting thread.

be interesting to see someones results if they have a dual battery charge system setup in their micra. also (food for thought) an uprated alternater.

these are standard modifications if you have a huge ICE install, or just have loads of electrics. if i could find room i would have a dual battery setup installed to.

 

[CMF_Yom]

Okay went for a quick spin to "get some milk."

Tried those diagnosis things there with the brake pedal - seems to be fine. ABS was nice and predictable tonight. brake pedal felt like it had no soul but I wasnt expecting a miracle. Brake pedal is not as progressive as I'd like it to be.

Very weird. Never had an ABS light turn on either. It operates FLAWLESSLY - just at the wrong time!

Mabye I'm still not used to ABS.

 

[cisco]

My pedal moves in a bit too far before they feel like they are really engaging rock solid. I would like it to feel like its engaging right near the beginning of the stroke.

Its better since I adjusted the pedal distance, but still a bit of movement there before engagement.

 

[CMF_Toma]

Are there ABS sensors in the rear brakes? Ive never had the ABS kick in while hand-braking around corners. Only when slidding to stops in the wet. Not that i use the hand-brake around corners (too much ) but just curious.

Yeh, my brake booster usually steals a few revs from the engine. Totally normal im told. As for pumping the brakes, maybe its building up enough pressure in the lines to not need the booster and it starts over compensating? Just an idea.

 

[cisco]

Yeah there are speed sensors on all 4 wheels.

The handbrake overrides the ABS so you can deliberately do handbrake turns etc. yay!

 

[CMF_micrat]

If you apply the brakes (pedal) while using the handbrake (wheels locked) you will find the abs kicks in instantly. If the rear wheels stay locked by the handbrake the abs prevents the brakes from functioning normally and you can't slow the car with the brakes (pedal) which can be quite dangerous if you need to wash off speed immediately. I rarely use the handbrake to aid turning (because p zero's are just too expensive), however I am thinking of playing with the abs electics so that the abs is overridden when the handbrake is on. It can be done very simply with an appropriate relay wired in quite easily.

 

[CMF_Tony]

Sorry guys i no its of the topic,Buy micrat any chance of some photos of your micra,it sounds pretty good in your member profile.