rpms drop when i pump the brakes

[nissan_star]

Is this normal? someone else noticed this, i had never before. the car was in nuetral and I pumped the brakes and the rpms dropped to a little below 500

[HIGHFIV5]

Possible bad brake booster.Check your booster vacuum line for leaks and suchand make sure its on there good.

[nissan_star]

Found two large cracks in the booster vac line at the 90* bends to the left of the one-way valve.

It doesn't drop rpms anymore, but isn't it supposed to increase rpms when i pump the brakes?

[HIGHFIV5]

If your booster is good and free of leaksyour RPM's shouldnt move neither up or down.I had the same problem though at one point andtried replacing the vacuum hose first with no such luck soI replaced my booster and my RPM's were no longer affected.Did you replace that cracked hose?

[nissan_star]

Not yet, I have a high temp tape solution right now. I don't daily it so it should last until Autozone gets hoses in.

[zachattack_5491]

Don't mean to threadjack, but mine rise when I pump the brakes. Is that linked to the same problem? I already replaced the MC, so only thing left is the booster.

[nissan_star]

someone else told me that is was supposed to rise, I didn't think so. He ended up searching and realizing the none of the cars he drive do that and thinks its fine.

For the record, this could end up being a good thread for brake info, so post back anytime

[HIGHFIV5]

Don't mean to threadjack, but mine rise when I pump the brakes. Is that linked to the same problem? I already replaced the MC, so only thing left is the booster.

I think it might be. Cause im pretty sureyour RPM's shouldnt be affected by braking.Mine tended to do the same. Itd either rise like yoursand other times itd drop i dunno it was odd.Anyways try the same thing...check your vacuum hose for leaks.Plug your engine side of your booster hose and see if ithelps your problem. If so it could be a leak in your booster diaphragm

[Klits562]

same problem and all my friends have come to the same conclusionvac leak in the brakes or bad brake booster.I havent looked into it yet but im sure its the problem

[nissan_star]

If it was leaking for me and rpms dropped and they are raising for you guys, would that mean that you have a blockage or something?

Hopefully it isn't a bad brake booster, I heard those are a female dog to take out.

Bottom line though, do your brakes feel strong? Mine felt weak and spongy until I fixed my leak. Its a night and day difference.

[HIGHFIV5]

If it was leaking for me and rpms dropped and they are raising for you guys, would that mean that you have a blockage or something?

Hopefully it isn't a bad brake booster, I heard those are a female dog to take out.

Bottom line though, do your brakes feel strong? Mine felt weak and spongy until I fixed my leak. Its a night and day difference.

Brake booster is real simple to take out.1. Disconnect the master from it. 2 bolts i think... And CAREFULLY bend it slightly outta the way. You dontneed much room.2. Remove the 4 booster nuts slightly above the brake pedal.3. Use a set of pliers or something and remove the cotter pin from thelil brake pin thingy and then remove that from the pedal.4. To reassemble go backwards. Real easy, shouldnt take much longer than a half hour.

And yeh it definitely makes a difference.I wasnt even able to skid before.Had to hit the brake real hard to stop, no vacuum assist :P

[zachattack_5491]

If it was leaking for me and rpms dropped and they are raising for you guys, would that mean that you have a blockage or something?

Hopefully it isn't a bad brake booster, I heard those are a female dog to take out.

Bottom line though, do your brakes feel strong? Mine felt weak and spongy until I fixed my leak. Its a night and day difference.

No mine feel fairly strong. But I have Q45 brakes, I dunno if that makes a difference. Replacing the booster isn't my main concern, the price is the killer for me. I can't afford $100 at the moment.

[Ilvemynissan]

You have a KA right? Well i know this about SR's.

Your RPM's should actuall drop a little bit, say 50-200 RPM. Your brakes are run by vacuum from the motor. There is a hose that is connected to your intake and thats where it gets it's vacuum. So if you tap your brakes while your in neutral then it's going to use some air that would otherwise go into the motor. If the rpms drop your running on the lean side, if the rpms go up your running rich.

[nissan_star]

You have a KA right? Well i know this about SR's.

Your RPM's should actuall drop a little bit, say 50-200 RPM. Your brakes are run by vacuum from the motor. There is a hose that is connected to your intake and thats where it gets it's vacuum. So if you tap your brakes while your in neutral then it's going to use some air that would otherwise go into the motor. If the rpms drop your running on the lean side, if the rpms go up your running rich.

Yes i have a KA.

But shouldn't it be the same for both motors? Boost or no boost don't the brake boosters do the same job? RPMs drop because your running lean and increase if you are running rich, so if you are running perfect they wont change at all, right? I am just trying to understand what you posted

[OutToWinPAHC]

No need for 2 thread for the same thing. I went into detail trying to help in the other thread you made.

One problems one thread, locked.