# Hard brake pedal after B13 brake upgrade



## B12Chris (Dec 14, 2011)

So yesterday I put my B13 vented rotors, calipers, and pads on my B12. Install went very smoothly. Bled the system, take it for a spin, and it really feels like I have no power brakes. The pedal is very hard (so there cant be air in the system), but I have very little braking power. Even if I stand on them, I can't even get the brakes to lock from 30mph. I inspected the calipers (from a junkyard) and the sliders moved freely, pistons moved, eta. I was thinking water boiling in the system, but they were hard right out of the drive.

Any suggestions?


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## jdg (Aug 27, 2009)

Water boiling in the brake fluid would cause a sloppy brake pedal, like there is air in the system, 'cause there's air in the system (i.e. steam).
Did ya check the booster yet?


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## B12Chris (Dec 14, 2011)

jdg said:


> Water boiling in the brake fluid would cause a sloppy brake pedal, like there is air in the system, 'cause there's air in the system (i.e. steam).
> Did ya check the booster yet?





B12Chris said:


> So yesterday I put my B13 vented rotors, calipers, and pads on my B12. Install went very smoothly. Bled the system, take it for a spin, and it really feels like I have no power brakes. The pedal is very hard (so there cant be air in the system), but I have very little braking power. Even if I stand on them, I can't even get the brakes to lock from 30mph. I inspected the calipers (from a junkyard) and the sliders moved freely, pistons moved, eta. *I was thinking water boiling in the system, but they were hard right out of the drive.*
> 
> Any suggestions?


I checked the booster, master cylinder, and lines, nothing seems wrong. Really confusing.


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## jdg (Aug 27, 2009)

Do the master cylinders from the B12 and B13 match up?
How about the proportioning valves?
I think I'd be jacking the thing up, spinning the wheels and checking the brakes by eye and making sure they're all actually working and that you didn't wreck (i.e. pinch) some brake lines during the swap...the rubber lines anyway. Sometimes they got a habit of collapsing internally without any evidence externally that anything is wrong.


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## LvR. (May 26, 2010)

Hmmmmmmmmmmm - this is why "upgrades" should be planned properly.

Hard pedal with virtually no travel after an "upgrade" is an indication that your master cylinder's diameter spec differ on the 2 vehicles - your current situation is saying that the mc is way too big - iow its displacing too much with the result that the booster is never triggered to assist.

Sometimes (but not always depending on hydraulic design parameters) you can confirm this if you still have drums in the rear .......................... handbrake adjuster on the backplates forced really low and handbrake down, pump the brakes a few times to seat the shoes properly and you will most likely find the pedal travel increases and the booster operation gets activated


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## B12Chris (Dec 14, 2011)

LvR. said:


> Hmmmmmmmmmmm - this is why "upgrades" should be planned properly.
> 
> Hard pedal with virtually no travel after an "upgrade" is an indication that your master cylinder's diameter spec differ on the 2 vehicles - your current situation is saying that the mc is way too big - iow its displacing too much with the result that the booster is never triggered to assist.
> 
> Sometimes (but not always depending on hydraulic design parameters) you can confirm this if you still have drums in the rear .......................... handbrake adjuster on the backplates forced really low and handbrake down, pump the brakes a few times to seat the shoes properly and you will most likely find the pedal travel increases and the booster operation gets activated


I've read a few other people do the swap without swapping master cylinders with no problem. I will do that test today though.

If I do have to upgrade the MC, is there one better then a stock B13 unit (i.e., one off a B13 SE-R, NX2000, eta)?


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## LvR. (May 26, 2010)

Depends how you define "better" .............. imo pedal feel is a huge function of original mc vs caliper displacement ratio and the size of the booster ................. and if the donor vehicle had disks iso drums at the rear its even more critical.

Without knowing the exact sizes and ratios of mcs and calipers its virtually impossible to predict "feel"


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## B12Chris (Dec 14, 2011)

LvR.;1349201[B said:


> *]Depends how you define "better"*[/B] .............. imo pedal feel is a huge function of original mc vs caliper displacement ratio and the size of the booster ................. and if the donor vehicle had disks iso drums at the rear its even more critical.
> 
> Without knowing the exact sizes and ratios of mcs and calipers its virtually impossible to predict "feel"


I was just hoping I could find one that's smaller diameter then the stock B13 unit. If I have to upgrade MC's, I want to really make it wroth my time. 

Played with the car a bit today. I noticed that once I let it sit for awhile at idle, then move forward a bit and hit the brakes, it has full braking power. But that very quickly goes away :wtf:

I tried that booster test today, and there was no change. I did kill the car, pump brakes and hold, then start up and the pedal gave a little, so I do know that the booster is in fact working. 

This is beginning to get really aggravating, lol.


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## LvR. (May 26, 2010)

Unfortunately I cannot suggest an exact replacement because I am in South Africa and have no experience with models and parts specific to other parts of the world - what I do know is basically what I posted.

I would anyway just confirm the basics wrt the booster - do you in fact have unrestricted and un-collapsed vacuum hose running to that.

Another suggestion to confirm the mc too big theory ...................... on both front calipers pry the front pads away from the disk about 2 or 3 mm (don't take it too far). Now while being very awake get the car moving around 10mph and then jump on the brakes - be aware the pedal is going to drop virtually to the floor! ..................... but that first application of the brakes with the pads away from the disks will force the booster to show its colors - if you have a sorta better first brake application pedal feel (ito stopping power not pedal travel) under those circumstances you also know the mc is too big - once again don't go driving over the dog or wife.

FWIW - going too small on a replacement mc will give you way more pedal travel and much better stopping power but you can scare the pants off anybody driving the car and they are not used to the specific pedal feel



> I noticed that once I let it sit for awhile at idle, then move forward a bit and hit the brakes, it has full braking power. But that very quickly goes away


Puzzling that .................... you sure you dont just have a sticking non-return valve in the mc on one of the cup washers?


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## jdg (Aug 27, 2009)

Or a rotten vacuum line feeding the booster...i.e. very little air flowing thru the line, therefore very slow "fill rate" at the booster itself.


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## dreamteam (Jul 29, 2005)

This is likely the result of something that got moved during the swap.
I am going to go with a vacuum line.
Check the amount of vacuum at the booster, then go to the source
of the vacuum.
Is there a big difference?


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## B12Chris (Dec 14, 2011)

LvR. said:


> Unfortunately I cannot suggest an exact replacement because I am in South Africa and have no experience with models and parts specific to other parts of the world - what I do know is basically what I posted.
> 
> I would anyway just confirm the basics wrt the booster - do you in fact have unrestricted and un-collapsed vacuum hose running to that.
> 
> ...


Awesome info, I will check all that tomorrow and see what I can find. Thanks alot.

I did, however, noticed that RockAuto has two different master cylinders for both the B12 and B13 sentras, 3/4" (19.0 mm) and 11/16" (20.6 mm). I guess its very possible that I have the 11/16" when I need the 3/4".


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## LvR. (May 26, 2010)

Perhaps a question first - why EXACTLY did you decide to change the brake system?................... imo a daily driver etc vehicle is more than adequately equipped with a reliable braking system that has seen a lot of development work go into it and for somebody to arbitrary start modifying it is imo a no-no


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## jdg (Aug 27, 2009)

LvR. said:


> Perhaps a question first - why EXACTLY did you decide to change the brake system?................... imo a daily driver etc vehicle is more than adequately equipped with a reliable braking system that has seen a lot of development work go into it and for somebody to arbitrary start modifying it is imo a no-no


 Some folks get wicked performance improvements with only a NISMO sticker  or Jegs or Summit or whatever...


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## B12Chris (Dec 14, 2011)

LvR. said:


> Perhaps a question first - why EXACTLY did you decide to change the brake system?................... imo a daily driver etc vehicle is more than adequately equipped with a reliable braking system that has seen a lot of development work go into it and for somebody to arbitrary start modifying it is imo a no-no


For starters, I don't leave anything I own stock, lol.

Secondly, while it may be a daily driver, I do alot of sport driving on twisty roads, and the car will be seeing alot of autoX. Those puny non-vented pancake brakes just had to go (plus, I over-heated and warped the hell out of the stockers when I got the car). 

Once I get this issue figured out, I'll be getting a set of EBC Yellow Stuff race pads and stainless braided lines.


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## B12Chris (Dec 14, 2011)

Confirmed that the pistons are the same, 48mm. RockAuto backs it up (SE-R B13 is 54mm). The B13 pads tho, are a just little bigger (wider) then the B12's. I see no reason why I would need a different MC or booster

??????????


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## LvR. (May 26, 2010)

Its starting to look like you are not telling us the whole story then - I also cannot see the obvious need for a new mc atm (sure the bigger pads will need a bit more pedal input to get the same pressure on their surfaces when compared to the smaller original pads).

Are you quite sure the booster was working properly before you started this whole spiell?

Are you quite sure the vacuum line is good (see the idea of testing vacuum at the motor and again on the booster to compare)

With that "pry the pads away" experiment ............... any change in pedal feel (not travel only power)?


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## LvR. (May 26, 2010)

My guess is the "conversion" was easy enough - if you cannot find obvious answers to these questions my suggestion is to put the original stuff back and reverse the process and see if the booster is still (?) working properly ito braking assistance and behavior .................... it will save you having to possibly buy/replace something that may not be faulty.


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## B12Chris (Dec 14, 2011)

LvR. said:


> I*ts starting to look like you are not telling us the whole story then* - I also cannot see the obvious need for a new mc atm (sure the bigger pads will need a bit more pedal input to get the same pressure on their surfaces when compared to the smaller original pads).
> 
> Are you quite sure the booster was working properly before you started this whole spiell?
> 
> ...


....:wtf: What possibly would I "not be telling"?

I put the old stuff back on, still had a hard pedal. Swapped a Maxima brake booster on and all is fine. Most likely reason for the hard pedal? The old booster had came full of oil for some reason.


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## LvR. (May 26, 2010)

B12Chris said:


> ....:wtf: What possibly would I "not be telling"?
> 
> I put the old stuff back on, still had a hard pedal. Swapped a Maxima brake booster on and all is fine. Most likely reason for the hard pedal? The old booster had came full of oil for some reason.


...............and you have to ask?:wtf:


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## dc588 (Aug 14, 2007)

nx2000 front calipers,b13 se-r entire rear brake system and B14 MC/booster . lot of stopping power.This is what im using at this time.


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## B12Chris (Dec 14, 2011)

dc588 said:


> nx2000 front calipers,b13 se-r entire rear brake system and B14 MC/booster . lot of stopping power.This is what im using at this time.


I was thinking about this setup, but think it would do more harm then good in my application. The NX2000 brakes are a good bit bigger (i.e. heavier) then the stock B13's. And then there's the fact I would need bigger wheels (again, more weight) to fit them. Thats alot more rotating mass and a bit overkill for occasional AutoX IMO. Now, if I was planing a big turbo build and would need braking at 120mph+, then it would be ideal, lol. I am however thinking on the rear disk conversion, if not just for the fact they're easier to maintain. 

I had no idea there was oil in the booster, I cannot tell what I don't know..


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