Brake pedal going to floor (Fixed- Rod length and booster air leak)

[sco_aus]

Hey guys.

So I thought with the addition of the 15/16 MC that this would go away, but to no prevail.

 

So my brakes are Hilux 4 pot (solid rotor version) front, Single pot Maxima (basically S13, R31 etc) rear, braided lines all round and 15/16 MC.

 

What happens is as I apply brake pressure it begins to brake, however it gets to a point and then goes to the floor and i only have about 15-20% braking capacity.  The lines were very thoroughly bled and there appears to be no leaks.  It did get a little better when I upgraded from the 7/8th, but it still has the same problem but with lsightly more braking capacity.

So has this happened to anyone else?  I don't know much about brakes and being one of the most important things on the car I want to get it right.

 

Cheers in advance

 

Scott

[Zedman240®]

Did you check the length of the rod when you changed the master cylinder? I know you have to do heaps of measuring to get that spot on. If it's too short, you can never get full travel of the master cylinder.

[sco_aus]

oh right, that makes sense, i did adjust that a while back for another MC.  Good call.  Ill try that tomorrow.  Any other ideas incase that doesn't work?

[xa1973]

Is your upgrade Master a new item or second hand.. if second hand put a kit through it..but first of all re bleed the system starting from the passenger side rear first etc, check your rod length

 

Ive found in the past what I thought was a thourough bleed has still contained air in the system, I generally use three to four bottles per fluid change

[sco_aus]

wow, ok.  Ill try that second. thanks

[Zedman240®]

Don't forget to bleed the master first! then the rest...

[sco_aus]

cheers

[Pigpen]

Hey Scott,

 

Are you running discs on the rear as well??

 

If so, did you think to take the little black valve out of the body of the MC???

 

I'm not sure if this will create the issue that you have - but it was just a thought in the back of the head.

 

good luck

 

Mick

[C.A.R.]

280ZX (15/16") MC doesn't have that valve...

[RBZ 260]

mine had the opposite effect. it will lock up  the rear brakes.

 

but only prob was the mc rod wasnt adjusted properly. it applied brakes well but didnt allow the rear cuircuit to relese. after 3 stopmps she be locking up and no go.since the rod didn't return to start the rears were always applied.u may have the opposite the rod being too short and running out of travel on your pedal.

 

personaly i hate brake bleeds and adjustments. such a pain.

 

 

[sco_aus]

Yeah, I couldn't agree more.  There is a reason I don't know much about brakes...

I reckon it will be the rod length  (he he), just gotta find time to fix.

[luke_mcmahon85]

I've had the exact same problem since doing the hilux/r31 swap...

 

So i Swapped in a 1 inch patrol master....same problem...

 

I had a bitch of a time trying to adjust the rod - so to try it out, I just removed the aluminium spacer and bolted the M/C straight to the booster... this had the effect of reducing the pedal throw by half....but still only very minimal braking...

 

I'm thinking it must be a bleeding issue... I'm going to start bleeding again from the master and be reeeeeally thorough (as this will be the 3rd time....)

 

Also, I'll obviously be putting the spacer back and adjusting the rod properly - does anyone have any hints on doing this?

[sco_aus]

Thanks for posting. 

Its kinda hard to explain, but unbolt the master from the spacer.  The rod will be protruding, its rounded on the end (thats what she said ).  There is a spined part that needs vice grips to stop the whole shaft from spinning, then there is the end part that has to be rotated on that also with a hex spanner part.  Its a real pain in the arse and it small amounts of movement can make a big difference, so just play around with it.

[sco_aus]

Alright, so I have good news and bad news.  The good news is, adjusting the rod has made them a lot firmer, the bad news is, my booster has an air leak, so i need a new one .  For anyone reading this with the similar problems, just pump the brake and listen for leaking air from the booster.  I actually discovered the leak when playing with the rod, i moved it sideways and heard air leak from it, so tried pumping the brake and heard air.

[PZG302]

Alright, so I have good news and bad news.  The good news is, adjusting the rod has made them a lot firmer, the bad news is, my booster has an air leak, so i need a new one .  For anyone reading this with the similar problems, just pump the brake and listen for leaking air from the booster.  I actually discovered the leak when playing with the rod, i moved it sideways and heard air leak from it, so tried pumping the brake and heard air.

 

Drive without the booster ya big girl!!!!!! ;D

 

It maybe worth a shot depending on how firm you like your pedal, I use a 1" M/C with no booster for 4 spot Willwoods and Saab/Volvo 2 spot rears.

 

For the race track it's fine, don't know if you cold live with it day to day though. My Charger will have a remote booster so I still keep the E38 factory look under the bonnet. The XR8 Brakes on it and the M/C I am running make it just too firm for every day. I might be able to put up with it, but if needed, the better half would never be able to work the brakes if she had to drive the Charger.

[sco_aus]

It is mostly a track car, but it is seriously firm atm (may have adjusted the rod too much).  Either way, I just want it reliable and since i still have a few thou to spend on it before its track ready, ill just stick with it being a street car for now.

[Zedman240®]

Don't forget there has to be a slight amount of play between that rod and master; you don't want the brakes dragging on. Jack it up and see if you can spin a wheel freely.

[sco_aus]

Good point, thanks