Brakes locking up

[nddavis2]

I have searched and read topics along this line but it seems none come to a real definitive solution.

I removed the abs master cylinder and replaced it with a non abs due to a non-functioning abs system. I also changed brake lines to the chase bays relocation kit so they are routed along the cross member. After a month or so, I started getting a gradual amount of pressure on the brakes during driving to the point they lock up. I can leave the car for a while and be able to drive it yet have the issue occur again. I have replaced the booster and the check valve and next up is the master cylinder. Before I do that, I'm looking for ideas/ opinions here. I can have the car running and remove the vacuum line from the booster with no effect to either the braking system nor the engine. Engine still runs like normal with maybe an occasional hiccup but nothing major but brakes remain locked. Car is currently on the side of the road waiting on brakes to cool off so I can limp it home without touching the brakes as its about a half mile from home. It went from occasionally happening to not making it 5 miles before it locked up.

What am I missing here? Other than the master cylinder, what is there to change out to solve this issue?

Thanks for the help.

[kruked]

Are all 4 corners locking up?

[nddavis2]

Yeah all 4 are locking up at the same time. I've heard brake booster, check valve, and master cylinder as potential causes. Wondering if I'm just missing something

[Mikester]

Removing the ABS, replacing the MC with a non-ABS MC and leaving the ABS booster is the perfect prelude to a Z32 upgrade... an MC is not going to start putting out more & more pressure to your brakes (unless the final little bit of air bubbles from bench bleed/brake bleed made their way out)... It isn't designed that way. If your brakes are locking more and more every day, then that tells me:

You probably need new tires. Brakes stop the wheels/tires from spinning- It's the amount of 'stick' between the tires and the road that is the difference between locked brakes and a smooth stop.

Replace your tires with some new, good quality ones and I bet the difference will be night and day.

Mike

[nddavis2]

Tires? The calipers are physically pressing the pads into the rotors as the car goes down the road making it impossible to move forward. How is this a tire issue? The tires have about 5,000 miles on them. I know an abs booster is good with the non-abs master for a front z32 brake swap as that was the intention originally. Now I just want to be able to drive the car again without the brakes slowly clamping on me.

[rawgarage]

In for a solution

[kruked]

Removing the ABS, replacing the MC with a non-ABS MC and leaving the ABS booster is the perfect prelude to a Z32 upgrade... an MC is not going to start putting out more & more pressure to your brakes (unless the final little bit of air bubbles from bench bleed/brake bleed made their way out)... It isn't designed that way. If your brakes are locking more and more every day, then that tells me:

You probably need new tires. Brakes stop the wheels/tires from spinning- It's the amount of 'stick' between the tires and the road that is the difference between locked brakes and a smooth stop.

Replace your tires with some new, good quality ones and I bet the difference will be night and day.

Mike


Z32 mc...

New tires...

WTF...



In for a solution

My only suggestion would be to try a new/another master cylinder.

I've never owned an s13 w/ abs.

Did you bypass the abs system when you swapped master cylinders?

[nddavis2]

I have replaced the master cylinder but haven't bled the system yet so I'll know tomorrow where that stands and update then.

I removed the abs module and brake lines associated with it then got the chase bays brake line kit as a replacement for lines along with a used master cylinder.

[kruked]

If I'm not mistaken, an s13 w/ an abs module has abs calipers. Maybe the calipers aren't functioning correctly because the abs module is bypassed...
If this is the case, a yet 'nother master cylinder won't correct the issue.

[nddavis2]

Calipers were changed to non-abs versions before I purchased the car.

[BigKriss]

never mind.

[Mikester]

Z32 mc...

New tires...

WTF...





Misread. I was under the impression that the brakes would lock up when the pedal was being pressed. Didn't realize they were staying locked with NO pressure applied.

Definitely abnormal considering he changed to a non-ABS MC and aftermarket lines to compensate. I removed the ABS and left the ABS calipers before going to Z32, basically did everything OP did above except I ran OEM non-ABS lines.

Anxious to see if MC fixes this.

[ANDY black s13]

Check the length of the push rod on the BMC you swapped in against the one you removed
I guess the old BMC push rod has a shorter length of push rod
and the longer push rod length of the swapped in BMC is causing the lack of caliper release
as the BMC can't return fully to its original stop position

[nddavis2]

You're going to have to help me here. In the fsm I see how to check the stroke of the push rod of the booster when brakes are applied that goes into the BMC and stops the vehicle. Also the other side that attaches to the brake pedal itself. Is there an additional adjustment I can make I have overlooked?

[ANDY black s13]

You're going to have to help me here. In the fsm I see how to check the stroke of the push rod of the booster when brakes are applied that goes into the BMC and stops the vehicle. Also the other side that attaches to the brake pedal itself. Is there an additional adjustment I can make I have overlooked?

Possibly I confused things as I was posting quickly and running late to go out :(
but what I should have posted was check for pedal free play of 3/4mm approx
from the pedal rest or stop you should be able to move the pedal slightly
then see or feel its moving the piston in the Bmc
the forked end of the booster push rod can be adjusted and the other end as well, possibly the push rod length BMC end needs to be shortened
if there is free play at the pedal end already
Im going on the theory the BMC piston's are not fully returned and stopping the fluid return so not releasing the calipers
as pedal pressure when using the brakes is far greater than the return effect from the caliper/bmc seals etc
If you unbolted the bmc say 4/5 threads when the brakes were locked on if they then released as the bmc moved away from the booster,
that would sort of confirm my guess at the pushrod length BMC end needs to be shorter

[nddavis2]

I got the BMC changed out and lines bled and was able to drive about 20 miles without any issue. By no means am I saying the problem is solved and I won't until I'm able to drive it much longer distances however as of now there is definitely an improvement.

[ANDY black s13]

did you swap it for a BMC with same number as in bm44 or bm50 etc?
not sure 100% what bmc you get fitted when lhd and abs/non abs
and curious if its fixed
even if they are same bm numbers,possibly the previous BMC could have
suffered like my OE s13 had as in the bore of the cylinder had corroded under the dust seal
and right up to the end of the piston seal so possibly the returning piston is binding in the corroded area causing a slight brakes applied situation
just an idea as mine was pretty bad looking,but it was working ok,
I swapped it for a BM57 for brake upgrades

[nddavis2]

I swapped in what I believe is the same number BMC however I can't confirm this as I have not looked for a number but only the exterior of it. I did not upgrade to a z32 BMC I know that however I can't say for certain the one I had in wasn't from an s14 but I'm almost certain the one I swapped to was an s13 as that's what I pulled it from.

[TheRealSy90]

The rod into the master cylinder from the brake pedal is not coming out far enough when letting off of the pedal. If it does not come out all the way, the pressure will not fully realease from the master cylinder. I had this exact problem after putting a small bolt in the pedal to hit the brake light switch after the stock plastic grommet came out. Just that little bit of difference caused my brakes to stay locked up, and caused me to replace the entire brake system before figuring out what the problem was.

[ANDY black s13]

I swapped in what I believe is the same number BMC however I can't confirm this as I have not looked for a number but only the exterior of it. I did not upgrade to a z32 BMC I know that however I can't say for certain the one I had in wasn't from an s14 but I'm almost certain the one I swapped to was an s13 as that's what I pulled it from.

using a 13 bmc on a 14 might be the issue
as I was going to use a s14 booster/servo with a z32 bmc on my 13
but the s14 booster pushrod was a different length at the pedal end of the rod
by what looked like 20mm+ length difference,
and there was not enough push rod to adjust it to fit the pedal
so binned the idea and reused the s13 booster
the mix up of 13 bmc on 14 booster maybe the issue with your car
as chap above me mentions pushrod length and brake lock on issues

[nddavis2]

Thanks for all the help everyone. A lot of good information in here. Hopefully the most recent BMC change has taken care of my issue. If not I will next adjust the rod to the pedal from the booster or the rod from the booster to the BMC. Car will be down for a couple months as I do a vq35de swap in it but after that I'll let everyone know.