Driver side brakes are LOCKED!

Knightspirit

Well-known member
Sep 22, 2019
251
84
Mount Shasta, CA
So I was coming home the other day from a local trail, and my driver side brakes locked up - weirdest thing. I was able to pry the pads apart with a crow bar and get the car home. I then ordered a caliper rebuild kit, which came today and I just rebuilt that caliper. Upon testing it - the damn brakes locked up again! So now I am thinking master cylinder? Anyone have this happen to them? To get it home this time - I loosened the brake line to release the pressure - and didn't touch the brakes all the way back. I just replaced the brake line as well as part of a 2" lift. This is a D1.

Any thoughts on this??
 

Tugela

Well-known member
May 21, 2007
4,754
562
Seattle
That's scary, glad the lockup didn't cause bigger problems. What condition were the pistons in when you rebuilt the caliper? Any pitting or rust? And which caliper is locking - front or rear? If the front, this could be an opportunity to make the upgrade to Defender 90 or 110 calipers. Defender rear calipers have different advantages and are also a popular swap.
 

Knightspirit

Well-known member
Sep 22, 2019
251
84
Mount Shasta, CA
Pistons were actually OK - broke a seal getting them apart, replaced everything anyway since I had the new parts. This is driver side front. Calipers are good I think. Would a master cylinder create a lockup in just one wheel?
 

Knightspirit

Well-known member
Sep 22, 2019
251
84
Mount Shasta, CA
Found this thread:

But this looks like maybe there was no ABS? If I trace the line back from the wheel that is locked up - it goes directly into the ABS module - not to the MC - so I don't see how a bad MC could be the cause:

IMG_5132.JPG

Anyone have any experience with this? Do I need a new ABS module?
 
Last edited:

Knightspirit

Well-known member
Sep 22, 2019
251
84
Mount Shasta, CA
OK - what about disableing the ABS system. I want to see if it still locks up with the system off. I have pulled the fuses under the hood and the 5 amp fuse under the dash - now I am getting a battery light and a really annoying tone that stays on. How can I disable this without the battery light and tone? Does just pulling the 5 amp fuse under the dash disable it without pulling the others? Anyone running with ABS disabled now?

Thanks!
 

Levi

Well-known member
Jul 27, 2004
559
26
Cheyenne, WY
Would a master cylinder create a lockup in just one wheel?

I think the proportioning valve will put all the braking to the front or rear if there is a failure/leak but someone might need to correct me on that. I had to replace mine right after I replaced the master cylinder and brake lines. Maybe something to keep in mind, IDK.

OK - what about disableing the ABS system. I want to see if it still locks up with the system off. I have pulled the fuses under the hood and the 5 amp fuse under the dash - now I am getting a battery light and a really annoying tone that stays on. How can I disable this without the battery light and tone? Does just pulling the 5 amp fuse under the dash disable it without pulling the others? Anyone running with ABS disabled now?

Thanks!

Just pull the fuse under the dash and all you should get is a solid ABS light. Probably 99% here have the ABS disabled.
 

Knightspirit

Well-known member
Sep 22, 2019
251
84
Mount Shasta, CA
Well - disconnecting the ABS did nothing - still locks up after going just a short distance. I ordered a used ABS module - so I will replace that and see if that fixes it just to get back on the road, but I can see that re-plumbing and bypassing the module is the best way to go.
 

discostew

Well-known member
Sep 14, 2010
7,706
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Northern Illinois
I would try to figure out for sure where the fluid is being trapped by the system. If you had the brakes locking up you could crack the line loose at several places and figure out just where it's getting trapped. Do any warning lights come on when it happens? Start at the abs modulator, the line positions might be marked on the housing. So if the right front is locking up and you crack that line loose at the modulator(valve block) see if the wheel frees up. If it does you can be prettty sure its inside the modulator. If you crack that line loose and the wheel still binds, then you need to work your way closer to the caliper.
 
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Knightspirit

Well-known member
Sep 22, 2019
251
84
Mount Shasta, CA
I would try to figure out for sure where the fluid is being trapped by the system. If you had the brakes locking up you could crack the line loose at several places and figure out just where it's getting trapped. Do any warning lights come on when it happens? Start at the abs modulator, the line positions might be marked on the housing. So if the right front is locking up and you crack that line loose at the modulator(valve block) see if the wheel frees up. If it does you can be prettty sure its inside the modulator. If you crack that line loose and the wheel still binds, then you need to work your way closer to the caliper.
Yes - I did exactly that - cracked the line at the modulator - and it squirted out under pressure - and the brakes unlocked. Then it locked up again shortly after that - so I did it again twice more to get home. No warning lights at all. So I think it is the modulator. I'll follow up after I install the used one that I purchased.
 

discostew

Well-known member
Sep 14, 2010
7,706
1,015
Northern Illinois
So from there the next place should be the master. Just to make sure. I think your probably looking at the abs modulator doing this. But just to be safe crack the line loose at the master when it locks up.
 

p m

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Staff member
Apr 19, 2004
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La Jolla, CA
www.3rj.org
Sometimes the piston inside the m/c does not completely return to original position, trapping fluid in the lines.
There's an easy check you can do: unbolt the master cylinder from the vacuum can, put one or two washers on the studs, and reinstall the master. See if locking up the wheels goes away or not.
 

Knightspirit

Well-known member
Sep 22, 2019
251
84
Mount Shasta, CA
Maybe I'm missing something here - but I only have one line from the MC to the modulator - there are not four, just two (I think the other one goes to the proportioning valve). So considering that only one wheel is locked up I can't see how it could possibly be the MC? Worth checking though obviously....
Thanks!
 
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