Break Pedal Losing Pressure before a Stop /ABS light - Newbie

[NeilMo]

Hi All, this is my first post and I'm a new owner of a 1997 FZJ80 with Factory Lockers. been on the hunt for a while.

The ABS light was on when I bought it, anyways i brought the cruiser home, and noticed the previous owner had the abs sensor harnesses unplugged near the wheels. I plugged them back in, and after a few miles of driving the ABS light went off. But then a few miles later I noticed then when I'm braking, the pedal feels fine until literally right before a complete stop and the pedal loses pressure and sinks toward the floor a couple inches and then regains pressure. There doesn't seem to feel a loss in actual braking, just the pedal moves. Any idea what this is? If any of you guys have a hydroboost diesel truck, it kind of feels the same as when there is air in the system. So I'm guessing I should maybe flush the entire system? Any tips on a complete flush and flush of abs? or maybe i need new abs sensors?

Thanks for the help. I'm sure this will be the first of many. Any go nice on this newbie for the first round - haha

 

[mrsleeve]

Sounds like a failing wheel speed sensor and it’s triggering the abs in some way, hence why the po had them disconnected

 

[Kernal]

Did the brake issue start immediately after reconnecting one or more ABS sensor harness connectors?? Did the brakes work normally before doing that??

Have you tried disconnecting the ABS sensor that you just reconnected to see if braking (the pedal going to the floor) went back to normal?

Start by checking the fluid level in the reservoir
Check around the Master Cylinder, ABS pump, and all lines and calipers for leaks.


Welcome to Mud

 

[NeilMo]

Did the brake issue start immediately after reconnecting one or more ABS sensor harness connectors?? Did the brakes work normally before doing that??

Have you tried disconnecting the ABS sensor that you just reconnected to see if braking (the pedal going to the floor) went back to normal?

Start by checking the fluid level in the reservoir
Check around the Master Cylinder, ABS pump, and all lines and calipers for leaks.


Welcome to Mud

Thanks Kernal, the braking was fine with the ABS sensors disconnected and didn't start acting up until I plugged them in. I was happy to have the ABS light turn off on the dash, but not so happy about the feeling of losing brake pressure. Lol

 

[mrsleeve]

That should tell you right there its likely not a mechanical issue, its a ABS issue (so long as your fluid levels are at least close to correct). and likely induced by 1 or 2 wheel speed sensors detecting wheel lock up thats not acctually happening when you get close to a complete stop, and activating and reducing line pressure on the affected wheel(s) and taking the pedal feel away from the brake pedal as it does that, and those process then extend your stopping distances

Hence why the PO unpluged them and just dealt with the light on the dash to maintain full brake pressure to the calipers at all times.

Soulution is to figure out which wheel is affected and most likely replace that sensor, or see if the reluctor ring is damaged. Could be a broken wire of failed connector as well

 

[Kernal]

@NeilMo : Try disconnecting the ABS sensor that you just plugged back in, then report back if it fixes the braking issue.

 

[NeilMo]

That should tell you right there its likely not a mechanical issue, its a ABS issue (so long as your fluid levels are at least close to correct). and likely induced by 1 or 2 wheel speed sensors detecting wheel lock up thats not acctually happening when you get close to a complete stop, and activating and reducing line pressure on the affected wheel(s) and taking the pedal feel away from the brake pedal as it does that, and those process then extend your stopping distances

Hence why the PO unpluged them and just dealt with the light on the dash to maintain full brake pressure to the calipers at all times.

Soulution is to figure out which wheel is affected and most likely replace that sensor, or see if the reluctor ring is damaged. Could be a broken wire of failed connector as well

Thank you so much mrsleeve, I think you've described what's happening perfectly. I'll take a look at the wheel speed sensors, and just unplug them again in the meantime