94 FZJ80 - Brake pedal pulses when approaching stop (1 Viewer)

[Archy]

94 FZJ80 - Brake pedal pulses when approaching stop

94 FZJ80
ABS and Check engine lights both work (light up at startup).
Searched and only saw one other mention of an issue like below, however the post was very light on details.

When approaching a complete stop, the brake pedal pulses until complete stop. This does not feel like a physical brake issue. It very much feels like ABS locking up the brakes. Overall stopping feels like normal (other than the pulse). No ABS light on after the brief light up on startup.

To diagnose, I pulled the ABS fuze and the issue went away completely. My next step is to jack the vehicle up and pull the ABS speed sensors, looking for rust on the knuckle affecting sensor mounting or metal on the sensor itself. It confuses me as I figured if it was a speed sensor then the ABS light would be on all the time. Does anyone have any additional thoughts or guidance on this?

Thanks!

 

[thedoughboy]

When you say pulsing, how aggressive are the pulses? ABS will be aggressive. A warped disc will be moderate. I had moderate pulsing, which was corrected by having my discs resurfaced. But, they'd pulse again after ~5000 miles. Finally replaced them with OEM and have never looked back.

 

[jpoole]

Speed sensors that are dirty or spaced too much tend to be more likely to trigger as the signal can be marginal. On my 80 this has most often manifested itself as ABS actuation when I hit sharp bumps that were enough to cause the ABS sensors to loose the tone ring signal.

If this pulsing went away with ABS being disabled then you've done a good job of narrowing the scope of the issue. Improving sensor signal strength does seem like a good next step if ABS functions normally in most situations. Clean the mounting surfaces and the ends of the sensors so that they are getting best signal possible as a start. You may also need to take other steps like change the bushing/bearing inside the spindle that supports the stub axle or other changes that may be related to position of the tone rings front or rear so that you don't lose signal when you shouldn't.

Of course, there could be other issues like shorts that open up with braking or play/looseness in other parts of the system that are activated with braking, etc. so keep an eye out for these as well when you are in there.

 

[Archy]

When you say pulsing, how aggressive are the pulses? ABS will be aggressive. A warped disc will be moderate. I had moderate pulsing, which was corrected by having my discs resurfaced. But, they'd pulse again after ~5000 miles. Finally replaced them with OEM and have never looked back.

Pulse is pretty aggressive, feels like it is active pressure. Will inspect everything when I pull it apart. Thanks!

 

[Archy]

Speed sensors that are dirty or spaced too much tend to be more likely to trigger as the signal can be marginal. On my 80 this has most often manifested itself as ABS actuation when I hit sharp bumps that were enough to cause the ABS sensors to loose the tone ring signal.

If this pulsing went away with ABS being disabled then you've done a good job of narrowing the scope of the issue. Improving sensor signal strength does seem like a good next step if ABS functions normally in most situations. Clean the mounting surfaces and the ends of the sensors so that they are getting best signal possible as a start. You may also need to take other steps like change the bushing/bearing inside the spindle that supports the stub axle or other changes that may be related to position of the tone rings front or rear so that you don't lose signal when you shouldn't.

Of course, there could be other issues like shorts that open up with braking or play/looseness in other parts of the system that are activated with braking, etc. so keep an eye out for these as well when you are in there.

Agreed, and thanks!

 

[TomH]

Use the procedure in the FSM to read the ABS codes, then you will know which sensor is the problem. In my case I had a loose rear wheel bearing. Tightened it up and the pulsing never returned.

 

[Archy]

Use the procedure in the FSM to read the ABS codes, then you will know which sensor is the problem. In my case I had a loose rear wheel bearing. Tightened it up and the pulsing never returned.

Would there be codes if the ABS light is not on all the time? Currently the ABS light is only on at startup. ABS light stayed on when I pulled the ABS fuze to diagnose. Thanks!

 

[Rusty Marlin]

Would there be codes if the ABS light is not on all the time? Currently the ABS light is only on at startup. ABS light stayed on when I pulled the ABS fuze to diagnose. Thanks!

Yes, it records faults that aren't necessarily displayed. As does the Cruise Control.

 

[Archy]

Yes, it records faults that aren't necessarily displayed. As does the Cruise Control.

Got it, on it and will report back. Thanks!

 

[DrDuc]

Make sure the pins on your brake calipers are well lubed and the calipers can slides on them when you apply the brakes.

 

[swamp-thing]

i was wondering if maybe a faulty abs sensor would do this as well?

 

[Archy]

Reporting back, ran through the procedures in the FSM, and it looks like all but one was spot on with the manual. Pretty sure I screwed up the one that didn't match. Going to rerun all tests again later. Still no ABS code, just a steady double blink every 3ish seconds.

I felt the brake pulse while performing some of the test. I thought ABS was disabled while running through the tests?