Brakes & ABS

[Andy]

I have an annoying problem with the ABS (I think) 'pulsing' the brake pedal.

This happens probably 80% of the time when slowing to almost a complete stop, or actually stopping, at low speed & under gentle braking ie approaching roundabouts, traffic lights etc .

The wheels are definately nowhere near locking up.

The pedal only 'pulses' for a second or so & the car stops ok.

Braking hard does not seem to cause the problem or make it any worse.

Its been like it for a while now & is an annoyance, has anybody any ideas on what could be causing this, somebody did suggest the rear load sensing valve, but not sure which way to adjust it as I havnt got pressure guages etc as suggested on Lcool, could this be the problem or something more deep rooted. I have cleaned up the wheel sensors when doing bearings etc but no different

There is quite a bit of weight on the back with rear bumper & twin wheel carrier, LR fuel tank etc

Its a 94 12 valve 80

Thanks

 

[Paul_Humphreys]

It is one of two things.

1st, the magnetic but that picks the signal up from the abs ring on the CV not working correct. Cost a lot to fix.

2nd, the ABS ring has grease on it (guess how I know this one!!). Takes a lot of time to fix.

Paul

 

[Andy]

Paul,

Did you have the same then?

what about getting another sensor thingy & trying it wheel by wheel to see which one is causing it?

Are they expensive?, they only seem to be magnetic bits on a lead!!!

 

[Rob]

Andy the abs sensors are very expensive new from toyota.

There is a abs diagnosis that can be carried out, it is described in the RM315E full service manual. This way you will know which corner is at fault.

 

[Paul_Humphreys]

I have the grease on the abs ring one. Sorted it now. But see Robs post about sorting it out.

Paul

 

[Ian Rubie]

what about getting another sensor thingy & trying it wheel by wheel to see which one is causing it?
Are they expensive?, they only seem to be magnetic bits on a lead!!!

Toyota will not sell a single front sensor, you have to buy both and the loom between the two

My pedal did the same until I replaced the sensors.

Ian

 

[Graham Stirling]

It's worth checking that it's not just a warped disc.

Can you disconect the sensors to see if it makes a difference?

 

[Paul_Humphreys]

It's worth checking that it's not just a warped disc.

Can you disconect the sensors to see if it makes a difference?

Just pull the fuse.

Paul

 

[Andy]

Changed discs, but it was diong it before then,

I dont think its grease on the abs ring as replaced cv s, (but didnt make a concious effort to check at that time).

looks like i'll have to check out the abs diagnosis.

Ian, how expensive are the sensors??

Andy

 

[Guest]

I had that problem, it was solved . . eventually, when I had new slotted discs fitted, I don't think it was fitting the slotted discs themselves that cured it, I think the old discs were probably warped.
Chas

 

[Jon Wildsmith]

Were there any changes you made to the truck that coincided with this problem starting?

 

[Andy]

, No I cant recall that therte were any changes that 'caused' it, I have racked my brains trying to think when it started & the only one that I can think of was fitting the l/r tank, thats what gave me the idea that it may have been someting to do with the valve at the back & the weight rearwards.

Some times it does seem to be more frequent than others though and doesnt seem to affect the stopping power, but having said that it only happens at very slow speeds, when almost at a stop & only for a second or so.

yesterday it seemed to happen every time & then another day its not nearly as frequent.

Andy

 

[Jon Wildsmith]

It might be worth running some of the tests in the FSM and if you have an osciloscope check the amplitude of the signal being produced at low speed - it might be that old age is causing a weak signal from the sensors.

 

[Ecky Thump]

This might not mean anything but....

After my 2" lift, mine had the same problem until I finally managed to adjust the load sensing valve correctly.
All the braking was going to the front prior to this causing the ABS to kick in often.

If you have added a lot of weight to the back then maybe the valve arm needs adjusting to compensate.

 

[Andy]

ill try that, & see what happens, which way did you adjust the arm, shorten or lengthen it?

 

[Ecky Thump]

On mine the adjuster sticks up from the back axle and I had to wind the nuts uphill several turns.

With you adding weight to the back, I suspect you will have to wind it down as I reckon all your braking will be on the back axle.

As the axle goes up into the body the control arm pushes up which I think means more brake power goes to the loaded axle i.e. the rear

Please, someone correct me if I have that wrong.

With mine it was just a case of trial and error until it seemed about right, I did ask if there as any way of testing it but no-one could help.
I think you would need a four wheel drive rolling road to check it properly but then you would need figures from somewhere to work from.

 

[Julian Voelcker]

The best 'technical' approach to adjusting LSPV is to drive down a gravel track when fully loaded and brake hard with the ABS fuse pulled.

All being well the front and rear brakes should lock up at around the same point. If they don't you can adjust the bias front by adjusting the setup of the LSPV.

As a golden rule when we do standard 2.5" suspension lifts we drop the LSPV by 1/4" and then fine tune on the back axle.


Going back to the ABS issue, the key thing is to run the ABS diagnostics and that should point you to the problem. If it is not coming up with a specific problem, pull the sensors and clean off any metal bits from the end (don't worry about grease, it doesn't make any difference!!!!) and then make sure the surface that the ABS sensor pushes onto is clean and free from rust (ideally get it back to bare metal and then treat to stop further rust).

I did go to the extent of getting an oscilliscope to do more detailed diagnostics however have yet to use it, most problems are down to damaged looms or poorly seated sensors (later ones were shimmed to get the right gap).