Weird braking behaviour - 80 series - maybe ABS related?!?

[Dave_S]

Hi all

Okay, the latest mystery to be solved...

We noticed that the 80 series brakes were not the best and that as you pull to a stop there is sometimes a "pump" from the pedal (almost like ABS kicking in).

The front discs were a bit worn (and possibly warped, as Jan reckons she cooked them running over the TT mountain road a while back), so we changed out the front discs and the pads all around, and freed off a couple of stuck calliper pistons.

Anyway, the brakes are better, but we've still got this weird ABS-style pump from the pedal just as you come to a stop (it doesn't do it any other time and there doesn't seem to be any material driveline shunt).

I'm tempted to replace the front callipers (given the sick pistons), but I'm concerned that there is something else weird going on. I know sod all about the ABS system, so wouldn't know where to start in identifying/fixing any issues there...

Anyone any ideas before I throw more money at this thing?!?

Thanks guys, appreciate any help!

 

[madmanmart]

Had this on my dads old 80, it’ll be the abs kicking in.
You could pull the abs fuse and see if it stops to confirm.

 

[Andy]

I had this, & it was front wheel bearings needed a small adjustment

 

[fbnss]

something to do with the sensors or reluctor ring (if thats what its called)and a shim maybe...

 

[Dave2000]

I have seen and rectified this many times on customers 80's and once on my own, the problem is almost certainly wear in the hub bush where the CV comes through, more prevalent as you run over a simple bump or man hole cover as your braking, the sudden adjustment of the gap between the tone ring and sensor often sets off or triggers the ABS for a second or two, it can catch you out as the brakes release momentarily when you don't expect them too, this often lets the car roll on an extra foot or so. You could take out the ABS sensors and apart from giving them a clean, they may have a shim under them? Remove the shim and replace the sensor, careful though the bolt can break off when removing/tightening. With the shim removed (assuming you have one) then see how you go. It is rare the sensor gets 'clipped' by the tone ring, and the shim you are removing will only be a few thou, shim or not get ready to pull the wheel/caliper/disc and hub, knock out the brass bush and replace, two type are now available, use whatever is the easier to get hold of or cheapest, they amount to the same thing.

Regards

Dave

 

[fbnss]

some people are more elequent than me

 

[Dave2000]

Proper posh where I was dragged up init!

Regards

Dave

 

[Dave_S]

Cheers guys - appreciate the quick response on this - looks like I'll be rolling about on the drive again (sigh!). Anyone got an idiots guide to pulling the sensors, I've never done this before. Thanks again.

 

[Dave2000]

Very easy, wheel off, sensor is mounted in the top of the hub, release bolt and give a good spray with your favourite release agent, then GENTLY twists them side to side so they are moving/rotating in the holes and ease them out, they look tough but the cabling is getting a little tired now, so if your not careful you could inadvertently bring in another problem.

regards

Dave

 

[Dave_S]

Excellent - thanks D2000 - I'll get on this next week.

 

[Dave_S]

Forgot to mention... I pulled the ABS fuse and the dodgy braking behaviour disappeared. I'll strip the ABS sensors and check later, but for now the immediate issue has been identified. Thanks again for the advice guys, this is what this forum is all about

 

[Andy]

I’d still check the wheel bearings, a little wobble in them can activate the abs, but with the abs effectively disconnected the wb’s could still be loose/ worn etc & u might not have any indication of it

 

[Dave_S]

Fair call Andy - I'll cover off both. Wheel bearings were done a little while ago, so should be good, but I will double check in any case.

 

[Andy]

If they were done recently, it may be that they’ve just ’bedded in’& just need re tourqing

 

[Dave2000]

I agree the wheel bearings can cause this problem, but if they were fitted correctly they should not need any further adjustment.

Regards

Dave