A strange ABS issue

[woodypk]

Hi guys.

For a while now I've had a strange problem with (what I assume to be) the ABS kicking in for no reason whatsoever. It doesn't happen very often and It's never happened while going any faster than maybe 10-15 mph, but only ever happens when I quickly depress the accelerator pedal and then quickly depress the brake pedal with a very short time period in between. I'm talking less than half a second from pressing accelerator to brake.

Just to explain a little more... The first time this happened was when I pulled out of a car park junction quickly and then noticed there was a speed bump in front of me, so had to quickly hit the brakes after I had just quickly accelerated out of the junction. ABS kicked in and I got the obvious vibration on the pedal but it really hindered my braking speed and I hit the speed bump faster than I wanted to.

It feels strange because the three or four times it's happened, it kicks in even when I'm 101% sure that the wheels were not going to skid anyway.

As said before, it doesn't happen very often, but I'm concerned for the fear that one day, it may not be a speed bump in front of me but something that I really do not want to hit such as a pedestrian or even worse.... another MR2.   s:roll: :roll: s:roll:  

Does anyone have any ideas where I can start looking or heard of this happen before?

Thanks for the help in advance.

[shnazzle]

Once again I'm jumping on the bandwagon of the ABS posts because I've had this a few times as well. But only since going onto coilovers.

Are you on stock suspension woody?

[woodypk]

The current setup is stock with lowering springs. I never had this issue on my PFL over the two years It was on the road. That car was bone stock.

[Carolyn]

I know Jonbill had a similar issue.  At the time, I suggested that he lean the muck out of the ABS rotors.  
I don't recall what the result was.  Knowing Jon, he will respond to this with whatever info he has.

[phaeton]

I suggest you slow down, be more observant & drive within your limits.

[cptspaulding]

I suggest you slow down, be more observant & drive within your limits.

  s:lol: :lol: s:lol:    s:lol: :lol: s:lol:    s:lol: :lol: s:lol:   Harsh! Even by my standards.

[Wabbitkilla]

What tyres, what pressures, how old are the tyres?
When was the last time the brake fluid was refreshed?
What disks, are all calipers working correctly?

[shnazzle]

Brake fluid changed last year. All brakes absolutely fine.
In fact, did a brake test last week for laughs from 60mph to full stop and abs barely kicked in. Stopped like hitting a wall.

Tyre pressures peachy on low mileage AD08Rs

[woodypk]

I suggest you slow down, be more observant & drive within your limits.

As stated, 10-15 mph may be a fair few leptoms, but I'm almost certain that these speeds are within my limits. I appreciate your concern none the less.

Tyres are T1Rs 30psi front 34psi rear and replaced full set in January.
I'm not so sure on when the brake fluid was replaced, I checked the level which is OK - good shout though, I will look into this. How can you tell if your brake fluid has degraded/needs replacing?
I've just replaced all disks, pads and dismantled and re-greased all the calipers.

I'll have to have a look if the ABS rotors are gunked up. Thanks for the advice.

[Wabbitkilla]

Ok, start with tyre pressures, thnkfully your tyres are all quite new, try setting them to 26fr and 36rr
Brake fluid does degrade over the years, best to replace every 5 years or so.
Disks and pads are also fresh so they will be very bitey, best to smoothly wear them in rather than stamping on the brakes because you're rushing to the stop line.

Give it a couple of hundred miles and see what they're like then.
ABS is usually solidly reliable on these cars, the only time where i had problems was with oversized wheels and rubber that had gone hard on the front but was fresh on the back ... so I was basically getting different levels of grip, which is what abs is all about.

Good luck

[woodypk]

It's a real strange one. When I said the brakes were new, I meant new-ish. Maybe 600 miles on them now. I'm really not sure what it is. It's strange how it only ever happens in very specific circumstances.

I'll definitely have a go at changing the tyre pressures. I've played around with different pressures over the 3 years I've owned MR2s and each gives a different feel. Thanks for the advice.

[Carolyn]

I drove Jonbill's car when it had the problem.  Remarkably similar symptoms.  You could PM him.

[topsyde]

I think Mr Roadie 2 had the same symptoms and his mechanic found there was a crack somewhere in one part of the brakes ! can't find the post but the post was only about 6 months ago as I can remember

Jim

[woodypk]

Thanks for the help guys. I'll have a good look when I'm on my shift break. I'll try and get a hold of Jonbill too. I really appreciate all the advice. You're a good lot really, no matter what they say...

[ChrisGB]

Out of curiosity, which pads? I've had pads on the daily that where very grabby and caused the ABS to trigger too early, making for very long stopping distances.

[woodypk]

They are mintex discs and pads. They stop well and had no issues even when I used them on the PFL.  

It's a hard problem to explain because it happens so prematurely when the ABS should not even be near coming on. Can anyone, very simply, explain where I can find the sensors or any other components which may be worth checking? Thanks.

[shnazzle]

I'm on eBay mtecs. Have been before these issues started.
Mine literally started pretty much as soon as the BCs went on

[Wabbitkilla]

Ah, Mintex!

I have Mintex M1144 pads on my Lotus.
When the weather is particularly cold or wet they are very wooden when you just start using the brakes. Excellent when there's a little warmth in them but crap when cold and / or wet. I am pretty certain this will be a good part of your problem. You just have to learn to treat them with respect until you have a little warmth in them.

[jonbill]

Funnily enough, I still have my problem but I'm planning to have a go at it today, so I'll report back.

I'd characterise my symptom as ABS kicking in about 40% of the time when braking from 10 or 15 mph. So yes, similar!

[woodypk]

Please let me know If you find anything out of the ordinary, Jon. I'll then have a look myself and report with my findings too.Thanks

[shnazzle]

Ditto

[Bossworld]

Do you get any lights (ABS or otherwise) coming on when it happens?  I've been without my car for three weeks but I'm sure my brakes used to feel strange at 20 or below.  Part of me thought it was the gearing in these cars which seems to do far more of the braking than I'm used to, so I tried knocking into neutral a few times rolling up to lights and found it more pronounced.

[Carolyn]

Been doing a bit of research.
number one cause is build-up of dirt on the face of the sensor.
number 2 build up of rust/corrosion collecting in rotor teeth.
number 3 sloppy wheel bearing changing distance from sensor to rotor.
number 4 sensor not fully seated.

[phaeton]

Been doing a bit of research.
number one cause is build-up of dirt on the face of the sensor.
number 2 build up of rust/corrosion collecting in rotor teeth.
number 3 sloppy wheel bearing changing distance from sensor to rotor.
number 4 sensor not fully seated.

They all seem logical options, along with
driver hitting brake too hard despite their protestation that they don't feel a wheel is locking
Warped discs causing grab
Slightly sticking caliper/piston causing grab

[tricky1138]

I'm following this too, as have the same symptoms, although I have put it down to winter tyres and a slightly sticking caliper.

Will see what its like with my summer tyres over the weekend!  s:) s:)