Hi everyone. I've looked through the archive and can't find any references to my issue, so here goes...

We bought a 2008 Grande Punto 1.9 M-Jet Sporting a few months ago when we probably should have walked away. However, we are where we are, and the latest - pretty troubling - issue concerns the brakes.

When you brake (at any speed - it's happened to me at around 50mph and to my wife at under 10), the nearside rear wheel locks with very light pressure on the pedal and before the ABS cuts in. This has the effect of sending the car sliding across to the left, which is quite unnerving. Not to say potentially lethal.

No warning lights are coming up on the dash and no codes on the diagnostics.

With the help of our local garage, we have so far tried changing all discs and pads (they needed it anyway), purging / bleeding the circuit, swapping tyres front to rear and side to side to see if wear was a factor. It's not, still always the nsr wheel locking.
And the latest thing we've tried is a new ABS pump to see if it was sending the wrong pressures to the different wheels. No joy.

We are reaching the end of our patience; the car was bought to be a courtesy car for our business and until this is definitively sorted, we can't allow customers to drive it.

Our next step is to change the nsr caliper to see if that helps, but it's a slim hope.

Does anyone have any bright ideas as to what might be causing the issue?

I feared a bent/cracked chassis, but apparently that's unlikely.

All constructive thoughts welcome!

Are the brake pipes OK? Could be stuck calliper as well, on the other side, causing too much pressure on the near side.

Thanks for the thoughts - I haven't checked the pipes, but I will.

Flexi hose to the caliper been changed
They have been known to collapse internally

Thanks Chris.

Have you considered stripping the caliper down and servicing it?..It could be the caliper is binding on the sliders,or the piston is stuck etc.
Personally I would strip and clean all four..at the least you would eliminate it being a caliper

Like others said it sounds like a mechanical rather than a hydraulic issue.

Check the run out on the disc make sure nothings bent.

Check it's the correct caliper as well. You never know sometimes with second hand cars.

Caliper mounting bracket always worth checking to make sure it's ok.

I like "perelaar"s proposal of opposite caliper seized, that makes very much sense and is really my favourite since the ABS pump has already been changed ! On the attached drawing one can see that front and rear are separate circuits, each sharing their own pressure line and sets of valves into the ABS block...

BRs, Bernie

If someone here helped You fix -or better, understand- your issue, hit the thanks icon @ bottom right corner, it's free and makes us feel helpy ;-)

Thanks TigerTom and Bernievarian. I've gathered all the advice and I'll take it to my mechanically-skilled friends at the garage.
I'll report back - hopefully with a winner!

Jim C said:

Thanks TigerTom and Bernievarian. I've gathered all the advice and I'll take it to my mechanically-skilled friends at the garage.
I'll report back - hopefully with a winner!

Click to expand...

I need to update my previous answer:

The master cylinder is separated into two circuits, each one driving TWO brakes as I said, BUT not the rear vs the front pairs !
The brakes are paired in a DIAGONAL patern: Front Left with Rear Right and Front Right with Rear Left !!

So You might find the (suspected) seized caliper at the front ...

BRs, Bernie

If someone here helped You fix -or better, understand- your issue, hit the thanks icon @ bottom right corner, it's free and makes us feel helpy ;-)

You are right Bernie - system is crossed: Front Right + Rear Left. My suggestion here is one of these brake caliper seized. So if rear brake is braking so strong, there could be 2 possibilities here:
1, seized rear caliper in open position (less likely) - you can check it's free movement of rear wheel (don't forget to release parking brake)
2, seized from caliper in open position (more likely) - it's not braking well but rear is braking strong

I think ABS is ok because you changed it to another unit - but here - isn't there some procedure to set new ABS unit to work properly through diagnostics? Throug MES you can check also ABS's functionality (bleeding valves for example) for each wheel... ABS's function is also EBD (electronic brake distribution) which handle correct pressures between front and right brakes). So check docs if there must be also some calibration procedure throug diagnostics for new ABS unit...

Hi Jim,

there is a time when one has to throw the towel.

If all the basics and DIY'able (crushed pipes, seized caliper, etc.) have been checked, that time has come for your car to meet a specialized Guy and his brake bench. Don't feel ashamed or guilty, it happened (or will) to each of us ...

BRs, Bernie

If someone here helped You fix -or better, understand- your issue, hit the thanks icon @ bottom right corner, it's free and makes us feel helpy ;-)

Bernievarian said:

Hi Jim,

there is a time when one has to throw the towel.

If all the basics and DIY'able (crushed pipes, seized caliper, etc.) have been checked, that time has come for your car to meet a specialized Guy and his brake bench. Don't feel ashamed or guilty, it happened (or will) to each of us ...

BRs, Bernie

If someone here helped You fix -or better, understand- your issue, hit the thanks icon @ bottom right corner, it's free and makes us feel helpy ;-)

Click to expand...

That's a good idea.
Get it onto the brake rollers at an MOT station and see how each wheel performs. Quite likely the opposite one to the seiziing one is the culprit.

Thanks once more. The garage I'm working with *is* an MOT station with brake rollers - that's what makes it all the more puzzling!

Jim C said:

Thanks once more. The garage I'm working with *is* an MOT station with brake rollers - that's what makes it all the more puzzling!

Click to expand...

... and they can't find what's wrong ?

Disconnect the ESP module (unplug the cable) and test without it.

Check wheel speed sensors also, and a diagnostic on them.

cmosfxx said:

Disconnect the ESP module (unplug the cable) and test without it.

Click to expand...

Hi Chris,

could you be more specific (as per what and where to disconnect)?


Cheers, Bernie

Any light poping-up at the dashboard ? ASR/ESP warning would go on if an abnormal situation was detected, see what eLearn says about it:

"ASR/ESP warning light: the warning light flashes when the system cuts in to warn the driver that the ASR system has intervened due to road surface grip conditions. When the control unit detects an error in the ASR or ESP function, it turns on the warning light in fixed mode."

BRs, Bernie

If someone here helped You fix -or better, understand- your issue, hit the thanks icon @ bottom right corner, it's free and makes us feel helpy ;-)

and a few bits more:

"Via the CAN line, ABS control unit M50 is connected - from pins 15 and 26 - to the engine management control unit M10 and, from pins 14 and 25, to the Body Computer M1 and the instrument panel E50, to manage the ABS warning light and, if the problems concern the EBD function, the low brake fluid level/handbrake applied warning light, in addition to the ESP/ASR warning light."