Front brakes out of balance - MOT failure

[Roger Blassberg 0]

I took my VR (with 288mm front brakes) for its MOT, and it failed on out of balance braking with the nearside showing lower pressure. The pads and discs are brand new, and the calipers and sliders are not siezed. I dismantled the "offending" nearside caliper yesterday, and there is no sign of corrosion in the bore or on the piston, the piston moves easily and the slider pins are bright, polished, greased and straight. The dust seal is in good order and properly located. There is no binding - the piston releases properly. The flexible hose appears to be ok, no bulges or damage, and flows ok when bleeding.

 

Obviously I have bled the system. There is no pulling to one side under normal, moderate braking. ABS seems to be functioning, the light comes on and then off.

 

Anything else that could cause this? The car has not been used for the past few years, but I have replaced just about everything as detailed above.

 

Best wishes

 

RB

[malaki 0]

Are both the pads meeting the the disc with no corrosion on either face and was it that one giving low efficiency or the other showing to high or was it the rate of rise and fall that was causing the imbalance

[Supercharged 2]

Could be a collapsed hose and I'd expect you to really fee the imbalance on the road under heavy braking as the MOT spec allows for a fair bit of imbalance before a failure is given

[malaki 0]

You have to be out by over 25% to fail an mot on front brakes must be hose what was the reading on the opposite rear if low could be master cylinder

[plummer 0]

Had a NCT(Irish MOT) fail for the same and changing the hoses sorted me out.

[davidwort 0]

could the disks/pads be contaminated with oil from the replacement?, just another possibility. I'm assuming they were bedded in after the new parts were fitted, although I doubt one side would be so far out because of just that.

[Roger Blassberg 0]

The nearside front is the offending one; it failed on both ultimate stopping force and on rate of rise of pressure. Rears were balanced on both criteria.

 

As originally stated, discs are brand new with no corrosion, and the pads are new too.

 

It seems to be a hose issue based on your comments.

 

Thanks

 

RB

 

---------- Post added at 02:31 PM ---------- Previous post was at 02:22 PM ----------

 

David,

 

on your comments, I did give the discs a good going over with brake cleaner on both faces. The pads were straight out of the box. I didn't get a chance to give the brakes a proper bedding in as the car is neither MOT'd or taxed but, as you say, the lack of bedding in would be reasonably equal.

 

As above, I'll put new flexible hoses on and go from there.

 

Best wishes

 

RB

[Roger Blassberg 0]

Just to close this, after having dismantled and rebuilt the caliper and bled out the system, the problem has disappeared. I have new front hoses but not yet fitted them, so I have a spare set to put on sometime.

 

The other good news is that I now have a brand new MOT and can drive the car again, after nearly 4 years off the road. It's like falling in love again with a long, lost girlfriend!! Thank God that I didn't get rid of it when I bought the Stype R. New timing chains, guides, tensioners, all cooling system plastics, clutch, tyres, refurbed Speedlines, complete discs and pads all round, all brake pipes and most flexibles. Thoroughly cleaned interior (electric leather Recaros), spic and span engine bay. Just a few minor bodywork imperfections to sort out now.

 

Even Mrs B has shared my enthusiasm and pleasure, so maybe she can stay after all (I'll leave it to you to guess which one I mean........).

 

A "Good Day" !!!!!

 

Best wishes

 

RB

[davidwort 0]

so I wonder if it was new thick pads and full width new discs pushing the pistons back to where they hadn't been for a long time :) glad you got it sorted always nice to hear one going back onto the road