Allegro Club International

[Colin T]

My car has a front brake imbalance of 18% and only just passed the MoT.

I suffered from warped discs last year, and when they were replaced the garage told me that the calliper pistons were all free.

What could be causing this? I can only think of the pistons or yoke - can I check these without having to from the hydraulic system? What else could be at fault?

Any help would be greatly appreciated!
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Hell has frozen over...... the car formally known as 'Heap' is back on the road!

[M. Irvine]

Colin,

As you have said I would be wise to check that everything at the caliper is working correctly. I would also check the pads for grease contamination and even temporarily swap a pad from one side to the other to see if it has any effect. Be very careful doing this if any unusual wear of the pads has taken place. (The pad materials can vary slightly).

Also, do the brakes 'pull' on the road? Are the front tyres the same make and with similar tread depth? Were the tyre pressures correct?

Roller brake testers don't always respond like a normal road surface. My 1100 had brake front unbalance for many years but I could never find any cause and the car stopped in a straight line under heavy braking on the road. One year I stayed in the passenger seat (a very understanding tester!) and the brakes were quite even! Don't tell VOSA!

Merv.
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[Colin T]

Thanks for the reply Mervyn - I had new pads fitted when the discs were swapped (well, three new pads - the fourth wouldn't fit apparently, Laurence said he had the same problem and filled it down to fit. I have now filled my fourth down so need to fit it. Could having one old pad cause the problem i.e. slight differences in material and age/wear? I don't use the brakes a massive amount in relative terms as the majority of my mileage is motorway.

I'll have to check to see if they pull. I usually slow down as gently as possible and try to avoid slamming the brakes. I'll try an emergency stop and see in what direction the car heads.

The front tyres are identical make/depth, but at the MoT I'm not sure if I did check the tyre pressures - I hadn't used the car for a couple of weeks at least due to snow and the test station is one minutes walk from my house, I remembered that I wasn't critical about doing the pressures just for the MoT, but I am usually (every week, even though I only use the car once/twice a week). The pressures do tend to rise/fall identically for both tyres.

Could wheel imbalance be a factor? I swear my car developed a wobble/vibration after I last had them all balanced, when they had the weight amount changed by quite a bit (I reckon the balancing machine might have been dodgy! I need to get them rebalanced to prove it though).
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Hell has frozen over...... the car formally known as 'Heap' is back on the road!

[M. Irvine]

I cannot see that tyre/wheel unbalance could have any effect on brake balance, so from what you have said, the most likely cause is a material variation.

Merv.
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ALLEGRO = Agile, Lively, Legendary, Economical, Genial, Reliable & Outstanding.

[Laurence]

Hi Colin,

Since you have completed the repairs etc to the brakes, have you bedded the brakes in?

I know what you mean when you mention the snow/ice etc we've had recently, so you haven't taken the car out much, which means the brakes are a bit 'green'.

I don't use my VP 1500 that much although I drove it to Stafford for the Christmas holidays & have just got back from a weekend in Beddau, South Wales.

I always 'scrub' the brakes in @ the start of the journey, just to make sure all is OK & that the brakes are efficient.

I drive the car with the handbrake partially applied (one click on), & wait a few seconds until there is a noticeable 'drag' & then release the handbrake fully. This means they are scrubbed-in

I also 'drive against' the brakes a couple of times to make sure all the brakes are scrubbed in. I make sure that no-one is following, then apply the brakes with my left foot for a few seconds & apply the accelerator with my right foot.

Bedding-in new brakes needs 6/10 stops of moderate force slowing from 35/40mph to about 5mph in quick succesion.

On the way to the MOT test station, I always scrub the brakes in so they are efficient for the test.

[Colin T]

Hi Laurence, the brakes were done in July or August (new discs and three new pads). It's taken me a log time to get around to filling down the fourth pad, so I'll fit it this week and get the brakes bedded in thoroughly and see how it is.

I worked out that I should only need to use the brakes fewer than 20 times between York and my Dad's house in Hampshire. Most of my braking is from 30mph or less.

I might wait until the brakes are bedded in, then arrange for a brake imbalance test and go for a run immediately beforehand to scrub in the brakes as you have said.
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Hell has frozen over...... the car formally known as 'Heap' is back on the road!

[Colin T]

Well, I've tried to fit the new pad to the offside outer position but failed. I couldn't get the yoke to move back far enough, it was fouling the new pad by about 2mm at least. I tapped the inner piston into the calliper and then tapped the yoke towards the outside of the car, but it didn't move far enough.

I have now read the manual and it says to release the bleed nipple one turn in addition to what I was doing, so I'll give that a go and see if that does the trick.
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Hell has frozen over...... the car formally known as 'Heap' is back on the road!