Help - Failed MOT on brake imbalance

[oakleydad]

This is the first time my Elan has been for an MOT (purchased 1 year ago) and keeps failing on brake imbalance - see report attached. The report is in order 1st page was first test etc. I replaced the front brake callipers with refurbished ones, no difference. The pads are in good shape, I have bleed the breaks, taken it for a 20 + mile blast to make sure the brakes have bed in. The car pulls up straight doesn?t pull left or right.
I was wondering if the testing station is being too draconian (not really sympathetic guy who runs it - I don?t think he actually like cars)
It really frustrating ? the weather is fantastic at the moment and I cant use the car.
Any advice would be really appreciated.

scan.pdf

Brake imbalance report

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[memini55]

Looking at the report, keep in mind we don't have these on our side of the pond, I see the word pass on brakes and handbrake? I know I am missing something, is it the fact the fronts are light in relationship to the backs?

Does your +2 have servo's? One could be not working to the task. Ours had servo's and I took them off and like the braking without them.

Sorry not much help.
Mark

[nebogipfel]

Those MOT report forms always confuse me but as Mark says it does appear to say Pass in all the categories.

What is he actually not happy with?

It sounds like your best solution would be to find another garage for your test.

There must be one on the FBHVC list.......... http://fbhvc.co.uk/mot-garages/

[UAB807F]

I'm also struggling with this one, it seems to say "PASS" in all the right places. Just looking at one sheet it says "Lock Imbalance" of 50% on the rear axle with a limit of 25% which I'd guess might be what he's on about, but it still says "Pass" and all the others are quite low.

If the guy can't (or won't) explain in simple English using the data from the test as to where the fault lies, then I'd be tempted to take it somewhere else. It'll cost you another ?50 or so, but you might get a bit more help next time.

[JJDraper]

Are the tyres the same on the back wheels? Could one be less 'sticky' than the other, leading to a different lock up reading? Try shifting wheels from front to back. Just a thought...

Jeremy

[oldelanman]

I presume the failure is the 34% max imbalance recorded on the front brakes?

Brake test rollers run at very low speed (around 2mph) so they do not properly simulate braking under normal driving conditions and can produce "faults" which do not manifest themselves on the road...ie brake imbalance on the rollers does not necessarily give rise to brake pull on the road and this can make it difficult to diagnose and rectify.

From your description you've changed the calipers but not the discs and brake pads....so I suspect that's where your problem lies. Maybe a slightly scored disc or glazed pads on one side ? If it's just the pads, roughing up the surface may be enough to overcome the problem. Unfortunately though, as the brakes don't pull to one side on the road, you won't know if you've fixed it without another test - and another potential failure.

Another thing which can cause spurious roller test readings is if tyre pressures are not equal left and right - I assume you've checked them?

Good luck.

[elan_fan]

If you haven't changed the pads, swap just one pad from each front side to "mix" the pads in case you have got a problem with the pad sets. Also tell your man to use the tapley on it, or take it to another garage and tell them it has a limited slip diff as they cannot put it on the rollers as the machine doesn't work properly and they have to do it old school. TBH if you are taking a Lotus Elan to a bloke who doesn't like cars you are asking for trouble a bit, whats next, is he going to tell you that the pedal box is flexing and needs bracing? On the flip side though there is no reason why an Elan should not pass this test so keep persevering. Oh how old are your brake hoses?

[oakleydad]

Thank you all for you advice on this subject. As I understand it the imbalance is measured as a % of the braking force between the left and right side and has varied between 34% on the first test, then 30% on the second then 44% on the last. I think the limit on the front is 25%. I have 6 month old braided hoses on the front, tyre pressures are the same on both fronts (28psi) I have a single servo and that seems to be working fine and anyway what beats me is there is a single pipe line from the master cylinder to a 4 way "splitter" - 1 input, 2 lines to the fronts and 1 to the back which is then split again to the rear callipers. I'm going to swap pads around as was suggested, check the disks and bleed the brakes again. Im also going to take to a more sympathetic MOT testing station next week.
Stay tuned and I'll let you know what happens !

[oakleydad]

After my last post, I looked through the list of classic car mot stations that "nebogipfel" posted - and blow me down the garage I was thinking of going to take it to is listed !

[alexblack13]

You could also just try leaving it with them to 'fix'.. If that is the only issue. Just tell them to fix it and then go pick up your car with shiny new mot.

Then as a wee test and with MOT in mitt.. Ask him to show you another test being done....

Bet that would put the wind up them.

Al. ....

[nebogipfel]

After my last post, I looked through the list of classic car mot stations that "nebogipfel" posted - and blow me down the garage I was thinking of going to take it to is listed !

Hope it solves your problem

[simonknee]

Clapham North Motors post162434.html

[oakleydad]

Latest update - Replaced the 6 month old Goodridge front brake hoses yesterday with the same new ones, old ones looked OK though. MOT today the garage new the history (see previous posts) so put the car straight on the rolling road to test - still break imbalance - 200Kg force on rhs and 150Kg on lhs. Really helpful though didn't charge for the test, so next thing is to swap over the pads and disks from right to left, to see if the problem moves. Again the garage will put it on the rolling road to check it out before the full MOT.

[Chancer]

Are you sure its not just a weight distribution problem?

A polite way of saying a fat ba5tard MOT tester

Assuming your car is RHD from the figures you give it seems to me to be reason, put 4 bags of cement on the passenger seat next time or find a thinner tester

I used to have similar problems on my bike engined Caterhams but usually on the handbrake, I once had to hang on the back of the car for the SVA tester for him to get the right readings but that was more that his manual had the brake testing figures for a heavier Rover engined vehicle

[oakleydad]

Conclusion - I swapped the disks and pads from left to right to see if the problem would move, and while checking the pads (on the weaker side) I noticed patches that went worn and also the pads were not even thickness across the face (about 1mm difference) Some deft work with course sandpaper to flatten them down and then reinstall. Took it to a new MOT station just down the road and it passed - no problems (apart from an oils leak). Thanks for all your posts - the lesson here is to check the obvious things fist it would have saved me a lot of time. But I reckon I can do a front brake overhaul now in 2 hours from start to finish !