Front brake imbalance

Post by **vanzep** » Mon Oct 20, 2014 11:25 pm

I have just fitted my new OEM brake master cylinder and im glad to say the occasional pedal creep (intermittent brake issue - spongy and goes all the to the deck normally in only town traffic but comes back on line after a few minutes) has gone and i can now stand on the brakes for the first time in years

I went back to my MOT station and asked them to retest the brakes and compare them to result from my MOT two months earlier. The brakes still have the same efficiency so the new master cylinder has cleared the pedal creep issue but the whole system is operating exactly as before which is not a major problem but i can see from the print out that there is an 10-12% imbalance in the front brakes whilst the rear brakes are spot on.

My question is what could cause this large an imbalance....
also does anyone have any reading from a mot/brake test?

Front calipers have been fully refurbed, brand new oem pads fitted, barely used set of mintex discs.
Its possible that one or both the mintex discs have a slight warp in them.

whew ive got that off my chest now

any thoughts or input would be appreciated

Post by **simonc** » Tue Oct 21, 2014 4:59 am

Good morning @vanzep, I read your post with much interest. I don't know if my saga is of any help but please take a look at my story regarding my brakes, perhaps once the guys take a look at what I'm asking and come back with their usual helpful direction, it may help you a little.

Here's the linky thing (please go to page 2 for the most recent news)

http://www.ludegeneration.co.uk/chassis ... 14009.html

89 UKDM BA4 4WS (resto job!) · Post by **wurlycorner** » Tue Oct 21, 2014 10:27 am

Brake imbalance around that sort of percentage is not unusual vanzep.

Pic of the brake test results for my 4th gen at last MOT, which had a 16% imbalance on the front and passed (rear brakes failed on that occasion but that's by-the-by).

macky_6 · Post by **macky_6** » Tue Oct 21, 2014 11:40 am

Could it be anything to do with wheel alignment? Can cause the car to pull to one side under braking?

Post by **Merlin** » Tue Oct 21, 2014 11:41 am

@3rd gen steve is your man for MOT questions

89 UKDM BA4 4WS (resto job!) · Post by **wurlycorner** » Tue Oct 21, 2014 12:59 pm

It's just a natural difference you'll always get from one side to another.

All sorts of things come into play...
Different length pipe runs, different diameter bore across sides (so different amount of fluid on each side, different amounts of resistance to the fluid flowing etc.) different behaviour of the flexi pipes from one side to the other (one might expand more than the other, also affecting the fluid pressure into the caliper) different efficiency of each caliper to the other, different resistance to the pad moving in the carrier, difference in the actual coefficient of friction between the disc and the pads on one side to the other etc. etc.
It will never be a perfectly balanced system.
And that's before you get into the tolerances in transferring the force into the roller and then tolerances in the machine measuring from one side to the other.

Post by **Thebusofwoe** » Tue Oct 21, 2014 1:04 pm

That % is absolutely normal chap. Anything more than 40-50% difference is a problem!!!

Post by **Merlin** » Tue Oct 21, 2014 1:07 pm

Do you feel the car pull to one side while braking?

Just to show off my 5th gen had less than 3% imbalance on the brakes when Steve MOT'd my car earlier this year

89 UKDM BA4 4WS (resto job!) · Post by **wurlycorner** » Tue Oct 21, 2014 1:15 pm

Scott560 · Post by **Scott560** » Tue Oct 21, 2014 6:49 pm

I replaced my discs/pads over a year ago before a track day, and they are now showing as 337 and 322 so that's about 5% diff.

I suspect if you have recently changed bits and pieces, it will take a while for things to settle/wear accordingly.