Technical rear brakes balance

[Pandaki]

We passed KTEO (MOT equivalent) today...
All good exept the rear left brake is -20% and the guy told me to check and balance the brakes. Is that a DIY task or we have to go to the hospital?
To my ears it doesn't sound too bad... it doesn't affect handling either too much or at least at a feelable level...

But can it cause more damage if I leave it as is for a while?

 

[jangcy]

But can it cause more damage if I leave it as is for a while?

If you try to brake emergency at 100km/h it may turn your car around...

If brake pipes are not dented or smashed it could be rear brake "cylinder" (maybe some leaks) or rear brake shoe are differently worn.

 

[Pandaki]

If you try to brake emergency at 110km/h it may turn your car around...

I had that situation when returning from Serbia. The car went straight...

and I was driving on ice a few days ago and I wanted to try the winter tyres' ice braking behaviour... again brakes on the car on a perfect straight line...

that's what i mean feelable level

 

[jangcy]

So maybe there was some dust, mud ect on tyre etc when car was testing....that's way there was some different...
or when you had that situation brake was ok and then started small leak...good to open it and check inside...

 

[Pandaki]

Yeah I'll have a check of the drum and the shoes when I find some time...

The guy there used the word "regulation" or "adjustment" or "calibration" and gave me the idea that it's something there to adjust the force or somthing like that...

Must be somthing with shoes or drum though cause I got the same efect with handbrake as well.

It must not be something urgent though... I hope... cause at the momment i'm out of time... and money

And I believe I won't destroy something else if I live it like this (for a while), or no?