Rear Brake Imbalance

Todd Umptious

Hi all, had a search around and found quite a few threads on the topic but I'm hoping someone might be able to shed some light on my own situation.

Failed the nct recently and part of the fail was the rear brake imbalance which is at 32% while the limit is 30%. From some of the other threads their imbalance seemed much larger so I'm wondering what might remedy the problem for me.

I had the drums off a few months ago while doing the bearings and didn't notice anything out of the way with the shoe's etc. but naturally I was more focused on the bearings then.

The rear nearside tyre needs changing also and from the figures on the nct report that side seems weak when braking though I'm not sure if that would have big impact.

The figures on the report are:
Brake Effort

Nearside: 0.820kN
Offside: 1.200kN

Ovality
Nearside: 9%
Offside: 7%

Imbalnce
32%

The parking brake passed with:

Nearside: 0.820kN

Offside: 1.340kN

Parking Brake Effort 22%

Imbalance
39%

Car is a Corsa B without ABS.

Basically I'm just trying to figure out the best way to go about tackling the problem, all advice/input is appreciated:)

blackbox

If the friction surfaces are clean I expect it is due to a sticking piston in one of the rear cylinders.

Todd Umptious

I've seen the sticking piston mentioned a few times elsewhere, any tips on diagnosing it? Would it be more likely the weak side is sticking?

CJhaughey

Pull the rear drum off and see what the pistons do when someone pumps the pedal, Be careful don't pump the piston right out of the cylinder!
When you push the pedal, both pistons should move the same distance, if one seems to come out while the other one stays put thats usually a sticky piston.
You can clean them up and get them working again which is a cheap fix but they aren't very much to buy new.

Wheelnut

What about the obvious possibility that you got grease on the lining while doing the bearing?

Cogsy88

Maybe the the heat from the failed bearing seized one of the pistons. Also check the flexi pipes connecting to the drums as one of them could be perished causing an imbalance.

CJhaughey

I think post#2 covered that.

Cogsy88

Sorry can't see any mention of flexi pipes in post 2

CJhaughey

Cogsy88 wrote: »

Sorry can't see any mention of flexi pipes in post 2

We posted at the same time, I didn't mean your post I meant Wheelnuts about contaminated linings.

MAYOMICK

My car failed NCT a few years ago on a weak rear brake.The pistons seemed ok so I sanded the pads and disc on the weak side and it passed no problem.Since I always give that side a rub before NCT

nct tester

Todd Umptious wrote: »

Hi all, had a search around and found quite a few threads on the topic but I'm hoping someone might be able to shed some light on my own situation.

Failed the nct recently and part of the fail was the rear brake imbalance which is at 32% while the limit is 30%. From some of the other threads their imbalance seemed much larger so I'm wondering what might remedy the problem for me.

I had the drums off a few months ago while doing the bearings and didn't notice anything out of the way with the shoe's etc. but naturally I was more focused on the bearings then.

The rear nearside tyre needs changing also and from the figures on the nct report that side seems weak when braking though I'm not sure if that would have big impact.

The figures on the report are:
Brake Effort

Nearside: 0.820kN
Offside: 1.200kN

Ovality
Nearside: 9%
Offside: 7%

Imbalnce
32%

The parking brake passed with:

Nearside: 0.820kN

Offside: 1.340kN

Parking Brake Effort 22%

Imbalance
39%

Car is a Corsa B without ABS.

Basically I'm just trying to figure out the best way to go about tackling the problem, all advice/input is appreciated:)

Its quite possible that it only needs adjustment considering both the footbrake and handbrake are weak on the passenger side. The driver side reading are very good for a car that size. You could even adjust both sides, letting off the drivers side slightly, and adjusting up the passenger side. Best thing to do first if you dont have a lift (d.i.y. job) is get the back of the car up on axle stands and pull up the handbrake one notch at a time and check the resistance at both rear wheels.

Wheelnut

CJhaughey wrote: »

We posted at the same time, I didn't mean your post I meant Wheelnuts about contaminated linings.

I pointed out a reason why it could be contaminated, I don't think post 2 did that.

Eddie Smart

Try to clean the drum inside, use fine sanding paper, adjust the shoes up, make sure the wheel turns freely after the assembly. Your brakes imbalance so close to pass rate, so I hope you don't need to replace drums, shoes and brake cylinders.

Todd Umptious

Thanks for all the replies, ended up taking longer then I expected to get at the car so apologies for the delay.

After getting the drums off and giving the brakes a once over I decided to replace the pads. The passenger side has a lot of wear, it hasn't gone metal to metal but there isn't a whole pile of life left in them so now seems a good enough time to replace the lot.

All hoses and pipes were grand but I will need to give the passenger side piston a bit of t.l.c as it wasn't coming as far, only a marginal difference but may as well sort it when adjusting everything.

I'll report back after the re-test. Thanks again for the input.