Rear brake imbalance

[JonC37]

Hi I hope someone can help. My Aygo failed the MOT for rear brake imbalance the nearside brake was much worse than the offside. I replaced on both sides the cylinders, shoes, adjusters, drums and fully bled both sides and adjusted the shoe gaps both sides. The retest failed with no  improvement. I am at a loss what to try now. Both flex hoses look fine. Is it possibly abs sensor or pump please?

[flash22]

foot brake or hand brake what is the imbalance figure

[Parts-King]

Handbrake cable sticking? Look for the simple things rather than worrying about ABS and pump

[JonC37]

Sorry footbrake. Difference of 39 between the 2 sides

[JonC37]

Handbrake is fine and both rear cables move freely

[flash22]

change the flexy hose it may have got clamped, crushed or failed internally

N/S hose 90947-W2021

 

[JonC37]

I actually have 2 flex hoses but they looked fine and flow was fine when bleeding 

[JonC37]

I actually have 2 flex hoses but they looked fine and flow was fine when bleeding. I assume with abs as there is a wheel sensor and abs pump behind the battery 

[flash22]

Hoses can look fine but collapse internally or close up under pressure

[JonC37]

Ok thank you very much I can fit the new hoses I have. Is it unlikely to be the wheel sensor? I assume servo and abs pump is ok as 3 wheels are fine?

[flash22]

hose, incorrect assembly of the rear brakes or a issue with the ABS valve for the affected wheel

you will get an error code and ABS light if it was the ABS sensor you would also be aware of it under heavy breaking - I assume the ABS light comes on and goes out when the car is started

[JonC37]

Yeah the abs light goes out fine. Brake assembly is fine and has virtually the same reading (2% improved) from the first MOT so shows brake components are not the issue 

[JonC37]

Is it possible the abs valve could affect just nearside rear?

[flash22]

ABS effectively splits the brakes into 4 - a line to each wheel the valve simply pulses the wheel that has lost traction by comparing wheel speed, yaw and steering angle

abs will throw a code if it has an issue

[Vandals01]

Try a full brake bleed i.e: Bleed the front as well as the rear.

Ideally, using a pressure bleed kit that forces brake fluid down the brake reservoir 

(Some car uses diagonal system where Front Left and Rear Right is one system.  Front Right and Rear left is another.  So trap air on the front could affect the rear.  Also the pressure should flush out any potential dirt or debris in the pump or ABS module.)

 

Next brake hose on the rear.

 

If that fails too, Brake master cylinder and ABS pump I guess...

[flash22]

it did cross my mind that it could be trapped air in the ABS block (which requires the ABS to be actuated with a scan tool) but you would feel that through the pedal. The same goes for the master

the rear brake is not sticking on - it's not getting the correct pressure to that wheel - the weak link being the flexy hose which maybe be expanding under pressure

incorrect assembly may be an issue it may have been put together wrong in the past

 

https://www.megazip.net/zapchasti-dlya-avtomobilej/toyota/aygo-38483/kgb10-56113/kgb10r-ahmrkw-919798/brake-tube-clamp-17856443

[Stecha]

On 8/2/2024 at 4:35 PM, JonC37 said:

Hi I hope someone can help. My Aygo failed the MOT for rear brake imbalance the nearside brake was much worse than the offside. I replaced on both sides the cylinders, shoes, adjusters, drums and fully bled both sides and adjusted the shoe gaps both sides. The retest failed with no  improvement. I am at a loss what to try now. Both flex hoses look fine. Is it possibly abs sensor or pump please?

I suggest, after you've done all that and if nothing else works,  possibly a rear wheel bearing fault

[flash22]

An ABS fault will put the ABS light on and log a code = instant MOT fail, if it was a physical issue with the bearing you will hear it and the tester will feel the play unless he has a white stick and a guide dog

[JonC37]

Thanks again for all your help. I rebuilt all the brakes around 4 years ago and did the rear brakes again this time so pretty sure the assembly is fine. I have bled all 4 wheels with a pressurised bleeder using about 1.5L of fluid so it's been bled to death. The fluid flow through the failed wheel was good when bleeding so happy no hose blockage. I ruled out the servo as I think that would affect more than 1 rear wheel. I don't have the diagnostic software to check the abs module, I do have another module but unsure if this needs remapping? I can change the hose to eliminate that. The issue is I can't really measure the brake performance at home.

[Vandals01]

1 hour ago, JonC37 said:

The issue is I can't really measure the brake performance at home.

You might be able to, but it certainly involves a second person.

Chock the front wheels, jack the rear of the Vehicle up and put it on jack stands.  One person in the driver seat, held the brake pedal steady with a foot.  Another person outside spin the wheel by hand and feel the resistance.

Not a very scientific way, but at least it will give you a rough idea.

 

Oh yeah.  Make sure the parking brakes are adjusted to the SAME TO both sides before you try the Peddle.  If the parking brake are out (say one side grip much harder than the other side), it will give you that brake imbalance.  Which was exactly the case on my friend's 2010 Smart ForTwo.  After the adjustment (to make sure each hand brake click gives similar amount of resistance), the brake imbalance went away.

[dads Taxi x3]

Hi so how did it got what was the problme an how did  you fixed it