Changing Only One Side Brake Pads - Nothing Could Go Wrong?

[zakmuh]

Hi Everyone,

My 2005 Pug 407SW rear nearside brake is binding - causing a rapid pad wearing (4mm left and on the other side 8mm left).

I need to sort out the caliper (or the hand brake cable or both?) and then change both sides pads. According to the theory, I should change the pads on both sides for equal braking.....

Now...why there is nothing wrong with current braking, no pulling to a side? So I can only change the worn one and leave the other as it is?

Please share your points

Many thanks

[Mammasaid]

Pads are bought in sets of 4 (2 per axle) therefore use all 4 and have nice even braking performance.

[zakmuh]

Thanks and thats what I will do regardless.

But as the matter of fact, having one side thicker pads to the other, I can't see how the braking would apply an uneven force? The hydraulic pressure pushes the pads till touches the disc- so the distance between the pad face to disc doesn't matter

Cheers

[Krikkit]

I think it's more that the worn pads will be replaced with a different set - giving slightly different frictional properties which can lead to axle imbalance.

[Peanut Gallery]

If the composition of the pads is exactly the same, and they have been treated exactly the same way, then I doubt you would feel no difference in the braking. However, getting the composition exactly the same, baked the same, etc, is neigh on impossible! - two snowflakes and all that.

Also as you will be winding back the calipers to take the new pads on the near side, then this caliper will have slightly more ease of movement than the offside one, should you not change the offside one.

In the future, will you check the nearside brake thickness, see it is fine, and not look at the offside brake thickness?


Though to be fair, I admit I have been wrong and changed only one side of a rear drum brake, one side had stuck on, and you had to take apart the bearing etc to get the drum off. I knew both had been changed recently anyway, so the other side was fine.

[zakmuh]

The master cylinder transfers the force to all 4 wheels through 4 pipes- equal brake fluid. So the reservoir give more fluid if required. Therefore the braking force applied equally.

This is my understanding but please do correct me, if I'm wrong

[stevieturbo]

zakmuh said:

Hi Everyone,

My 2005 Pug 407SW rear nearside brake is binding - causing a rapid pad wearing (4mm left and on the other side 8mm left).

I need to sort out the caliper (or the hand brake cable or both?) and then change both sides pads. According to the theory, I should change the pads on both sides for equal braking.....

Now...why there is nothing wrong with current braking, no pulling to a side? So I can only change the worn one and leave the other as it is?

Please share your points

Many thanks

Well clearly there is something wrong with the current braking otherwise the pads would not be wearing unevenly.

[paintman]

Check the handbrake cables aren't incorrectly adjusted - or seized - & holding the pads to the disc on one side of the car.
The lever on the caliper needs to be in contact with the stop when off. Same issue on the 307.

Edited by paintman on Tuesday 7th February 19:40

[Peanut Gallery]

zakmuh said:

The master cylinder transfers the force to all 4 wheels through 4 pipes- equal brake fluid. So the reservoir give more fluid if required. Therefore the braking force applied equally.

This is my understanding but please do correct me, if I'm wrong

In a very simple system, yes, the master cylinder does provide an equal pressure. I have had a twin system master cylinder fail, so I had normal braking front right and back left, front left and back right did not do any braking. Interesting driving.....

If the system is working correctly, you will get the same PRESSURE on the brake pads on both sides, but note that different brake pads can apply different braking force for the same pressure.

[trickywoo]

If you do that you'll always have one side that needs to be replaced before the other.

Nobody is going to ever sell you two pads so you'll always have two 'spare' from a set.

If it was a rushed 'get you home' job done in a less than ideal location I'd do one side and then the other ASAP.

[zakmuh]

Hi,

I'm back with an experiment result:

I replaced the particular worn pad with a new one and did a 250-mile drive to London on M1. When it was safe on the straight stretch on the motorway, I applied braking firmly and took my hands off the steering wheel to check if the car gets pulled to one side - nope, it went on straight line without any side pulling.

I did a thorough research + watching brake system videos, I'm certain that regardless of pad thickness, when you depress the brake pedal, it puts equal force on all four discs. The reason being...we rewind the piston , replace pads and then pump brake until the pressure is reached. This takes 3 to 5 pumps.

Thanks for everyone for their advice. I will change all four pads for rear brake to keep them all in same thickness

Cheers

Edited by zakmuh on Tuesday 21st February 11:58

[HustleRussell]

zakmuh said:

Hi,

I'm back with an experiment result:

I replaced the particular worn pad with a new one and did a 250-mile drive to London on M1. When it was safe on the straight stretch on the motorway, I applied braking firmly and took my hands off the steering wheel to check if the car gets pulled to one side - nope, it went on straight line without any side pulling.

I did a thorough research + watching brake system videos, I'm certain that regardless of pad thickness, when you depress the brake pedal, it puts equal force on all four discs. The reason being...we rewind the piston , replace pads and then pump brake until the pressure is reached. This takes 3 to 5 pumps.

I love how you think you're educating people on braking systems now

[zakmuh]

Lolz Ta for that Russell

I'm not a mechanical engineer, nor a brake system expert. Lots of people, including me, have been in a situation where one pad is worn and you gotta get to destination B within a limited time frame. In this moment you can't take it to the garage and replace all of them. The quickest one is just to change that single pad and then sort all them out later, professionally.

[John in Cornwall]

Brake pads are replaced in sets of four because that's the way they come. Manuals always say, 'replace all four pads at the same time', but is this an urban myth?

in my long experience no sets of pads wear down evenly - it's quite frequently the case that one side, or even one pad, will have much less wear than the other. This may indicate a fault (for example, a binding brake on one side) but not necessarily.

Let's conceive of a situation whereby you've saved these 'not so worn' pads and use them to replace the very worn ones next time they are replaced, is this OK? In my view, 'Yes', because it's difficult to see what the problem would be. Ah, you say, but the pads will be slightly scored and the discs will have slightly different scoring, so the braking efficiency will be impaired. Theoretically, yes, but the breaking pressures are so great that the effect will be negligible - and what's the difference with new pads on a worn disc? Also the pads will bed-in very quickly whether new or 'reused'. One could also say that 'part-worn' ( realistically only 'nearly-new' would be worthwhile) second-hand pads could be used - don't throw up your hands in horror - people say 'never use part worn secondhand tyres because you don't know where they've come from' - but what about the tyres on that secondhand car that you've just bought (how do you know they haven't be kerbed, etc?)?

What is true is that discs do wear out once to every two to three sets of pads, and, yes, if the disc is scored it will wear out the pads quicker.

In my view there's little point in putting NEW pads on one side only, but I think there is a case for keeping part-worn pads and using them next time to replace the very worn ones. Just make sure there isn't a reason why the pads are wearing at different rates.