New brake pads are spongy

Soldato
Joined
2 Aug 2012
Posts
7,809
It can cause a spongy pedal. With worn (scored/ridged) discs the clamping force is concentrated on a very small area of the pad (until it wears level to the disc) surface and in these high pressure area the can pad deform. More likely to be air in the OPs case though since a caliper was replaced.

+1

Though the effect is not great when only replacing single axle sets. However Brakes can feel very strange for the first hundred miles or so if you replace pads "All round" while retaining old disks! I advise people who wish to do this to do one axle at a time, a week apart if they do not want to replace disks at the same time!

The imperfect contact between new pads and old disks also means that all the heat of braking is generated at these points rather than over the whole disk surface. heavy braking before pads have bedded in can cause local overheating of the disks and is a major cause of disk warping after pad replacement. That is why you need to brake little and often untill the pads have bedded in propery.
 
Associate
Joined
11 Nov 2009
Posts
204
what car is it? It does sound like he has air in the system.

The handbrake should have between 3 and 7 clicks for mot standards

my order would be slacken off handbrake readjust to corect level and bleed the brakes

Alex
 
Associate
Joined
30 Oct 2009
Posts
473
Location
Camberley
Bet he bled the system with the rear brake compensator closed.
The car needs to be lowered onto the rear axle to open the compensator otherwise bleeding the rear is near impossible.
 
Associate
Joined
30 Oct 2009
Posts
473
Location
Camberley
Not a problem as your not doing the process.

on most cars there is a valve which is linked to the rear axle. As the suspension moves up and down on the road surface it alters the amount of fluid that is allowed to the rear calipers.

My betting was the mechanic has jacked the rear up which causes the wheels/axle to drop. Then changed the caliper and tried to bleed the system. As the axle was down the valve would have been closed, making bleeding difficult.

Take it back get them to bleed it again.
 
Soldato
OP
Joined
10 Jun 2010
Posts
5,158
Location
Scotland
Not a problem as your not doing the process.

on most cars there is a valve which is linked to the rear axle. As the suspension moves up and down on the road surface it alters the amount of fluid that is allowed to the rear calipers.

My betting was the mechanic has jacked the rear up which causes the wheels/axle to drop. Then changed the caliper and tried to bleed the system. As the axle was down the valve would have been closed, making bleeding difficult.

Take it back get them to bleed it again.

Yes, he did jack it up as he works from his home and doesn't have a ramp. Most likely what it is.

Thanks for the explanation.
 
Soldato
OP
Joined
10 Jun 2010
Posts
5,158
Location
Scotland
Took the car to another mechanic, a friend of my dads. Anyway to cut a long story short. He put it on the ramps and bled them again.

They're now back to normal and feel a hundred times better.

Thanks very much for all the advice. I would have drove around for weeks expecting it to improve going off the advice of the other mechanic.

Cheers again.
 
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