V70 Brakes: Brake Pedal, No Resistence on 1st Press

[Ben960]

Hi, I have a strange issue with my brake pedal where after I start the car & pull away the first application of the brakes results in the pedal going nearly to the bulkhead & not feeling like there is any power assistence but if I lift off the pedal & press again it works fine. It doesn't do it again until I have switched off & restarted the engine & pull away again.
Also it seems to be ok if I brake in reverse for the first time just not forwards.
My Volvo is a V70 2.4 2006 & I did recently have a wheel sensor replaced although this was a few weeks before this problem surfaced.

Has anyone got any idea's?
Thanks,
Ben

[Ben960]

Update: The brake pedal now drops to the bulkhead everytime & is accompanied by a sound similar to a brake pad worn down to the metal. The brakes will still function if the pedal is pumped but I'm going to leave it until my mechanic can have a look now as it's too dangerous to drive.

[Kev0607]

There's a few things it could be;

1. A leak in the system, like a split brake hose or weeping brake caliper. Check all the calipers to see that they're dry (If wet, that would indicate a leak). Also check the master cylinder to see that the brake fluid is at the correct level.

2. Master cylinder not working properly

3. Brake servo leaking

You did the right thing by letting a mechanic have a look. Let us know how you get on.

[Ben960]

Just got the car back with one new caliper, new pads & new fluid & the brakes seem to working fine now. My mechanic said the inside pad had delaminated on the newer caliper that I'd only replaced a couple of years ago & on the older caliper which was seized the pad was missing completely from the metal back although a small piece of the pad had wedged into the piston causing it to move sideways.
My mechanic says the master cylinder may be on its way out as when the engine is running & the brake pedal is pumped the pedal still slowly goes back to the bulkhead, I've noticed this whe I've changed my brakes before but I'd always assumed it was a Volvo thing.

[Kev0607]

Originally Posted by Ben960

Just got the car back with one new caliper, new pads & new fluid & the brakes seem to working fine now. My mechanic said the inside pad had delaminated on the newer caliper that I'd only replaced a couple of years ago & on the older caliper which was seized the pad was missing completely from the metal back although a small piece of the pad had wedged into the piston causing it to move sideways.
My mechanic says the master cylinder may be on its way out as when the engine is running & the brake pedal is pumped the pedal still slowly goes back to the bulkhead, I've noticed this whe I've changed my brakes before but I'd always assumed it was a Volvo thing.

Glad the issue was sorted. I did think it was going to be related to either a caliper, a brake servo or faulty master cylinder (As noted above).

Your car isn't a diesel by any chance? If so, a sinking brake pedal whilst the engine is running at low RPM or idle is actually quite common & is considered normal. Its known as "diesel creep" (see below).

http://www.nbsbrakesupplies.com.au/t...ke-pedals.html

On that note, a sinking pedal at low RPM/idle appears to be common on Volvo's in general (not just diesel ones). As you drive, that pedal pressure should get firmer due to vacuum being generated (They shouldn't feel as spongy then). The first thing mechanics think of is there's an issue with the master cylinder because they press the brake pedal & it sinks to the floor whilst the car is idling. On many cars (Volvo, VW, Mercedes), this is just a normal characteristic of the brake pedal whilst at idle.

If you're brakes are spongy all the time whilst driving, then that could be related to the master cylinder or air somewhere in the system. However, if you drive the car & the brakes feel fine & stop the car well etc, then I wouldn't replace the master cylinder for the sake of doing it due to reasons mentioned above.

[Ben960]

Thanks for confirming that, it's not a diesel it's a 2.4 Petrol 170 but thats exacly how th pedal feels at idle. I'd guessed it was probably one of Volvo's fancy ways of not over stressing the braking components!
At least the brakes feel firm when I'm driving now so I'll just have to keep an eye on the pads to make sure they don't delaminate again. The pad in the newer caliper that delaminated still had a good 7 or 8mm left & was a Brembo which I've always thought was a quality make so I'm hoping the issue was caused by my previous ABS sensor problems possibly overheating the brake pads by repeatedly tapping the brakes while driving normally.