Great brakes, grotty pedal.

[Laney760]

Last year I had a nice new pair of high quality discs (and new pads) put on the 940 and the difference in the braking was amazing and I promised myself I'd have these discs put on the other axle at the next service, which I did recently, new discs and pads were put on the other axle.

However the brakes are fantastic but the pedal is spongey and there is a lot of play before you actually get to the brakes. My usual mechanic didn't do the work, another guy did. My usual mechanic doesn't think it is air when I took it back for him to take a quick look and neither do I, it doesn't feel like air but one morning when I got in the car this week and put my foot on the pedal first thing there was a really loud noise like a woodwind instrument at a concert which is making me wonder if it is air?

Fluid was last changed in 2015, about 60 thousand miles ago. My garage said that they'd checked the fluid and it had no water in it but are happy to change it for me if I want.

I don't recall having this pedal issue after the first set of discs were put on last year but to be fair the pedal had gone spongey before this 2nd set were put on.

Car has done best part of 200 thou, she had new clutch and brake slave cylinders in 2012, about 100 thou ago and has never had a new master cylinder.

[griston64]

Could be the vac hose and or valve from the servo ?

[Laney760]

Originally Posted by griston64

Could be the vac hose and or valve from the servo ?

Cheers, I'll get them to check.

[griston64]

Originally Posted by Laney760

Cheers, I'll get them to check.

You can still get the valve and the hose from Volvo

[Laird Scooby]

Sounds horribly like what happened to me while changing the front pads and renewing the fluid on my other beast the other day Ellie - master cylinder gave up the ghost!

Do you ever get times when the brake pedal either goes hard (with or without any actual braking happening) or goes straight to the floor with no braking and then release and it's back to what is passing for normal again?

[Forrest]

Originally Posted by griston64

You can still get the valve and the hose from Volvo

I replaced mine with these parts:

https://www.ebay.co.uk/itm/164147187091

https://www.ebay.co.uk/itm/223664955687 (The 8mm ID option)

That hose, like the original, is very thick and tough and stands no chance of going onto the fittings unaided. However, soaking the end in hot water from the kettle makes fitting it a breeze.

If I were doing it again I’d make the replacement slightly longer so it could be routed along the top of the bulkhead rather than over the cam cover like the original.

[griston64]

Genuine Volvo hose I bought fitted no problem at all

[Laird Scooby]

To test for the master cylinder :

Engine off, pump the pedal slowly a couple of times to exhaust the vacuum assistance from the servo.
When the vacuum is exhausted, pedal should feel fairly firm with minimal travel. Put a lot of pressure on the pedal and hold it. If the pedal starts dropping, however slowly, it's almost certainly the master cylinder.

To check for the servo working correctly :

Start the engine (preferably after the above test) and let it idle for a couple of minutes to build up a good vaccum. Switch off.
Wait 3-5 minutes and there should be enough vacuum left to give at least one vacuum assisted press of the pedal.
Once the vacuum is once again exhausted, maintain the pressure on the pedal (not necessarily full presssure, just what was used to check for vacuum assistance) and restart the engine.

As it starts, vaccum assistance should return and the pedal should move down a little to allow for the assistance. It should stop at that point but if it continues to sink towards the floor with little or no reserve travel, it's the master cylinder.

[Laney760]

Originally Posted by Laird Scooby

Sounds horribly like what happened to me while changing the front pads and renewing the fluid on my other beast the other day Ellie - master cylinder gave up the ghost!

Do you ever get times when the brake pedal either goes hard (with or without any actual braking happening) or goes straight to the floor with no braking and then release and it's back to what is passing for normal again?

Hi Dave

No, I don't get that but sounds like what happened when my 760 master cylinder went when I was out in the overtaking lane!

[Laney760]

Originally Posted by Laird Scooby

To test for the master cylinder :

Engine off, pump the pedal slowly a couple of times to exhaust the vacuum assistance from the servo.
When the vacuum is exhausted, pedal should feel fairly firm with minimal travel. Put a lot of pressure on the pedal and hold it. If the pedal starts dropping, however slowly, it's almost certainly the master cylinder.

To check for the servo working correctly :

Start the engine (preferably after the above test) and let it idle for a couple of minutes to build up a good vaccum. Switch off.
Wait 3-5 minutes and there should be enough vacuum left to give at least one vacuum assisted press of the pedal.
Once the vacuum is once again exhausted, maintain the pressure on the pedal (not necessarily full presssure, just what was used to check for vacuum assistance) and restart the engine.

As it starts, vaccum assistance should return and the pedal should move down a little to allow for the assistance. It should stop at that point but if it continues to sink towards the floor with little or no reserve travel, it's the master cylinder.

I will do/check this, cheers