Brakes problem

Hi folks,

A very strange thing happened to me a few weeks back. I was in town doing some bits and pieces and I did a lot of driving around in my 760. I stopped for a crossing, and when it was free to go I put my foot on the gas peddle and the car shifted but with protest.
So I stopped and felt the front wheels which where abnormally hot. So I think the frond brakes must have been braking for a while. Anyway, to cut a long story short, I had no tools with me so I decided to drive home with frequent stops to let the front disks cool of. After a few miles they loosened up and seem to be honky doory, so I carried on home as normal. Now yesterday I was stuck in a traffic jam on the York ring road and as I was stopping and going and stopping and going the same problem accured again and when back on the dual carriage way towards Leeds everything loosened up again.
I can feel the break peddle having no free travel during these incidents.
I have checked if the pistons in the callipers are stuck, but they seem to move quite freely.
Has anyone any suggestions on what it might be?

Tulip :-(

1990 760 Turbo Auto Saloon B230FT 226.500

If the pistons move freely then I suspect the brake fluid or even the master cylinder. Try bleeding the brakes with freesh and good fluid.

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1995 Volvo 945 LPT Auto +170k
1991 Volvo 945 GL Auto +150k
1989 Volvo 765 Turbo Auto +150k
1988 Volvo 745 GL +220k

[ivor940]

I remember reading in a "Car Mechanics" magazine article on servicing a 940 that the front caliper assembly was known to seize on the carrier ( even though the piston could be free). This means that the pad on the non-piston side will be held against the disk while the piston side one could be free. They recommended removing the piston ( sliding) part of caliper from the fixed part of the caliper( attached to hub) and cleaning off corrosion / debris and applying Coppaslip (or similar ) to the sliding metal surfaces of the caliper. Hope this is of help.

ivor940


VOC member

Hi Ivor940,

Thanks for the tip, I'll give it a go

Rob

1990 - 760 Turbo Auto Saloon - B230FT

Hi George,

Thanks for replying.
I blead them but no success. I thing a new master break cylinder should be given a chance. I'm in the States at the moment. Do you know if break cylinders as sold in the UK where the same as in the US?
I have a feeling that due to the weak Dollar parts like this might be quite cheap.

Best Wishes

Rob
(Tulip)

1990 - 760 Turbo Auto Saloon - B230FT

[Peter Milnes]

The rear brake balance valve should be checked as they sometimes cut off all rear braking effort and are a pig to bleed properly when they are on the way out.

All the best, Peter.

[classicswede]

It could be condition of brake flexis - they can collapse internally and act as a semi one way valve. The pressure from applying brakes forces past the restriction and it can be slow to return. This does not happen everytime - it can depend on various factors including how hard the brake pedal is applied. we had this happen on a 200 series. For what they cost it could be worth renewing anyway unless you know their history. It is also important to cahnge brake fluid regularly (every 2 years).
Dai

Hi Dai,

Thanks, I'll give it a go.

Rob (tulip)

1990 - 760 Turbo Auto Saloon - B230FT

Hi Peter,

The rear brake balance valve was changed last August together with all the pads (front and Back)and the fluid, and brakes worked OK till recently. I think that Dai has a point because I don't know how old the flex hoses are, ie. I never replaced them. However thanks for replying though,

Rob (tulip)

1990 - 760 Turbo Auto Saloon - B230FT