Braaaaakes, before I start

[Laird Scooby]

Originally Posted by Skyedriver

OK, Volvo master cylinder no longer available..
A couple of on line suppliers such as "Onlinecarparts" and "Bestpartsstore" advertise them but have no knowledge of these companies. Price £113 + P&P (about £9 poss more to Scottish Highlands)
Skandix don't list them, nor Biggred, Braydon/Sentinel put me on hold them cut me off.
Jamie at Parts for Volvo did a search and came back with no longer available.
Few second hand ones on ebay but that's just buying possible trouble.

It's part no. 3530354 if anyone has a known good one.

Cheers

Online/Bestparts are generally fairly good, both on quality/price and delivery. As far as i could tell, BiggRed listed a repair kit, also found this one from your prat number :

https://www.autohausaz.com/pn/6819771

There are several interchangeable parts too it seems :

https://www.yoyopart.com/oem/7090311/volvo-3530354.html

However, it might be you need to match what you've got make for make.

[Skyedriver]

M'C ordered from Bestparts, no note yet re delivery
Ditto front pads
Fresh bottle of Dot 4 at the ready

Thanks to all who offered advice

[Skyedriver]

Bringing this to a happy conclusion.

One debonded front pad
One knackered Master Cylinder
One seized caliper slider

This on a car that a month ago posted good readings on an MoT brake test.
That was less than 1000 miles ago.

Anyway M/C and pads came from Bestcarparts which along with another name that escapes me is part of a German seller Autodoc it seems.

All back together and bled with my 30+ year old Gunson Ezibleed.

Managed to change the plugs inc the back one while the M/C was off.
And slotted the heat shield holes for easy removal for future access.

Thanks to all who offered assistance.
If anyone wants a knackered M/C to rebuild before it goes in the bin, drop me a line.

Tony H

[Laird Scooby]

Originally Posted by Skyedriver

Bringing this to a happy conclusion.

One debonded front pad
One knackered Master Cylinder
One seized caliper slider

This on a car that a month ago posted good readings on an MoT brake test.
That was less than 1000 miles ago.

Anyway M/C and pads came from Bestcarparts which along with another name that escapes me is part of a German seller Autodoc it seems.

All back together and bled with my 30+ year old Gunson Ezibleed.

Managed to change the plugs inc the back one while the M/C was off.
And slotted the heat shield holes for easy removal for future access.

Thanks to all who offered assistance.
If anyone wants a knackered M/C to rebuild before it goes in the bin, drop me a line.

Tony H

Glad you got it all sorted Tony! The other name that escapes you is probably onlinecarparts, i've found they're linked with bestcarparts in the past, probably still are.

You'll have a PM shortly, do you happen to know the make of the master cylinder at all?

[Buryan]

SKYEDRIVER - YOUR BRAKES - I have had exactly the same very dangerous problem with my V70 about two years ago. The answer is the ABS. Remove the fuse for the ABS and the brakes are back to perfect normal. I started to experience your problem and disaster neatly happened. There was a temporary light and a row of parked cars with the main traffic flowing past me in the opposite direction, on a busy main road. I applied the brakes - sponge and virtually nothing else. I pumped the brakes - not a lot of braking and I shot between the line of parked cars and the ones approaching. HOW I never hit anything, I shall NEVER know. By the time I came to a halt, I was a quivering wreck! The garage could find nothing wrong with the brakes at all - no loss of fluid - and has no idea why they work perfectly when I remove the ABS fuse and are LETHAL when the ABS is connected. Fuse in for MOT. Fuse out as soon as the car passes. No problem ever since. Obviously Volvo should be asked if this is a known problem.

With best wishes,
Buryan aka Kenneth!

[Laird Scooby]

Originally Posted by Buryan

SKYEDRIVER - YOUR BRAKES - I have had exactly the same very dangerous problem with my V70 about two years ago. The answer is the ABS. Remove the fuse for the ABS and the brakes are back to perfect normal. I started to experience your problem and disaster neatly happened. There was a temporary light and a row of parked cars with the main traffic flowing past me in the opposite direction, on a busy main road. I applied the brakes - sponge and virtually nothing else. I pumped the brakes - not a lot of braking and I shot between the line of parked cars and the ones approaching. HOW I never hit anything, I shall NEVER know. By the time I came to a halt, I was a quivering wreck! The garage could find nothing wrong with the brakes at all - no loss of fluid - and has no idea why they work perfectly when I remove the ABS fuse and are LETHAL when the ABS is connected. Fuse in for MOT. Fuse out as soon as the car passes. No problem ever since. Obviously Volvo should be asked if this is a known problem.

With best wishes,
Buryan aka Kenneth!

When was the brake fluid last changed? Also what about pads? It sounds very much like a master cylinder fault, and a dangerous one at that! Could also be an ABS modulator fault, either way you need to get it sorted as driving around in 1.5T of unbraked Volvo isn't going to be pleasant for you or what/whoever you hit!

[Ian21401]

Purely out of interest and not a criticism.
I don’t understand how a master cylinder fault can manifest itself when the ABS is operative but not when the ABS is disabled.

[Buryan]

Ian - I don't understand it either and neither does my local MOT garage.

Laird Scooby - you say an ABS Modulator fault - can you explain that to me please? How does the ABS 'modulate' and what happens when it is 'modulating'?

Thanks.

[Laird Scooby]

Originally Posted by Ian21401

Purely out of interest and not a criticism.
I don’t understand how a master cylinder fault can manifest itself when the ABS is operative but not when the ABS is disabled.

Originally Posted by Buryan

Ian - I don't understand it either and neither does my local MOT garage.

Laird Scooby - you say an ABS Modulator fault - can you explain that to me please? How does the ABS 'modulate' and what happens when it is 'modulating'?

Thanks.

My suggestion is based on the theory the master cylinder is marginal at the moment - borderline failure if you prefer.

The valves within the ABS modulator take a bit of pressure to overcome them., however as far as i've always been aware, if the unit goes into "failsafe" mode (eg when a fuse has failed) it reverts to normal braking mode so doesn't operate the valves within the modulator. As such, it operates like a normal braking system.

With the system operational, because a slight bit of extra pressure is needed to open said valves, that could be enough to cause the seals in the master cylinder to temporarily let fluid by. Also air within the system may cause the same problem.

It could be that if the fluid hasn't been changed in a long time or if the bleed nipples weren't opened when renewing the pads, some dirt has been forced back into the modulator and is holding something open within.

Might well be worth changing the brake fluid completely and see what improvements occur. Use an Easibleed, apart from getting the car in the air with the wheels off, the whole job only takes about 20 minutes with one of those.

When the ABS system is operational, it will detect if a wheel stops turning prematurely - locks in other words under braking. It then pulses the fluid to the caliper associated with that wheel - modulates the pressure - to release and re-apply the brake on that wheel to aid effective braking.