S40 V40 Cars: - Master cylinder or ABS? Spongy and rumble

oliverpervasive · Aug 30th, 2019, 15:35

S40 1998 x reg 1.8 petrol auto

Recently developed spongy brakes when driving/ignition on
No lose of brake fluid from expansion tank
No sign of any leaks around wheels/ all nipple bleed areas etc

However when I set of there is an initial rumble like the abs has come on for just a second.

Do you think it is a faulty master cylinder?
None of the other articles mention this funny rumble/vibration noise so just wondering if it could be something else like a faulty abs unit.

Many thanks for your thoughts :-)

OP

oliverpervasive · Aug 31st, 2019, 18:04

Buying a Pagid brand replacement master brake cylinder from Eurofarts for £100.
Looked on PFV for a volvo master cylinder but could not find one. Off to Tesco to buy a turkey baster to empty the reservoir.

No codes have come up but I think this model has only the basic ECU info to OBD11

oliverpervasive · Sep 3rd, 2019, 19:48

So tested master cylinder as per Haynes manual - seems fine (phew can take the new one back as not taken out of box)
Next suspect was servo - seems fine = hold vaccum. Grommit lubed - all looked good.
We disconnected this ( stuck bung in the valve) and drove without assisted brakes - needed lot of force on pedal - we still got the one second rumble as you accelerated off.

It must be something to do with the ABS. Possibly the self test it does.
Took it for a burn on gravel road - wacked on brakes - ABS kicked in fine.

We tried driving with the boot up to see if we could positively ID the rumble as coming from ABS - but too tricky and dangerous.

Im not sure what to try next = possibly wheel sensors giving bad reading?
No error codes coming up.

magnuz · Sep 3rd, 2019, 23:24

Also check the reluctor rings around the CV joint. I have known them to split.. The sensor will detect the wider tooth gap where the split is & the system may think the wheel is about to lock!

oliverpervasive · Sep 9th, 2019, 16:11

I washed it including a spray under arches,reset the ECU and took it for a thrash and emergency brake repeatedly......erm ….its all gone.

No ABS/rumble when first set off or spongy brake.

I'm not sure what we did which fixed it but its fine now.

My friend reckons it was lubing the grommet on the servo/my bet is the ECU.

Never had any error messages or lights.
Ho hum.

Aug 30th, 2019, 15:35	#1
oliverpervasive Member Last Online: Feb 4th, 2021 14:56 Join Date: Jul 2008 Location: london	Master cylinder or ABS? Spongy and rumble S40 1998 x reg 1.8 petrol auto Recently developed spongy brakes when driving/ignition on No lose of brake fluid from expansion tank No sign of any leaks around wheels/ all nipple bleed areas etc However when I set of there is an initial rumble like the abs has come on for just a second. Do you think it is a faulty master cylinder? None of the other articles mention this funny rumble/vibration noise so just wondering if it could be something else like a faulty abs unit. Many thanks for your thoughts :-) OP

Sep 3rd, 2019, 19:48	#3
oliverpervasive Member Last Online: Feb 4th, 2021 14:56 Join Date: Jul 2008 Location: london	ABS it is - I think. Not sure on next step. So tested master cylinder as per Haynes manual - seems fine (phew can take the new one back as not taken out of box) Next suspect was servo - seems fine = hold vaccum. Grommit lubed - all looked good. We disconnected this ( stuck bung in the valve) and drove without assisted brakes - needed lot of force on pedal - we still got the one second rumble as you accelerated off. It must be something to do with the ABS. Possibly the self test it does. Took it for a burn on gravel road - wacked on brakes - ABS kicked in fine. We tried driving with the boot up to see if we could positively ID the rumble as coming from ABS - but too tricky and dangerous. Im not sure what to try next = possibly wheel sensors giving bad reading? No error codes coming up.

Sep 9th, 2019, 16:11	#5
oliverpervasive Member Last Online: Feb 4th, 2021 14:56 Join Date: Jul 2008 Location: london	ABS rumble - brake sponge - All gone I washed it including a spray under arches,reset the ECU and took it for a thrash and emergency brake repeatedly......erm ….its all gone. No ABS/rumble when first set off or spongy brake. I'm not sure what we did which fixed it but its fine now. My friend reckons it was lubing the grommet on the servo/my bet is the ECU. Never had any error messages or lights. Ho hum.

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Aug 31st, 2019, 18:04	#2
oliverpervasive Member Last Online: Feb 4th, 2021 14:56 Join Date: Jul 2008 Location: london	Buying a Pagid brand replacement master brake cylinder from Eurofarts for £100. Looked on PFV for a volvo master cylinder but could not find one. Off to Tesco to buy a turkey baster to empty the reservoir. No codes have come up but I think this model has only the basic ECU info to OBD11

Sep 3rd, 2019, 23:24	#4
magnuz Ancient Last Online: Apr 15th, 2024 17:03 Join Date: May 2012 Location: chesterfield	Also check the reluctor rings around the CV joint. I have known them to split.. The sensor will detect the wider tooth gap where the split is & the system may think the wheel is about to lock!

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