1997 M90 Clutch decision

[barkster1971]

Get a dogdish flywheel and buy a hd sachs diesel clutch off ebay for £116.

[classicswede]

All petrol 940's with the M90 gearbox had a DMF so you will have the 240mm DMF clutch

[Laney760]

Can somebody explain to me please? Is the DMF separate to the clutch. Can I just renew the clutch without renewing the DMF? I don't have any of the symptoms of a failing DMF.

[Clan]

Originally Posted by Laney760

Can somebody explain to me please? Is the DMF separate to the clutch. Can I just renew the clutch without renewing the DMF? I don't have any of the symptoms of a failing DMF.

yes of course , a petrol engine is kind to the Dual Mass Flywheel , no huge pressure pulses from the diesel crankshaft to deal with .. It is a piece of cake to get the gearbox out and replace it anyway unlike today's Front wheel drive cars ..

[Clan]

Originally Posted by Laird Scooby

Back then clutches were made using asbestos too!

Good for heat though and also softer than the newer materials it has been replaced with as it doesn't chew the driven and driving plates (and in the case of brakes, discs and hubs) the way the newer stuff does - being soft it has higher friction coefficients as well.

There is a problem about not noticing a huge caravan on the back - you forget it's there! Suddenly you find yourself in the outside lane at 90 with blue lights flashing in every direction and an instant ban for being 30mph over the speed limit.

The clutch itself is the essential weak link in the transmission - it is designed to fail before anything else. An explding clutch disc isn't nice, makes a hell of a row as it bounces round the inside of the bellhousing but nowhere near as much row as you and/or your passengers would make if the propshaft disintegrated and made a bid for the comfort of the cabin!

Assuming the clutch is in good condition and has been used properly, what you say is true, that once engaged there is no slip. However, with a large weight dragging the car backwards, especially up a steep hill where the forces of gravity will work against it, the limits of the friction in the clutch assembly will be approached. Once reached and it starts slipping, it will continue to slip. This just gets worse and worse until it's virtually impossible to drive anywhere.

As for "people who tow know exactly what they're doing" - a sweeping generalisation, have a look at a few of these "caravan fails on dashcam" :

https://www.youtube.com/results?sear...ils+on+dashcam

Plenty to choose from!

Not at all , The clutch is designed to take the full engine torque and more ,
how ever much the caravan weighs, or steep the hill The engine can never produce more torque than it was designed for can it , If the clutch slips when towing or not it is worn or faulty and needs replacing ...

[Laird Scooby]

Originally Posted by Laney760

Can somebody explain to me please? Is the DMF separate to the clutch. Can I just renew the clutch without renewing the DMF? I don't have any of the symptoms of a failing DMF.

I'll have a go Ellie but to be honest, i've never needed to get involvoed with DMFs so don't know a wild amount about them.

Referring to my picture further up about the clutch, the flywheel is in very simple terms in two vertical halves. In other words, instead of one thick disc, it's two thinner discs and the one closest to the clutch disc is joined to the one on the back of the engine by an arrangement of springs.

This gives you two flywheels or dual flywheels and i think the "Mass" part of Dual Mass Flywheel came about as it sounded better!

The arrangement of springs creates a suspension type effect but in a rotary motion rather than up/down as with your normal springs and shock absorbers This reduces vibration and increases the power and torque handling of clutch.

Because of the spring arrangement inside the DMF, they become a wearing item with the rest of the clutch. That's why many garages replace the DMF with the clutch as a complete assembly so if there's any come-back, the parts are guaranteed.

Many garages view them as a "black art" because they don't fully understand them (can't say i blame them really! ) so that's probably why your local "trusted garage" has said they'll do it if it's a normal clutch but not if it's a DMF so you might be better off going to Volvo and asking for a firm price and description of what clutch you have and/or are likely to need.

Hope that makes some sort of sense!

[Laney760]

Originally Posted by Laird Scooby

I'll have a go Ellie but to be honest, i've never needed to get involvoed with DMFs so don't know a wild amount about them.

Referring to my picture further up about the clutch, the flywheel is in very simple terms in two vertical halves. In other words, instead of one thick disc, it's two thinner discs and the one closest to the clutch disc is joined to the one on the back of the engine by an arrangement of springs.

This gives you two flywheels or dual flywheels and i think the "Mass" part of Dual Mass Flywheel came about as it sounded better!

The arrangement of springs creates a suspension type effect but in a rotary motion rather than up/down as with your normal springs and shock absorbers This reduces vibration and increases the power and torque handling of clutch.

Because of the spring arrangement inside the DMF, they become a wearing item with the rest of the clutch. That's why many garages replace the DMF with the clutch as a complete assembly so if there's any come-back, the parts are guaranteed.

Many garages view them as a "black art" because they don't fully understand them (can't say i blame them really! ) so that's probably why your local "trusted garage" has said they'll do it if it's a normal clutch but not if it's a DMF so you might be better off going to Volvo and asking for a firm price and description of what clutch you have and/or are likely to need.

Hope that makes some sort of sense!

Hi Dave

I spoke with them today and the garage said they would only replace the clutch and not the DMF if that is what I want and the DMF doesn't need replacing but they are quite happy to renew both.

[classicswede]

Originally Posted by Laney760

Can somebody explain to me please? Is the DMF separate to the clutch. Can I just renew the clutch without renewing the DMF? I don't have any of the symptoms of a failing DMF.

DMF is Dual Mass flywheel. Just like with a normal flywheel the clutch bolts to the flywheel as normal. What does change is the springs that would normally be in the friction plate are moved into the flywheel. You can use them more than once but with many cars there is so much labour involved its not worth taking the chance.
The 940 is a very quick clutch to change so unless its making any noises you should be fine to reuse it

[TonyS9]

The 940 DMFs are fairly reliable in my experience. I've abused mine and no significant issues. It not like VW ones that don't last well atall.

A clutch (and/or DMF) change mainly need the driveshaft disconnected and gearbox out, which isn't a big task with a proper lift. I did it myself with axle stands and trolley jack.

Still a soft pedal confuses me. The pedal force will be linked to the cover plate springs, hyraulics and friction in the system. You tend to find the friction builds up especially the ball pin plastic cover wears away. There is no really difference hear with a DMF. The spings Dia mentions is just the slack take up dampers, not the clamping springs.

Is there any lift in the pedal? can you lift it higher with your foot? Everything is plastic and you can loose clutch travel as it wears slots in the pedal and drive boss in the mater cyl.

[lynns hubby]

Does the 940 actually have a proper DMF. As I recall when I changed the clutch on our first 940 it was not the modern make up of springs and gubbins, which are a right pain. The flywheel was just made up of an inner and outer bonded together with rubber as the damping medium.
For what its worth, over the years I fount the weakest point of the system was the operating fork that tended to wear through on the ball stud which meant a gearbox out to replace.