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 Post subject: Heavy Duty Clutch for Volvo 740?
PostPosted: Mon Nov 18, 2019 8:23 pm 
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Joined: Sun Sep 03, 2017 7:57 pm
Posts: 7
Does anyone know if a heavy duty clutch kit is available for the 740 series cars with the 2.3 single overhead cam four cylinder engine?
I installed a OEM Sachs kit in our 740 and it slipped from new. It improved somewhat over time but 18,000 kms later it has started slipping again. Since it looks as if It will have to be replaced again I'd rather have a heavier pressure plate and disc to replace it with.
Thanks,
Stephen


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 Post subject: Re: Heavy Duty Clutch for Volvo 740?
PostPosted: Tue Nov 19, 2019 9:42 am 
Haha, I just built a W24 Octo-Turbo, now what?!
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Joined: Wed Dec 21, 2005 8:40 pm
Posts: 3442
Location: Calgary, Ab
Hi Stephen

Is your flywheel a flat or dished? (8.5" / 216mm clutch disc for flat flywheel and 9" / 229mm for dished) Turbo or non-turbo? Cable or hydraulic clutch? Did you have the flywheel machined? Did you replace the rear main seal while you were in there?

If you've got a non-turbo, there's really no reason why your clutch would slip that a "high performance" clutch would solve. If you have a Turbo, you've got to increase boost to well over 15 psi to make enough torque to have one slip. This is all provided you've got no oil leaks contaminating the clutch, that you've got proper geometry on the flywheel, and that your clutch is adjusted correctly.

The Turbo cars and anything from 1990 on were fitted with a dished flywheel (thick built up rim of cast iron flywheel around the perimeter of the clutch disc, very heavy) and if these are machined incorrectly and the relationship between the pressure plate mounting surface and friction surface is not maintained, you risk reducing the clamping force on the clutch disc. I'm not sure what flywheel the non-Turbo 740s came with but I'm pretty sure they're dished as well. Flat flywheels from earlier cars are pretty tough to accidentally screw up because the mounting and friction surfaces are naturally on the same plane.

Early 740s (I think '84-'85, maybe '86?) occasionally came with cable clutch pedals and these need to be properly adjusted as is the same for any mechanically-actuated clutch. The later 740s have hydraulic clutches and adjustment is not necessary (or possible, I believe) and these are far more common I believe.

The Sachs clutch is a good one, but I guess it's possible you got a bad example. I wouldn't bother searching out a heavy duty unit if your car isn't highly modified.

For reference, a flat flywheel (modified to run on a 1990+ engine):
Image

And a dished flywheel, for a 1990+ engine (earlier ones don't have the holes around the perimeter):
Image

The dished flywheel is extremely heavy for super smoothness, but most people ditch these for a flat flywheel to remove rotating weight. The flat flywheel can be modified to take a larger diameter clutch disc, and is vastly preferred for performance applications, but again there's not much wrong with either clutch assembly.

There IS one thing that triggers a memory though: at some point I helped install a flat flywheel clutch into a friend's car, and that particular disc had mounting rivets that were on a non-standard diameter. They rubbed on the flywheel, which didn't allow the flywheel face of the disc to properly contact the friction surface. We had to have a machine shop nip off a chamfer on the flywheel to clear the rivets and this setup worked just fine behind a modified Turbo. I've never seen this issue before or since, not to say that it couldn't happen. When I had Turbo Volvos in the past, I only ever run flat flywheels, nearly always on the smaller OEM replacement clutches because I'm cheap, and I never leave my engines alone so I know very well that they don't have much of a slipping problem until you go REALLY crazy (and then you risk breaking transmissions if you use a clutch that grips).

However, to answer your question: Yoshifab offers a number of options, they're good to the Volvo guys. Or you can google SPEC who make both styles in various flavours, and Sachs makes a performance clutch for the dished flywheel. Centerforce seems to have gotten out of the Volvo game. I'm sure there are others you can find too.


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 Post subject: Re: Heavy Duty Clutch for Volvo 740?
PostPosted: Thu Nov 21, 2019 9:37 am 
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Joined: Sun Sep 03, 2017 7:57 pm
Posts: 7
Hi Ugly Duck, in answer to your questions:
Fitted new rear main seal, transmission input shaft seal, cleaned everything totally oil free checked flywheel for cracks, scoring etc and was ok. Scoured the surface prior to assembly (Flywheel not resurfaced).
Flywheel flat, cable clutch...not sure of the disc diameter as the correct OEM Sachs clutch kit was ordered and installed. Transmission is 4 speed with overdrive.
All we can think is that we got a pressure plate that wasn't quite right as the clutch pedal seems almost too easy to push. Probably going to order another Sachs kit and look for anything that might contribute to the symptoms. Will get Flywheel resurfaced this time.
Thanks,
Stephen


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 Post subject: Re: Heavy Duty Clutch for Volvo 740?
PostPosted: Fri Nov 22, 2019 9:05 am 
Haha, I just built a W24 Octo-Turbo, now what?!
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Joined: Wed Dec 21, 2005 8:40 pm
Posts: 3442
Location: Calgary, Ab
Resurfacing is a good idea, but I'm personally way too cheap to do it unless the friction surface is really bad, so 90% of the time I do exactly what you just did, with perfect results. The flywheel does have to be in good shape though. Glazing will make the clutch slip, and glazing is most likely to happen WHEN the clutch is slipping - it's a bit of a vicious circle. If something wasn't quite right on your flywheel-to-disc surface you might have started the glazing process while it should have been bedding in (you said it slipped from new).

That being said, the flat 8.5" flywheel / clutch combination has twice the gripping force that a standard B230F requires and should last 250,000 km. As a younger man (who drove hard) I put years of 200+ Turbocharged horsepower and more torques than that through the same clutch/flywheel that you have (same "resurfacing" procedure as well) and it never slipped once. Something's definitely not right in your combo - these clutches never really wear your leg out in stop & go traffic but they're not THAT easy to push.

Hopefully after all this slipping your flywheel isn't heat cracked.


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 Post subject: Re: Heavy Duty Clutch for Volvo 740?
PostPosted: Tue Nov 26, 2019 7:11 am 
Bone stock

Joined: Sun Sep 03, 2017 7:57 pm
Posts: 7
Both my wife and I are very careful to not let the clutch slip if it can be avoided and back off the throttle at the slightest indication of the onset of slipping, to avoid the friction heat generated.

I work at AutoMann where we service a lot of British sports cars and also restore them. All we can think is that the new pressure plate is not functioning properly and for some reason is not generating the proper pressure to clamp the driven disc.

At any rate I think it will come down to getting another Sachs clutch kit and doing the job over again.

I appreciate your comments and observations as discussion can throw light on things one may not have thought of.

I drive a two year newer 740 wagon and have to say that it has been a truly great car. My wife and I would love to find a low mileage example to replace her aging 740 which is coming up to 500,00 kms. We keep getting notes left on the windshield asking if we want to sell it so they are still in demand.
Cheers,
Stephen


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