I'm in San Francisco, California. I have a 1984 244GL with 4speed + overdrive transmission that seems to be slipping. The unusual thing is that I don't notice the car slipping in 4th or overdrive when I'm on the freeway, however when I am cruising up steep hills and accelerating hard in 2nd or 3rd, the engine over-revs for the speed I'm going.

The car has done 144,000 miles and I'm not sure if a new clutch is warranted (or part there of) or if I just neet to have it adjusted in some way. The clutch does not seem to engage until late when I'm releasing the pedal.

Can anyone shed some light on this for me and possibly suggest a course of action.

Thanks,

Adrian.

A clutch will slip first, and slip most, when it experiences the highest torque requirements. A clutch is required to transmit the most torque when the transmission is engaged in the highest gear (such that the clutch turns slowest).

In other words, you'll first notice a slipping clutch in 4/OD, then 4th, then 3rd, then 2nd, etc. By the time your clutch has begun to slip in 3rd, the car should have long since limped to the garage for a clutch-ectomy.

If you really have a slipping problem, I'd guess it's the OD which is called on to transmit higher levels of torque in lower gears (because the tranny multiplies torque in lower gears).

If you replace the clutch, be sure to also replace the rear main engine seal.

Don Foster (near Cape Cod, MA)

Good morning Don...

Thanks for making me look like an idiot. :-)

You obviously have more knowledge and experience than I do, so I'll take your word for it (and Adrian should too!). But I'm still not sure that I understand. Wouldn't the engine revv higher in a lower gear? E.G., at 25mph in 3rd gear and at the same speed in 2nd, wouldn't the engine be producing more power in 2nd gear, since as you say, the tranny multiplies torque in lower gears? I know that my car will accelerate sluggishly at this speed in 3rd gear, and downshifting produces a better result. Wouldn't the engine be producing less torque in 4/OD, since the engine is turning slower (and the transmission is "over driving" it)? I understand that torque isn't exactly linear, but I also know that this engine produces more torque at around 3000rpm than it does at lower revvs (136lbs@2750rpm). 3000rpm in 4/OD would probably have you rolling in excess of 80mph.

Also, why would the O/D have an affect on the low gears when it's locked out of everything but 4th?? Does this have something to do with the "sprague" gear that has been mentioned on the BB?

Thanks for helping an amateur understand.... :-)

Good morning, Rob...

"...the engine revv higher in a lower gear?"

Yep.

"...at 25mph in 3rd gear and at the same speed in 2nd, wouldn't the engine be producing more power in 2nd gear..."

I think you're confusing your engine's wide-open-throttle performance with what's required to maintain a fixed speed, say 50 mph.

In your example with a vehicle at a fixed speed, other than the slight extra losses caused by the higher RPM, the engine will produce the same power. Of course, in some circumstances, an engine is unable to produce the needed power, and hence we downshift from 3rd to 2nd.

Power is the product of torque times speed (rpm). So if you halve the speed, you must double the torque to produce or transmit the same power.

The relationship is: P=TR/5252 where "P"=horsepower, "T"=torque, and "R"=rpm.

The clutch is between the engine and tranny, and obviously transmits (only) torque. If called on to transmit too much torque, it slips.

To drive a car at a fixed speed, say 50 mph, you can run in 2nd gear, and the engine spins fast and produces a certain torque—and whatever it produces is sufficient for 50.

Then, if you shift to 4th gear the engine and clutch speeds drop. But you must still send then same final power to the differential to drive 50. The clutch is now going slower, so must deliver more torque to maintain the same power at the diff.

"...that this engine produces more torque at around 3000rpm than it does at lower revvs..."

Yes, but that's not the issue. Your engine can produce increasing torque at higher speeds AT WIDE-OPEN-THROTTLE. We're not discussing engine performance. We're discussing clutch performance and what the vehicle requires for power at a fixed speed.

"...why would the O/D have an affect on the low gears when it's locked out of everything but 4th??"

You're right, it doesn't. The only comment I made was that the clutch must again deliver higher torque when the driver shifts from 4th to 4/OD, because again the RPM drops—but exactly the same power is required at the differential to maintain vehicle speed. Thus, the clutch (which is before the OD) must transmit higher torque.

4th/OD places the toughest torque requirement on the clutch because the engine is going slowest.

Don Foster (near Cape Cod, MA)

A question popped into my head while I was reading your very informative posts on these transmission/clutch issues...

- Using an M46 trans, when shifting from 4th to 4th/OD, is it best to depress the clutch pedal? Or is the OD a sort of 'miniature' automatic transmission (as I read in a Chilton manual) and a mere push of the OD button is enough? I've asked a couple of Volvo shops and they both kind of dodged the question. Also couldn't find anything in the archives.

Thanks for helping a new owner of an old Volvo better understand his old brick.

- Ron G

_______________________________

Ron,

My 1988 740 Owner's Manual says to "depress the clutch fully....when engaging/disengaging OD"

Happy hollidays.

Ron --

"...when shifting from 4th to 4th/OD, is it best to depress the clutch pedal? Or is the OD a sort of 'miniature' automatic transmission..."

Opinions vary. It is sort of a "miniature" a/t. Personally, I like to use the clutch. But an argument to the contrary is that the gentle friction encountered during shifting (under load, no clutch) helps remove glaze that has formed on the clutches.

I have an old POS '82 wagon, 4/OD, that I bought with 116k miles. It now has 347k miles. I've always used the clutch when engaging/disengaging OD, and it still shifts solidly, smoothly, crisply, without chattering or slipping. So I acknowledge the other point of view, but ignore it completely because of my experience.

Each to his own.

Don Foster (near Cape Cod, MA)

Adrian,

Where in San Francisco?

If the transmission is slipping that badly, you probably need a new clutch. The cable can be adjusted with relative ease, but if the pedal is really engaging that late, it probably won't do you much good. The OEM cables last forever (original on my '84 at 287,000 miles) and rarely need adjustment unless they are installed improperly.

Depending on your level of experience/ability, this can be a DIY job. The parts aren't very expensive, but it is a time consuming ordeal. You would have to remove the transmission crossmember and drop the tranny to get at the clutch. Most "shadetree" mechanics (myself included) aren't brave enough to dig into the bowels of their transmissions. :-)

My best advice to you is to find a reputable independent Volvo/import shop near you (e.g. don't let your corner gas station do it), and have them look at the car. I can't even guess what they might want for a complete clutch job, but I wouldn't imagine that it would be insanely expensive. If you decide to have it done (if the car is otherwise in good shape, why not?), ask them about replacing the rear main seal and tranny mount while they are in there. Might also want to have your u-joints checked. The labor for having these parts replaced individually later on will really take a chunk out of your wallet. Best to have them replaced (if needed) while everything is already apart.