Temporary "Loss" of Gears

slantvaliant · Post by **slantvaliant** » 14 Nov 2012, 20:24

My son was driving the 850 (1993, non-turbo, 5-speed) at 65 MPH in fifth, with everything seeming normal. With no warning, the engine RPM spiked and the car started to lose speed. Coming off the gas let the engine return to idle RPM. He shifted to fourth, but letting the clutch out did not help. The car continued to coast. “No gears!”
He coasted the car to a parking lot. No gear worked. No unusual noises, smells, or feels.
Two days later, I finally got home from my business trip and went to check the car. Everything felt normal. The car even drove normally. We drove it home without further incident.
A few searches here and elsewhere showed that at least one similar report involved a halfshaft becoming disengaged.
I think it might be a halfshaft, temporarily slipping out of place then somehow finding its way back. Possible? Fixes?
Clutch problems seem unlikely considering the failure mode and lack of odor.
Do you have any ideas? Until I can explain it, it’s going to be hard to trust the car.

Post by **jblackburn** » 14 Nov 2012, 21:48

A half-shaft would not disengage and then reengage of its own accord.

A slave cylinder losing hydraulic pressure may be possible. It can be made to work again once it builds up pressure or the pedal is pumped a few times.

Ask your son if the clutch pedal seemed to lose pressure.

slantvaliant · Post by **slantvaliant** » 15 Nov 2012, 08:52

He said that the clutch and shifter felt normal during this episode.
If the slave cylinder lost pressure, would that cause the clutch to disengage?

Post by **jblackburn** » 15 Nov 2012, 09:23

I can't really think of why it would do this just cruising along in 5th gear. Without a smell, it doesn't sound like the clutch is slipping or overheated to the point it can't grab anymore.

My GUESS would be that either the pressure plate is weak and not holding consistent pressure at high torque loads (such as going up a hill), or the slave/master cylinder isn't keeping consistent hydraulic pressure. The second sounds unlikely without a clutch pedal doing weird things (like sticking near the floor or being squishy), but I guess it is possible.

Try this: go out and floor the car around 2500 RPM in 3rd or 4th gear. See if the engine lets go or slips a little bit. Try again with a high-power, 5000 RPM shift between 1 and 2.

Post by **rmmagow** » 15 Nov 2012, 09:39

I experienced something like this years ago on a RWD Toyota Celica, but that was total failure due to the flywheel bolts shearing. How is the flywheel attached to the crank in a Volvo?

slantvaliant · Post by **slantvaliant** » 02 Dec 2012, 09:34

Thanks for the input!

I finally got the time to work on the Volvo. Apparently, the driver's side halfshaft was not locked in place. Two new clues from the second incident: a small leak of transmission oil under the car, and the fact that with the car on jackstands, there was no differential action between the front wheels. Turning one didn't cause the other to turn at all. Sliding under, I saw this:

On disassembly, the snap ring seemed a little too relaxed.

There's a new halfshaft in there now ("While I'm in there ...") , and the car drives just fine.

What bothered me was that the condition disappeared for a while. The car lost power to the wheels and was pushed into a parking spot, where it sat for a while. When I got there, it drove normally. Apparently, the splines had re-engaged enough to work. Later, it lost power to the wheels again.

Anyway, it's good to have it back on the road.