Transmission "sprag" clutch noise?

WesternRoadtripper1
Wed, 06 Oct 2021 18:37:22 +0000
Maintenance/Repairs

For a couple of months, I had been hearing a momentary faint groan sound like something rubbing, from the left front of my Sienna. Being intermittent, it was impossible to reproduce for a mechanic. The sound was two or three squeaky sounds taking only a second or two total. I heard it only at walking speed, such as maneuvering out of a parking space, and only once in a while. It didn’t seem related to turning the wheel, though the rare appearance of the sound, and quick duration, made it hard to be sure.

As preparation for a month long road trip, I had just had other work done on the car: new brake master cylinder and power steering pump, and a thorough check of the front end parts - all passed. I then drove 5500 miles without incident except for the phantom front end noise.

A few weeks later, on a short trip in the eastern Sierra Nevada area, on the drive up a challenging steep and narrow mountain road for probably 30 minutes, I heard a much louder and dangerous sound from the same area of the car as I turned on the twisty road. At that stage, turning the wheel while stationary DID create noise, a more severe friction kind of scraping / grinding sound. I imagined a bad bearing like a strut, wheel bearing, or axle.

I crept down the hill in first gear. By the time I reached the bottom, the severe noise had vanished, as had the phantom soft sound. Two days later, on a shorter less steep road, I did hear the mountain road noise again while not rolling, but much less severe.

I’ve now driven close to 500 miles with NONE of these noises appearing!

Back home, I went directly to my regular and very experienced mechanic. He and another skilled co-worker checked the front end parts and found no issues, bearings moved fine, steering gear tight, etc. However they detected a sound they described as a bit like “shuffling a deck of cards” coming from the transmission. They apparently heard that sound with the car on the lift, not in motion, or with weight on the suspension.

That shuffling sound was not the minor noise I had been hearing, nor the severe one from the mountain road.

The mechanic went to the extent of calling a local transmission shop for insight on this, and the conclusion was that it was likely a “sprag” in the transmission. I’ve now seen a drawing of that kind of device, and learned that it serves a function like a clutch.

Curiously, the “shuffling cards” sound was present in both Dodge Grand Caravans I’ve owned, and I have also heard that same sound in parking lots from Caravans negotiating parking spaces. My mechanic once mentioned this as a normal transmission sound. So maybe what they heard is normal in this car?

I’m beginning to think that the faint and brief rubbing sound could be brake noise, since I had recently replaced discs, calipers, pads, and hoses.

Could it be that the sprag noise is not a concern? By its design, this part probably makes a bit of noise when shifting, but it’s too faint to hear from the driver seat. Maybe I shouldn’t worry about that sound?

So what could have produced that serious noise on the mountain road? What would a very steep sustained climb with almost constant turning do that doesn’t happen on milder terrain? Could there have been a heat factor resulting from the sustained climb that put extra stress on a bearing, or the rack? Would that have faded when the stress of climbing and constant turning was reduced significantly?

The transmission has about 50k on it. Would the sprag noise mean impeding doom, a failure that would leave me stranded? Or does it make noise for a long time, and gradually produce poor performance?

My dilemma is that the engine runs fine, very low oil consumption (1 quart per 2000 miles), good gas mileage, the front end seems fine, and it has new brakes, power steering pump, and brake master cylinder. So I’m reluctant to junk it because of a couple of vague phantom noises.

And I’ll stay off that road to the Ancient Bristlecone Pine Forest, in this car at least.

4 posts - 3 participants