When in for an oil change mechanic said the sprag clutch was bad. Replacement would cost $1100. Not replacing could damage R.E.A.D to the tune of $4700. What are symptoms of bad sprag clutch and can that be diagnosed during an oil change?
What is a Sprag Clutch? A sprag is a one way metal roller clutch. Picture going to an event such as a concert, fair, basketball or football game, where you pass through a turngate, when you give the usher your ticket , notice that the turngate does not go backwards? This is a sprag at work.
one way bearing roller clutch detail_700
Sprags are used in many industrial products other than automatic transmissions. Essentially, the inner race is locked in place by a shaft that it attaches to, the yellow/ metal thing in the middle is the actual roller clutch element and the race on the outside will only turn one way, because of the internal configuration of the element and race. Thus it locks in one direction and spins free in the other direction. Transmissions make wide useage of sprag assembly’s. Most automatic transmissions such as a 700R4 have 2 sprags or more depending on how many speeds it has. The only transmission I know of without sprag elements is the Chrysler TF 604 front wheel drive automatic overdrive transmission.
In most cases a failed or broken sprag requires that the transmission be replaced. I have seen mechanics put a sprag in backwards, the second that sprag comes into use, Kapow , the transmission becomes junk. Like a carpenter, check it twice, fix it once! If you are a transmission rebuilder, that is. Generally speaking a sprag fails due to mileage and lack of slippery new automatic transmission fluid, which should be maintained regularly. Abuse is another reason for sprag failure, either intentional abuse or over working your vehicle can cause a sprag to break.
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I do not think he would know if it was bad by doing a oil change unless your tranny was acting up. and I am guessing you would know it was not acting right.
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This. I smell a scam/ripoff. Have the vehicle checked out at a good independent transmission shop and, depending on what the shop says, maybe find a new place for oil changes.
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The sprag clutch allows the READ drive for the alternator to turn only in one direction.
You can see the READ drive in front of the alternator in this image.
What are the symptoms of a bad sprag clutch?
Grinding.
Tester
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Agree especially if it was a IFFYLUBE
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The Rear Engine Accesory Drive is the part that drives engine accessories. It’s a mechanical coupling directly to the engine instead of rubber belts (years ago they were called fan belts). They tend to make noise as they wear out.
Here’s a link to a Volvo forum discussing this problem in a different Volvo car:
Rear End Accessory Drive in XC90 3.2 - Volvo Forums - Volvo Enthusiasts Forum
As for the price, it doesn’t sound out of the ballpark to me, but prices vary widely around the country, and many shops (and some of the people posting here) don’t even know what the heck that part is.
That would include me, LOL. But any time a shop tells me I need a part I’ve never heard of I make sure my wallet is secure, start asking questions, and–unless it’s our regular mechanic–get a second opinion. Fortunately, he’s very good about making sure we understand what needs to be done and why, something I’d expect from any shop where I intended to do repeat business.
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Many alternators have an overrunning clutch in the pulley as seen below. The alternator overrunning clutch on the Volvo is not easy to get to. For a technician to identify the noise during routine service is admirable.
I suspect the oil service was being done at the dealer, and perhaps this is a pattern failure for this system. Once a tech knows what to listen for and identifies the noise, it’s a slam dunk to recommend the service when it’s needed. I’m sure you’ve done the same thing. I know I used to look at every GM intake gasket and every Ford Escape brake hose that came in the door.
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