If you have found your way to this site, I imagine you have either been told you have a bad Volvo, Range Rover, or Jaguar (also known as Ford) READ/R.E.A.D. unit, or you’re a mechanic or shop owner wondering what is involved in rebuilding a Volvo READ unit as I call them, because that is what I used to work on. R.E.A.D stands for Rear End Accessory Drive.
The first thing I tell anyone who thinks they have a bad R.E.A.D. unit is that 75% of the people I have been contacted by who think they have a bad READ unit, didn’t. People hear a bearing noise in the READ area, and assume it is a bad READ unit. The most common cause of noise in that area is the one-way clutch on the accessory side of the R.E.A.D. unit. I’ve also seen noisy idlers, water pumps, and A/C compressors diagnosed as failed READ units.
Back to the one-way clutch on the READ unit. We have a theory that a failing or failed one-way clutch on the READ unit may be what causes the bearings in the READ unit to fail. So I always recommend replacing the one-way clutch when rebuilding, or installing a rebuilt unit. I would say used as well, but I cannot endorse installing a used unit as you never know how long it is going to last, and it is a lot of work to remove and install the READ unit. I know a lot of people who have installed used units with no issues, but I know I would never take the chance.
The READ unit cannot be purchased from the manufacturer. The official position is that the READ unit and Engine Block are a machine fit, and cannot be changed from one engine to another, so if the READ unit that came off the car cannot be rebuilt, then the engine has to be replaced. In my opinion, there may be some misinformation here. I don’t see the machining of the block, and the READ as being any different that the machining of an engine block, and cylinder head. I won’t get into all the specifics, but the drive gear has to be parallel to the crankshaft, and the drive gear has to be parallel to the shaft in the READ unit, so I don’t see how the machining of one block can be any different than any other.
To determine if the READ has failed, or it’s another component, remove the drive belt. If the noise goes away, it is most likely not the READ unit that is making the noise. If the noise is still there, it is usually the READ unit, and it will need to be rebuilt, or replaced with a rebuilt one.
Back to the one-way clutch for a moment. If you are rebuilding, or installing a rebuilt unit, there is also a one-way clutch on the front of the alternator. Make sure you check this one-way clutch as well while you have everything disassembled, or it will come back to haunt you.
There are essentially 2 ways to rebuild a READ unit. The first is with the kit from the manufacturer. The other way is to rebuild the unit with the bearing kit I sell below. The Volvo kit includes everything inside the READ unit, as well as a new drive gear. All the hard parts in the READ unit have to be in good shape to use the bearing kit. That has been about 90% of the units I have rebuilt.
If you want to rebuild the READ unit, you will need the timing chain tool kit to get the READ unit off the engine, and the special tools to remove the sprocket from the READ unit. I sell rebuilt units, the bearing kits, and the sprocket tools below.
Here is a link to the removal and rebuild instructions from Volvo: https://1drv.ms/b/s!AqPSJvgQqA6OxPkJFHxVj74ts7aZAg?e=zV5Pdj