2005 d12 accessory pulley driving device oil leak

Recently an oil leak has developed behind the pulley that drives the fan belt and alternator belt. Now the front of the alternator and ac compressor are covered with oil. The bearing feels ok however just the oil seal is bad. Need to change the whole driving device to get it fix. The part (20838388) is pretty expensive $800 + 150 core at the dealer but the job look simple enough that I might be able to get it done myself in couple hours. Anyone done that would like to share some advices?

Look like I need to take off the fan blade off to make room to slide the pulley hub out. The alternator also need to be out to get to 1 bolt next to the fuel pump. And the fuel pump doesn’t need to be touched. Pretty simple, right?

 

Your walkthrough is very detailed. I guess this thing goes bad on high mileage d12 very often. Mine is at 850k.
When I changed the high pressure power steering hose last time I noticed the alternator mount is missing the inside corner. Don’t know if is like this from the factory or someone used an angle grinder to delete it afterwards.
I don’t plan on changing the fuel pump this time since the I don’t think the bearing on the accessory drive is bad. I don’t feel any play on the bearing at all. And someone probably has replaced the pump before I got this truck in 2010. It is bare aluminum instead of green like the rest of the engine. The only thing is when I put the new accessory drive into the block I need to match pump shaft into the drive gear hole carefully. Look like some newer style pumps don’t have the long shaft when I look online. But I don’t know my pump has the shaft or not.

Don’t think I will be having problem getting the pulley off this time. One morning not too long ago when I started the truck in i heard a big rattle coming from under the hood. The 6 bolts on the pulley all came loose and covered with oil. 2 bolts actually went missing. The pulley was ready to fell off. In the end I have to replace both belts and got 2 extra short m8 8.8 grade bolts for the pulley. Any bolt that is longer than the original will hit the drive housing. This drives me into changing accessory drive this time.

 

My bracket has the bolt delete mod.

 

I ended up getting an used one 20838388 from the junk yard for $120 instead of paying 800 plus core from Volvo. It is just too pricey for what it is. 120 is actually less that the core deposit the dealer wants. Found one with smooth tight bearing and no seal leak in pretty good shape. The o ring it comes with feel nice and elastic and probably reusable. And it looks and feel just like a brand new o ring from my water pump kit...

Here is a fun fact. It seems like the accessory drive, water pump and air compressor all share the same gear side o ring dimension. I have a rebuilt water pump kit from Volvo that comes with 2 o rings and they are interchangeable with the old o ring I got from the junk yard. Even down to the color is the same.

On the left is the accessory drive and the old o ring I got from a junk yard. On the right is a rebuilt water pump kit. The gear side mating dimension is the same on both. Now I don’t get why a rebuilt accessory drive costs double of a rebuilt water pump. They are just replacing a bearing and a seal and I don’t think one is twice as difficult to rebuild that the other one. Only difference is there are plenty of aftermarket water pump makers.

 

With the weather so nice today in Jersey I finally able to get it done this afternoon out in the parking lot. It took me from noon to around 4. And I still had time to change out a slack adjuster before sunset. So it was a pretty straight forward job. Here is a recap I hope will help the next guy tackling this in the future.
I was able to just slide the fan blades forward and hanging it on the center hub. That already gave me enough space to work on the pulley and the accessory drive unit. The fan blade will not touch the radiator at all so there is no need to worry it will scratch up the cooling fins. But be extremely careful when unbolt the 9/16 nuts from the fan. I dropped one inside the gap behind the radiator and spent like 20 minutes trying to fish it out with a magnet it was not fun. Each of the 9/16 nuts will also have a spring washer and a flat washer. Mine is a kysor fan clutch. Dropping any of them in to the gap when taking off or putting on the blade is the worst thing. Try to tighten the nuts in a star pattern when mounting the fan blade. The accessory drive itself is held on by two 14 mm bolts and a t50 torx. T55 won’t even fit and t47 is a bit loose. Be ready to spray everything with red brake clean. The torx head need to be really clean to fit a t50 bit socket and you can’t really see directly. Green brake clean is totally useless. Get a least 2 cans of red brake clean. Inspect the fuel pump shaft for any play. It should turn easily when twisting with your fingers. The 14mm bolt under the fuel pump I need a really long extension to clear the power steering hose and oil filler tube when breaking it loose. A swivel head ratchet is also helpful.
In the end, I spent more time on trying to fish out the lost fan nuts and fighting with the seized alternator power studs than anything else.