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XC70 Transmission AW55-50SN No Drive - Problem found... C1 frictions burned and Drum cracked

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Tone944
Posts: 13
Joined: Sun Feb 19, 2017 12:44 pm
Year and Model: 2003 XC70, 2006 XC9
Location: Newcastle, Australia
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Tone944

XC70 Transmission AW55-50SN No Drive - Problem found... C1 frictions burned and Drum cracked

Post by Tone944 » Tue Jun 20, 2017 4:15 am

Ok, so... I'm hoping this will help somebody else who might come across this problem. This is my first auto trans overhaul and I'm learning heaps!

Here's a bit of a quick history:

1. For few hundred km's before the car had no drive, I noticed what appeared to be some slip in the transmission with a slight shuddering. I actually initially thought the shuddering was an engine mount issue. (we had an issue with an XC90 that had noise/vibration due to an engine mount)

2. It got worse to the point where I meant to tell my Wife not to drive that car, but forgot, she took it out and got stranded with absolutely no drive, in forward or reverse. After it had cooled, I managed to drive around the corner from where it was stranded, then nothing at all. After it was towed home and totally cooled, still absolutely no drive, forward or reverse.

3. After a fair bit of research (big thanks to this forum and others!), I realised at the very least, I need to overhaul the valve block and possibly put a master kit through the box. I also found a lot of evidence to check the bushes as they can cause low oil pressure.

4. I launched into it, removed a plethora of engine components, ready to remove the engine.

5. I then decided that I should just lower a corner of the sub-frame and remove the valve body and give it a good check over. I found a few things that were of very slight concern, a couple of slightly tight valves, but not enough to cause a full "no drive" failure. Of course, the oil was very dark and horrible! But the VB looked as if it had a mod kit through it some time, the solenoids had aftermarket end caps.

6. Since the VB wasn't in that bad shape, I continued to remove the gearbox. What a mission!!! I removed a Subaru outback gearbox in less that 2hrs in the driveway. This thing was a huge job, there were so many things to remove to get access.
In brief the procedure I used was:
a) remove lots of engine wiring and accessories,
b) remove RHS drive shaft,
c) unbolt steering rack and sway bar,
d) remove cat support, take lower control arms off at ball joint ( I unbolted the 2 bolts holding the ball joint to the stub axle housing, instead of the 1 bolt holding it in the wishbone, much easier!),
e) support engine with a support frame across the engine bay,
f) remove sub frame (actually was quite light and easy to handle by hand),
g) Drop engine and gearbox far enough to work on it,
h) unbolt drive shaft from angle gear (jacked the rear off the ground to rotate when necessary, dropped it when needed to hold the shaft still while unbolting.)
i) Unbolt and remove angle gear. No need to unbolt the exhaust at the turbo, it has enough flex and since the mount on the cat is removed.
j) unbolt most of gearbox, leave 1 bolt at the top in
k) unbolt flex plate bolts through the starter hole, there are 6 torx bolts, turn the engine at the crank pulley which is now easy to access since the engine is dropped a bit.
l) connect my engine crane to the gearbox - there is a lift point that a shackle can go through.
m) remove the final bolt and wiggle and jiggle until the trans comes free
n) drop the trans and roll it out under the car. I didn't actually have the car that high, just mounted on stands slightly behind the sub-frame mounts. I'll post a pic...
IMG_3462.JPG
7. I then got the box into my workshop and started to dismantle. So far I've only taken the first cover off, but I've found enough already!

So here's the verdict...

The first few clutches I took apart seemed in OK condition, nothing obvious. All the bearings and gears looked immaculate, even though the oil was very dark. At this point I decided I would take things to a very helpful local automatics guy to advise my on the amount of wear once I had a few more things removed.

I then noticed a build up of stuff on the turbine shaft hall sensor, closer exam it seemed to be metallic particles. Then I thought I should run my finger around the lower area of the casing, which was full of grit. At that stage I knew I was sure to find a serious failure somewhere.

Turns out that when I pulled the input shaft, that the drum appeared to be discoloured. Then, the steels and frictions where really difficult to remove, they were all caked together and lots of grit around. When I did get some apart it was very obvious that this had been seriously overheated. All the frictions were in a real mess. See photo.
IMG_3475.JPG
I took what I had dismantled to the Automatics service guy, he mentioned that these often crack the housing of the C1 Drum, he inspected and found it had (see photo). Apparently, they crack, this results in loss of pressure on the C1 clutch, and then burning of the frictions. I also would expect that this might start off slight but quickly get worse, here's my theory; frictions start to wear, filter starts to clog, oil pressure drops, things spiral to worse very quickly from there.
IMG_3471.JPG
From here, I'm going to strip down the rest of the trans, assess parts needed, get parts quotes and see if it's feasible to resurrect this car.
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