Weekend Weirdness - Gearbox (?)

[Epic pooh]

I know there is a gearbox mega thread and that there have been plenty of threads on similar topics so sorry for this one - I've read them and lots more but I'm still confused (as usual).

Here's my issues:

1. Over the last 6 months or so my vehicle has developed a rough shift into 6th gear (only),

2. On two occasions it has had fluctuating revs (only when cold on the flat in 2nd under light throttle),

3. When doing heavy towing up Mt Vic at a fair rate of knots it made an as yet unexplained squealing noise (which at the time I thought sounded gearboxy - but not sure),

4. Yesterday after a very spirited run down Macquarie Pass (cmd shift, high rpm, very quick run down with lots of interference from Killjoy the computer) when setting back to auto mode I had a squealing kind of noise twice (which sounded gearbox but not sure).

5. When going up a very steep driveway (my folks), if I stop half way up, it seems to sort of slip then thud into gear - has been doing this for years.

6. I did about 2hrs of moderate low range running yesterday and it behaved perfectly in those conditions, smooth shifting etc - when I got back on the road it was smooth shifting for about 10 minutes then when the speed got up the rough shift into 6th reoccured (in both auto and sport).

7. Since the fluid change the vehicle has rolled backwards on steep hills more that it used to.

8. Have an as yet unexplained buzzing noise on startup (5 secs) that emanates from the general area of the transmission tunnel.

I've had a fluid change / pan conversion last year (130K) and earlier this year it visited the local AT specialist (145K) who checked fluid quality, level and verified no glycol contamination. He speculated that the TC maybe on the way out, but to him it seemed to be pretty ok (as he did not drive at speed or in any circumstance where oddness may happen). My normal mechanic is noncommittal and thinks it seems ok to him.

I'm going to send it to the dealer later this month to get them to look at/regas the AC and at that time I will get them to give their opinion on these issues.

But in the meantime, I'd love to have some informed speculation from the crowd about my issues (rough shift, squealing, thud) - thanks in advance for any comments :D

[Rich84]

If it's a sorta squeaky/groany noise, it does sound like the TC. Search 6HP26 squawk.

What ATF did they use when replacing it? If you drain a small sample of ATF, what colour is it?

My gearbox behaved (misbehaved) similarly to this when I did a double flush with Dexron VI spec ATF instead of ZF LG6.

Another double flush with LG6 cured it.

I still get shuddering and slipping, but I believe this to be the TC worn out.

[Epic pooh]

Thanks Rich, reading about the Jag squawk that seems like the noise I have - the car needs to be made to work very hard and thats when I've heard it - seems consistent with Jag owners comments about hearing the noise after giving the vehicle a hard run. Its interesting to see the Jag TSB about it which is just flush the fluid and get on with it - when I suggested this to the trans guy he advised against this but said he'd do it if I insisted (I think he wants to see if the TC needs doing before changing what he says is perfectly good trans fluid).

The trans was serviced with LG6 (unless the mechanic is telling porkie pies which I doubt). The fluid as of 6 weeks ago is the correct colour and was described as clean fresh and healthy looking.

Did you have the associated rough gearshift and what I perceive as slippage for want of a better way of putting it ?

[Rich84]

The jag problems seem the same as what I had too from using Dexron VI, but haven't had any squawk since.

My trans itself shifts very smoothly for all gears except for the 2-1 rollout shift which can be harsh if I, for example, roll up to an intersection, give way (but don't stop) then mash the throttle. If I ease into the throttle, it's smooth. Common 6HP issue.

My TC on the other hand makes all manner of noise - constant brrrrrrrr noise when under load in variable engagement mode, light groaning when taking off moderately, ripple strip noise when cold @ 50-70km/h. I also get a lot of slip. If I take off moderately, then accelerate harder, the engine will rev to 3000ish and I can feather it there at will, while the rest of the car catches up, changes gear and still sits at 3000rpm! Behaves much like a manual car with a slipping clutch. Again seems consistent with a bad torque converter - I will be replacing it in the next month or two.

The only other issue I've had with my trans is towing - if there's a lot of play in the hitch and the trailer tends to bounce around a lot, a particularly hard 'bounce' will set-off the "TRANSMISSION FAULT" message and then the TC completely unlocks, causing revs to go all over the place until the ignition is cycled. I've towed a 2t+ camper trailer all around Australia with a treg-style hitch (no slop at all) and only had the message once when the camper trailer actually became airborne over a bump. I believe the bumps are causing something to slip beyond a pre-determined value.

[Epic pooh]

Of what you've described, I only have the squawk - I don't think mine makes unusual noises (apart from the squawk) nor does it have any particular vibration, my 1-2 shift is smooth but 5-6 at speed (100+) is rough, it kind of has the feel that the gear has fallen into place rather than shifted if that makes sense.

I do have the small slip on a very steep driveway as I said, but in similar conditions off road this does not occur. Very odd. Thanks for those comments Rich, very helpful, particularly the price of the TC in the other thread - I can see why the AT guy was keen to see it play out rather than change the fluid (as a lot of your fitting price is no doubt the fluid !).

Ive had a recent trans fault message, but changed my brake pedal switch and found it very burnt and crusty inside from arcing out (good design that !) message not seen since and imo definitely brake pedal switch in my case.