I'm sure this must be gearbox, but what to do?

[HPsauce]

I've been getting the odd "thump" for ages now (years) and it sort of feels like the box "might" be changing gear then not rather quickly.
It's usually been associated with steep hills and corners so I'd also vaguely wondered if it was ESP-related in some odd way.

Anyway it was a bit more noticeable yesterday (and I wanted to have another "play" with the dodgy cruise control too) so I decided to go for a little "test drive" today in the snooker mid-session interval.

The cruise control did work normally the first time I tried it (until I braked), after that it wouldn't engage any more.

Back to the box.................
I tried driving in manual mode for quite a while, so that the only "automatic" changes would be down due to kickdown or slowing down. This is a PF system so no separate kickdown switch, so the kickdown mechanism (whatever it is) "could" be part of the problem.
I couldn't get it to thump or judder consistently, but it did happen several times. No "precise" pattern, but the following observations from today and before:
1. It definitely happens in 3rd gear, and quite likely in 2nd too (not really there long enough with my foot down! or 1st!! ) but not in 4th or 5th.
2. Sometimes it's just one thump, others it a judder of maybe 3 or 4 max over maybe a second or a tad more.
3. Engine revs just seem to rise normally but there is the feeling of a brief loss of power. Again I have wondered if the ESP is doing something at times.
4. The problem appears "typically" (but not definitely) going up a steepish hill in 3rd gear at 3000 revs or less. More often on a bend, but they're often the steepest bits anyway.
5. Kickdown works normally when I floor the pedal in typical situations, including from 4 to 3 and 3 to 2.
6. It probably has spent 99% of it's life in top (occasionally 4th) gear, being used almost exclusively on long journeys; no commuting or shopping trips!

So, any thoughts anyone both on what it is and what to do?
e.g. Time for a gearbox fluid and filter change?
(it's done over 120,000 miles and had no work as far as I know)
And if so, is there anyone trustworthy not too far from me - I'm near M40/M25?

[47p2]

Originally Posted by HPsauce

The cruise control did work normally the first time I tried it (until I braked), after that it wouldn't engage any more.

Could be a faulty brake light switch

[SyncroS8]

I'll be honest, from having looked inside one, it could be a number of things but all are internal and not easy to get to without having the transmission out of the car.

I would try talking to Chester Transmissions or any other good ZF Transmission specialist and describe the symptoms.

It sounds like a drum/unit moving forwards and backwards inside the gearbox but could just as easily be a sticking solenoid...

Have you plugged in and had a look for any error codes from the transmission?

MG

[HPsauce]

Originally Posted by SyncroS8

Have you plugged in and had a look for any error codes from the transmission?

Not recently, but I will probably this weekend.
Last time I did (few months back) there was nothing significant and it's been doing this on and off for years.

I do know that the previous owner, long long ago, had a chip replaced. He told me it varied the gear change speeds holding them longer for brisker mid-range acceleration (!). I wonder if that might be related?

I have an old receipt which just says "Supply program and install Superchip" plus 44-pin SMT nasp protection board and Eprom. No spec as to the actual changes.
I also have the removed chip which has a Bosch label. Looks like it was a soldering job.

[Amanda]

Sounds like gearbox on the way out As said speak to Chester auto
http://www.transcentre.co.uk/
They know their way around a zf gearbox .....they have repaired mine!!!!

[HPsauce]

Originally Posted by Amanda

As said speak to Chester auto

Thanks, I will.
Unless anyone can recommend somewhere a bit nearer to me... (M25/M40 intersection is not far)

[HPsauce]

Originally Posted by 47p2

Could be a faulty brake light switch

Working now, as described in the main cruise control thread.

Not sure what it was though.

[HPsauce]

Well more symptoms today, but I'm not sure how to interpret them.
Did a 90 miles there, 90 back, journey with roughly a 2-hour break.
(Went to see Ranj to look over the S8 he's thinking of selling - nice car!)

No issues at all on the way up, behaved impeccably. Just one "moment" of a couple of seconds on the way back.

I was maybe 3 miles into my return journey at a light-controlled roundabout (A46 south onto A45 West) stopped on entry. On moving off all was OK as I swung right onto and round, but as I started to turn left off the roundabout it juddered for maybe 2 or 3 seconds.

I was probably around 3rd gear and using "reasonable" (but not full) power as I was in the right of 3 lanes and knew it would quickly reduce to 2. Nothing "challenging" about so I wasn't trying hard, just making sure I wasn't in anyones way when the lanes reduced.

The rest of the journey, motorway, main roads and country lanes, was uneventful.
So, none the wiser really. Gearbox, ESP, Differential?

[SyncroS8]

If it's on a direction change, then it's more likely to be a diff related problem.

I would check the levels of the front and centre diffs as they have different oil chambers to the autobox and run different oil.

They commonly leak from the output shaft seals and very few people actually check them let alone change the oil.

You'll need a 10mm allen socket to undo the filling plug. Stick your finger and point downwards. If you get oil on the tip of your finger... it's ok. If not... you need some more!

MG

[HPsauce]

Originally Posted by SyncroS8

If it's on a direction change, then it's more likely to be a diff related problem.

Thanks, good tip.
The only thing is it can be made to happen in a straight line and is pretty much confined to 3rd gear.

BUT you've given me some goods ideas for testing to narrow it down.

In case anyone's wondering the tyres are all the same size and wear level.