Gearbox troubles
I recently bought a 2004 Vauxhall Signum 2.2 direct petrol auto with 76,000 miles that turned out to be a bit of a dog. In six months, I’ve replaced the rear springs and shocks (broken and leaking) and rear discs and pads, along with the front droplinks, roll bar bushes, steering rack, tailgate switch and gas struts, and fixed two leaks in the tailgate. I still need to replace the rotted exhaust. However, the most serious problem was the auto gearbox, which was jerky and occasionally slipped and then thumped into gear. Eventually, the gearbox fault lamp appeared, accompanied by the fault code ‘P7015 input speed sensor fault’. The transmission fluid was cloudy like strawberry milkshake; when I heated it, the cloudiness boiled off, indicating it had been contaminated with engine coolant.
Apparently, this is a common fault with automatic Vectra C/signums. I suspect this was a historic problem where a new radiator had been fitted but the gearbox had never been flushed properly. I was quoted £2500 for a rebuild, so I decided to do it myself. It is an Aisin Warner AF23JD AW55/50 5-speed 'box.
I stripped the gearbox and cleaned out the old sludgy fluid. All the friction parts looked perfect, but I replaced them as a precaution as I’d read that the water can degrade the bonding of the friction material. I fitted new clutches, brake band, filter, all new O-rings/ seals and a new complete valve body, ensuring that the correct valve body was fitted as there are four variants. The whole procedure was fairly straightforward with an ATSG service manual that I had downloaded. I fitted an air-cooled transmission cooler in front of the condenser and piped the transmission fluid to this cooler to remove any risk of contamination in the future. I had the gearbox adaptions reset by a specialist firm and, within a few days, the gearbox was running very smoothly.
The only problem I have now is that when I change from ‘Reverse’ to ‘Drive’ it engages with a bit of a thump. If I go from ‘Reverse’ to ‘Neutral’, pause for a few seconds and then select ‘Drive’, it engages smoothly. This can be annoying when parking or doing a three-point turn. I thought perhaps it might be the engine/gearbox mounts, but they appeared to be OK when I had them off – there were no visible cracks, but perhaps they’ve gone soft?
The weird thing is that going from ‘Drive’ to ‘Reverse’ is OK. Also, when the engine is cold it’s fine, but perhaps the solenoid timings are slightly different when cold? Or perhaps the fault is related to my tightening the gearbox mounts (the donut type with three ribs) when the engine was still suspended from a hoist? Could I have put some kind of tension on the engine/ gearbox mounts that releases when going from ‘Reverse’ to ‘Drive’ quickly? Incidentally, the fluid level is OK. Rob Veltze As you say, this was a common problem and there was a field remedy bulletin issued advising that the radiator should be replaced with a modified unit. Of course, once the failure has occurred this is like locking the stable door after the horse has bolted!
There was also a field service remedy that dealt with a jerk when selecting gear (1915) and this may be applicable in your case. The problem in this instance was that the plunger of the SLT (throttle linear solenoid) had a slight deviation. Of the three large solenoids in the valve block, this is the one at the front of the gearbox.
If there is not a problem with this solenoid then it could still be a valve body fault and you may still be suffering from contamination. Unfortunately it is almost impossible to ensure that 100% of the old fluid is removed without replacing the torque convertor.
Although your problem could involve the mountings on the gearbox, I would find this less likely, although you will appreciate that I am making an appraisal purely from your description and without seeing the car myself. You have described the process as being quite straightforward and this makes me feel you must be quite competent. It is a task that many would not tackle and the settings of the brake bands and installation of the fluid pump are quite precise jobs, so I must congratulate you for taking them on!