4th gear jumping (auto box)
 

Just recently, I've been noticing a small jump or slip after manually shifting from Drive to 4 whilst decelerating. The box shifts down ok but after 3 seconds or so from when 4th gear engages and takes up the momentum on the overrun, it has a little slip and then continues to let the car overrun. It's consistent every time I do it. No other anomalies are apparent in any gear under any other circumstances.

Any ideas?

Dougie.

When was the transmission fluid last changed?

I don't know if it ever has been but I suspect never. In fact, I've planned for changing it once some good weather stabilises as I've done on all my previous 75s. The tranny's otherwise responsive, moreso than others I've had. Is this symptom a known issue with old fluid?

Dougie.

I've still not unearthed any further info. Any clues anyone?

Dougie.

Hi Dougie,

Most automatic transmission apparent faults are down to one of two things, or both of them:

• Engine tune
• Transmission fluid level

What's the mileage of this engine Dougie?

Simon

Evening Simon,

Thanks for that. It's 137k as per my sig.:}

Dougie.

See what happens in sport mode ... thats what your style of driving is for... :D

Thanks Dougie and apologies for not thinking to read your sig! :o

I wouldn't expect an internal automatic gearbox problem at that mileage but you could check the resistances of the valve solenoids.

But before delving into that, ensure that your engine is running perfectly. The slightest irregularity here can result in the sort of symptoms you've described. For example, you might have read my thread a few months ago when my idle speed was high. At that time some of my gear changes were more of an abrupt snatch than a smooth transition. As soon as the idle was corrected, the gearbox returned to normal. :}

Simon

Same, which makes sense as it drops the gear via the same process in the box.

The engine's never run better since I serviced it a couple of months ago. It's noticeably quieter since I treated the injectors, and it's consistently giving an extra 6-7 mpg which I did not expect. (The filters were awful tbf.)

This last week, the momentary 4th-gear-on-overrun slippage issue disappeared so I'll keep a close eye/ear on it. I'd have to read up on how to check the solenoids' resistance. I've also diaried an ATF change in a couple of weeks.

Dougie.