940 auto transmission glitch
 

Hi Guys, a wierd thing has just started with my 940 Auto. It does not want to "hold" in 4th [overdrive]. 1st, 2nd, 3rd are great, no slip and pulls smoothly/changes smoothly. BUT you cant feel it drop in to 4th, not unless you ease off the throttle slightly, ...then it eases in as you see the revs drop, but the moment you touch the throttle pedal to gently maintain the speed, it slips back down to third and obviously..the revs shoot up.
Ive tried the overdrive switch when it is in 4th and yes, it does operate and lock it down to 3rd. so that seems to be working.
Its almost as if the kickdown cable is too tight, but have slackened the adjustment off and tried it with more than the specified "slack" of 2mm.
i did add in to another thread to say i was going to change the auto oil, but not got that far yet. could it be the oil strainer is clogged and the box mot picking up sufficient oil from the sump pan? afterall, its clocked 206,000 so am aware its as good as new, but the rest is still so good and the engine still has loads of energy its a shame to declare it junk yet.
any advise [as aways] appreciated.

There's a lot of info on this online, try searching "AW71 overdrive"

The 4th gear is locked out using a solenoid which can get gummed up, a fluid flush will help a lot.

I had similar symptoms and ran 8 litres of fluid through it and it now holds 4th from 60mph upwards. I need to do more though as I have to lift the throttle to get it to shift at all.

I've also bought a solenoid replacement blank but have yet to fit it. That just removes the lockout function so it operates as a 'normal' 4 speed box.

thanks for the info. Ive spoken to "Volvo Parts" [aarrggh] and they want ...sorry would of wanted £166.60 for the solenoid...IF AVAILABLE, but now sadly Obsolete, not even held by their classic parts dept.. but the states have plenty at approx £34 plus shipping....if anyone else interested, volvo part number ref is 1239928 if you need to cross reference.
so before i venture under the motor, especially in this weather. will await the new solenoid, then replace and do oil flush same time, not unless its ok to do the flushing at the radiator cooling end? it it ok to remove the return pipe to the gearbox off the cooler and drain from there?

Don't flush it! Not with nearly 300k miles on it!

Do a "part-change" instead, drain the sump, either by removing the drain plug or using an oil extraction pump (about £15 on ebay and no crawling underneath!) and refill to the correct level using new fluid. I use Carlube ATF-U and have found it's an excellent fluid and suited to the Aisin-Warner box very well.

The first part-change will probably give you an instant improvement, do another in about a months time then another about a month later. This will in effect change all the fluid very gently and get a lot of dirt/contamination out of the box while reducing the risk of blowing seals with new, much thicker, fluid.
It also gives the seal conditioner present in the new fluid time to work which will help the seals much more than flushing it through with umpteen litres of new, thick fluid that could easily blow a weak seal to oblivion.

After the 3 part-changes, do one part-change a year to maintain the service changes at the right interval. ;) :D

Thanks for the advise on oil change, yes, ive already got the oil you suggested on an earlier post, found a reasonable supplier on ebay, far cheaper than local stores.
I dont have a drain plug on the box sump, only the dipstick pipe that bolts to the side of the sump pan, so will give your second suggestion a go too.

Many thanks again for the reminder, always greatful.:star:

Another option if the problem is related to the solenoid, giving you 123 and overdrive permanently.

+1 for some 'ebay special' ATF though. I bought Dexron III when I needed to do a complete change. Something like £2 a litre.

Here's the oil extraction pump i was on about, i'm sure there are others cheaper on ebay in the UK but gives you an idea what to look for :

https://www.ebay.co.uk/itm/Fluid-ext...tf3mPkShojEutw

The drain plug on my AW-71 is quite well hidden in a recess in the transmission sump pan so you might have one, it's just hiding! :lol:

Another thought on the lack of overdrive - what is the temperature gauge doing? Mine doesn't want to go into overdrive at any speed/throttle opening unless the engine is above a certain temperature, not sure if there's a thermal switch somewhere to inhibit overdrive below a preset temperature.
If so it might even be a thermo-vacuum switch so it might be a broken vacuum hose as well - all worth checking! ;) :D

A blocked filter screen causes slip, as in, no drive at all, but I can't see it stopping the overdrive working. I'd go for the partial replacement of ATF and see what happens.

How's the fluid level ? If it's sufficiently low, the transmission will sometimes act like it's gone into and out of neutral when it drags air up instead of fluid. You'd notice it on cornering and at the bottom of hills if it was bad enough because it would slip, then bang as it circulated fluid again.

Someone brought a 940 to me once that wouldn't change up the box unless the engine was screaming, and you still had to lift almost right off the accelerator even then before it would change up.
I noticed the fluid level was so low there was no reading on the dip stick, even when hot, and once topped up, it was still hesitant. The only way I managed to get it to behave as it's meant to, was by slackening the kickdown cable by trial and error until it worked properly.

I did think about possibly getting a replacement filter screen, but when i was on the phone to my local dealer earlier this afternoon to price up an overdrive solenoid, i asked about a screen & gasket....yet another item Obsolete and non at classic parts stock.
The oil level is fine, its one of my weekly checks i do its hardly ever dropped, apart from when i replaced the radiator.
the drive takes up from low revs fine, nice and smooth.no harsh clunks or backlash, pulls evenly through the 3 speeds no issue, doesnt drop out or hesitate.
its just the 4th/overdrive.
But will start on the partial oil changes with the "carlube ATF-U".

What colour is the fluid when you check it? Should be a nice pinky red.

Mine was a horrible coca cola colour which explains a lot.

If yours is clean I'd go straight to the solenoid as a partial change (good info from laird scooby) won't do much.

I don't know if that link above is the mod to bypass it, but that sounds easy enough. I had a friend visiting from the us and he brought me a blanking plate to remove the solenoid altogether