Harsh Gear Changes

[ng4xjs]

My late AJ16 has developed a seemingly intermittent harsh 1st to 2nd (automatic) gear change. More noticeable when cold but can do it at any time. If I lock it out of first then smooth as anything. I know I have a mechanical with one of the rear drive-shaft universal joints and was half wondering if that may be the problem. Doesn't exhibit these faults when accelerating under load from a standstill.

All thoughts gratefully accepted. I have had the fluid changed recently but this made no difference. Anyhow the fluid that came out was clean(ish) and no lumpy bits.

Happy days
Nick

4.0L AJ16 (1994)

[Tris]

My 4.0 Celeb does a similar thing, sometimes it will hestitate in first for almost a second before banging into second. This happens mainly once the car has warmed up.

Has anyone tried something like Lucas Transmission Fix or similar for this issue or will it have to be a gearbox rebuild?

[ptjs1]

Nick / Tris,

How much of the fluid was removed when it was changed? These ZF24 boxes respond very well to having clean fluid and unblocked filters. Remember also that if you just drain the box, you'll only get 2.5 out of a total of 9 litres out. You either need to do multiple drain and refills or else do a "pressure drain" by disconnecting one of the oil cooler return pipe and filling whilst the box is pumping out the old fluid.

Cheers

Paul

[Tris]

Hi Paul, thanks for your reply!

I had the fluid changed and a brand new filter fitted by a local independent garage at the end of March this year, no idea when it was last done prior to this.

I'll take your advice and get the fluid changed a few more times over the summer and see how it goes before considering additives.

Roughly how many miles do you think should be adequate between fluid changes?

Thanks.

[ng4xjs]

Hi Paul
I need to do something, that's for sure.and yes more fluid needs to come out. Have you ever gone down this route?

Cheers
Nick

[poprivet]

Do I recall something about the electrical connection to the gearbox might need cleaning when shift problems happen? More experienced owners here in the later models may be able to confirm or deny.

[ptjs1]

Pop,

I have also heard about shift issues relating to the integrity of the wiring plug.

1-2 Harsh shift? My suggestion:

- Check the fluid level. Low level often causes 1-2 thump
- Check the transmission mount
- Check the diff mounts and radius arm mounts. Wear here often manifests itself in thumps
- Change the fluid and filter.


As regards changing the fluid:

They key thing on changing auto fluid is the difficulty in changing as much of the old fluid which sits in oil lines, the cooler, the torque converter etc. If you just drain and fill the box you'll have done only approx. 2.5 litres out of a total of 9 litres so you'll still have 72% dirty fluid in there! When I did my last filter change, I did three drain and refills via the dipstick tube with 10 mile runs in-between each change. I then dropped the sump. changed the filter and refilled. I then did three more drains and refills with 10 mile trips in-between. That was the only way that I felt comfortable that I'd eventually changed most of the old fluid.

I did initially try my suggested route of disconnecting the auto cooler return line and doing a "push" flush. But the position of the joint is a real pain unless you drop the gearbox mount, which I wanted to avoid. And the insulation above the box starts to crumble as you disturb it. So, I just relied on my approach of 7 changes. By my calculation and assuming that all oil eventually mixes through the box, pipes, cooler and converter, I ended up having changed just over 90% of the original fluid. I've then done a drain and refill every 12 months so I should have pretty clean fluid all the time.

It MAY be that a garage will do multiple flushes or a "push" flush. But my guess is that most places just do a single drain and filter change, so you'll still have most the old dirty fluid in the system!

Fluid is relatively cheap. So just do lots of drains and refills.

PAul

[Tris]

All set for a few fluid changes, all I need now is a weekend free of rain and back pain!

[Tris]

I did the first fluid change today and yes, it really needs doing! Second change pencilled in for tomorrow.

[ng4xjs]

Hi Tris - Has your fluid change made any noticeable difference to how the transmission peforms?

Kind regards
Nick

[Tris]

I think it made things a little bit smoother but it's still mainly old fluid in the system. I'll report back after a couple more changes.

[Tris]

Here's the result of today's ATF change, No.4 - Still going in strawberry and coming out chocolate!

1st to 2nd can still be a little jerky but doesn't seem quite so harsh now.

[ptjs1]

Keep the changes going, Tris! Fluid is cheap!

Remember, after 4 changes, you've still got over 1/4 of the old fluid still left in there.

Good luck

Paul

[Tris]

Cheers Paul, I've still got another 18 litres of fresh ATF to run through her yet!

[Tris]

Change No.6...