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[JamesV6CDX]

Hi guys

Having a small autobox issue. Nothing major that it can't be used, but here are the symptoms:

When cruising at say, 50mph - I hit sports mode and press the loud pedal down - it changes into a lower gear as expected and pulls very well. However if you let off the throttle, especially suddenly, it then changes back into top gear with a nice thump.

In addition to that, the gearbox doesn't always seem capable of selecting which gear to use between third and top. It often seems to "hunt" between the two gears and not settle into one. And sometimes, it is reluctant to change into top when it really should - Eg when cruising on the flat at 60mph/70mph under light throttle, it may take half a mile or more before it decides to go to top gear again, and when it does it's usually with a thump again.

If I apply the speed gradually on the flat from a standing start, it changes into top gear nice and gently and locks up without any problem at about 50mph. Selector lights are NOT flashing.

Now here's the history.

The AR35 on the car was a donor box from a slightly earlier car that, when we got it, had a thrust washer failure. The gearbox was taken apart by Mr Sassanach, who replaced the thrust washer with the uprated Sonnax one and he had a good look inside the box - confirming that all seems well mechanically. It was then fitted to the car, with new ATF.

Because we think this box is mechanically sound, Sassanach is suspecting a solenoid issue may be causing this - and I must say that seems to make sense.

So, looks like I need to drop the sumps and look at the solenoid.

My question is - which solenoid controls the gearchange between 3 and 4 - and is it just this one solenoid or is it a combination? Should I change them all for known good, or if it's just one - where is it?

I would really appreciate any advice and thoughts

[johnnycboy]

james

unfortunately after speaking to TB at Newent he had similar problems with a box which did the same into third gear, and even after rebuilding the box it still done the same - possibly another gearbox needed.  The only reason i say this is i have a similar problem and need to source another gearbox.  hopefully yours may not be as serious. hth

[JamesV6CDX]

james

unfortunately after speaking to TB at Newent he had similar problems with a box which did the same into third gear, and even after rebuilding the box it still done the same - possibly another gearbox needed.  The only reason i say this is i have a similar problem and need to source another gearbox.  hopefully yours may not be as serious. hth

The only reason it could need a new box is if something mechanical wsa shagged...  :-/

[johnnycboy]

james

unfortunately after speaking to TB at Newent he had similar problems with a box which did the same into third gear, and even after rebuilding the box it still done the same - possibly another gearbox needed.  The only reason i say this is i have a similar problem and need to source another gearbox.  hopefully yours may not be as serious. hth

The only reason it could need a new box is if something mechanical wsa shagged...  :-/

My faults exactly.  I'm only referring to TB's example as a possibilty.  I have problems with third clunking into gear after hard acceleration, if accelerating normally i get the clunk and thats only after the temp gets up to operating.

[Entwood]

Mark-DTM posted a link to an indepth description of the box the other night, right down to solenoids and bands .. but I can't find it .....

Edit : .. found it ..

http://images.omegaowners.com/downloads/Autobox_Docs/4L30E_Article.pdf

[JamesV6CDX]

Mark-DTM posted a link to an indepth description of the box the other night, right down to solenoids and bands .. but I can't find it .....

Edit : .. found it ..

http://images.omegaowners.com/downloads/Autobox_Docs/4L30E_Article.pdf

Cheers Nige, super

[Kevin Wood]

Have you tried reading the codes from the autoboxECU (I think my Cheapo Tech2 will at least attempt this)?

It strikes me that if there is an intermittent solenoid circuit, or if the autobox is not responding to an input to the 3/4 shift solenoid for 1/2 a mile, it would have logged a fault.

Incidentally, my autobox sticks in 3rd for a while after descending a gentle incline, or coasting, prompts it to change down. It seems there is a bit too much hysteresis on the engine load for this shift point, because it's not until you get on the power for a few seconds that it decides to go for 4th again. Might be a case of TADTS.

Mine also changes with a thump occasionally. I think if it's accelerating at full throttle in sports mode it's geared up to do a "hard" change due to the engine output torque being high. If you suddenly come off the gas it doesn't respond quickly enough and does a hard change with very little applied torque and shunts the drivetrain a bit.

When you say it "hunts" between two gears, do you mean the change is not smart, that it slips or hesitates half way between gears or that it's just making an inappropriate choice of gear?

Remember that the ECU is in charge of deciding which gear to use so the mechanicals of the gearbox are irrelevant to gear selection. If the change itself is ropey that will be down to the gearbox but if it's just making duff decisions you have to think about the inputs the ECU is using to decide on gear selection...

Do you know what autobox firmware you are running? Just wondering if you're used to the later firmware, or even if your autobox ECU has been changed at some point and it's not configured for the right engine, etc. Might be worth a Tech 2 session just to make sure all is well.

Kevin

[JamesV6CDX]

I have tried your code reader as this crossed my mind - unfortunately it just crashes out the software with a fatal exception or simelar

It doesn't slip - just chooses between the two gears too often.

You're right, a Tech2 session would be marvellous.

Mark, I don't suppose you're around on Saturday evening for a plug-in are you? I am up your way

[Kevin Wood]

It's difficult to say without experiencing your car, it's just that of all the faults you mention I could say the same about my (presumed good) gearbox with 70K on it. Maybe your problems are more severe and due to a fault but equally it might turn out that you're worrying about nothing.  :-/

Kevin

[JamesV6CDX]

It's difficult to say without experiencing your car, it's just that of all the faults you mention I could say the same about my (presumed good) gearbox with 70K on it. Maybe your problems are more severe and due to a fault but equally it might turn out that you're worrying about nothing.  :-/

Kevin

It is very much hit and miss and as I say not a severe fault at all....
Just that I know it's there.

Maybe a code read - and presuming all good, a firmware update and ATF change, should see it better  

[iainb]

I agree with Kevin.Before ripping the car apart check for gearbox faults and upload the latest software. Then get someone you trust to drive it and see what they think. I have noticed on my own car several of points that you have raised, the thump when lifting off in sports mode and the feeling that it cant makeup its mind what gear tobe in, to mention just 2.
 My attitude is it works leave it alone, I dont belive in neglecting my car. That would be foolish

[johnnycboy]

It's difficult to say without experiencing your car, it's just that of all the faults you mention I could say the same about my (presumed good) gearbox with 70K on it. Maybe your problems are more severe and due to a fault but equally it might turn out that you're worrying about nothing.  :-/

Kevin

It is very much hit and miss and as I say not a severe fault at all....
Just that I know it's there.

Maybe a code read - and presuming all good, a firmware update and ATF change, should see it better  

I had the firmware update done 2 weeks ago. ATF changed twice in 2 days about 2 weeks ago. no faults in gearbox ecu (read by proper Tech 2).  Still have same symptons

as said before though yours may be something completely different and nothing to worry about though

[Martin_1962]

Sounds like old firmware

[big-o-bob]

I had a problem simular to yours.  My 2.5 v6 struggled to find top gear.

It turned out to be the EGR valve.  (Exhaust Gas recirculation).

It is located on the top left of the engine bay, very easy to change.

It may be worth a try.  I believe you can unplug the electrical plug to test it (but don't just take my word for it).  Good luck

[Danny]

Sounds like old firmware

that was my thought, when i had mine updated to version 9 i was told that it was beneficial for the cruising speeds to stop it hunting around, and would also stop it doing it when towing aswell