Loud rumble/vibration in 4th only on petrol

[vs_wagon]

I have a dual-fuel VS S2 auto wagon. This problem only occurs when the car is running on petrol...

When the speed hits about 80km/h and it kicks into 4th there is a really loud and strong rumble/vibration, possibly coming from the rear end. It's now so bad that it feels like I'm driving over a cattle grid. If I back off it goes away, but comes back as soon as I accelerate. Also, if I stay in 3rd and go past 80km/h it doesn't do it!

It's the fact that it's fine on LPG that confuses me. I have changed the fuel injectors, fuel pump and fuel filter a couple of months ago. No difference.

Any ideas?

 

[hako]

Sounds like the lockup clutch (TCC) is playing up as thats the speed and gear that it usually engages....however the fact its OK on gas is a bit strange unless the ECU which controls the transmission acts differently on gas ??? It might pay to check with an auto trans specialist...

 

[stocky]

sounds like it could be a tailshaft problem, dunno why it would only happen on petrol though.

 

[vs_wagon]

Sounds like the lockup clutch (TCC) is playing up as thats the speed and gear that it usually engages....however the fact its OK on gas is a bit strange unless the ECU which controls the transmission acts differently on gas ??? It might pay to check with an auto trans specialist...

Thanks guys. I think you might be right hako. :thumbsup:.. a little more research yields this from an unnamed forum:

"...a shudder in the transmission when the torque converter lockup clutch engages and disengages... The TC lockup occurs at light throttle just over 90kph in 4th gear."

And this from www.freeengineinfo.com:
"If the TCC is bad one of three things will usually happen. First, the vehicle will tend to rev up and down as it engages and disengages, not being able to keep the converter clutch locked up. Second, the converter clutch will engage randomly in gears that it shouldn’t even engage in usually. Third the clutch doesn’t want to disengage."

Anyone care to estimate the cost for replacement (I assume?) of the lockup clutch?

 

[Cursed CX8]

the entire torque converter needs replacing, get it done sooner rather than later because the strange actions of the TC can cause other issues within the box. I cant see it costing more than $500-$700

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CC

 

[vs_wagon]

I just spoke to an auto transmission mechanic who suggested to check the spark plug leads... sounds much cheaper, fingers crossed. I'll report back.

 

[vs_wagon]

Update: the leads are fine. 5 Kohms on the left and 2.5 Kohms on the right...

I'll be taking it in for the experts to diagnose/fix this one.

EDIT: No actually I'm going to replace the plugs first as they are old...

 

[vs_wagon]

Update: I replaced he spark plugs and the problem is still there... I'll do the leads as I'm told that they could still be bad even with good resistance readings, and what the heck it'll cost me more just to walk in the door of the mechanic so I may as well.

 

[ephect]

im going to agree with the others and say its your lockup in ur torque converter..

Its good changing your plugs and leads if you havent done them for a while, but i dont believe its going to fix the problem your have with the rumble. because its only in 4th.. if it was plugs or leads, it would do it no matter what gear..

 

[vs_wagon]

I've now replaced the leads and so far it seems to have fixed the problem. However, the problem was a bit intermittent (probably should have mentioned that) so I'll give it a few days before I celebrate just yet.

Thanks again for the advice. Hopefully I can officially close this one next week.