Problem No.23 - Slipping Auto Box

[Ian_C]

Another little problem. . . . . . . .

When driving along in 5th then accelerating the revs rise briefly before the car starts moving any quicker.

When accelerating rapidly the revs rise by upto 500 before the car starts accelerating.

At less acceleration (mild), it takes less revs before the car starts moving. Exactly the same as if the clutch was slipping and then getting take up.

The amount of 'slip' is the same each time and the amount of slip is linked to the amount of acceleration requested..... and at 'full beans' the car still goes some. It's just this slipping pause is an issue.

As I have not managed to make it to W124 works as yet, I wondered what all the opinions of the fault could be.......Google searching shows it could be Torque Converter problems. I am just looking for ideas in case I need to take it to another garage in a hurry when things go wrong. (Pease of mind/cost worries

Thanks

Ian

 

[BlackC55]

I take it the ATF level is ok. This tends to cause slippage.

 

[Ian_C]

I would like to think so as Ian at W124 and myself only changed the fluid a month ago. (Car is doing 1000 miles a week). No sign of any leaks, unless it needs a top up a few weeks after the ATF fluid has been changed.

Thanks

Ian

 

[BlackC55]

It is worth double checking it, just to be sure. It is often best to start at the basics then go from there.

 

[Ian_C]

One assumes I need a gearbox dipstick......If so I'm off to W124....

So to speak....

Ian

 

[BlackC55]

Make sure the gearbox is at operating temp. It is most important. I am sure Ian knows this.

Good luck and let us know what the outcome is.

 

[Ian B Walker]

Waits with baited breath, tools ready, warming up the ramps, kick starting Brain, Mb Preston put on Alert, Box of matches ready

 

[Ian_C]

Ian I would always warn you before turning up. You know me.....(Plus was in MK today)

I hope to be 'ahhhemmm' working from home later in the week, thus will give you a ring and bring tea and bacon in (....what do they call them - Barm cakes).....

Ian
P.S. Washed the car tonight so that may have helped ))

 

[Dieselman]

Ian
I can't understand the problem. You say that when you accellerate the revs rise before the car accellerates. Well that's normal, the torque converter is allowing ht eengine revs to raise to a level of higher torque before transmitting drive.

I think you are worrying over nothing, unless the ATF is low, but I don't think so.
Your description doesn't sound like flaring.

I take it 7.5 litres of fluid were added at the change.

 

[Ian_C]

DM,

I was wondering.....So your concuring that an auto box when when crusing at 70-80 will be fine, then when you need to press on a bit, the revs will rise 200-500 and then the car starts getting faster.

When removing foot from gas after getting to desired speed, revs drop back to normal cruising revs, withou this overhead of 200-500 revs

Ian
P.S,. Working from home on Friday looks likely so maybe over to Merc Heaven W124 works......For the little jobs to put mind at rest.

 

[Ian B Walker]

Ok with me mate

 

[Dieselman]

DM,

I was wondering.....So your concuring that an auto box when when crusing at 70-80 will be fine, then when you need to press on a bit, the revs will rise 200-500 and then the car starts getting faster.

When removing foot from gas after getting to desired speed, revs drop back to normal cruising revs, withou this overhead of 200-500 revs

Ian
P.S,. Working from home on Friday looks likely so maybe over to Merc Heaven W124 works......For the little jobs to put mind at rest.

Yes.!

Everytime you accellerate the torque converter will allow slippage to increase the available torque. Once additional torque is no longer required the revs match the road speed.
Your car has a torque converter lock up clutch but it only locks under high speed, low load conditions, at all other times the lock up is inversely proportional to speed and load.

If you said the gearbox was flaring on shifts then that would be different but revs rising then speed catching up is normal for any auto box.
If the gearbox was slipping the ECU would register a fault and lock the gear selection into the last good gear.

 

[Bazzle]

Ian
I can't understand the problem. You say that when you accellerate the revs rise before the car accellerates. Well that's normal, the torque converter is allowing ht eengine revs to raise to a level of higher torque before transmitting drive.

I think you are worrying over nothing, unless the ATF is low, but I don't think so.
Your description doesn't sound like flaring.

I take it 7.5 litres of fluid were added at the change.

x2 Beat me

Bazzle

 

[Ian_C]

Yes.!

Everytime you accellerate the torque converter will allow slippage to increase the available torque. Once additional torque is no longer required the revs match the road speed.
Your car has a torque converter lock up clutch but it only locks under high speed, low load conditions, at all other times the lock up is inversely proportional to speed and load.

If you said the gearbox was flaring on shifts then that would be different but revs rising then speed catching up is normal for any auto box.
If the gearbox was slipping the ECU would register a fault and lock the gear selection into the last good gear.

And there was me thinking it was getting worse. Just me being paranoid.

Just the vibration at 90+ to think about now.

Ian
P.S. Cleaned up the wheels and painted the calipers...Looking good

 

[Glenn Smith]

Ian
I can't understand the problem. You say that when you accellerate the revs rise before the car accellerates. Well that's normal, the torque converter is allowing ht eengine revs to raise to a level of higher torque before transmitting drive.

I think you are worrying over nothing, unless the ATF is low, but I don't think so.
Your description doesn't sound like flaring.

I take it 7.5 litres of fluid were added at the change.

I agree, this is normal, unless you have an auto with a lock up torque converter, which will (at a given speed) lock the converter and give direct drive as a manual. The amount the revs rise is dependant on the model, my jag seems to have a lot of slip compared to the Mercedes, but it has a lock up and only 4 speeds (so it needs the benefit of torque conversion more.) There is a test, called stall test, this is done with every thing at working temperature, basicly you hold the car on the brakes put in drive and floor it, take note of the max rpm you reach and compare with the standard figures (don't hold throttle flat for more than 5 secs) The results will give an indication to the condition of box and engine performance.

 

[Ian_C]

I agree, this is normal, unless you have an auto with a lock up torque converter, which will (at a given speed) lock the converter and give direct drive as a manual. The amount the revs rise is dependant on the model, my jag seems to have a lot of slip compared to the Mercedes, but it has a lock up and only 4 speeds (so it needs the benefit of torque conversion more.) There is a test, called stall test, this is done with every thing at working temperature, basicly you hold the car on the brakes put in drive and floor it, take note of the max rpm you reach and compare with the standard figures (don't hold throttle flat for more than 5 secs) The results will give an indication to the condition of box and engine performance.

..And gives you an idea if any parts in the drivetrain are about to break

 

[Ian_C]

Well done boys, a top up of ATF got everything back to normal, nice smooth changes....

W124 Works sorted it again....

Cheers

Ian

 

[Dieselman]

So how come it was low?

 

[Ian_C]

Not sure, keeping an eye on it......And checking for drips...

 

[BlackC55]

Well done boys, a top up of ATF got everything back to normal, nice smooth changes....

W124 Works sorted it again....

Cheers

Ian

Glad you got it sorted.

Saved you a few quid too!!