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#553863 - 08/03/04 10:22 PM What cause automatic transmission to slip?
sifan Offline


Registered: 10/21/03
Posts: 933
Loc: Maryland, USA
I am thinking of installing a bypass filter for automatic transmission oil. Will the bypass filter help stopping or preventing transmission slipage? What are the causes behind the slipage?

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#553864 - 08/03/04 10:37 PM Re: What cause automatic transmission to slip?
Dan4510 Offline


Registered: 05/19/03
Posts: 2363
Loc: Texas
Slippage is usually a mechanical problem. It is caused by the clutches wearing to such an extent they cant hold anymore.

Dan

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#553865 - 08/03/04 11:13 PM Re: What cause automatic transmission to slip?
Matt_S Offline


Registered: 12/02/03
Posts: 3094
Loc: Metro Detroit
Let me add that when clutches in an automatic wear to such a point as Dan stated, a rebuild is the only real fix.

Also, where slippage isn't caused by clutch wear, it can also be caused by low line pressure, also a sign of an impending rebuild, as the low pressure is usually caused by old, deteriorating seals. If that's the problem, Berryman's B12 Chemtool can sometimes gain you a few months, but it's not permanent.

Finally, if you have slippage caused by low line pressure, it will wear out the clutches in a hurry. No fluid or filter is going to help you once this starts.

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#553866 - 08/03/04 11:51 PM Re: What cause automatic transmission to slip?
sifan Offline


Registered: 10/21/03
Posts: 933
Loc: Maryland, USA
What factors can accelerate the clutch wear inside an automtaic transmission besides high mileage use? For example, do fast acceleration/de-acceleration with a lead foot on the gas/brake pedal, or constant stiff hill climbing contribute to clutch wear?

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#553867 - 08/03/04 11:54 PM Re: What cause automatic transmission to slip?
patel Offline


Registered: 04/08/04
Posts: 116
Loc: huntley,IL
cause for X'tion slip

If it new then,
1) Overfill
2) underfill
3) oil smell bruned

If old X'tion over 100K mile then as said Mechanical problem

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#553868 - 08/04/04 12:09 AM Re: What cause automatic transmission to slip?
sifan Offline


Registered: 10/21/03
Posts: 933
Loc: Maryland, USA
Tell me if this is a correct statement: For an almost new AT the ONLY possible cause of pre-mature clutch wear is overheating of transmission oil assuming oil level is ok.

Driving conditions have no effects to the clutch wear at all???

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#553869 - 08/04/04 12:56 AM Re: What cause automatic transmission to slip?
Matt_S Offline


Registered: 12/02/03
Posts: 3094
Loc: Metro Detroit
Constant shifting will wear clutches. Hard acceleration will also cause additional wear in addition to the causes already mentioned. How new are we talking?

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#553870 - 08/04/04 01:01 AM Re: What cause automatic transmission to slip?
sifan Offline


Registered: 10/21/03
Posts: 933
Loc: Maryland, USA
15k miles on the AT.

Doesn't AT nomrally slip all the time during gear shifting?

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#553871 - 08/04/04 09:08 AM Re: What cause automatic transmission to slip?
tpi Offline


Registered: 01/25/04
Posts: 200
Loc: So. CA
quote:
Originally posted by sifan:
Tell me if this is a correct statement: For an almost new AT the ONLY possible cause of pre-mature clutch wear is overheating of transmission oil assuming oil level is ok.

Driving conditions have no effects to the clutch wear at all???

No, an almost new transmission may fail for many reasons. Factory defective parts. Slipping, soft, shift flare can be caused by how the clutches are operated as well as the clutches themselves. It was pointed out earlier low line pressure is frequently a problem, and could be caused by overheating the seals.

I've head of newer computer controlled transmissions which used a timed shift sequence. For a given load and speed and throttle input the shift (where a clutch pack is active) uses a timed feedback. The shift should complete in a certain amount of time, and pressures are compensated to insure it does.

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#553872 - 08/05/04 12:27 PM Re: What cause automatic transmission to slip?
Gary Allan Offline


Registered: 09/28/02
Posts: 39806
Loc: Pottstown, PA
quote:
Doesn't AT nomrally slip all the time during gear shifting?
Well ..sort of. The older automatics (the only thing I know =dam/n reliable), to allow a "smooth" shift, would start disengaging one applied element (either a clutch or a band) while actuating the next in the shift sequence. This could be called slippage but you'll notice that your tach, if you have one, doesn't indicate that the engine sees any "runaway". That is, it doesn't slip ..but the opposing forces of band/clutch application (one losing its grip as one is gaining it) DOES wear on components. They all shed metal and friction material.

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#553873 - 08/05/04 07:58 PM Re: What cause automatic transmission to slip?
cangreylegend Offline


Registered: 05/13/03
Posts: 392
Loc: Toronto, Canada
Can someone explain the reasons behind why overfilling can cause slippage?

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#553874 - 08/05/04 08:51 PM Re: What cause automatic transmission to slip?
Gary Allan Offline


Registered: 09/28/02
Posts: 39806
Loc: Pottstown, PA
Although I've seen several automatics that could care less about moderate overfill, the main side effect is aeration. The fluid gets whipped up in the rotating mechanicals of the trans and gets air entrained into it. It then pumps this aerated fluid that can now be compressed ...pressure is lost and faulty applications occur. Friction occurs where there was solid applied pressure before ...that is, slippage.

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#553875 - 08/08/04 07:04 AM Re: What cause automatic transmission to slip?
QuadDriver Offline


Registered: 10/25/02
Posts: 712
Loc: Pennsylvania
to explain an auto tranny in laymans terms (and this applies to all but honda) the clutch packs are 'wet' and in any normal state, freely rotate with no apply pressure and somewhere, somehow, at least one band grabs when running in any gear.

Bands grab hold of drums or shells and stop them or allow them to go. The use of bands is what makes an automatic 'change gears' - i'e' it allows the rotation in different ways of the planetary gearset causing reduction. If a band slips then you are in a way 'in 2 gears at once', meaning the full reduction is not felt and things goto crap in a hurry. But, once a band is applied, hydraulic pressure squeezes at least 1 clutch pack somewhere and completes the power tranmission circuit. if hyd. pressure is too low, the clutch will slip.

you have heard the term 'flare' - that is where a pack applies too slowly as a bad somewhere is released while under load and as a result, the power tranmission circuit is interrupted like you would on a manual - this makes the clutch pack goto crap in a hurry also.

of course this goes up in compexity as planet-sets or extra shells/drums are added (for example the GM 440T4/4T60/4T60E could be a 7F/3R speed tranny is someone felt ambition due to the creative use of a dual planetary gearset.)

but at any rate, 'slip' as you are asking about most likely came about from low line pressure - of which there can be many causes - sticking gov, bad throttle pressure, cut seal - but after a few times you start experiencing a mechanical slip caused by the loss of friction material on bands and discs....in all cases its time to pull it out and play in red juice, there is no 'fix in a can'

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