How long does A/T last?

[pompy]

The Auto tranny on Mom's '91 300E has now done 237 000kms from new and is still operating soundly.
However, during a recent drive in it after quite a while, I could feel the shifting has become a little abrupt and it holding onto 3rd before shifting into 4th a tad longer than it probably should.
Shifting from 1st to 2nd has always been abrupt but never has the box been sluggish. Upon a cold startup however, selecting D or R is as smooth and quick as can be and there is no whine/groan/clonks from the tranny at any speed/temp.
That said, it is almost due for its 240 000km makeover which is a "maintenance plus additional" service - meaning it is due for new trans oil and filter.
Will that make much of a diff to the shifting? It has had all the necessary trans oil and filter changes according to schedule during its life.
What causes abrupt shifts - the t-converter or a worn tranny?
Is it true that some "adjustments to the box" can be made?
How long can A/T's last?
I honestly think there is still some good mileage left in that box - judging by other poorer A/T Mercs I've driven.
I would be nice to get it shifting smooth again

[s class]

Tranny life depends on proper servicing, plus the lifestyle it has been subjected to.  A tranny that has done its mileage mostly in city stop-start will have a considerably shortened life compared to one that has done mostly open road mileage.  Harsh treatment like towing also shortens the life. 

Harsh shifting is usually due to three things : modulator problems, engine vacuum problems or ageing seals in the tranny.  The seals in the tranny age and harden regardless of mileage. 

Harsh shifting when cold, follwed by slurring when warm usually indicate that a rebuild is around the corner.  My W140 has reached the point of slurring a little now at 314000km.  My 280SE W116 only lasted to about 300 000km before severe band slippage and ultimately tranny failure.

And no, I really doubt you have torque converter problems. 

Many people claim that a proper service on the tranny can give it a new lease on life, but my experience has been that once the symptoms of wear emerge, not much can mask it. 

[pompy]

When we bought the vehicle 3 yrs ago it came straight out of Sandton, JHB - and although it had only 169 000kms on the clock, incl FSH, I guess it had sadly spent most of its life commuting short distances in and around JHB.
That, and Mom's enthusiastic driving style which entails constant flatout pull-offs in 1st gear in hilly DBN has probably shortened its potential lifespan.
However, I think there is still some life in it - I'll wait and see how it performs after the service.
In any case I think I'll wait 'till the box starts jerking from one gear to another or untill it starts slipping before I'll have it rebuilt.
BTW, I think its reliability in years and mileage outdoes any other newer/new brand.

Which brings me to the next point: How do I go about it?
Our mechanic does engine and tranny rebuilds as well - is a rebuild good enough?
Or do I have to look for something from Merc?
My main criteria is that it needs to shift as smooth as when it was new.
And I would also like to get the damned thing to pull off in first without having to select 1st via the selector or flooring it! Is there a mod that one can make in order to achieve this or would a 126 300Se box bolt on?

[s class]

I'm not informed enough to comment on conversions.

As to your questions about a rebuild - I'm not quite sure what you are asking - are you asking if rebuilds must be done by MB or is an independant OK?  The answer is that MB would send out the tranny as out-work to an independant tranny specialist anyway. 

A rebuild isn't strictly necessary until you start to get slippage at the point of shifting from one gear to another.  Generally, the first sign you will see is slipping when engaging reverse.  Some several thousand km later (maybe 10 000km) the first to second change will start slipping.  Eventually the second to third change as well. 

I'm not sure you really need a rebuild yet.  What I would recommend is taking the car to a tranny specialist to get the pressures checked out.  Get the pressures in spec and it may be transformed. 

When my 280SE's tranny failed and I removed it at about 310 000km, I fitted a tranny from a 1974 donor car.  I'm not sure what the true mileage was on that car, but that tranny has since done another 125 000km in my 280SE, and its stilll good, though the shifting is a little harsh - but it is a 34 year old tranny !

[jbrasile]

Dear pompy,

It is better to have a transmission that shifts firmly than one that slips. From what you report, it sounds to me like your box is fine. I would advise you to have it serviced properly, drain the fluid from the tranny as well as the torque converter, change the filter and that's it, I would not look into a rebuild until you start getting some slip that can't ne corrected by a band or pressure adjustment.

Also the 1-2 shift you report is probably a 2-3 shift since the transmission on 91 300E's start in second gear unless you step all the way down on the gas pedal or select L on the gear lever, that shift is always a litle harsher that the 3-4 shift even when those cars were new amd if you do start in 1st the 1-2 sometimes can really be jerky, but that is normal for this car.

Regards,

Joe

[pompy]

Hi S-class,

From what you describe it sounds to me as if that tranny will run to at least 300k - thanx for clearing up some misconceptions that I had.
BTW, selecting R when hot or cold is the smoothest and quickest shift of all - a good sign?
Concerning the rebuild question: I wanted to know if a rebuild from an independant would be good enough or if a reman unit from the agents would be the better option? I now realise that the agents don't supply reman's...

Joe, thanx, I have heard before that these cars aren't the smoothest of shifters, but had trouble believing it as my old 350 shifts smoother than the 300...
As for the 1-2 shift I reported - that is what I meant as I always select 1st manually on each pullaway, instead of having to floor it. 2-3 and 3-4 is still OK.

BTW, I've noticed that shifts are def smoother at sea-level and harsher at high altitude ie JHB.

[kolin]

here is my 3cents worth pompy
i do know that if there is slippage, it creats heat in the box, auto boxs dont like too much heat.
changing the fluid and filters will help alot.
i used to change ATF every 10k with other auto's and got way way less problems.,
ask the mechanic at the merc dealership who they send the boxes to and go direct to them

[jbrasile]

pompy,

The 350 has a 3 speed auto that is noticeably smotther that the box in your car.

The quick amd smooth R shift in my opinion is a good sign.

I believe if you ever need a rebuild, it is better to get a reconditioned unit directly from Mercedes-Benz, that is what I would do anyway. Here in Brazil it would be prohibitive to go that route and we have a local builder (former dealership tech) who is excelent, but given a choice I would go main dealer.

One little tip,  if you are stopped  want to take off in 1st but have the transmission do the shifting, bring the lever to L and then back to D, that will make it take off in 1st evrey time, lot's of people don't know that so if you are already doing it sorry to be repetitive, if not try it out, it's a lot of fun.

Regards,

Joe

[kolin]

hey Joe
thats really interesting, putting the box into L then into D, but thought the 350's which have a 3 speed always pulled off in 1st anyway.

[jbrasile]

Kolin,

350's and 450's always start in first, 280'S in second and I believe the "L to D" trick works on them as well.

Regards,

Joe