Overdrive or not 525td Auto

Hi

I am trying to ascertain as to whether my car has an overdrive or not, it has a 4 speed zf box. this is to do with a former post I made on here with regards to a repair.

http://www.bmwcarclubgb.co.uk/forum/forum_posts.asp?TID=8720&TPN=1

I have been told that the 4 speed does not have an overdrive and this is very relevant as trading standards are looking into not only my case but several others, all of which have got horror stories about the same trader

As they are considering taking legal action against them

Cheers Rob

Rob

I have a 98 S 523i SE with a Steptronic Auto box. I'm new to BMW's but I know a reasonably amount about Auto boxes and how they work but I'm not sure about how Beamer autos are set up but they all work the same.

I can offer some general advice about auto boxes though.

I guess you must be in North England somewhere as you went to a tranny specialist in Cumbria.  If you don't object to a trip North of the border I can recommend an excellent tranny specialist near Kilmarnock.  Give another tranny specialist a phone and ask them if they know about ZF boxes and if they have overdrive units fitted but don't mention your recent experiences. 

£800 is about right for a reconditioned tranny or a complete strip down and rebuild of your existing one.  Clutch bands would require a complete strip down I would have thought.

If your car has an overdrive you will hear it change into that overdrive gear and the engine revs will drop. 

Overdrives do not add extra oomph to your car, they are a gear for high road speeds, if anything they will sap oomph as the engine revs will be even lower for a given road speed if your car has overdrive.  Overdrive is like another gear only used at fast road speeds.  The car will then need to change down from overdrive and then down from say 4th to 3rd to get any perfermance.  Overdrives are sometimes engaged by pressing a button somewhere on the dash (more so on manual cars when you are in top gear). 

Sport modes work by getting more power out of the engine by making the auto box change up later and at higher (more powerfull) engine rpm's.

Kickdowns drop the auto box down a gear or a couple and opens the throttle/adds more fuel (in old cars you had a kickdown cable which did this, today its all electrics), which gives you that extra oomph to overtake. 

Winter modes make the tranny engage third gear and pull off in 3rd to limit the torque to the road wheels therefore limiting wheel slip.

In todays newfangled all electric autoboxes all the gear shifts are controlled electronically before any mechanical shifting is done. 

Park up the car, and move off and count the gear changes.  Pick a quiet stretch of road where you can end up doing 60 mph+, turn off the fan and radio as some gear changes are very slight and don't change the engine rpm much.  Accelerate steadily by applying constant throttle and watch the engine rpm dial for drops which will mean it has gone up a gear.

If your car has a 4 speed auto box plus an overdrive.  You should hear a change from first to second (1), second to third (2), third to fourth (3) and a 4th and final change from fourth to overdrive (4).  If it has overdrive you should be able to count 4 changes.  Bearing in mind you will already be in first gear when the gear lever is in drive!

Hmm wait a minute.....

Some auto cars have torque convertor lock ups.  This is like an overdrive but doesn't involve another gear train.  This locks the input and output shafts of the torque convertor so that you get no slip from the tc so it is direct drive from engine to the tranny.  But you can still count it as a gear change as the engine revs drop when the tc lock engages.

Personally, and I stand to be corrected by others as I am new to BMW's, I would have thought auto BMW's would have 4 gears and a torque convertor lock up in 4th rather than 4 gears and an overdrive.

Most modern cars have torque convertor lock ups rather than overdrives.

I don't know how you would distinguish between a torque convertor lock up change and an overdrive change.  Phone another tranny specialist in another part of the country and ask them if it has an overdrive unit.

I don't know if thats much help.  How old is your Beamer?  Haynes do a manual for the old Series 5 (Series 5 before the E39) which may tell you about the auto boxes (They give a description about the auto box if it has torque convertor lock ups or overdrives etc well they did in my Vx Senator manual) and a manual for the Series 3 from 98 onwards and I don't imagine will be a huge difference to the auto boxes in the Series 5's E39

Sorry some of the above may have confused you and not actually helped you.

I want to know more about my auto box in my Beamer too.

Andrew