gear change

[Johnboy312]

hi guys since taking my engine out for total rebuild leaving the gearbox in place with the converter i lost a small amount of trans oil all was great on the rebuild and after 500 miles i have noticed when cold the gears change ok but seems to stick in 3rd once it has warmed up its ok does this sound like it needs topping up was thinking to drop the pan and change filter and oil but i have not got the filler tool can someone help i have not done one of these 740 box before is it a screw in type connector for putting the trans oil in thanks

[Timm]

If you are not getting Trans Failsafe messages then the gearbox is doing exactly what it has been asked to do by the EGS (transmission ECU). The two most likely causes are:

Incorrect tyre sizes or pressures, especially across the same axle - the gearbox will hold gears if it thinks it is turning a corner, poor tyre-matching fools the EGS into thinking you are cornering. This also affects the ABS/ASC/DSC:

http://www.meeknet.co.uk/e31/Timms_bmw_wheel_and_tyre_page_htm_files/Gen%20BMW%20Tyre%20Size%20effects%20on%20ASC.pdf

The gearbox fluid is either getting too hot (caused by a blocked transmission cooler), or the gearbox temperature sensor is faulty and is reporting a high temperature - the EGS will hold gears to reduce torque and ATF temperature.

[Johnboy312]

hello timm thanks for info im not getting any codes regards the tyres i think i can count this out has once it has reached normal running temp i dont have any problems at al . if i was to start it from cold this will happen .but if i leave it say ticking over in the drive for 4 mins or so the drive away its fine smooth shift also after the fist run i can park up 2-4 hrs and this will be fine no shift problems i do have correct pressure in the wheels im thinking the bit of trans oil i lost when removing the cooler and pipes this could be it has i never had this problem before the strip down of the engine

[Timm]

It is normal to hold the gears longer when cold - this process allows the engine and catalytic converters to reach temperature quicker....

[Johnboy312]

It is normal to hold the gears longer when cold - this process allows the engine and catalytic converters to reach temperature quicker.... ah thanks timm its just that i have not noticed this higher than normal revs going through the estate before but as i stated when the temp indicator is 1/4 way up its fine and i dont rag the car in its gears anyway i may be worrying for nothing but ill keep close watch in regards thanks mate for your insight