Astra automatic gear ratios - plonker
I have a 2001 Astra automatic 1.6 8 valve. At 60 mph on a light throttle the tachometer shows 2,500 rpm.
Could someone confirm that this fits in with lock up engaging in 4th gear. I'm really just trying to satisfy myself that the gearbox is operating OK.
Astra automatic gear ratios - Number_Cruncher
Try here;

astra.autokacik.pl/download/ople-2001.pdf

Number_Cruncher
Astra automatic gear ratios - Aprilia
Sounds about right, but tacho may not be accurate enough because the engine speed drops by only a couple 100's rpm when lock-up comes in. If you drive on a flat road and accelerate briskly (1/2-3/4 throttle) to 55mph then ease back gently you should see the rev-counter needle suddenly drop by couple hundred rpm. Similarly, at stready 60mph just ease the throttle down and you should see rev counter needle jump up a couple hundred rpm as it comes out of lock-up.
Astra automatic gear ratios - plonker
Thanks Aprilia, I'll try out your suggestions. What I've noticed is that if I ease off the throttle at say 60 ish, the revs actually fall off noticeably and immediately which make me wonder if the transmission really is "locked".
Astra automatic gear ratios - Number_Cruncher
Using the info from the website,

Assuming 175/70 R14 tyres, and a fourth gear ratio of 0.74, and a final drive ratio of 4.12


v=(3600/1609.3)*(((14*25.4e-3)/2)+(175e-3*0.7))*(2*pi*2500/(60*0.74*4.
12))


v =

57.7

which is close to the 60mph you mentioned above. The calculation for rolling radius is a bit dubious, but is close enough for an approximation. To be accurate, you would need to count the number of tyre revolutions per km.

Number_Cruncher
Astra automatic gear ratios - plonker
Thanks Number Cruncher for the website - and your calculations.
Astra automatic gear ratios - Aprilia
Yes, but rmember that speed can be anything for 0-10% fast. Also rev counter at 2-3000rpm can be out by a couple of hundred rpm (they are usually fairly accurate around idle by can be a bit inaccurate at higher rpm - there is not requirement for them to be accurate).
Astra automatic gear ratios - Number_Cruncher
Yes, but rmember that speed can be anything for 0-10% fast.
Also rev counter at 2-3000rpm can be out by a
couple of hundred rpm (they are usually fairly accurate around idle
by can be a bit inaccurate at higher rpm - there
is not requirement for them to be accurate).



Indeed, I was quite surprised when the estimate came out as close as it did!

Number_Cruncher
 

Ask Honest John

Value my car