What is proper RPM when coasting?

S_Mazza

Registered User
When I coast on the highway, my Thunderbird idles at a steady 1500 RPM in OD. I think it's about 1000 RPM in Neutral. I think this is too high. What RPM do your cars coast at?

(I think this may be related to a problem I have with a low and rough idle at stoplights. In Park and Neutral, the idle seems fine. I know some others on this board have posted about similar problems, but I haven't found any solutions. Yes, I searched.)

Thanks in advance.

Steve
 
Maybe I dont understand your question. You should never coast. When you coast you are not in control. If you mean idle in gear 1000 rpms. is high. My car run at 800 at a idle after it warms up. I hope that helps.
 
In OD your converter is locked meaning you will coast at whatever rpm relates to the speed you are going just like a 5spd car. In neutral the motor will idle at 1000-1100 if you are coasting and 6-800rpm when sitting still. Drive idle can be up to 200rpm lower dpending on year and EEC code.
 
...while we are ON the subject ........

XR7 Dave said:
In OD your converter is locked meaning you will coast at whatever rpm relates to the speed you are going just like a 5spd car. In neutral the motor will idle at 1000-1100 if you are coasting and 6-800rpm when sitting still. Drive idle can be up to 200rpm lower dpending on year and EEC code.
Hey Dave, how can I tell if my car is REALLY in overdrive?? I've never had Overdrive before, so I can't tell just by the feel, if I am slippin IN or OUT of it. At 2k rpm I am at 70mph and by the digital computer, getting 28-30 mpg. I have NO idea if the rear gear ratio has ever been changed. Thanks. :)
 
ThunderTurkey said:
Hey Dave, how can I tell if my car is REALLY in overdrive?? I've never had Overdrive before, so I can't tell just by the feel, if I am slippin IN or OUT of it. At 2k rpm I am at 70mph and by the digital computer, getting 28-30 mpg. I have NO idea if the rear gear ratio has ever been changed. Thanks. :)

The 4th gear is overdrive. You should be able to feel your transmission shift 4 times. Your transmission will not allow 4th until 45 mph and it will downshift at 35 mph back into 3rd at 35.

I have listed below the gear ratios of a stock 89-93 auto. Since 4th gear is below 1.0 it is an overdriven (overdrive has a faster output speed than input speed), thus being called an overdrive gear.

4th 0.67
3rd 1.00
2nd 2.32
1st 3.75
 
Based on your rpm's you are in 4th gear. 2000rpm is about 70mph. Because the torque converter slips in 1&2, you can often get all the way to 3rd with feeling only one shift. My AOD shifts early and will often the shift from 1-2 is hardly perceivable and other times it seems to shift straight from 1-3.

That is great mileage too! My AOD gets about 21mpg and it is bone stock. I might need new O2 sensors. :(
 
XR7 Dave said:
My AOD shifts early and will often the shift from 1-2 is hardly perceivable and other times it seems to shift straight from 1-3.

Do you think this is bad? Because mine is doing that all the time. 1-3 shifting.
 
I doubt your AOD is actually skipping the 1-2 shift, but under a light load it may be only staying in second for a very brief time. Will it stay in second gear longer when under heavy acceleration?

I know that after I had my AOD rebuilt on my '90, the TV cable needed slight adjustments to set the shift points so that it would stay in second gear longer. When I first got it back from the shop, it would not stay in second even under severe load on the dyno.

I didn't do the adjustments myself, but adjusted too far one way, the AOD would seem to "Skip" second and immediately go into third, and too far the other way, the AOD would not drop back into first when coming to a stop. The Guy that did my Tranny build had been a Ford master Tech for fifteen years, so I just trusted his experience and got out of his way.
 
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