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Overdrive and lockup

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Old 06-27-2017, 06:45 PM
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Default Overdrive and lockup

On my trip last weekend the MPG was just under 20 but thought it should have been better. Stock 2003 LM4 5.3 engine with stock 4L60E trans. Rear gears are 3.73 with a 26" tire. Car is a '39 Chevy at 3300 lbs. How can I tell if it goes into overdrive? Lockup?
Old 06-27-2017, 08:43 PM
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You can tell if it has locked up the converter by driving it at speed, when you think the converter should be locked up touch the brake lightly. Do not let off the throttle. Look at the tach if you have one and if it was locked up, the RPMs should go up by a couple hundred or so RPM.
Same with OD. If you think you should be in fourth, look at the tach, down shift to manual third. RPMs should drop.
Also, if you have a scanner or access to one, you can look there.
Old 06-28-2017, 09:42 AM
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Originally Posted by sowbelle
You can tell if it has locked up the converter by driving it at speed, when you think the converter should be locked up touch the brake lightly. Do not let off the throttle. Look at the tach if you have one and if it was locked up, the RPMs should go up by a couple hundred or so RPM.
Same with OD. If you think you should be in fourth, look at the tach, down shift to manual third. RPMs should drop.
Also, if you have a scanner or access to one, you can look there.
Darn. I just tried this and the RPM rose when downshifting. Will be taking it to AAMCO later today.
Old 06-28-2017, 10:35 AM
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Originally Posted by sowbelle
You can tell if it has locked up the converter by driving it at speed, when you think the converter should be locked up touch the brake lightly. Do not let off the throttle. Look at the tach if you have one and if it was locked up, the RPMs should go up by a couple hundred or so RPM.
Same with OD. If you think you should be in fourth, look at the tach, down shift to manual third. RPMs should drop.
Also, if you have a scanner or access to one, you can look there.
I think you have that backwards. When you downshift with throttle at steady state, your RPM will rise...

Originally Posted by gsteele
Darn. I just tried this and the RPM rose when downshifting. Will be taking it to AAMCO later today.
You are good....it should rise..

T,
Old 06-28-2017, 12:31 PM
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Originally Posted by TomM
I think you have that backwards. When you downshift with throttle at steady state, your RPM will rise...



You are good....it should rise..

T,
Whew! Thanks.



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