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Old 05-24-2020, 04:10 PM   #1
diyforever
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Red face RPMs increase when engage Laycock overdrive, hmmm?

It's my understanding that when an overdrive is engaged, the RPMs on the engine should decrease. However, on my 1930 A I have a laycock overdrive and a tach which shows RPMs increase when I engage. The speedometer reading goes up approx 10 mpg which I understand since speedocable is attached to original 3 speed transmission. Anyone shed some light on why engine RPMs increase?
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Old 05-24-2020, 04:29 PM   #2
Bob C
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Default Re: RPMs increase when engage Laycock overdrive, hmmm?

If the speedometer cable is before the overdrive them why would the
speedometer change when you go into overdrive?
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Old 05-24-2020, 05:01 PM   #3
briphaeton
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Default Re: RPMs increase when engage Laycock overdrive, hmmm?

You need to switch the on to off and the off to on. My speedometer and tach drops while in overdrive.
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Old 05-24-2020, 05:44 PM   #4
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Default Re: RPMs increase when engage Laycock overdrive, hmmm?

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Originally Posted by briphaeton View Post
You need to switch the on to off and the off to on. My speedometer and tach drops while in overdrive.
Yup, the switch is reversed so he starts off in O/O and then changes down.
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Old 05-24-2020, 06:45 PM   #5
diyforever
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Default Re: RPMs increase when engage Laycock overdrive, hmmm?

Bob, I'll double check the connection on the speedocable.
Just wondering about the switch connection. Does it mean that I should switch the connection on the switch attached to the transmission tower? OR ?
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Old 05-24-2020, 07:31 PM   #6
Jack Shaft
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Default Re: RPMs increase when engage Laycock overdrive, hmmm?

Does it feel like its in overdrive?
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Old 05-24-2020, 08:21 PM   #7
CarlG
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Default Re: RPMs increase when engage Laycock overdrive, hmmm?

Overdrive installed backwards??
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Old 05-25-2020, 02:55 AM   #8
Synchro909
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Default Re: RPMs increase when engage Laycock overdrive, hmmm?

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Overdrive installed backwards??
Or up side down????
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Old 05-25-2020, 08:44 AM   #9
rotorwrench
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Default Re: RPMs increase when engage Laycock overdrive, hmmm?

The speedometer would have to be geared in to the output shaft of the overdrive for it to give an accurate reading while in overdrive. The Laycock has to have the solenoid turned on for it to shift into OD planetary drive.
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Old 05-25-2020, 01:25 PM   #10
briphaeton
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Default Re: RPMs increase when engage Laycock overdrive, hmmm?

The transmission switch takes it out of overdrive if you try to go into reverse gear while in overdrive, because that would damage the overdrive. You need to change the plate on the dash switch that reads on and off. The position that reads on is really off and off is really on. If the speed changes in and out of overdrive the speedo is connected to the transmission. Went your in overdrive the speedo is going to read around 10 mph slower.
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