Doug Nash 4+3 question
Thread Starter
Instructor
Joined: Jan 2015
Posts: 203
Likes: 2
From: Port Costa CA
Doug Nash 4+3 question
1988 C4 , What rpm should the engine be running while in 4th overdrive?
The issue I have is while in 4th and engaging the overdrive it does not seem to shift into another gear but when I let off the throttle it coasts like it is in overdrive.
If I disengage the OD it seems to shift down a gear.
So in other words while say on the freeway in 4th with OD engaged applying throttle the engine is running high RPM"s
This to me does not seem correct?
The issue I have is while in 4th and engaging the overdrive it does not seem to shift into another gear but when I let off the throttle it coasts like it is in overdrive.
If I disengage the OD it seems to shift down a gear.
So in other words while say on the freeway in 4th with OD engaged applying throttle the engine is running high RPM"s
This to me does not seem correct?
Le Mans Master
Joined: Jun 2009
Posts: 6,528
Likes: 752
From: South Dakota
No one can give you the rpm's at speed because there were 2 different OD ratios per the codes below. Generally the Z51 cars had the MK2 option and the base cars had the MH5 option. They need to know which one you have. Then some people could calculate or observe their cars to help determine the rpm.
MH5 = 0.60
MK2 = 0.68
When you are driving in 4th gear on the highway at a steady cruise, if you engage the OD, the rpm should drop 32% or 40% and feel like a shift. When you disengage the OD it should also feel like a shift and the rpm should jump 32% or 40%.
As for the feel of coasting, There is no torque converter for allowing slippage, so it should feel like a manual transmission whether the OD is engaged or not. Unless it is going into or out of OD, the rpm should not change at a specific speed at cruise throttle. If it is allowing the rpm to drop with less throttle (without a change to OD engagement) there is something wrong.
MH5 = 0.60
MK2 = 0.68
When you are driving in 4th gear on the highway at a steady cruise, if you engage the OD, the rpm should drop 32% or 40% and feel like a shift. When you disengage the OD it should also feel like a shift and the rpm should jump 32% or 40%.
As for the feel of coasting, There is no torque converter for allowing slippage, so it should feel like a manual transmission whether the OD is engaged or not. Unless it is going into or out of OD, the rpm should not change at a specific speed at cruise throttle. If it is allowing the rpm to drop with less throttle (without a change to OD engagement) there is something wrong.
Thread Starter
Instructor
Joined: Jan 2015
Posts: 203
Likes: 2
From: Port Costa CA
No one can give you the rpm's at speed because there were 2 different OD ratios per the codes below. Generally the Z51 cars had the MK2 option and the base cars had the MH5 option. They need to know which one you have. Then some people could calculate or observe their cars to help determine the rpm.
MH5 = 0.60
MK2 = 0.68
When you are driving in 4th gear on the highway at a steady cruise, if you engage the OD, the rpm should drop 32% or 40% and feel like a shift. When you disengage the OD it should also feel like a shift and the rpm should jump 32% or 40%.
As for the feel of coasting, There is no torque converter for allowing slippage, so it should feel like a manual transmission whether the OD is engaged or not. Unless it is going into or out of OD, the rpm should not change at a specific speed at cruise throttle. If it is allowing the rpm to drop with less throttle (without a change to OD engagement) there is something wrong.
MH5 = 0.60
MK2 = 0.68
When you are driving in 4th gear on the highway at a steady cruise, if you engage the OD, the rpm should drop 32% or 40% and feel like a shift. When you disengage the OD it should also feel like a shift and the rpm should jump 32% or 40%.
As for the feel of coasting, There is no torque converter for allowing slippage, so it should feel like a manual transmission whether the OD is engaged or not. Unless it is going into or out of OD, the rpm should not change at a specific speed at cruise throttle. If it is allowing the rpm to drop with less throttle (without a change to OD engagement) there is something wrong.
Safety Car
Joined: Oct 2007
Posts: 4,426
Likes: 229
From: Pennsylvania
No one can give you the rpm's at speed because there were 2 different OD ratios per the codes below. Generally the Z51 cars had the MK2 option and the base cars had the MH5 option. They need to know which one you have. Then some people could calculate or observe their cars to help determine the rpm.
MH5 = 0.60
MK2 = 0.68
When you are driving in 4th gear on the highway at a steady cruise, if you engage the OD, the rpm should drop 32% or 40% and feel like a shift. When you disengage the OD it should also feel like a shift and the rpm should jump 32% or 40%.
As for the feel of coasting, There is no torque converter for allowing slippage, so it should feel like a manual transmission whether the OD is engaged or not. Unless it is going into or out of OD, the rpm should not change at a specific speed at cruise throttle. If it is allowing the rpm to drop with less throttle (without a change to OD engagement) there is something wrong.
MH5 = 0.60
MK2 = 0.68
When you are driving in 4th gear on the highway at a steady cruise, if you engage the OD, the rpm should drop 32% or 40% and feel like a shift. When you disengage the OD it should also feel like a shift and the rpm should jump 32% or 40%.
As for the feel of coasting, There is no torque converter for allowing slippage, so it should feel like a manual transmission whether the OD is engaged or not. Unless it is going into or out of OD, the rpm should not change at a specific speed at cruise throttle. If it is allowing the rpm to drop with less throttle (without a change to OD engagement) there is something wrong.
