When to use Over Drive ?
Thread Starter
2nd Gear
Joined: Mar 2009
Posts: 2
Likes: 0
When to use Over Drive ?
Hi All
New to Vettes. My Vette has the 4+3 manual tran with the over drive. The last owner put a generic switch on the side rather than R&R the stock set up. I have no idea what he has done to the electronic's. I start the car and by default the over drive is on. I think it is not on in 1st gear. When I drop my foot the kick down takes over and what a ride.
My question is will the tran last longer if I only use the over drive for high way use? A mechanic told me only use the over drive for the high way only and avoid driving the car with it on. The guy who sold me the car told me to use the over drive all the time. Who is right ?
New to Vettes. My Vette has the 4+3 manual tran with the over drive. The last owner put a generic switch on the side rather than R&R the stock set up. I have no idea what he has done to the electronic's. I start the car and by default the over drive is on. I think it is not on in 1st gear. When I drop my foot the kick down takes over and what a ride.
My question is will the tran last longer if I only use the over drive for high way use? A mechanic told me only use the over drive for the high way only and avoid driving the car with it on. The guy who sold me the car told me to use the over drive all the time. Who is right ?
Last edited by Orlydj; Apr 16, 2009 at 12:59 AM.
Team Owner
Joined: Jan 2003
Posts: 20,306
Likes: 242
From: Summerland B.C. Canada
Like most people here, I only use OD on the highway. I use the clutch when disengaging and engaging OD, it's easier on the 20+ year components.
OD on is default when the car is first started, once the motor gets to a certain temp and a few other parameters (about 125 on my 86), OD will engage.(the switch is useless until the temp has been reached.86)
OD on is default when the car is first started, once the motor gets to a certain temp and a few other parameters (about 125 on my 86), OD will engage.(the switch is useless until the temp has been reached.86)
Le Mans Master
Joined: Aug 2000
Posts: 8,838
Likes: 31
From: Australia
Dependent apon speed conditions I found it convenient to drive in 3rd O/d which is not far off 4rd direct which gave you the ablity to kick it down for a pass without having to change gear
http://corvetteobsession.homestead.c...formation.html
http://corvetteobsession.homestead.c...formation.html
Team Owner
Joined: Dec 1999
Posts: 34,873
Likes: 487
From: Lacey WA RVN 68-69
NCM Sinkhole Donor
My 87 has the 4+3 and like most others, I tend to use the OD once I get on a freeway or roads where the speed limit is 50 or more. For some arterials where speeds are 40 to 45 MPH, I'll use 3rd gear and OD. 3rd + OD will provide a slightly lower RPM that 4th and no OD.
I also depress the clutch pedal when manually engaging the OD as it saves the shock on the driveline and is easier on the internal components. But for freeway kickdown, I'll let the unit do it's own thing; at freeway speeds the shock or jerkiness is not that bad.
The default operation is OD on with a couple of exceptions. Water temp has to be at a certain level before the unit will operate and if you used more than a certain percentage of throttle in low gear, the OD will not come on unless you engage it on with the switch.
The OD will also automatically "kick down" just like a auto trans when you are in 4th and OD and it will upshift once you let up on the gas.
You didn't say what year car you have, but this link will show the proper operation of the OD based on the year.
I also depress the clutch pedal when manually engaging the OD as it saves the shock on the driveline and is easier on the internal components. But for freeway kickdown, I'll let the unit do it's own thing; at freeway speeds the shock or jerkiness is not that bad.
The default operation is OD on with a couple of exceptions. Water temp has to be at a certain level before the unit will operate and if you used more than a certain percentage of throttle in low gear, the OD will not come on unless you engage it on with the switch.
The OD will also automatically "kick down" just like a auto trans when you are in 4th and OD and it will upshift once you let up on the gas.
You didn't say what year car you have, but this link will show the proper operation of the OD based on the year.
Melting Slicks
Joined: Feb 2006
Posts: 2,753
Likes: 15
From: backwoods upstate ny
never 'lug' the engine (lug = under load at very low rpm) as lugging kills the engine bearings...if in doubt, just keep engine above 1400-1500 rpm when driving in any gear and/or o/d.
if your car is has the z51 option (like mine), you have the stronger o/d gears than the base 4-3 o/d, but also have a different o/d ratio than the base o/d...z51 o/d in 2nd and 3rd is closer to next higher non-od, not really worth using the lower gear + od...i only use od as 5th gear, always in/out using third pedal to save the anemic friction discs that engage/disengage the o/d.
if your car is has the z51 option (like mine), you have the stronger o/d gears than the base 4-3 o/d, but also have a different o/d ratio than the base o/d...z51 o/d in 2nd and 3rd is closer to next higher non-od, not really worth using the lower gear + od...i only use od as 5th gear, always in/out using third pedal to save the anemic friction discs that engage/disengage the o/d.
Last edited by redrose; Apr 16, 2009 at 09:04 AM.
Thread Starter
2nd Gear
Joined: Mar 2009
Posts: 2
Likes: 0
Thanks to all
I started following every ones advice. The car is a 1988. The syncro's are not so hot. If the clutch pedal is not fully engaged I can feel the grind and it is harder to shift. The OD does have a powerful bang I can see why every one press's the clutch.
Thank You
Thank You
Slingshot
Joined: Dec 2001
Posts: 3,817
Likes: 24
From: Charlotte NC
Like most people here, I only use OD on the highway. I use the clutch when disengaging and engaging OD, it's easier on the 20+ year components.
OD on is default when the car is first started, once the motor gets to a certain temp and a few other parameters (about 125 on my 86), OD will engage.(the switch is useless until the temp has been reached.86)
OD on is default when the car is first started, once the motor gets to a certain temp and a few other parameters (about 125 on my 86), OD will engage.(the switch is useless until the temp has been reached.86)
This is exactly how mine works as well.
Slingshot
Joined: Dec 2001
Posts: 3,817
Likes: 24
From: Charlotte NC
Your car has a hydraulic clutch. If you find it hard to get into gear when shifting, it may be the hydraulic clutch acting up and not the synchronizers in your transmission. I have had to replace my clutch slave cylinder three times over the years. During the car's 23 year history I have replaced the clutch disk and pressure plate once and have never touched the Super T10, or its synchronizers, other than changing the gear oil
Check it out....
Last edited by pmihaltian; Apr 18, 2009 at 09:49 PM.
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Racer
Joined: Mar 2004
Posts: 252
Likes: 1
From: Troy Illinois
I have a 1985 4+3 and I do not turn the overdrive on unless I am on an interstate and maintaining a speed over 55 - 60. The button on my shifter is designed to turn the overdrive off and on once the temperature reaches 140 deg. There is a chart that shows how each year 4+3 is designed to work and it will tell you how your 88 is designed. Search Doug Nash 4+3 and it should show up.
Racer
Joined: Sep 2004
Posts: 258
Likes: 0
From: Coram NY
like agent86, my OD is active once the temp is 120 deg. i allow it to shift automatically into OD, and use the differnt combinations at all driving conditions. It is a misconseption that if you are not in OD, the OD unit is "disconnected" our OD units are integral to the operation of the transmission wether engaged or not. If you are experiencing symtoms like poping out of 2nd gear when you let off the gas, this is most likely due to the OD unit, same as slipping in reverse (like mine), and it doesnt matter if OD is on or off. I still do not know if I want to get a rebuilt unit or go for a new TKO. Oh, in forward gears my OD unit still operates fine.
Tom
Tom
Drifting
Joined: Apr 2009
Posts: 1,928
Likes: 93
From: Boulder City NV
Mine goes good in the forward gears although my OD button does not seem to affect anything. I just drive and let it think for itself. But my tranny is slipping in reverse pretty bad. I just got my 88, it was pretty beat and neglected. I'm thinking of having the trans and OD serviced anyway but it sounds like it maybe too late. Any recommendations??
Team Owner
Joined: Jan 2003
Posts: 20,306
Likes: 242
From: Summerland B.C. Canada
Macgruber, the clock is ticking . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Have you looked at the OD fluid level and filter ??
Melting Slicks
Joined: Feb 2006
Posts: 2,753
Likes: 15
From: backwoods upstate ny
jumping out of 1/2/3 or 4th gear is a problem in the 'front' part of the trans (the 'super t-10 part)...most likely worn 'noses' on the synchro dogs that are part of the gear...a 'new' 2nd speed gear will probly fix your 2nd gear pop-out, in extreme cases the 'synchro drum assy' will also have 'nose trouble' at the mating points where the 'dogs' lock in and also need replacement.
4-3 o/d has a 'sprag' that prevents slippage during o/d switch-over from 'straight-thru' to 'overdriven' modes (think of it as a giant 'ratchet wrench') while the 'friction disc paks' of both 'straight-thru' and 'o/d' are both unloaded...when the sT-10 part of the trans is shifted into 'reverse' gear, the sprag is not loaded (by design) and slippage at worn-down 'friction disc pak' in the 'straight-thru' part of the o/d results in a loss of power transmit...in forward gears, the sprag does what the 'straight-thru' friction disc pak should be doing (if discs not worn out)...if the 'o/d/ friction disc pak' is inoperative due to low fluid/ low pump pressure/ etc., the sprag will still provide forward vehicle drive at non-o/d revs.
Last edited by redrose; Apr 19, 2009 at 09:12 AM.