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shifting speed for 4+3 Tranny

bobmo

Active member
Joined
Apr 28, 2003
Messages
37
Location
Lancaster, VA
Corvette
1987 Bright red, 1974 coupe--Basket case
Good morning all
I have an 87 Vette coupe, 4+3 tranny.
I have been driving her daily since my other day car is out of commission. Now my dilmena is this.
When I shift thru the gears and go into 4th Overdrive. I need to be over 56mph or it bucks and moans like I was trying to take off from a light in 3rd.
The other OD speeds seem pretty high as well but the normal flow of traffic is about 55 and its driving my crazy.
Engine RPM is about 1400 at this speed.

Any clues?
Thanks
Bob
 

John '85

Well-known member
Joined
Mar 22, 2006
Messages
57
Location
Fremont CA
Corvette
1985 Red Coupe TKO500 Z51
I usually dont engage the overdrive until I am at 2000 rpm on the highway, I think 1400 is too low for 4th overdrive. I will try to duplicate your problem on the drive home tonight.
 

bobmo

Active member
Joined
Apr 28, 2003
Messages
37
Location
Lancaster, VA
Corvette
1987 Bright red, 1974 coupe--Basket case
Thanks John
I did find a solution this past weekend that seems to have solved the problem.
I had'nt driven the car most of the summer, but I need it now for my daily drive.
I did the basics this weekend and found one of the spark plugs was loose. I pulled all of them, cleaned them up and she is running MUCH better.
I also think my smaller CATs are plugged so that will be the christmas replacement item and I hope will be the cure.

According to the book. I should be able to drive at 45mph in 4th OD.
That really labors the whole system at about 1100 rpm.
So much for the book.
Merry Christmas
 
M

magoo

Guest
I had a similar problem with my 86, alot of bucking and jerking at speeds where it seemed abnormal, mostly when slowing down. Mine did it in OD or not. One day my clutch linkage came apart under the dash. When I went under there to fix it I found alot of wires not nicely bundled. It seems someone had either dealer installed or replaced the cruise control unit and not done a very nice job. Of course while I was in the area I neatened everything up and checked that all the pins in the various plugs where making good contact. After replacing the $5.oo, 25 cent plastic clip at the clutch pedal I closed everything up and my bucking problem was gone. I have no idea which connector it was or why but it is now a real pleasure to drive. Maybe someone else can explain it, but I just thought I'd offer it to think about. Good luck,
Mike

PS: My cruise control always worked so I never expected it to be part of the problem.
 

c4cruiser

Well-known member
Joined
Feb 22, 2002
Messages
971
Location
Lacey, WA USA
Corvette
87 Gold Z52 Coupe 02 EB Z51 Supercharged Coupe
I have seen engine speed as low as 900RPM with my 87 when OD is engaged in 4th gear. If the engine is running properly, there should be no jerking or bucking. It can be hard to accelerate with light throttle, but even at low RPM's, the engine has enough torque to increase vehicle speed.

I don't use the OD at low speeds, but I do run 3rd gear w/OD when posted speed limits are around 40 to 45 for longer stretches. The engine runs about 300RPM lower than 4th w/ no OD.
 

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