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High RPMs....normal?

advracer67

Jr. Member
Joined
Jan 29, 2010
Messages
117
I finally have my 1977 stock barn find on the road. This is my first EB so I'm not sure what normal is.

On the highway the truck sounds and feels good up to 50-55. Then it sounds like the RPMs are going a bit too high. I don't have a tach so I'm going by sound and feel. I tested it and it is going through all 3 gears on the automatic transmission.

Is This normal? If so can the gearing be changed so I can cruise comfortably at 65? This truck will not be taken off-road.
If not normal what do you think it could be?
 
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advracer67

Jr. Member
Joined
Jan 29, 2010
Messages
117
Stock size tires no increase in size
stock transmission and rear end - I have no idea on the gearing
 

Explorer

Bronco Guru
Joined
Mar 2, 2008
Messages
4,390
Loc.
Raphine, Virginia
Look at the data plate on glovebox door. the last number on top is axle code, will be 18 for 3:50 gears, 03 for 4:11's, 04 for 4:57's. Couple others will designate lockers. That will tell you what it came with, but things get changed.
 
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advracer67

Jr. Member
Joined
Jan 29, 2010
Messages
117
I just happen to have a picture on my work computer. It says 18

Do I have a low gear ratio? This is new to me. If I have to change the gears do I have to do it to the front drive as well?
 

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Explorer

Bronco Guru
Joined
Mar 2, 2008
Messages
4,390
Loc.
Raphine, Virginia
3:50 gears are normal. It could either be they were changed(doubtful) or you are just use to late model vehicles. You can verify the ratio, I'll let someone else answer that one for procedure.
 

broncnaz

Bronco Guru
Joined
May 22, 2003
Messages
24,341
Got to figure that in the 70's 55 was the speed limit vehicles were setup to run that way. Over 55 and yes older vehicles seem like they are very high in the rpm range but there really not. I wouldnt worry much about it and no I wouldnt regear your better off putting some slightly taller tires on next time although 33in is about as tall as you should go with 3.50 gearing. But still your only going to change the RPM's by about 200 RPM with the tire swap differance. You next best bet would be stock sized tires and a OD transmission swap.
But still the ford small block engine really needs to rev to be happy runnning it 75 mph with stock tires may be a bit high in the rpms but it wont hurt anything.
 
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advracer67

Jr. Member
Joined
Jan 29, 2010
Messages
117
Thanks that information helps and puts my mind at ease. I was afraid I'd cause some real damage going over 55
 
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