Hope fully I'm posting this in the right section.
Truck specs
63 f100
4.9l 300 w/Aod transmission
Holley 4150 carb
Ford 9" rear end
OK so here's the problem the engine will not hold speed in OD gear. Truck will shift into OD at 60mph and from there it slowly loses rpms no matter how much gas I give it until it downshifts into 3rd then it gains rpms. I've already set the pressure on the TV cable to 35psi. Is this a timing issue or carb issue. I'm at loss as here. Any help is greatly appreciated

 

Amast Welcome to and the Slicks Forum.

Qusetion, Have you tried to shift it out of OD to see if the engine would regain rpms?


John

 

Engine will regain rpms once I shift into 3rd. Becomes a constant situation where it shifts between od and 3rd because it can't keep the rpms to keep it od gear.

 

If you can operate the truck in 1 to 1 ok but it looses rpms in OD, makes me believe it's the rear ratio.

Sounds like you may have something like a 3.00 ratio when you need a 3.75. Sounds like it is dropping the rpms to a level that it can't maintain.


John

 

I'll have to look what gears I have in the there. Probably won't be able to get that done till the weekend.
Thanks for the help.

 

It could be low fuel pressure from a clogged filter or weak fuel pump.

Clogged air cleaner.

Vacuum problem.

Timing could need adjustment.

Or just a worn out engine.

 

Engine is a fresh rebuild. I've ran thru the basics as you mentioned except for the fuel filter. I would think that if it was the fuel filter it would act like it does through out all the gears?

 

Does it run and perform well when not in OD?


John

 

Runs fine in all other gears. Just the overdrive gear that it's lacking power.

 

Then it's most likely the ratio. The engine is turning rpms below it's power band and can't keep up. Get it out on a big road and drive it 70 mph or more and try OD. Bet it will work there.


John

 

If it makes a difference the problem is at highway speeds.

 

That points away for ratio then. The engine is not getting what it needs. You can get better advice on that from others.


John

 

I would run it up to 80 or 90 MPH and see if it will hold. If it will, it is definitely geared too tall.

 

You’re thinking same as me.


John

 

Yup. Just that if it has something like 3.25's in the rear end, you will have to be going a little over 80 MPH to even be turning 2000 RPM. If it has 3.00's you will have to do 90 to get to 2000 rpm.