Best options for regearing (or replacing) a rear end

[85lebaront2]

I'd forgotten, so thanks for reminding me. Yes, if you are having carburetion or ignition problems that could easily lead to poor enough performance that it can't maintain speed when it should.

What is being described is probably one of the reasons the AOD was dropped on the 300 after only 1 or 2 years, the other is probably the torque of a good 300 probably destroyed the AOD if it was used hard.

When Ford upgraded the AOD to first the AOD-E and then the 4R70W the OD for the 300 had to wait for the E4OD.

I had a 1977 F150 with the 300 and a C4, the man I bought it from said he had the C4 rebuilt because it had burned up. My former Dept. Manager has a 1987 F150, 300 with a C6, again probably due to the torque output of the 300.

[ScubaSteve]

David/1986F150Six with his '86 300 six and 3.08 gears and the 4-speed OD transmission said it does really well on the highway. Looking at the calculator his would be turning 1714 and yours 1618 at 70 MPH. So it looks to me like either you are geared just a bit too tall/high or maybe the AOD's TV cable is maladjusted?

I don't have any experience at all with the AOD, but just scanned the factory shop manual section on it (Documentation/Driveline/Transmissions/Automatic Transmissions/AOD) and didn't find a symptom listed that describes your problem. But, if it were maladjusted it might come out of OD too early.

From what I read any changes to the idle speed or other adjustments to the carb can affect the TV linkage. Have you had work done on the carb?

But if the AOD's TV linkage is correctly adjusted, then maybe a gearing change is in order. I've often thought that 3.55 gears coupled with an AOD's .67:1 OD would be a good combo. With 30" tires you'd be turning 1865 R's at 70 MPH, and should be able to handle most hills w/o shifting out.

If you decide to go with 3.55 gears you can probably find a complete 8.8 rear-end with that ratio in a salvage yard. That was a very common ratio in the f150 with an AOD behind the 302. I find my truck with an AOD and 3.55 is still a little too high for me with 29" tires. I never use overdrive until I get on the interstate as drive seems to be best for anything 55MPH and below. I am planning to re-gear to 3.73 or maybe even 4.10 later this year.

[FuzzFace2]

If you decide to go with 3.55 gears you can probably find a complete 8.8 rear-end with that ratio in a salvage yard. That was a very common ratio in the f150 with an AOD behind the 302. I find my truck with an AOD and 3.55 is still a little too high for me with 29" tires. I never use overdrive until I get on the interstate as drive seems to be best for anything 55MPH and below. I am planning to re-gear to 3.73 or maybe even 4.10 later this year.

What is the over drive ratios between the AOD and what Dave has in his truck as I think he has the 3sp od stick tdans?

Dave----

[1986F150Six]

David/1986F150Six with his '86 300 six and 3.08 gears and the 4-speed OD transmission said it does really well on the highway. Looking at the calculator his would be turning 1714 and yours 1618 at 70 MPH. So it looks to me like either you are geared just a bit too tall/high or maybe the AOD's TV cable is maladjusted?

Gary, did you figure this with 235/75X15 tires? My RPMs were higher and the truck wore 215/75X15 tires.

 

[Gary Lewis]

David/1986F150Six with his '86 300 six and 3.08 gears and the 4-speed OD transmission said it does really well on the highway. Looking at the calculator his would be turning 1714 and yours 1618 at 70 MPH. So it looks to me like either you are geared just a bit too tall/high or maybe the AOD's TV cable is maladjusted?

Gary, did you figure this with 235/75X15 tires? My RPMs were higher and the truck wore 215/75X15 tires.

I used 235's.

[1986F150Six]

I used 235's.

With the original 6K tachometer, 70 mph = 2,000 rpms.

With the 4K, followed by the NOS 4.5K tachometer, 70 mph = 1950 rpms.

[ratdude747]

With the original 6K tachometer, 70 mph = 2,000 rpms.

With the 4K, followed by the NOS 4.5K tachometer, 70 mph = 1950 rpms.

Sounds like a gearing change might be in order then. I'm about 200RPM lower than you... I'll confirm this the next time I take it on the highway (which actually might be tomorrow???)

[1986F150Six]

Sounds like a gearing change might be in order then. I'm about 200RPM lower than you... I'll confirm this the next time I take it on the highway (which actually might be tomorrow???)

Depending on what you are reading, the 300/4.9L engine develops maximum torque [most efficient operating range] @ 1600 - 1800 RPMs. That is why for best gas mileage, I drove this truck @ ~60 - 62 mph ~1700 RPMs.

[ratdude747]

Depending on what you are reading, the 300/4.9L engine develops maximum torque [most efficient operating range] @ 1600 - 1800 RPMs. That is why for best gas mileage, I drove this truck @ ~60 - 62 mph ~1700 RPMs.

I read max torque is at 2000. Maybe that's EFI though.

---

Drove it some today (and driving to MO tomorrow, and back the day after). I'm getting 1550-1600 RPM at what I estimate to be 68MPH. To get to where you're at, I'd be looking at a 3.2725 ratio per my calculations (a bit steeper actually, since you reported a slightly slower speed). 3.55 may be too steep... I did see 3.3x gear sets on Summit Racing though.

[Gary Lewis]

I read max torque is at 2000. Maybe that's EFI though.

---

Drove it some today (and driving to MO tomorrow, and back the day after). I'm getting 1550-1600 RPM at what I estimate to be 68MPH. To get to where you're at, I'd be looking at a 3.2725 ratio per my calculations (a bit steeper actually, since you reported a slightly slower speed). 3.55 may be too steep... I did see 3.3x gear sets on Summit Racing though.

Max torque for an '84 is at either 1400 or 1600 depending on the model. You can see that here: Documentation/Engines/300 Six and then the Specifications tab. Scroll down to the page on 1984.