New gears really going to help with mpg?

[gwstang]

I have measured the mpg 3x and I am still only getting 15 mpg with the freshly rebuilt '90 5.0 HO with my 600 edelbrock carb sitting on top.  The AOD tranny has a 2000 stall converter behind the engine.  I purchased the 3.55 gears recently to install which I will do this weekend. I am just wondering if the mileage will go up any.  I think it's staying in 2nd and 3'd too much right now because I have to get to around 60 mph before it will hit 3'd and around 65-70mph before it will drop into 4th o.d..  Damn I sure thought this combo would be getting better mileage even with the 2.80 rear gears. I am using a new dist. with vacuum advance and the timing set at 12 deg btdc.  Any guesses if the mileage will improve with the 3.55 gears or not?  Hoping it will shift sooner for sure, but the yowzer factor may kick in with the new gears....lol.  :)

[AzPete]

Depending on what you have in there now, mpg may go down. If you have stock type 3.00 or so gears, expect a drop.

It sounds like the shifting points are part of the problem.

My '66 gets 13 mpg, on a fun day, I can get it to 9.....lol

[guruatbol]

I dropped 2 MPG when I put 3:55s in the 65 with the TKO in it.  The 67 still has stock with a T5 and I get 25-28 depending if I use CA gas or not.

Mel

[silverblueBP]

Who owns a vintage car and cares about gas mileage  :craz :craz


I get 4-8 mpg.........like I care.


I would guess it'll get worse the higher you go. The engine will be turning higher rpm's at highway speed.

[buening]

What % of city/highway is the car used for?

[midpack]

but the yowzer factor may kick in with the new gears....lol.

I sure hope so!!  At least for a while... :lol

You know about the "one two one" shift right? TBH, that was about the only thing I liked when I had an AOD in the Fox...

[Rob Z]

Depending on what you have in there now, mpg may go down. If you have stock type 3.00 or so gears, expect a drop.

It sounds like the shifting points are part of the problem.

Agree with this.

Not sure about the AOD, but my C4 has an adjustable vacume modulator to controll shifts. A shift kit will also change shift points. If you do not go into 3rd befor 65 or 70 (without your foot in it) there is a shift issue.

How does it do around town. Say 30 to 35 traffic. Are you always in 2nd????

[johnpro]

Agree with this.

Not sure about the AOD, but my C4 has an adjustable vacume modulator to controll shifts. A shift kit will also change shift points. If you do not go into 3rd befor 65 or 70 (without your foot in it) there is a shift issue.

AOD's are mechanically modulated with the TV cable, unlike the C3, C4, C5, C6, and FMX.  You cannot really adjust the shift points.

15 mpg wouldn't be bad for city driving or combo of city/highway.  It would be horrible for highway alone.

I get about 22 mpg on the freeway with 3.50:1 gears.  I get horrible mileage around town because it's too much fun to put my foot into it.

You're going to like it a lot with the 3.55:1 gears in back.

[gwstang]

What % of city/highway is the car used for?

About 50/50 on city/hwy mileage.

[gwstang]

"You know about the "one two one" shift right?"   Uhmmmm, no not really.  Tell me? 

[gwstang]

"How does it do around town. Say 30 to 35 traffic. Are you always in 2nd???? "

Yes and also stays in 3'd a lot.  I think this is the problem and the loss of mpg's, by not making it into o.d. around town at all.  Of course 2nd is a lot of fun....lol. 

[gwstang]

"You're going to like it a lot with the 3.55:1 gears in back."     Yeah baby!  I'm hoping it will turn it into a whole 'nuter machine....!!!!!!  :ecit :ecit :ecit

[gwstang]

"I dropped 2 MPG when I put 3:55s in the 65 with the TKO in it"...Hey Mel, did you really like the oommmphh factor of the new gears?

[guruatbol]

Well, between the lower 1st to 2nd gears on the TKO vs the C4 and lower 1st to 3rd vs the T5 in the 67 and the gears in the rear and the trak-lok in the back, well, it is no animal, but it is awesome for the HP from the stock 289.

I am lacking some work on the power plant.  When I decide to do that, well it will then be an animal.

Oh, ask anyone here who has seem me drive it, I do drive it like I stole it, always!

Mel

[midpack]

"You know about the "one two one" shift right?"   Uhmmmm, no not really.  Tell me? 

Goes like this... put your shift selector into 1 (low) and go... shift into 2 as the RPM's climb, as soon as it shifts into 2nd, move the shifter back to 1 (low). This will hold the gear in 2nd for as long as you like... or until you break something!!
It gives a somewhat manual feel to an automatic transmission. 

[blue65coupe]

Going from 2.80 to 3.55 is a big difference.  That's what I did.  I wish I had put in an AOD due to the rpms on highway driving.  I miss the 2.80 on the highway.  Not only for rpms but at 75 mph I could lay into it and it had a long way to go.  The 3.55 is certainly fun around town.  Your gas mileage will go down.  Being that I stuck with the c4 I wish I would have went with a 3.25.  Just keep the 2.80 pumpkin and switch it out if you ever take a long trip if you're worried about mileage.  That's what I'm planning on doing if I can get it to MBB III.  I'd suspect though you running an AOD with 3.55 vs. me with a c4 that you'd end up significantly better off on highway mpg.

[B67FSTB]

Momentairely I have a T5z trans with 2.80 gears and its not driveble around town.Highway yes .
I have a 3.20 rearend laying around and planning to switch. I expect it will be more driveble around town.
3.55 is the best choise but I think for highway use not so, if it is for a very long distance.
You drive a mustang and the horse is thirsty.Comes with the hobby.

[tarafied1]

The key is what you do with your right foot! You'll love the 3.55's. I had an 85 GT 5.0 5speed that came with 2.73's and when I broke the rear I swapped to 3.55's and it was like a whole different car! But more tempting to put your foot in it.

and the AOD shift points can be tweaked a little, if you adjust the TV cable. The trans sounds like the TV cable is "tight" meaning the trans thinks your foot is in it more than it is. The TV cable controls the pressure and the shift points.
Here is a link on how I adjusted mine... just be careful. They way it is now is on the safe side (meaning it will shift higher but pressure will be higher). You may want to get a pressure gauge so when you get the shift points lower you can verify you have the correct minimum pressure.
http://www.txchange.com/aodadj.htm

[2ndgen]

Hmm....

Although the TV cable can affect the firmness of shifts and appears to alter the shift point, it is NOT the correct way to alter shift points on an AOD. The TV cable is for adjusting line pressure.

The AOD shift points are modified by either altering the weight in the governor on the tailshaft (this can be done while the transmission is in the car) or by valve body modification.

Ford made three different governor weights, a low, medium and high RPM version for different gearing and applications. As I recall the lighter the weight, the faster the output shaft had to spin and hence the later the shift point.

Since I built a "franken AOD" using the wide ratio gear set of a 4R70W, I had to switch the governor weights to lower my shift points since my output shaft now spins slower in relation to the engine in 1st gear... I also had to use a modified valve body since the spacing between gears was altered too.

Good luck,
-Rory

[tarafied1]

Hmm....

Although the TV cable can affect the firmness of shifts and appears to alter the shift point, it is NOT the correct way to alter shift points on an AOD. The TV cable is for adjusting line pressure.

I agree, I was just suggesting that it might not be adjusted correctly to start with if the shift points are too high and warning if he does adjust it to make sure the pressure doesn't get too low.
quote from website

Adding TV to attempt to correct pinging, chugging or lugging won't work. It Just causes thumps, bumps and extra wear. Set the TV so that the shifts are smooth and not late.

[tarafied1]

you got me thinking though, maybe the gearing change will help with the shift points as the tail shaft will be spinning faster with the 3.55's?

[2ndgen]

Yes, as relates to car speed. The gears will have no effect on the shift point in relation to engine RPM. The AOD has no idea what the vehicle speed is; it can only relate engine RPM and throttle position to output shaft speed.

-Rory

[tarafied1]

 so since the tail shaft rpm will be faster with the lower gear for the same car speed, the shift points will be different for the the car speed?

[2ndgen]

Perhaps a contrived/simplified example will help...

Suppose you have a car with an AOD that behaves as follows:

At 4800 RPM it shifts and the 2-3 shift is at 40 MPH with 3.0 rear gears...

You could change the governor weight to increase or decrease the shift point as it relates to engine RPM

If you change it to shift at 3500 RPM the 2-3 shift will happen at a lower speed, say 35 MPH

If you change it to shift at 5500 RPM the 2-3 shift will happen at a higher speed, say 45 MPH


Now instead of changing the governor weight, you change the rear end gears...

It you change to 2.5 rear gears it will still shift at 4800 RPM, but the 2-3 shift will be at a higher speed, say 45 MPH

If you change to 3.5 rear gears it will still shift at 4800 RPM, but the 2-3 shift will be at a lower speed, say 35 MPH

Note that all numbers above are made up, it is not meant to imply that changing the governor weights maps directly to rear end gear ratio changes, and there are other factors that affect shift points that are being glossed over in the interest of clarity/simplicity.

Hope this helps...
-Rory

[midpack]

Perhaps a contrived/simplified example will help...

Suppose you have a car with an AOD that behaves as follows:

At 4800 RPM it shifts and the 2-3 shift is at 40 MPH with 3.0 rear gears...

You could change the governor weight to increase or decrease the shift point as it relates to engine RPM

If you change it to shift at 3500 RPM the 2-3 shift will happen at a lower speed, say 35 MPH

If you change it to shift at 5500 RPM the 2-3 shift will happen at a higher speed, say 45 MPH


Now instead of changing the governor weight, you change the rear end gears...

It you change to 2.5 rear gears it will still shift at 4800 RPM, but the 2-3 shift will be at a higher speed, say 45 MPH

If you change to 3.5 rear gears it will still shift at 4800 RPM, but the 2-3 shift will be at a lower speed, say 35 MPH

Note that all numbers above are made up, it is not meant to imply that changing the governor weights maps directly to rear end gear ratio changes, and there are other factors that affect shift points that are being glossed over in the interest of clarity/simplicity.

Hope this helps...
-Rory

Or you could just put a T5 in it!!  lololol :nk