c4 to aod swap

I've done some searching but I have not had much luck so I figured I'd ask here.  Has anyone in the group done a c4 to aod swap on a bullnose?  This would be the 1980-81 crowd.  I have an '82 flareside 300/6 that a c4 was swapped in previously, but it needs a rebuild.  If I hit the gas hard it slips and then makes a bell-like ringing noise when I get out of the gas.  Unless it's just a torque convertor issue.  Years ago I got an aod out of a '90 f150 with a 5.0.  What changes do I need to make this work.  I know overall there's only a 1/2" difference in length and I need to move the crossmember.  I would need a 300/6 aod flexplate and possibly change out the selector on the column.  The rub is this, the aod probably needs a rebuild as well.  C4 costs $120 for a kit, the aod is over $200 plus whatever swap pieces.  It would take a while to realize the fuel saving benefits of the aod.

I drive a 300 with an AOD. Here's some notes and thoughts based on what I know:

-You'll need to swap carbs to one with provisions for the TV cable and also obtain the TV cable (and bracket if the hole for it isn't in yours). If the TV cable isn't connected, you *will* burn the transmission on the first drive.

-The overdrive is nice but if you have a 3.08 rear end (or similarly shallow gearing), it can be a pain to drive. AOD's have a very shallow OD... you'll be turning 1500RPM at 65mph. While the 300 is pretty torquey, it's not *that* torquey at that low of an RPM if you hit a hill or steep(ish) overpass. AOD's can be a bit temperamental with downshifting/upshifting; there's a very narrow sweet spot in the TV cable adjustment, and even with it set there, I still have to manually shift out of OD for hills when using cruise at interstate speeds (not so bad at 55-60mph local highway speeds though). Bad enough I've sometimes considered regearing to 3.55...

yup. that about covers it. the gearing is the biggest point that i was going to make. the aod has a .67 od and if you have a gear matched to a 3 speed whether it be a manual or auto it may need to be changed.  im building one now that was a three speed and 300/6 and came with the 2.47:1 rear axle. it is now a 5.0 with aod  and a 3.31:1 axle. if i had left the 2.47:1 in place it would have driven like a 1.65:1 in od. gearing matters greatly! that equates to roughly 1155/1175 rpm at 60 mph. where does your engine make its torque? gear it to be 16-1800 rpm at 60 mph and you should have good drive ability.

mat in tn wrote

yup. that about covers it. the gearing is the biggest point that i was going to make. the aod has a .67 od and if you have a gear matched to a 3 speed whether it be a manual or auto it may need to be changed.  im building one now that was a three speed and 300/6 and came with the 2.47:1 rear axle. it is now a 5.0 with aod  and a 3.31:1 axle. if i had left the 2.47:1 in place it would have driven like a 1.65:1 in od. gearing matters greatly! that equates to roughly 1155/1175 rpm at 60 mph. where does your engine make its torque? gear it to be 16-1800 rpm at 60 mph and you should have good drive ability.

60 MPH would be good if that is what your high way speeds are.
Around me the speed is 65 to 70 MPH and NO ONE drives them speeds!
At 75 you get run over but I try and stay at the 70 MPH limit.

MY truck also gets a little better MPG at 70 mph speed even with the over drive.
81 Flare Side NP435, 2.75 rear gear, 0.27 over drive (advance Adapter).
The RPM at 65 in over drive is the same speed in direct at 55 MPH, about 1800 RPM.

I do have a 2.47 rear that was in my parts truck that had a SROD over drive transmission.
Dave ----

The other issue with an AOD on a 300 is the same as the C4 on a 300, neither transmission is really good in that application due to the 300s torque at low rpm. There is a reason Ford moved up to C6s and E4ODs behind the 300.

If you can find an AOD from a 351W (1980 or around there cars) these have beefier internals and will hold up better.

If you stay with the C4, try to find the 300 specific parts (front band, input and direct clutch drums) these are the choice when building a performance C4. I had one I built in my 1964 Falcon (with a slight case of snakebite), it would chirp the tires on a WOT 1-2 shift and 2-3 was BAM, right now!

i was considering replacing my c6 with an aod about 20 years ago but never quite felt right about it. its my first truck and it always seemed right just as it is. wanting more mpg but not willing to re engineer too much to get it. 300/ c6 is just about as good as it gets for reliability. and "ole reliable" has been just that for over thirty years now. if i never pulled a trailer i would consider installing a much lower gear like a 2.79  but im running 32" tall tires with a 3.08 now. it seems to do just fine in every way except mpg. you cant have it all!

So that brings up an interesting point.  I’ve mentioned in other posts that since mine is a f100 it had the small bolt pattern wheels but at some point the front was switched to the big 5x5.5 pattern.  It still has the 9” rear in it now.  I did pick up an 8.8” to swap in so all four wheels are the same and I grabbed a set of turbines to go with it.  The gearing of that 8.8” might have to come into play unless there is a cheap way to switch the 9” to the bigger pattern.

axle shafts
what year f100?

vicp21 wrote

So that brings up an interesting point.  I’ve mentioned in other posts that since mine is a f100 it had the small bolt pattern wheels but at some point the front was switched to the big 5x5.5 pattern.  It still has the 9” rear in it now.  I did pick up an 8.8” to swap in so all four wheels are the same and I grabbed a set of turbines to go with it.  The gearing of that 8.8” might have to come into play unless there is a cheap way to switch the 9” to the bigger pattern.

The 8.8 almost always came with either 3.08 or 3.55 gears, all the way up to 1996. I've read where people said that they did come with other ratios, but I'd say it was rare in the f-series pickups. It was pretty common to find 3.55 gears in 8.8's when behind an AOD in the pickups.

I think the only way to convert your 9" to the smaller bolt pattern would be to find another whole rear diff out of a 1980-1982 with that small pattern. They didn't exist before or after, so they're relatively rare I'd say. As far as I know, and Gary or somebody can correct me if I'm wrong, but the small bolt pattern went away in 1983 when the 8.8 was introduced.

I'd be slapping that 8.8 in if it was me

Yep, the small bolt pattern was only 1980 - 83 on the F100's with power brakes and a GVW from 4600 to 4700 lbs.

Rembrant wrote

I think the only way to convert your 9" to the smaller bolt pattern would be to find another whole rear diff out of a 1980-1982 with that small pattern.

vicp21 wrote

 ......unless there is a cheap way to switch the 9” to the bigger pattern.

 I'm pretty sure vicp21 is asking how to swap their small pattern 9" to 5 on 5.5 to match the front hubs and turbine wheels.

A pair of 9" axles can be had for as little as $250, but I don't know the length or how many splines on the inboard end.

ArdWrknTrk wrote

vicp21 wrote

 ......unless there is a cheap way to switch the 9” to the bigger pattern.

 I'm pretty sure vicp21 is asking how to swap their small pattern 9" to 5 on 5.5 to match the front hubs and turbine wheels.

A pair of 9" axles can be had for as little as $250, but I don't know the length or how many splines on the inboard end.

DOH...my bad...I misread that or misunderstood it, or both lol.

Correct!  Yes it has power brakes and originally was the small pattern and a c6 according to the tag, but the city of Dearborn made some changes at some point on its life.  I’ll have to check both axle and see what I’m dealing with.  I would need shafts and drums from a dentside f150 to keep the current axle and gear ratio.  I doubt the 8.8 is going to have anything taller than 3.55 in it which will make that thing scream going 65

So you already have a 2.79 gear in a 9" and and just need axles with bigger flanges and brakes. EDIT: Sorry it was Mat who mentioned the short gear.....

This can be arranged not too expensively but the axle length and spline count needs to be known.

if we were talking about a five-speed manual with od then there is just the matter of torque at a certain rpm for the gear and speed. but we are not. we are considering an aod automatic. this requires a certain amount of rpm to actually pump the fluid which it needs to operate correctly. keep in mind the analogy of filling up a bucket which has a hole in it. the pump must not only build pressure but do it at an increasing rate as rpm increasing all while a designed amount of pressure and flow are being lost through the process. this is something that rears its head when tv cables are misadjusted. valve bodies do NOT seal perfectly everywhere. they direct the volume of fluid flow in a variable manner. all this to say if the pump is not turning enough then pressure may be lower than needed.