Posted by Cowboy (IP: 216.161.250.98) on May 25, 2000 at 11:25:10:
In Reply to: AOD posted by Morty on May 24, 2000 at 00:55:28:
Copied this from Marks Maverick page, GREAT info!
C4 to AOD Transmission Swap (from Dan Jones, m203253@ws2200.mdc.com)
--------------------------------------------------------------------
The C4 to AOD Transmission Swap
or
How I Spent My 1994 Christmas Vacation
by Dan Jones
As promised, I performed the C4 to AOD transmission swap in my parent's 1971
Mustang convertible. The reason for the transmission swap was to gain the
benefits of the AOD's 0.675:1 overdrive gear (lower cruise RPM, increased MPG,
potentially better acceleration). The car in question is powered by a mild
302 (600 CFM Holley, dual plane intake, mild cam, dual exhausts) and, before
the swap, had a perfectly good C4 transmission. While this is essentially a
bolt in job, there are lots of little details that you should be aware of to
make things go smoothly. These details, in no particular order, include:
Procuring the Transmission
Extension Housing
Converter Compatibility
Gear Ratios
Working with Aluminum
Transmission Jack and Jackstands
Transmission Tunnel Clearance
Exhaust System Clearance
Transmission Crossmember and Insulator
Flexplate Diameter and Balance
Block Plate
Nuts and Bolts
Starter
Driveshaft and Yoke
Mechanical Interlocks
Shifter Operation
Speedometer Gear
Electrical Connections
Throttle Valve Operation
Hydraulic Fittings
Dipstick Tube
Drain Plugs
Transmission Fluid
Shift Kits and Transmission Coolers
To give you an idea of what's involved in a swap like this, I've covered my
experience with each of these details in the paragraphs below. I've also
listed some comparative weights, dimensions, and gear ratios at the end of
this posting.
Procuring the Transmission
--------------------------
If you're pulling the AOD from a car, getting all of the related stuff
(bolts, electrical connector, dipstick tube, converter, yoke, block plate,
linkages, levers, shifter, hydraulic fittings, etc.), will make life a lot
easier. However, we used a transmission purchased from a friend of my Dad's
who rebuilds transmissions. The price was right ($150 rebuilt), but we
had to come up with all the bits and pieces. Because of the Christmas
holiday, getting all the right pieces was harder than usual, but we managed.
Extension Housing
-----------------
When purchasing your transmission, be aware that there are two tailshaft
lengths used on AOD's. The short model is the one that is closest to the C4
in overall length. I forgot to measure it but the SVO catalog says it's 10.1"
long. The catalog also indicates the short extension housing AOD was used in
all passenger cars except rear wheel drive Lincoln Marks and Continentals (not
sure about the Town Cars), 2WD F-150 trucks built after 11/81, and 83-85 E-150
vans. Also, don't confuse the AOD with the AOD-E, which uses electronic
control. There are also extension housing variations among C4's, with a short
tailshaft model (6 5/8") used on some pickups and vans. Our C4 was the
standard tailshaft model (13 1/8") that was used in most most applications.
Converter Compatibility
-----------------------
The AOD transmission and torque converter are a matched pair. The AOD uses a
hollow two piece input shaft (one shaft inside the other) for lock-up purposes
and requires a specific torque converter. This arrangement is used to bypass
the converter torque multiplication in higher gears (60% in third and 100% in
overdrive) for better fuel economy. This is an attractive feature when using
a high stall speed converter, since locking up the converter eliminates the
excessive slippage (and the attendant heat generation, RPM rise, and increased
fuel consumption) associated with such converters. On the down-side, the input
shaft is weaker than a similarly sized solid one piece design and you lose the
torque multiplication effect.
Gear Ratios
-----------
The first three gears of the AOD and C4 are of similar ratio. We were looking
for longer legs and increased fuel economy so we left our rear end gears alone.
If better acceleration is the goal, a ring and pinion swap may be in order.
The beauty of this swap is that the AOD's 0.67:1 overdrive ratio can make a
3.73:1 ring and pinion act like a cruising 2.50:1 ratio. Come to think of
it, we've got some extra 3.50:1 gears so maybe I can talk Dad into swapping
them in.
Working with Aluminum
---------------------
Like the C6 and C4, the AOD has an aluminum case so use a never-seize
compound on the aluminum threads (e.g. bolting the the insulator to the case).
Also, when working with small aluminum threads (e.g. dropping the pan), I
prefer a beam-type torque wrench so I can tell when I'm approaching the
desired torque value. I don't trust the click-type wrenches on the little
stuff.
Transmission Jack and Jackstands
--------------------------------
Despite its aluminum case, the AOD is no lightweight. I measured 150 lbs
(without fluid or converter - as measured on Mom's bathroom scale) for the
tranny and 34 lbs for the converter, so a transmission jack is recommended.
Get the car up in the air as high as possible to give yourself some room to
maneuver. We used a pair of stacked railroad ties underneath each front tire
and a pair of tall jackstands under the rear axle housing.
Transmission Tunnel Clearance
-----------------------------
The AOD is beefier around the middle than the C4, so it uses up more space
in the transmission tunnel. Our '71 Mustang was designed to swallow a C6
so there was no problem. It might be tight on cars with narrow tunnels
(like 65-66 Mustangs), but I'm told they will fit with no problem.
Exhaust System Clearance
------------------------
No problem here on our particular car (dual exhaust without a crossover).
We could have installed the AOD without ever touching the exhaust, but we
decided to unbolt the pipes from the exhaust manifolds for extra working
room. This will vary from car to car so be prepared for potential exhaust
work. Since I had the pipes unbolted from the manifolds, I took the
opportunity to put in new exhaust donuts.
Transmission Crossmember and Insulator
--------------------------------------
The only bit of true fabricating that was required for this swap was the
transmission mount crossmember. While the AOD and C4 overall lengths are
within a half inch of each other, the mounting pad for the insulator on the
AOD is 2 inches farther aft, so the crossmember mounting point needs to be
moved an equal amount. Whether you need to buy or fabricate a custom cross
member depends on the car you're swapping the transmission into. On some
full-sized cars, it's supposed to be as easy as switching to a second set of
aft mounting holes. However, on most of the unibody cars, like Mustangs, a
custom mount is required. Since I planned to do the swap over Christmas
break, in another state, and was spending someone else's money, I decided to
purchase a custom crossmember, rather than fabricate one. I purchased it
from Auto Creations, a shop that specializes in overdrive transmission swaps
into older Fords. Besides the mount, they also sell a throttle valve (TV)
cable kit and can set you up with miscellaneous parts (block plates,
flexplates, etc.), if you can't get them locally. They also have a list of
cars from which you can pirate the linkages (ones that came with carbs or
throttle body injection and AODs). Their mount retains the stock insulator,
fit as advertised, and was well made. They were also very helpful when I ran
into problems with the flexplate, taking measurements for me over the phone.
Even though they were officially closed over the holidays, they stayed in
phone contact with me to make sure things worked out. If you're contemplating
this swap, I suggest you give these guys a call. I've included their number
and address towards the end.
Flexplate Diameter and Balance
------------------------------
One of the more important parts of the swap is to choose the proper flexplate
for your application. The integral bellhousing AOD requires a flexplate with
164 teeth (approximately 14 1/4" diameter with an 11 7/16" torque converter
bolt pattern) for proper starter placement and converter compatibility. The
C4, however, uses a detachable bellhousing that is matched to one of three
different flexplate sizes (148, 157, and 164 teeth). The 148 teeth flexplates
are comparatively rare, having been used in cars like the V8 Mustang II. The
157 teeth flexplates were generally used in 289/302 small and mid-sized cars,
while the 164 teeth flexplates were used in 289/302 full-size cars and
351W/351C applications. The C4 164 teeth flexplates and the AOD 164 teeth
flexplates will physically interchange, but there are two balance weights
(pre-'81 302's use a 28.2 oz-in balance weight, '81-up 5.0 HO's are 50 oz-in),
to be concerned with. I haven't had a chance to verify but I think all 351W's
and 351C's used 28.2 oz-in balance factors. Also, the catalog I looked at
suggested that 1981 and up non-HO 302's are still 28.2 oz-in (at least to
1990). Anyone know for sure? In my case, the flexplate in the 1971 Mustang
came with 157 teeth and a 28.2 oz-in balance factor, so it required replacing.
Since they both have 164 teeth and 28.2 oz-in balance factors, I was under the
impression that flexplates from either a 351W w/AOD or early 289/302 w/C4 from
a full-size car would work. Looking through the books at the parts store
showed that these were not common part numbers, and listed the 351W part as
working with an AOT, not AOD, transmission. Not knowing if the AOT indicated
a subtle variation that I was unaware of, I decided to order the early
289/302/C4/full-size part (OEM D1AZ-6375-A, Saginaw XF15). This turned out to
be a mistake. When we put the converter and transmission up to the engine for
a fit check, the modeling clay we had put in the crank pilot showed the
converter snout was barely making contact. Apparently there is a difference
in flexplate depth. It all would have bolted together and the starter may
have even managed to reach the flexplate teeth, but there would have been no
support for the converter and the starter would have eventually chewed up the
flexplate. Procuring a 351W/AOD flexplate over the holidays turned out to be
an ordeal (dealers wanted 14 days), but it was required for proper converter
snout to crank pilot placement, while retaining the proper diameter and
balance. We finally found a transmission supply house that had the right
piece. We put the 351W/AOD next to the early 289/302/C4/164 teeth part and
there was a difference in height. Since then I have checked some aftermarket
catalogs and they show the same part number for both applications, so buyer
beware. The part we finally obtained was from Sealed Power and corresponded
to OEM E0AZ-6375-A (164 teeth flexplate, 28.2 oz-in balance factor, 351W
with AOD applications). If you're swapping an AOD onto an '81 or later 5.0,
you'll need the AOD flexplate (164 teeth, 50.0 oz-in balance factor, for 5.0
with AOD applications). I think the OEM part number for the late 5.0/AOD
is E2AZ-6375-A, but I didn't verify this. In a pinch, you could swap (weld)
balance weights between flexplates to get the proper balance factor. If you
choose to do this, remember that the balance factor is a moment of inertia
(distance time mass) so keep the product of the distance from the weight to
the center of the flexplate and the balance weight (plus any additional weld
weight) equal to a constant (either 28.2 or 50.0 oz-in).
Block Plate
-----------
A block plate (the thin stamped sheet metal plate that fits between the engine
block and transmission housing) which matches the large AOD bellhousing is
also required. This plate provides the correct starter location and engagement
depth for the torque converter snout in the crank pilot (assuming you have the
right flexplate). We used one from an early 289 full-size application (C4
with the large bellhousing).
Nuts and Bolts
--------------
The bosses on the AOD bellhousing are thicker than those of the C4, so longer
bolts are required. We didn't have enough of the proper length (2 1/8 to
2 1/4" long bolts), so we cut down a few longer bolts to get the desired
number of threads. Use a stiff piece of wire as a gauge to make sure they
don't bottom out. You can re-use the C4 torque converter nuts on the AOD
converter but it's a good idea to use new ones since these tend to round off.
Also be aware that the AOD is a mixed standard transmission, despite what the
METRIC embossed into the pan may imply. Some bolts are metric, others are not.
Generally, the tranny internals are metric, but the places where the tranny
connects to the car (insulator, hydraulic fittings, speedo-drive, etc.) are
not.
Starter
-------
The original starter was retained and aligned properly.
Driveshaft and Yoke
-------------------
When we first put the the yoke into the tranny, it appeared we would need to
shorten the driveshaft by an inch or so. This was unexpected since the AOD
is only a 1/2 inch longer than the C4. Upon closer investigation, it became
apparent the yoke was the problem. We had to trim the C4 yoke to get it to
fit properly. The AOD yokes must be a bit shorter, so pick one up if you can.
Mechanical Interlocks
---------------------
The '71 Mustang has a mechanical interlock which locks the shifter into park
whenever the ignition key is in the lock position. I'm not sure what year
this first appeared on Fords, but I know my '66 doesn't have it. You could
bypass the interlock but we kept it functional. This required removing the
TV/shifter shaft assembly from the AOD (involves dropping the pan and filter).
Using the original C4 lever as a guide, we cut a spare lever and welded it on
the shaft. This caused a problem since we were unable to remove the small
circular grommet that seals the end of the concentric cylinders of the
TV/shifter shaft assembly without damaging it. The C4 has a rubber O-ring
in this area but the AOD uses a special formed piece which, like the flexplate,
wasn't easy to find over the holidays ("Sure we've got one but you'll have to
buy the $119 rebuild kit to get it").
Shifter Operation
-----------------
We retained the C4 floor mounted shifter in the Mustang. Eyeballing the AOD
and C4 shift levers, it looked like the hole in the AOD shift lever would need
to be moved a bit so we welded up hole and drilled a new one. Once everything
was assembled, we adjusted the linkage to get proper engagement of the gears
and interlocks, but the pointer was off. It turns out the hole was probably
in the right spot to begin with. I believe there is a quite a bit of
variation in Ford shift levers (especially between floor and column mounted
shifters, but also between body styles), so this will need to be checked on a
case by case basis.
Speedometer Gear
----------------
The speedometer driven gear assembly from the '71, including bolt and retaining
clip, slipped right into the AOD. I didn't get a chance to verify the ratios,
but the speedometer operated normally. There may be some variation (seven and
eight teeth gears?) with the AOD drive gear (the gear inside the tailshaft
housing), so you may have to change driven gears for proper calibration.
Electrical Connections
----------------------
The AOD uses a four pin electrical connector for the reverse/backup lamps and
neutral sensing switch. We didn't get one with our tranny, so we soldered
some wires on and used a liquid rubber compound to insulate. If you end up
soldering, be careful not to melt the plastic housing that holds the pins in
place.
Throttle Valve Operation
------------------------
The AOD does not use engine vacuum and a modulator valve to sense load.
Instead, a throttle valve is used which moves proportional to throttle pedal
travel. Unlike a kick-down rod, the TV linkage has to operate throughout the
full travel. This is one of the most important parts of the swap to get
right. Failure to do so will cause poor shift quality and can ruin the
transmission. When adjusting the linkage, it is safer to err on the side of
hard shifts. There are a several ways of implementing the TV linkage. A rod
arrangement was used on AOD cars equipped with carbs and TBI while a cable was
used on SEFI cars. We were planning on getting the linkage off a variable
venturi (VV) carb from a local junkyard that had a stack of them, but they
had recently tossed them all out. We ended up adapting the kick down rod to
serve as the TV linkage. The trick is to ensure the proper range of travel of
the transmission TV lever for the entire carburetor throttle range. We had
another AOD equipped car to look at to get the proper lever orientation and
ratios. You also need a way to adjust the linkage to vary shift feel.
Alternatively, you could adapt a TV cable from an EFI application or purchase
one of Auto Creation's TV cable kits. For more information on alternatives, I
suggest you get a copy of the May 1990 issue of Super Ford magazine. The
article "A-OK AOD" contains a sidebar on adapting the AOD to non-stock
applications. Ignore the part about your stock flexplate and block plate
working just fine and pay close attention to the linkage descriptions.
Hydraulic Fittings
------------------
The hydraulic fittings on our AOD were larger than those of the previous C4.
After the existing lines were trimmed to their proper length, two adapter
fittings (1/4" (ID) pipe, 5/16" (OD) tubing) were used to mate the fittings
on the transmission lines to the AOD case. I believe the lines on our car
were not original since they looked like new and had quite a bit of excess
length. They were also harder than any factory line I've dealt with. Even
though we used the proper tubing benders and double flair tools, the lines
were very hard to work with.
Dipstick Tube
-------------
With a minor bending of the the attachment bracket, the AOD dipstick tube went
in easily. The AOD tube proved to be shorter than the C4 tube and ended up in
close proximity to the export brace, so a long neck funnel was required to fill
the transmission. Of course, this will vary from car to car.
Drain Plugs
-----------
One thing I forgot to do was to install a drain plug kit when I had the pan
off. B&M makes an inexpensive kit that, along with our stock converter's
drain plug, would make it very easy to do complete fluid changes.
Transmission Fluid
------------------
AOD's take a lot of Dextron-II transmission fluid (the C4 used type F). The
Chilton's we checked for capacities quoted 24 pints (12 quarts) for a totally
dry transmission like ours.
Shift Kits and Transmission Coolers
-----------------------------------
This particular car is not subjected to much abuse so we didn't install a
shift kit or auxiliary transmission cooler. To begin with, we'll simply
adjust the TV linkage to give firmer shifts and see how it works out.
For performance applications, the guys at Auto Creations recommend a Karl
Baumann shift kit and the Thunderbird C-servo upgrade. Because we might be
putting an AOD behind my brother's 351W and a friend's 351C-2V, I did some
research on AOD durability and performance modifications. There are several
things that should be done to an AOD, if you want it to live behind a high
performance engine. It may be several weeks before I can get to it, but I'll
try to post a summary of my findings.
Unfortunately, I haven't had a chance to drive the car yet, since I had to get
back to St. Louis. I left the car up on jackstands, with the wheels spinning
in all gears. I'll get some time behind the wheel the next time I'm in Ohio.
While there are lots of little details (and a couple major ones), this is
definitely a do-able swap, especially if you get all the related parts from
the same car. I've included all the variations that I am aware of, but
remember YMMV. As a reference, I've included some comparative C4 and AOD
dimensions and weights, plus a bunch of gear ratios. Email me with any
corrections or additions you may have. Also, before I sign off, allow me to
thank all of you who responded to my request for AOD information.
Cheers,
Dan Jones
m203253@ws2200.mdc.com
P.S.
I'm going to send a copy of this posting to Auto Creations and ask them for
any input they might have. I'll post any additional info at a later date.
Based upon my positive experience with them, I'm going to work with them on
a couple of other swaps in the future. When I mentioned I was going to post
this write-up to the list, they said they'd give me a break on prices for any
referrals so tell Dave I sent you. They can be contacted at:
Auto Creations
19201 Meadowvale Rd.
Elk River, Mn 55330
(612) 441-5567
C4 and AOD Dimensions
---------------------
Overall Length (bellhousing to tailshaft housing end, flat-to-flat):
AOD - 30 3/4"
C4 - 30 1/4": If I put an AOD trany in my 73 Mav with a 302 would I have to get a custom drive shaft or would the stock one fit it?
: Thanx