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I am in a bit of a dilemma and wanted to get your suggestions. The FMX on my 73 with a 351C was suffering from “morning sickness”, but the last time I took it for a drive around the block it was slipping and I even thought I might not make it back home. In the end I did make it home but have decided it is time to do something about it.

 

About a  year ago I bought a used AOD that came out of a 92 mustang with about 50k miles that included the transmission, torque converter, cross member, flywheel, cooling lines, radiator, fan, shifter, dipstick, TV cable (no bracket), and driveshaft (I think that covers everything I got). I was told it was running fine and the guy selling it was only doing so because he was going to swap in a T5. I saw the mustang, the T5 and he seemed like an honest guy. I bought it thinking I would eventually swap this into my Mustang in the future. However, I do not believe I have the ability to do the swap myself. I have worked on cars with things like suspension, changing belts, intake/carb swap; but nothing as involved as a transmission swap. I read Mister 4x4’s AOD conversion thread and kind of have an idea of what is needed, but still think it is a bit too much for me to do in my garage. I am especially worried about having to modify the cross member, cooling lines, neutral safety switch/shifter and adjusting the TV cable since I have never done any custom fabrication work. I have asked around in some shops that specialize in classic mustangs in Houston and the price they quote me for the swap is way too high for me (close to $3-$4k).

 

I have also asked about getting the FMX rebuilt and it comes down to two options with two different shops:

Option 1 costs $700 (which includes a rebuild kit with clutches and bands; and labor to remove/reinstall the transmission, but does not include rebuilding/replacing the torque converter or any other hardware that is not included in the rebuild kit which would be additional if required) with a 1 year warranty. He said he would check the torque converter and if it still has “more than 50% life in it”, then there is no need to rebuild/replace it.

Option 2 costs $1200 and is a full rebuild that includes anything that might be needed (including torque converter and any other hardware he might need to pull off from an FMX transmission core he has), includes labor to remove/reinstall the transmission and comes with a 2 year warranty.

 

The only mods to the 351C 2V is a 4 bbl intake and Edelbrock carb. It also came with a duraspark 2 ignition and a flowmaster exhaust system (with stock manifolds) from the previous owner. It currently has a 9 inch open differential with 2.75 or 3.0 gears. I really only plan to use it as a weekend cruiser that I can step on and  enjoy a little power. My current future plan (other than the transmission) would be to install 3.5-3.89 gears and possibly change to a locking differential.

 

After writing all this I come to realize that I should probably just rebuild the FMX and sell the AOD. As far as my two options with the rebuild: option 1 leaves me with an extra $500 IF (and that is a BIG “if”) nothing else needs to be replaced. If the torque converter needs to be replaced then that would add about $200 to the total if I buy one from Summit or any other online store. While option two includes everything being rebuilt for the extra $500 and an extra 1 year of warranty. As far as the warranty is concerned I would assume that since this is only a weekend cruiser (and I only really drive it every 2-3 weeks), the transmission would probably not suffer too much wear. What would you guys suggest?

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Doing the trans swap is really not that hard. I swapped out my FMX for a T5 so converted from an Auto to a Manual in my garage with no issues. I had never tackled anything like this before and just did my research and only ordered the individual parts I would need. I think you would be amazed at the difference in feel driving with the AOD Vs the FMX even without changing the rear gears. I had 2.75 gears and the difference was with the T5 was night and day. I eventually swapped out the rear gear for a 3.70 traclok and holy crap what a difference. If you are looking to go to a 3.50 or higher gear eventually the AOD would be a huge benefit if you do any type of highway cruising. Also do some research, but I believe I read somewhere that the FMX crossmember bolts up to the AOD.

73 Grande H Code. Headman long tube headers, T-5 Transmission, 3.70 Traclok, Lowered 1" all around, Aussie 2v heads w/ 2.19 intake, 1.71 exhaust, screw in studs, full roller cam 608/612 lift 280/281 duration LSA 112, Quick Fuel 750 CFM double pumper, AirGap intake.

 

- Jason

 

 

082-hot-rod-power-tour-2017-1970-1970s.jpg

 

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To save on costs, why not remove and replace the trans yourself and just pay for the rebuild? It is pretty straight forward and lots of info here on how to do it. Good luck.

 

Both shops said they have to remove/install for the warranty to be valid.

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To save on costs, why not remove and replace the trans yourself and just pay for the rebuild? It is pretty straight forward and lots of info here on how to do it. Good luck.

 

Both shops said they have to remove/install for the warranty to be valid.

 

That's standard in the industry. No one wants to stand behind a tranny when they have no idea if the installer knows what they're doing. 

 

I'd say the $1200 option is pretty reasonable with the 2yr warranty. Make sure he uses a new/reman converter and get him to install a shift improver kit.

 

 

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How much do you plan on driving it ???  If your planning on doing alot of highway, the AOD would be nice, other than that, stick with what you got. 

 

I have no advice on which way to go with the rebuild except  - flip a coin

73 ragtop, 1999 Mustang Bright Atlantic Blue Paint, Phoenix Engine 302-335HP,  Edelbrock Carb & Performer manifold; c4 with 2000 stall and shiftkit; 3:55 auburn limited slip differential, Hedman shorties; Car Chemistry Exhaust

 

Classic Air; Tilt Steering Wheel; 1999 Chrysler Sebring bucket Seats ; power windows;

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I have been in the exact same position as you and our cars sound very similar. Mines a 73 convertible with 351-2v with eldebrock intake, I switched the eldebock carb for a Summit and couldn't be happier. 2.75 open rear end with 245/60 BFGs.  Originally intended to swap the FMX for an AOD but then changed my mind to a 4r70w. No question that an upgraded trans is a huge improvement, IF you need it to match the use of you car. If you go that way be aware that you will definitely need to change rear gears also to get the benefit.

 

While still on the "wish-list", I have found that I really didn't need to make the swap to be happy with the car. I use my car as a daily driver. It has almost 95000 miles on it but the engine was rebuilt approx 13000 miles ago by the PO. Runs pretty strong but not a race car by any means.

 

I had the FMX rebuilt last year. Full rebuild with a stage 4 shift kit was $900. Shifts are firm but not too harsh. Even with the 2.75 gears, it will spin the tires(tire) anytime I want to. After driving it every day rain or shine for a year now everything from stop and go city traffic to 85 mph highway runs I have found that for now the FMX suits my needs.  Last Mustang I had I did swap a C6 to a Tremec 3550 and 3.89 gears. Huge improvement and was perfect with the built 427FE in that car but I used it differently - it was definitely a hot rod.

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I just went through the same issue.  I ended up buying the rebuild video from Bad Shoe Productions and an FMX rebuild kit.  The video was about $40. (an excellent product).  The kit was about $100.  I paid a local tranny shop $20 to reinstall a piston seal.  I have not reinstalled the rebuilt FMX  yet, so i can't comment on how it works.   Rebuilding is not difficult.  You just need to be organized and pay close attention to details when working on the valve bodies to make sure you get everything back in the same way it came out.  

 

After all of my research, If I had an AOD, I would do the swap - since nobody seems to regret upgrading to an AOD (or a manual).  

 

If you decide to rebuild yourself,  I have a homemade spring compressor you can borrow (i'm on the SW side of Houston).

 

Good luck.

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@mudbilly - don't plan on using it as a daily driver so probably less than 200 miles a month I would say.

 

@mbrew2 - sounds as if you were describing my car. It is also a 73 convertible. I have come to believe that the FMX fits the use I have planned for this car and do not really need to go with the AOD swap. It would be nice to have overdrive, but not an absolute necessity. I am glad to hear you are able to spin your tire at will with a very similar drivetrain to mine.

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I just went through the same issue.  I ended up buying the rebuild video from Bad Shoe Productions and an FMX rebuild kit.  The video was about $40. (an excellent product).  The kit was about $100.  I paid a local tranny shop $20 to reinstall a piston seal.  I have not reinstalled the rebuilt FMX  yet, so i can't comment on how it works.   Rebuilding is not difficult.  You just need to be organized and pay close attention to details when working on the valve bodies to make sure you get everything back in the same way it came out.  

 

After all of my research, If I had an AOD, I would do the swap - since nobody seems to regret upgrading to an AOD (or a manual).  

 

If you decide to rebuild yourself,  I have a homemade spring compressor you can borrow (i'm on the SW side of Houston).

 

Good luck.

 

 

I found those videos from Bad Shoe Productions while looking up FMX tutorials on youtube. All I found was a video of a guy with a French accent disassembling the transmission. I have zero experience with transmissions so I felt like I was not getting much out of it (especially since my transmission is still in the car) and he seemed to use some specialty tools. Did you find you needed any specialty tools besides the spring compressor you mention?

 

I do not have a transmission jack, only a floor jack from Harbor Freight. My cheapest option there would be to get one of those adapters they sell on eBay for about $50 that mounts to the floor jack, but do not know how well they work.

 

Did you do a stock rebuild, or did you add a shift kit? What are you doing about the torque converter?

 

I will send you a PM as I am interested in your experience rebuilding the FMX.

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The floor jack adapters will work, providing the saddle on your jack is removable and the pin is the right size. They are also available from Jegs, Amazon, and others.

 

Your floor jack probably won't reach as high or lower as far as a transmission jack.

 

 

“If you can't explain it simply, you don't understand it well enough.”

--Albert Einstein

 

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I have a FMX in my 69 Mach 1 and my 73 Mach 1. I rebuilt both of them in the past year. I have worked on cars for years, but had not rebuilt a transmission before. I ordered the FMX video from Bad Shoe Productions, and found it very straight forward. Ken is very knowledgable on the transmissions.

 

I purchased the spring compressor tool from Ken. I purchased the outer lip seal tool used from a transmission tool company.

 

As far as the transmission jack- I bored a hole in a 1x10 board and bolted it to the pad on my floor jack. Worked flawlessly after a little elbow grease.

 

All in all, I was able to rebuild both transmissions, with new stall convertors, rebuild kits, and shift kits for less than what one transmission would have cost for rebuild from local transmission shops.

 

 

 

 

Sent from my iPhone using Tapatalk

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  • 2 weeks later...

I have been considering dropping the transmission and give it a shot at the rebuild using the Bad Shoe Productions video. I have never removed a transmission before either, but have seen a few videos on what the process is and found this post as well:

 

https://www.7173mustangs.com/thread-tips-on-removing-fmx?pid=163242#pid163242

 

I took a look under my car and it seems part of the exhaust would need to be removed as well because the "H" pipe (red arrow) is right underneath the tailshaft housing. I have never removed exhaust parts either, but would assume I would need to unbolt from the exhaust manifolds (I do not have headers) and remove the clamps (yellow arrow) in the pic to remove that mid section. I would probably also have to remove that plate from the green arrow (I assume it's there because my car is a convertible) in order to remove the driveshaft. If I remove the exhaust part, is there a gasket where the downpipes bolt to the manifolds? I would not want to end up with an exhaust leak if I decide to give it a shot myself.

 

Thanks for the help guys.

 

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Yes Exhaust section comes out as you described. I used Red RTV to seal up when putting back together (I am running headers). The plate should not need to come out to remove the driveshaft. You would unbolt driveshaft from rear end. it will slide forward into the trans enough for the back of the shaft to drop down and then pull it out from the back. (replace U-Joints while you have it out). The FMX is heavy. A trans jack is very helpful. I didn't have one and dropped it down onto my chest and just muscled it out, would prob not try that again. Loosen the adjustment on the parking brake cable so you can unhook it from the passenger side so you are not fighting that as well. To gain clearance under the car I nailed together a bunch of scrap pieces of 2x12 lumber about 12 pieces high with 2x4's nailed to each end and jacked up and put one under each tire. Much safer than jack stands in my opinion plus keeps the weight of the vehicle on the tires and suspension. The list Mr. 4x4 has in his post is perfect except he left out to remove the starter.

73 Grande H Code. Headman long tube headers, T-5 Transmission, 3.70 Traclok, Lowered 1" all around, Aussie 2v heads w/ 2.19 intake, 1.71 exhaust, screw in studs, full roller cam 608/612 lift 280/281 duration LSA 112, Quick Fuel 750 CFM double pumper, AirGap intake.

 

- Jason

 

 

082-hot-rod-power-tour-2017-1970-1970s.jpg

 

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Getting the exhaust pipes apart can be a real headache. The exhaust clamps place a groove into the pipes, making it difficult to separate, limited working room doesn't help. At least yours aren't rusted together.

 

There is no gasket between the exhaust pipes and exhaust manifolds. Here is a thread about it:

https://www.7173mustangs.com/thread-351c-exhaust-gasket-donut-question?

 

 

“If you can't explain it simply, you don't understand it well enough.”

--Albert Einstein

 

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I have one of the Harbor Freight transmission jacks. Worked great on my Safari when I swapped the trans by myself, although there was a lot more access to the trans compared to the Mustang. You use a ratchet to raise and lower, easier to control than a hydraulic jack. Plus, with the casters, if the vehicle is up higher enough, you just roll it out from under.

 

I agree with 73Pony, build some wide wood platforms to put the wheels of the car on instead of jackstands. I have some I use that have 2x4s screwed down on top in front and back of the wheels so it cant roll....safety is everything! If the car is level things are usually easier.

 

I do find it curious how people look at things...I'm more inclined to do the aod swap than try to rebuild a trans.

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The list Mr. 4x4 has in his post is perfect except he left out to remove the starter.

 

Thanks for the kind words and heads up.  I updated it just now with 'unhook battery,' and 'remove starter.' ;)

Eric

mach1sig2.gif

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Here is a link to the wood stands I made for the car. Pic about 1/2 down the page.

 

https://www.7173mustangs.com/thread-t-5-conversion-complete?page=3

73 Grande H Code. Headman long tube headers, T-5 Transmission, 3.70 Traclok, Lowered 1" all around, Aussie 2v heads w/ 2.19 intake, 1.71 exhaust, screw in studs, full roller cam 608/612 lift 280/281 duration LSA 112, Quick Fuel 750 CFM double pumper, AirGap intake.

 

- Jason

 

 

082-hot-rod-power-tour-2017-1970-1970s.jpg

 

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  • 4 weeks later...

I found a guy selling an FMX. He said it was rebuilt, he bought a new converter, installed it on a 60s/70struck, but never ran it. Then decided to go with an AOD instead. So he removed it and stored it. He added some tranny fluid to the converter and transmission.

 

When comparing it to my transmission, there seem to be a few differences. The bell housing seems a little different as mine does not have the part in the yellow circle in the pic below. I assume the bell housing difference would not make a difference unless it affects the kickdown rod. Other than that, my transmission has 3 different rods attached to it. In the pic below, white goes to the shifter, red to the kickdown rod and green to the steering box. The other transmission does not seem to have the one for the steering box. Would that mean I would need to swap that part from my transmission to the other one, or can I just leave it unhooked?

 

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You bought a column-shifted FMX. The black bracket supports the end of the shift cable from the column. You can swap your current bellhousing onto the new unit without disturbing the transmission internals.

 

Personally, I'd swap the shift linkage bellcrank from your current correct transmission into the replacement. That way, everything will bolt up and work as the factory intended.

 

 

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You bought a column-shifted FMX. The black bracket supports the end of the shift cable from the column. You can swap your current bellhousing onto the new unit without disturbing the transmission internals.

 

Personally, I'd swap the shift linkage bellcrank from your current correct transmission into the replacement. That way, everything will bolt up and work as the factory intended.

 

 

I kind of thought that might the case since most trucks have a column shifter. I know they are different on the C4 and C6, but didn’t really investigate much about the differences in the FMX. I read in another forum that the tail shaft and housings are of different length and that both would need to be swapped to keep the same speedometer gear. Does anyone know if that is accurate? I measured the transmissions and they both seems to be the same length. Both tailshaft housings measure approximately 13 and 1/4 inches.

 

So the suggestion would be to swap the bell housing and also swap the range selector arm? The range selector arm swap would imply dropping the pan and valve body, correct?

 

 

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  • 3 months later...

So I ended up swapping the bellhousing and range selector arm/shifter linkage from my original transmission to the replacement. The transmissions were swapped this past weekend. (I ended up hiring a mobile mechanic and tagged along to learn) I took the car out for a short test drive and it seems to be working well. The transmission engages immediately, there is no delay or "morning sickness" anymore. I might have to adjust the shift points, but will have to do some research into how to do that. I felt it shifted a little funny under hard acceleration.

 

It was a short drive because my differential has a small leak and my registration is expired; and there is a constables office about a block from where I live. I will take it for an inspection now that it is driveable and get the registration. I also swapped the stock 2 bbl intake and carb to a Weiand intake and Edelbrock 650 cfm carb before the transmission started slipping badly. So I have not been able to really test drive it properly with the new intake/carb combo to check driveability.

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