OD trans options

[Mesozoic]

I've been pretty set on installing an overdrive transmission into my '71 for years, but am only now (after decades) actually going to do it. The car currently has a B&M Racing C6 transmission with a Hughes 3000 stall speed converter and 3.50:1 rear gears. It's great, but I want to cruise on the highway at reasonable engine speeds. My issue is whether I should stick with an automatic OD or switch to a manual transmission.

Some years ago I managed to get the entire clutch pedal assembly from a '71 Cougar, which I believe is the same as the '71 Mustang. Please let me know if that is not correct. I'm not really sure what my manual transmission options are, aside from a T56 6-speed or a Tremec 3550 TKO 5-speed. My car has a fuel injected 408 stroker that generates about 450 hp and over 500 ft-lbs of torque, so a T5 is out of the question (I think).

My auto options seem to point towards a 4R70W, which is easily rebuildable and will easily handle my power level. I do also have a '93 AOD, but the computer controlled 4R70W appears to be a better option.

I guess I'm not really sure what is going to be a total pain and what's going to be relatively simple to install. If there's a lot of fabrication involved that will make things hard for me.

 

[droptop73]

I went manual and it's the best modification I've made to the car yet. It drives and accelerates much more freely than the C-6 that was in there. A C-6 takes about 70 horsepower just to drive the trans... the T-5 I used requires about 10 horsepower to drive the trans. That may be reason enough.

 

[Mesozoic]

Yeah, but what does it really take to shove a manual into one of our cars? Aside from the bellhousing, clutch, flywheel, etc., is there a bolt-in crossmember to accomodate a T56? Does it fit within the transmission tunnel without any banging and mods? What about electricals? How do you implement a cable clutch with a '71 Cougar pedal assembly?

 

[CZ-75]

I ended up putting in a wide ratio AOD. I'm happy with it, but if I had to do it all over again, I probably would have gone the 4r70w just to have computer controllable shift points.

That being said, at freeway speeds, I'm getting similar RPMs with 3.89 rea end, as I was getting with the FMX paired to a 2.75 rear end.

 

[droptop73]

I used a late 90s T-5 with a with a V6 bell housing to fit an 11" clutch. The C-6 crossmember and mount worked with the T-5 and there was plenty of tunnel room. The late 90s trans has a 3/4" longer input shaft and moves the trans back a little bit for a better shifter location. As for clutch linkage... mine is all custom mechanical. I have a thread on here with the vast majority of the details. My route was semi bolt in if you plan to go with a cable.

http://www.7173mustangs.com/thread-c-6-to-t-5-swap

 

[Qcode351mach]

droptop has done the manual 5-spd conversion & he did a write up if you search his threads..I've just finished up the 4r70w conversion from a LARGE c-6..It's a direct bolt in. The hardest part of the whole deal was fabricating a custom shifter arm & linkage in order to USE THE STOCK SHIFTER..If your not concerned about using the stock shifter then a cable set can be made to work pretty effortlessly. You will need a new driveshaft if you have the large c-6 not sure about the small one at the minimum you need a new front yoke.. You will also need to mod the c-6 crossmember..The whole deal cost me around 3k which includes the baumann controller..wire harness..complete rebuild of the tranny..reprogramming kit..driveshaft..see my thread here.

http://www.7173mustangs.com/thread-green-72-fastback-former-429-460?page=5

 

[mjlan]

Modern Driveline sells a cable conversion for 71-73's, and using late model sbf parts makes it pretty easy. You'll need to verify your headers will clear the different bell housing.

I've done the T5 swap, you might be able to go with a beefed up unit at your power level, but most likely a TKO will be more durable. I'm not sure a T56 will fit without tunnel mods.

 

[Don65Stang]

Here's a good place to get some ideas flowing.

http://www.7173mustangs.com/thread-trans-gear-vs-rear-gear-vs-rpm-vs-mph

For a manual trans I really like the Tremec TKO with a 2.87 first gear and .64 overdrive. It has a 600 ft-lb torque rating.

 

[Jeff73Mach1]

My headers cleared my lakewood bellhousing- they are Hooker comps-just FYI.

With a manual transmission, at your power levels, you will be looking for more traction solutions than with an automatic. Don't underestimate the importance of this as I have similar torque from my 393 and I am working through it now and it looks like it will add a solid grand or more to my efforts

 

[Mesozoic]

My headers cleared my lakewood bellhousing- they are Hooker comps-just FYI.

With a manual transmission, at your power levels, you will be looking for more traction solutions than with an automatic. Don't underestimate the importance of this as I have similar torque from my 393 and I am working through it now and it looks like it will add a solid grand or more to my efforts

I have fully modified suspension, a rollcage, 335mm rubber on the rear, and less power and torque than my supercharged 5.0 that has only 255mm rubber, so I'm thinking it's not going to be too bad.

My main concern is cost. There's no way a T5 is going to handle things, even with the beefed up clusters. A T56 would be great, but they're expensive and huge. I'm thinking TKO as well, but not sure if I can find a good used core to rebuild or not. Additionally, I'd like to use as many stock/junkyard components I can to save money. I'm not going to the races, I just want to drive my sports car!

 

[Jeff73Mach1]

Just wanted to make sure you considered it. I forget to check out other cars mods sometimes.

How about a modified T-45? I'm running one from Keisler, but they are out of business. There is a company called the T-45 Source and using there shift fork assemblies and the 26 spline input shaft would give you a transmission capable of smooth high speed shifts and power handling in the range you are looking for. They make the conversion front plate and if you can rebuild the transmission you can install their parts yourself, if not they will build one for the right price. I have a message in to them about beefing up my transmission to see if they will commit to their transmission builds being up to 575 foot pounds of torque.

The shifter comes up in the exact stock location-the cross member is different, but available or buildable.\

As to the pedals-if you choose to run a mechanical linkage, I think the cougar pedals will fit fine, but IIRC the stock set up can be altered to swap brake pedals and add the clutch.

 

[Mesozoic]

Just wanted to make sure you considered it. I forget to check out other cars mods sometimes.

How about a modified T-45? I'm running one from Keisler, but they are out of business. There is a company called the T-45 Source and using there shift fork assemblies and the 26 spline input shaft would give you a transmission capable of smooth high speed shifts and power handling in the range you are looking for. They make the conversion front plate and if you can rebuild the transmission you can install their parts yourself, if not they will build one for the right price. I have a message in to them about beefing up my transmission to see if they will commit to their transmission builds being up to 575 foot pounds of torque.

The shifter comes up in the exact stock location-the cross member is different, but available or buildable.\

As to the pedals-if you choose to run a mechanical linkage, I think the cougar pedals will fit fine, but IIRC the stock set up can be altered to swap brake pedals and add the clutch.

I see that Modern Driveline offers their own pedal assembly, but considering I've got a '71 assembly to begin with I'd like to use it. I'm not interested in hydraulic clutch at all. I'm accustomed to driving my '89 5.0 with a Tremec 3550 and cable clutch, so I'd prefer to stick with the simplicity of the cable. I wonder if there's a simple way to convert the stock clutch pedal assembly to cable.

A Tremec 3650 or T-45 sounds good, but the bellhousing bolt pattern is modular motor only, apparently. I'm sure an adapter could be found, but I'd rather not go down that route. Plenty of good SBF specific transmissions to choose from.

 

[Jeff73Mach1]

Well the adapter plate front is reapply no big deal, but it is about 400 bucks. Either of the transmissions, the T-45 or the 3550 have a 1st gear ratio that is less than ideal.

I heard back and their cost to upgrade my transmission is fairly reasonable-it is that damn 1st gear ratio I am starting to get tired of dealing with

 

[mjlan]

The pedal swap is straight forward. Cougar and Mustang of this vintage is the same, and in slushbox cars, the brake pedal pivots on a shaft. Pull the shaft out and replace it with a clutch pedal, and either cut the auto trans brake pedal to fit a manual trans brake pad or swap the auto trans pedal for a manual trans one.

I would do the TKO route. You could possibly find a Ford aluminum bellhousing for this application as Ford sells them. I think that you'll need the smaller flywheel though. I swapped a 5.0/ T5 into a 71 I had and it was pretty straightforward, I used mostly original Fox-body 5.0 stuff with the Modern Driveline cable conversion and T5 crossmember...

 

[droptop73]

As for the clutch pedal, the Modern Driveline piece is real nice and retrofits to the stock power brake bracket. All you need to do is tack weld the bushings to the bracket and cut off the automatic brake pedal. Save the OE setup for a restorer and make a few bucks!!

 

[Don65Stang]

Either of the transmissions, the T-45 or the 3550 have a 1st gear ratio that is less than ideal.

...it is that damn 1st gear ratio I am starting to get tired of dealing with

I want to emphasise what Jeff is saying. The first gear ratio is vey important. Ideally the first gear final ratio (when adding the rear gears and tire size) should be between 9 and 11:1. The spreadsheet I referenced earlier shows this calculation/ ratio for various transmissions and rear gear combos based on an average 26" tire height.

I have a 3550 and the first gear starting ratio is all wrong like Jeff's T-45. Both of us greater than 12:1 final first gear ratios. It's great if you want a granny gear but winds out way too soon. It's almost instant redline in first gear when starting off.

 

[will e]

You are correct on the 'two low' for most applications. My sport trac sports a 4.17 first gear but it is a six speed transmission. It jumps out of first pretty quick but the goal of that transmission was to get the RPM's up. Second gear is like 2.37 or something. This works for a computer controlled electronic automatic but would be tiresome with a manual. Most of the time you would just start in 2nd.

 

[73Qcode]

Hey don would like to get copy of that sheet u posted earlier but cant dowwnload it thanks.Im wanting to change my transmision to aod with 3.73 gears rear not to sure what to do with trans or the options i have any help would be appreciated.

 

[Mesozoic]

I'm still very torn about whether I should move forward with a manual transmission setup or stick with an auto. I have a few pressing issues that are forcing me to make a decision soon, however. First, we're having our 1st child in mid July and the car has to be finished by then. Second, the headers on my wheezer don't fit the new heads very well (spark plug angles changed), so I'm going to have to have a new set fabricated... I want larger diameter primaries anyway (currently only 1 5/8").

The issue with fabricating new headers is that a) it's an expensive and time consuming job and b) headers that fit a '71 equipped with a 4R70W transmission will differ from those modified to fit a TKO 5-speed manual. The car has a C6 in it now so I'm assuming that the 4R70W is a pretty straightforward affair compared to the manual. I've heard the clutch fork location will require a different design on the driver side.

Anyhow, I'd like to hear some more thoughts on the subject of retrofitting a manual trans vs an overdrive auto...