Manual or automatic?

[tcanin00]

I'm having a hard time deciding if I want to convert my car to an AX15 5 speed with overdrive, a 46RE, or keep the 904 lock up and regear the axle. The plan for the car is to be a daily driver that might see some autocross action.

The car is a 1970 Dart Swinger and has a fuel injected 5.2 Magnum with an Xtreme Energy .480" cam with a Ford 8.8 axle with 3.73 gears. With low profile 17" tires it's turning over 3,500 rpm at 70 MPH, and that's why I need to add an overdrive or regear.

Option 1: Use the AX15 that I have from a Dakota so that I can use the 143 tooth flywheel that has the teeth for the crank position sensor. I know I would have to cut the torsion bar cross member and transmission tunnel for clearance, and that is not a problem. After some research on it's gear ratios it doesn't seem like the best option. So I started looking at the R154 Toyota version of the transmission and it's ratios are not much different. There is a company that makes a close ratio gear set that is closer to the ratios of a Tremec TKO/TKX for the AX15 for $2,800 plus shipping. A little pricey, but cheaper than a full TKO/TKX conversion.

Option 1A: keep the stock ratios of the AX15 and regear to 2:76. I read a thread on here that got down into the weeds about ratios versus the power band at different RPM's. Very good read, and it's what got me started thinking about this.
One of the points made is, provided everything else was equal, a car with an AX15 and 2.76 gears would pull as hard as car with a 904 and 4.10's. The same car with an A833 would perform similarly with 4.10 gears, but the ratio gaps would cause a substantial drop in RPM's between shifts.

Option 2: Use a 46RE. It's ratios are decent, and it has a good overdrive percentage. It would require tunnel and cross member clearance, too. Since I'm running a JTEC PCM, I could control the transmission directly with a stock PCM. This would be the cheapest swap, since all of the parts would be used. Even if I had to have on rebuilt, it would be around $1,500 or so. My concern is the stall speed of the torque converter with the cam. Would I need a looser converter for it?

Option 3: keep the 904 and regear to the 2.76-3.08 range. I've seen used gear sets going for $30-50 rebuild kits for $70-100. The cheapest option for sure. The 904's ratio gaps aren't terrible. Would I need a looser converter for the cam?

Pictures of the car in question.

 

[Ant]

I would take the easiest and cheapest route and keep the 904 and re-gear the rear end, but that's just me. It's really up to you if you want to tackle the project of retrofitting a different trans in the car.

 

[abodyjoe]

its personal preference i'd say.. for me i'm not cutting the torsion bar cross memeber on our original paint dart so all those swaps are out of the question. i went to a 2.76 gear. its ok. think i'll gather the parts to throw a 2.94 in it though... everything is a comprimise. ever think of a gear vendor on your 904? pricey but a 3.55 gear turns into a 2.76 with one.

 

[PROSTOCKTOM]

I like to advocate for the KISS Method.

Unless you plan to drive it alot a simple 904 is really economical and easy to work on.

The other options sound great, but do really want to go to that much trouble and expense?

Tom

 

[Dave999]

if you are going drag racing id say you will get easier consistency and have fun with an auto of some kind

if you intend it to be a multi use vehicle the manual does it, you can chase BMWs and Audis on the freeway, surprise a range of modern stuff away from the lights , light up the tyres as you leave coffee and cars.... drift it in the wet and hammer it along country roads.
i have a 4 speed keeps me happy
I do drag race it in an amateur way but really unless you have a lot of 4 speeds you are not gonna have the luxury of pinging the clutch time after time.... you will break something.
which is why i drive to the track run street tyres and just check to see if i'm going faster than last year... i drive in, I empty the car, do an afternoon of passes and get on the beer.

i don't have the time the money or the spare transmissions and clutches to be a consistent manual trans drag racer.. 904 line lock and slicks well it could be different

basically your intended use/application is worth thinking about.
if you drive A to B 90% of the time, when A and B are not 1/4 of a mile apart 4 speed is great. 3.23:1 3.5:1 3.7:1 in the back yeah... it goes and you are not doing ridiculous rpm at 70 mph, go with the softest lightest clutch you can get away with.... test stamp the peddle in 3rd at 40 no slip...all good. clutch plate is cheap transmission rebuild is not

Dave

 

[Icetech]

I would go manual if i had the choice... i really want to in my current car.. BUT.. i am cheap and changing the rear gears is the easy/cheap solution would suck for autocross though

 

[tcanin00]

I would take the easiest and cheapest route and keep the 904 and re-gear the rear end, but that's just me. It's really up to you if you want to tackle the project of retrofitting a different trans in the car.

I'm starting to think about that after my wife reminded me that I fix the car until it's broken, and it sits in the driveway instead of being driven.

 

[tcanin00]

its personal preference i'd say.. for me i'm not cutting the torsion bar cross memeber on our original paint dart so all those swaps are out of the question. i went to a 2.76 gear. its ok. think i'll gather the parts to throw a 2.94 in it though... everything is a comprimise. ever think of a gear vendor on your 904? pricey but a 3.55 gear turns into a 2.76 with one.

My car isn't an all original car, but it's rust free and solid. A rarity in the Rust Belt, for sure. I don't mind the fab work, but the amount of time involved is the deal breaker.
I'm sure 2.76 gears with the 904 would be a dog. That's why I intially wanted the 3.73's, so it would have decent acceleration without having to spend a fortune on building an engine. I haven't considered a Gear Vendor set up, but it's not a bad suggestion.

 

[tcanin00]

if you are going drag racing id say you will get easier consistency and have fun with an auto of some kind

if you intend it to be a multi use vehicle the manual does it, you can chase BMWs and Audis on the freeway, surprise a range of modern stuff away from the lights , light up the tyres as you leave coffee and cars.... drift it in the wet and hammer it along country roads.
i have a 4 speed keeps me happy
I do drag race it in an amateur way but really unless you have a lot of 4 speeds you are not gonna have the luxury of pinging the clutch time after time.... you will break something.
which is why i drive to the track run street tyres and just check to see if i'm going faster than last year... i drive in, I empty the car, do an afternoon of passes and get on the beer.

i don't have the time the money or the spare transmissions and clutches to be a consistent manual trans drag racer.. 904 line lock and slicks well it could be different

basically your intended use/application is worth thinking about.
if you drive A to B 90% of the time, when A and B are not 1/4 of a mile apart 4 speed is great. 3.23:1 3.5:1 3.7:1 in the back yeah... it goes and you are not doing ridiculous rpm at 70 mph, go with the softest lightest clutch you can get away with.... test stamp the peddle in 3rd at 40 no slip...all good. clutch plate is cheap transmission rebuild is not

Dave

I don't plan on drag racing. I know the relatively stock 318 wouldn't pull it out of 13 or 14 second passes without a 200 shot of NOS.
But yeah, I want the car to usable for regular driving and occasional messing around. Like accelerating onto the highway, or from red to light. There's been a couple times I've been fooling around and had other cars get in on it. It's all for fun, I'm not looking to race and I stop around 90 MPH.
I've read about guys making the Magnums work in front of 4 speeds. Jamie on Dead Dodge Garage on YouTube clearanced the back side of a 130 tooth flywheel to clear a Magnum flex plate. It worked for him, but I would be worried about affecting the balance of the flywheel.

 

[tcanin00]

I would go manual if i had the choice... i really want to in my current car.. BUT.. i am cheap and changing the rear gears is the easy/cheap solution would suck for autocross though

Yeah, the cool factor of having a 5 speed is what's making me think about it. I've had a few A bodies, but never a manual one.
I don't plan on full blown track days at Virginia International or the infield of the Poconos, just running over cones in parking lots. But I'm sure a manual car would be better at getting around a course than an automatic.

 

[tcanin00]

I like to advocate for the KISS Method.

Unless you plan to drive it alot a simple 904 is really economical and easy to work on.

The other options sound great, but do really want to go to that much trouble and expense?

Tom

I agree with you, no need to make this more complicated than it needs to be. I do plan on driving as much as possible since the Great White North makes us put away our toys for awhile.

 

[tcanin00]

Thanks for the responses and suggestions, all great things to think about.

 

[340sFastback]

You could do a low gear set in the 904, maybe a 294 rear gear, and get a custom torque converter to match. Its a compromise but a lot less work then an overdrive trans. Its a lot of pros / cons and personal preference.

 

[Dave999]

well and this will strike many as an odd suggestion and an option you probably won't want to pursue....... But i'll say it anyway

if you are running an auto floor pan A body car and don't want to cut anything but a hole for a stick and don't want to put the offset side on the tunnel for an a833
the Australian Chrysler Borgwarner single rail 4 speed fits
its a steel cased small toploader with a 300 ftlb rating that just needs a hole in the top of the tunnel for the shifter.
was used by chrysler behind 265 and 318 used by ford behind smaller v8s and of course retro fitted behind 340 etc...driven carefully
IBR diameter is the same as the common A833 size i.e not the huge feather duster overdrive size. 4.8 inch
the bellhousing pattern for the trans is the same as the smaller engine 3 speed pattern in all but 1 position. (just drill and tap the bell )

it uses a 727 yoke and seal
USA throw out bearings work
the input shaft is mopar length mopar spigot bush size
it has a rear mount that fits in an A-body using either square 1 or 2 stud or the spool style mount
Its single shifting rail fits under the torsion bars cross member

the only issue you have is finding one with a shifter and then shipping...but i know at least one guy in the states who took his out and replaced it with a tremec id suspect there are 2 or 3 around. smooth shifting ball bearing and thrust washer 4 speed that you fill with SAE30 or auto trans fluid

out of all of the "standard" transmissions (Borgwarner custom designed it for a US mid 60s mopar A body automatic floor pan and chassis as used in all Aussie Mopars till 82), this is the easiest retro fit/swap transmission you can get.. you can even squeeze one into a 61/62 with only a little bit of cutting (for the stick) and bashing to fit a bigger bell where the seam is at the bulkhead tunnel junction
cross member and original flooring stays intact...

image below shows Mopar specific kinked down shift rail. these used on Oz NZ and anywhere they exported the cars to... i.e indonesia UK Jamaica to name a few

easy to rebuild if you are willing to spend hours with grinding paste lapping in the poor after market synchros available today...most of them seem to have been dropped they are not round out of the box....

you can get ford versions of this trans without the kink and with a short 10 spline input shaft and a rear mount in the wrong place like a t5, they are not an easy fit. may as well just do the T5 instead.

Dave
Below the Borg Warner 4 speed that even borgwarner forgot they made. comes in close and wide ratio. Power brute and big fat monkey marketing stolen from US borgwarner GM product.

 

[Icetech]

For the money you are going to spend you could a gearvendors unit... if they made one for my trans i would have done that..

 

[67Dart273]

I thought I knew that AX15s had poor ratio choices, so do some research. They are not a particularly strong gearbox. I'd go Mopar A833 OD before I did that

 

[Dave999]

i agree if you go to the trouble of fitting an Aisin Warner box go with the R154 from the toyota supra turbo... if you can find one

slant 6 or 273 use a W58 easier to find and cost less, preferably the later style with the steel sandwich plate looks rusty at the mid plate not grey like tha alloy sandwich plate version
W57 and W59 are same box with not so good ratios W59 in 2WD is a pickup tuck box but many hilux/4 runners were 4WD so used this with a transfer box on the back
W57 used in lotus excel

Aisin Warner.... something to do with BorgWarner and toyota. for toyota trucks and cars from mid70s onwards

you can squeeze the ancient steel case w50 from a 1976 celica in without cutting the cross member if you are happy to have a slightly off alignment with the diff but it was designed to be behind a 1600CC motor with 70 HP...still very strong for what it is/was given its size but a 318 would kill it eventually....find one.... all got swapped into british sports cars of the 1960s

Dave

 

[MopaR&D]

I thought I knew that AX15s had poor ratio choices, so do some research. They are not a particularly strong gearbox. I'd go Mopar A833 OD before I did that

It'll last forever behind a 5.2 in a street car. @75slant6 has had one behind a 5.9 for years and drives it hard, I think it's still holding up?

They were designed and put together better than an A833OD that's for sure. I had an AX-15 behind a 4.0L in a Cherokee, I beat on it hard doing plenty of speed shifting and it still worked great when the car got totaled with 250k on the odo.

I'd swap one in with the 2.76 gears and not look back. Idk if you can get gears that tall for a Ford 8.8 but 3.0x would still work well. I think stock SN95 Mustang GT auto ratio was 3.08?

 

[75slant6]

Of those 3 options, I’d definitely do the AX-15 swap, unless you WANT an automatic, then I’d do the 46re. Like MopaR&D said, I’ve been running an AX behind a 5.9 magnum in my Duster for 10 years and 25k+ miles without the first problem. I currently have the car apart for a bigger cam, aluminum heads and efi but the AX will definitely be going back in. I originally had 3.23’s but 1st gear was useless other than starting off on a hill so I switched to 2.76’s. I plan to change my rear tires from 25.5” tall to 27-28” tall in the near future, so if I had it to do over, I’d do 2.94’s.

 

[340sFastback]

I'd swap one in with the 2.76 gears and not look back. Idk if you can get gears that tall for a Ford 8.8 but 3.0x would still work well. I think stock SN95 Mustang GT auto ratio was 3.08?

The standard axle ratio for an '87 - '93 5.0 fox body was 2.73 for both auto.and manual cars. Most fox body ppl swap out the 2.73 gears and throw them in the trash can.

 

[tcanin00]

You could do a low gear set in the 904, maybe a 294 rear gear, and get a custom torque converter to match. Its a compromise but a lot less work then an overdrive trans. Its a lot of pros / cons and personal preference.

I had read about some of the later 904's having a lower first gear. What kind of converter, or stall speed would you recommend?
I know it's going to come down to cost vs. time.

 

[tcanin00]

well and this will strike many as an odd suggestion and an option you probably won't want to pursue....... But i'll say it anyway

if you are running an auto floor pan A body car and don't want to cut anything but a hole for a stick and don't want to put the offset side on the tunnel for an a833
the Australian Chrysler Borgwarner single rail 4 speed fits
its a steel cased small toploader with a 300 ftlb rating that just needs a hole in the top of the tunnel for the shifter.
was used by chrysler behind 265 and 318 used by ford behind smaller v8s and of course retro fitted behind 340 etc...driven carefully
IBR diameter is the same as the common A833 size i.e not the huge feather duster overdrive size. 4.8 inch
the bellhousing pattern for the trans is the same as the smaller engine 3 speed pattern in all but 1 position. (just drill and tap the bell )

it uses a 727 yoke and seal
USA throw out bearings work
the input shaft is mopar length mopar spigot bush size
it has a rear mount that fits in an A-body using either square 1 or 2 stud or the spool style mount
Its single shifting rail fits under the torsion bars cross member

the only issue you have is finding one with a shifter and then shipping...but i know at least one guy in the states who took his out and replaced it with a tremec id suspect there are 2 or 3 around. smooth shifting ball bearing and thrust washer 4 speed that you fill with SAE30 or auto trans fluid

out of all of the "standard" transmissions )Borgwarner custom designed it for a mid 60s mopar A body automatic floor pan and chassis), this is the easiest retro fit/swap transmission you can get.. you can even squeeze one into a 61/62 with only a little bit of cutting (for the stick) and bashing to fit a bigger bell where the seam is at the bulkhead tunnel junction
cross member and original flooring stays intact...

image below shows Mopar specific kinked down shift rail. these used on Oz NZ and anywhere they exported the cars to... i.e indonesia UK Jamaica to name a few

easy to rebuild if you are willing to spend hours with grinding paste lapping in the poor after market synchros available today...most of them seem to have been dropped they are not round out of the box....

you can get ford versions of this trans without the kink and with a short 10 spline input shaft and a rear mount in the wrong place like a t5, they are not an easy fit. may as well just do the T5 instead.

Dave

View attachment 1716456621

Thanks for the suggestion of this transmission, it's another option for cars that don't have a lot of choices. I didn't think about the transmission tunnel being different for the manual transmission cars. I knew there was a hump for the shift linkage.

 

[tcanin00]

For the money you are going to spend you could a gearvendors unit... if they made one for my trans i would have done that..

Yeah, I looked at Gear Vendors. They're $3,200-3,600 depending on options. I liked the fact they offer a shorter version, since 904's have such a long tail shaft housing. The short version uses an 8" long tail shaft housing and a 4x4 output shaft.
What transmission are you running?

 

[Icetech]

Yeah, I looked at Gear Vendors. They're $3,200-3,600 depending on options. I liked the fact they offer a shorter version, since 904's have such a long tail shaft housing. The short version uses an 8" long tail shaft housing and a 4x4 output shaft.
What transmission are you running?

I run a 727 but it's pushbutton and they don't use a normal tailshaft And i was wondering earlier today why mopar used such long tailshafts on trains.. help not have super long driveshaft?

And.... if i could easily convert my car to a 5-6 speed i would do it in a heartbeat... could keep the 4.30s and still drive nice.. i have spent the last hour thinking bout if i wanna drop to 3.23 or 3.55... will be less fun but less annoying

 

[jos51700]

I run a 727 but it's pushbutton and they don't use a normal tailshaft And i was wondering earlier today why mopar used such long tailshafts on trains.. help not have super long driveshaft?

And.... if i could easily convert my car to a 5-6 speed i would do it in a heartbeat... could keep the 4.30s and still drive nice.. i have spent the last hour thinking bout if i wanna drop to 3.23 or 3.55... will be less fun but less annoying

Long driveshafts are bad. The longer that they get, the more balance becomes critical and then that limits drive shaft speed. That's why you got be careful switching to overdrive and crazy steep gears, the driveshaft speed has to taken into consideration.

That's why box trucks and the like have 3 and 4 piece driveshafts with multiple support points.