Early-A 4 speed auto opt

[Anthony Beauchamp]

Hey I have a 1966 Plymouth barracuda 318/904 with 4.10’s(or 4.11’s) it’s a factory floor shifter. My question is what all options do I have for a 4 speed automatic transmission? I want to keep the stock gear shifter.(is this even possible?) I don’t have a big budget nor want to swap to a manual transmission. I am familiar with the gear vendors option. But service every 5k, it doesn’t see that in years and if left in gear below a certain speed you can damage has anyone had a bad experience with it?

 

[RustyRatRod]

You have zero options that do not include cutting the floorpan. About the smallest 4 speed OD auto would be the GM 200R4. Even the later A833 manual four speed Chrysler transmission requires the four speed floor hump if your car is not a factory floor shifted manual.

 

[WV64Signet]

You would need this

[FOR SALE] - Early A body 4 SPD conversion kit

 

[AJ/FormS]

But service every 5k, it doesn’t see that in years and if left in gear below a certain speed you can damage has anyone had a bad experience with it?

I have a GVod.
But behind a Commando-speed.
I have mine set up for Gear-Splitting and so, I left the command module in the box.
The only trouble that I have had is forgetting to outshift it before backing up, which immediately killed it. This would not have happened had I been running the GV control unit.
If you leave it engaged and come to a stop, then take off again; chances are that it will keep enough pressure to not slip on take-off.
But, the unit will not hold pressure thru a stoplight. which means that it will slip on take-off for some distance, which varies with whatever rear gear has been installed. With 4.30s, it only takes a few feet to have adequate pressure.
I finally installed a couple of LEDS under my tach, a green one comes on, whenever the unit has been selected. A red one comes on if the trans is in reverse. Since then, I have had no more trouble.
But
I gotta tell ya Anthony, the buy-in is very steep, and gear-splitting a regular 904 is not worth the effort.
Knowing what I know now, I would not again go that route.
Your 4.10s tell me that you enjoy a spunky take off. and I'm assuming yur trying to get away from the hiway rpm. Am I right?
IMO, there are, or at least may be, better options for a whole lotta less money.
I want to show you something;
gears are just torque multipliers.
If you have a stock 2000 rpm type stall and say your engine puts out 300 ftlbs of torque at that rpm. Thru the 904 and thru the 4.10s this will put 300 x 2.45 x 4.10=3013.5 ftlbs into the rear axles. This is about what you are used to. and
65 =3445@ zero-slip
( From now on, all numbers will be calculated to zero-slip. Your tach may read 3>4% higher, perhaps as much as 5%)
But you can reconfigure this any way you want, and if it comes out to the same 3013.5 ftlbs it will take off exactly the same.
Say you had a trans with a 4.10 low gear and a rearend of 2.45, the new numbers would be:
300 x 4.10 x 2.45=3013.5.
Or say you modded your engine to get 330 ft lbs at Zero mph, and kept the 2.45 low gear. The rear gear to get 3013.5 would be;
3013.5/(2.45 x 330)= 3.73s;
and 65=3134@zero-slip.
Or say you got yourself an A999 with a 2.74 low gear, And the modded engine that makes 330#; the new numbers are;
3013.5/(330 x 2.74)= 3.33 gears.
and 65= 2800@ zero-slip
But say you dropped a 360 in there with a 2800Convertor and it makes 360ftlbs at 2800. the new numbers are;
3013.5/(360 x 2.74) =3.05s and
65=2560@zero-slip.
You see what I'm getting at?

Ok but, as you already know, your 318/904/4.10 combo has a killer first gear, and you know that you can sacrifice some of that; am I right?
Lets say you are willing to give up 10% of that which is ~300 ftlbs at the axles.
You have three good choices which are;
1) more Trans low gear or
2) less rear gear or
3) more torque. This choice comes with 3 possible solutions
a) a modified 318, or
b) a higher stall convertor or
c) a bigger engine.
Ok , I get that you are on a budget, so I'm not gonna recommend to mod the 318 .
And dropping in a JY 360LA is kindof a crapshoot,and a 5.9Magnum is getting pricey, so lets decide to keep the current 318.
But the 4.10s have to go.
And so does either; the A904 with it's lowly 2.45 low gear. OR
the 2000 stall convertor
So my suggestion is drop an A999 in there, with ratios of 2.74-1.54-1.00; which may already come with a 2400>2600 stall, and lets go with 3.23s and see what that gets us.
Now we are shooting for 2700Ftlbs into the rear axles, so
2700/(2.74 x 3.23)=305 ftlbs required, which, if you recall is very close to the 300 I started this exercise with, so no engine mods of any kind are required. And with the 3.23s and a Lock-Up,
65=2714. That's a drop of about 731rpm from 3445 with a modest 10% loss of Torque multiplication off the line.
The GVod would get you 3445 x .78=
65=2687, a drop of 760......
Your cost is;
an A999 core, A rebuild kit, a shift kit,
a set of 3.23gears, and a new speed-O gear
If you have an 8.75 you can swap them both around in less than a day.

>Ok to be fair, if you want the 3013.5ftlbs back, which is
3013/(2.74 x 3.23) =340 ftlbs in the engine, which is 40 more than the control engine. You can get some of that back with a mechanical-secondary carb, but better is a higher stall convertor.
>to be even more fair, the 200R4 has ratios of
2.78-1.57-1.00-.67od
This is very close to the A999 , but with 4.10s,
65mph=2308 @zero-slip
Your cost is;
the core and rebuiild kit, a shift kit, and probably a convertor,
an engine-adapter, a driveshaft, and a speedo-adapter,
>on the flipside
Even with a tired smog 360 short block, and the trans you now have;
2700/(2.45 x 3.23)= will require 341 crank ftlbs, which should be a breeze with whatever your current stall is.
Your cost is a 360 short, gaskets, and the 3.23s.
You can bolt your entire top end onto that 360, and in less that two days be having fun. and
65=2714 @zero slip, which is close to the same as with the GVod with 4.10s, which was 2687@ zeroslip.

Finally, the torque numbers I chose to work with, might be a little optimistic; but because I used the same numbers thruout the exercise, it doesn't matter.

 

[Anthony Beauchamp]

I have a GVod.
But behind a Commando-speed.
I have mine set up for Gear-Splitting and so, I left the command module in the box.
The only trouble that I have had is forgetting to outshift it before backing up, which immediately killed it. This would not have happened had I been running the GV control unit.
If you leave it engaged and come to a stop, then take off again; chances are that it will keep enough pressure to not slip on take-off.
But, the unit will not hold pressure thru a stoplight. which means that it will slip on take-off for some distance, which varies with whatever rear gear has been installed. With 4.30s, it only takes a few feet to have adequate pressure.
I finally installed a couple of LEDS under my tach, a green one comes on, whenever the unit has been selected. A red one comes on if the trans is in reverse. Since then, I have had no more trouble.
But
I gotta tell ya Anthony, the buy-in is very steep, and gear-splitting a regular 904 is not worth the effort.
Knowing what I know now, I would not again go that route.
Your 4.10s tell me that you enjoy a spunky take off. and I'm assuming yur trying to get away from the hiway rpm. Am I right?
IMO, there are, or at least may be, better options for a whole lotta less money.
I want to show you something;
gears are just torque multipliers.
If you have a stock 2000 rpm type stall and say your engine puts out 300 ftlbs of torque at that rpm. Thru the 904 and thru the 4.10s this will put 300 x 2.45 x 4.10=3013.5 ftlbs into the rear axles. This is about what you are used to. and
65 =3445@ zero-slip
( From now on, all numbers will be calculated to zero-slip. Your tach may read 3>4% higher, perhaps as much as 5%)
But you can reconfigure this any way you want, and if it comes out to the same 3013.5 ftlbs it will take off exactly the same.
Say you had a trans with a 4.10 low gear and a rearend of 2.45, the new numbers would be:
300 x 4.10 x 2.45=3013.5.
Or say you modded your engine to get 330 ft lbs at Zero mph, and kept the 2.45 low gear. The rear gear to get 3013.5 would be;
3013.5/(2.45 x 330)= 3.73s;
and 65=3134@zero-slip.
Or say you got yourself an A999 with a 2.74 low gear, And the modded engine that makes 330#; the new numbers are;
3013.5/(330 x 2.74)= 3.33 gears.
and 65= 2800@ zero-slip
But say you dropped a 360 in there with a 2800Convertor and it makes 360ftlbs at 2800. the new numbers are;
3013.5/(360 x 2.74) =3.05s and
65=2560@zero-slip.
You see what I'm getting at?

Ok but, as you already know, your 318/904/4.10 combo has a killer first gear, and you know that you can sacrifice some of that; am I right?
Lets say you are willing to give up 10% of that which is ~300 ftlbs at the axles.
You have three good choices which are;
1) more Trans low gear or
2) less rear gear or
3) more torque. This choice comes with 3 possible solutions
a) a modified 318, or
b) a higher stall convertor or
c) a bigger engine.
Ok , I get that you are on a budget, so I'm not gonna recommend to mod the 318 .
And dropping in a JY 360LA is kindof a crapshoot,and a 5.9Magnum is getting pricey, so lets decide to keep the current 318.
But the 4.10s have to go.
And so does either; the A904 with it's lowly 2.45 low gear. OR
the 2000 stall convertor
So my suggestion is drop an A999 in there, with ratios of 2.74-1.54-1.00; which may already come with a 2400>2600 stall, and lets go with 3.23s and see what that gets us.
Now we are shooting for 2700Ftlbs into the rear axles, so
2700/(2.74 x 3.23)=305 ftlbs required, which, if you recall is very close to the 300 I started this exercise with, so no engine mods of any kind are required. And with the 3.23s and a Lock-Up,
65=2714. That's a drop of about 731rpm from 3445 with a modest 10% loss of Torque multiplication off the line.
The GVod would get you 3445 x .78=
65=2687, a drop of 760......
Your cost is;
an A999 core, A rebuild kit, a shift kit,
a set of 3.23gears, and a new speed-O gear
If you have an 8.75 you can swap them both around in less than a day.

>Ok to be fair, if you want the 3013.5ftlbs back, which is
3013/(2.74 x 3.23) =340 ftlbs in the engine, which is 40 more than the control engine. You can get some of that back with a mechanical-secondary carb, but better is a higher stall convertor.
>to be even more fair, the 200R4 has ratios of
2.78-1.57-1.00-.67od
This is very close to the A999 , but with 4.10s,
65mph=2308 @zero-slip
Your cost is;
the core and rebuiild kit, a shift kit, and probably a convertor,
an engine-adapter, a driveshaft, and a speedo-adapter,
>on the flipside
Even with a tired smog 360 short block, and the trans you now have;
2700/(2.45 x 3.23)= will require 341 crank ftlbs, which should be a breeze with whatever your current stall is.
Your cost is a 360 short, gaskets, and the 3.23s.
You can bolt your entire top end onto that 360, and in less that two days be having fun. and
65=2714 @zero slip, which is close to the same as with the GVod with 4.10s, which was 2687@ zeroslip.

Finally, the torque numbers I chose to work with, might be a little optimistic; but because I used the same numbers thruout the exercise, it doesn't matter.

Thank you so much, this was extremely helpful I understand it now. The first gear launch is the reason I have no problem driving it in town, the smiles per gallon are real. I’ve been trying to convince myself not to build a 360 magnum. You just convinced me. What would you recommend I do transmission and rear gear wise? Could the a904 handle it? Would a shift kit make it less punchy out of first when I’m per say not on it hard?

 

[AJ/FormS]

I was trying very hard Not to take you in the bigger-engine direction, mostly because those early Barracudas, being some 300 pounds lighter than the next generation, are already pretty spunky with a 318.
This takes us in a new direction.
>My 68, weighs 3650 with me in it, and has a 360, which makes it
3650/360=10.14pounds per cube. This would be spunky even with a stock 2bbl engine.
<Your Early A is gonna come at say 3200 max with you in it, making her; 3200/318=10.06 pounds per cube, giving her the potential to be even more spunky than mine, even tho, shes "only" a 318.
>Mine was more than spunky at 335 hp; so that would be 3650/335=10.89 pounds per horsepower .
<For yours to be equally spunky, you would need 3200/10.89=294 hp.
>At 335hp, mine was 335/367=1.0955 hp per cube
< for your 318 to make 294hp, that would be 294/318=.9245 hp per cube..... which altho less powerful an engine, she is every bit as spunky in your lighter chassis.

Ok so that was the math.
now, getting 294 hp out of a 318 is pretty easy, not cheap, just easy.
However; the 318, by virtue of it's cid and stroke, will always be
two steps behind a 360, in terms of take-off power.
But is this a problem?
IMO, it is NOT, because the biggest tires that you can fit into your factory tubs are 255s and yur gonna have to move the springs to do it; whereas the 67 up cars will accept up to 325s on 10" rims.
If you can't make the tires stick, all you got is a tire-burner.
The point is that; any decent 318 with 3.55s is gonna waste the tires in your Early-A. Therefore; 294 hp may be the greatest idea.
The early 318s had a compression ratio of 9.2, and were rated 230hp crank; and they easily accepted a cam one or even two sizes bigger. , thus with headers and a 4 bbl induction, the were up close to 275hp or more with bolt-ons
But again, do you need even 275hp in that chassis?
IMO
NOT if you want to run hiway gears, and simultaneously have a punchy bottom end.

Lets go in a different direction
With the price of gas steadily climbing, you should be looking at gears like 2.94s or less, and your engine should be well able to burn the cheapest gas out there. With a 318, this usually spells the end of performance.
But I got an Idea.
Lemme work it out right here in real time.
Suppose you you found a LU A999, and a 2.94 rear gear. This would cruise at 65=2470, and the starter gear is
2.94 x 2.74=8.056
And lets say you do have a 9.3 compression ratio 318, and it has the stock cam in it. IIRC that 318 cam is 248/256/112, and so in at 108 the Ica comes to 52* At 600 ft elevation, the Wallace calculator predicts 160 psi, which is a daymn fine number.
of any cam you might think to put in it, with a later closing intake valve, the low-rpm torque will fall away. Low rpm being sub-3000. So IMO, at this point, I would NOT change the cam.
If you don't change the cam, then at low-rpm, you don't need headers, but you should have a free-flowing exhaust and not those puny 273 logs.
Any vacuum secondary or air-valve secondary is NOT gonna make a bit of difference at a stock stall of 2000rpm. But we need it after 3500, so you gotta have something.
So where are we?
Oh yeah we are stuck with a starter gear of 8.056. and we are still shopping for 2700 ftlbs into the rear axle. So
2700/(8.046)=335 crank ftlbs.
Now, your 9.2Scr 318 should have no problem coughing that up by 2800>3000; breathing thru the duals and the 4bbl now wide open. So the stock cam may not be smoking the tires, but it is moving along pretty good on 255 tires, She will need a SG differential.

So now we know what it's going to take to do both.
But what happens when the Trans shifts into Second?
The ratios are 2.74-1.54-1.00 and so the splits are .562/.649
Therefore, whatever rpm you outshift First at, the rpm will come to .562 of it. Your stock cam will power-peak at around 4400, and you will want to give her some rope, so say you outshift at 4800 which with 2.94s will be 41mph(10% slip). At the shift, the Rs will fall to 4800 x .562=2700, and she's gonna be a bit weak there. But Second will take you to 68 mph@4400, darn near perfect.
So then, the only downside of running this A999 is the 1-2 rpm drop to 2700. If this becomes a problem for you, the solution is simple; install a higher stall. Well on paper it's simple, but trying to find an aftermarket LU and 3000 stall I have hears is not easy.
Ok so I'll tell you what; lets back up the Bus and install an A998 which can be had without a lock-up. The 2.94s will let us do that. So now you can put any stall in there that you can imagine. I favor a 2800 for this. This changes the cruise rpm by not more than plus 5%. We previously figured that to be 2470 so now I'll estmate 2544 at 3% slip. Still a fairly good number.
However, I'm favoring the A999LU because; How often are you gonna be stuck at 2700rpm in Second at 41mph?

Ok so lets wrap it up;
Since we know that the 4.10s have to go, and just about everybody has a set of 3.23s or less kicking around that he would be more than willing to swap for a 4.10, I would consider this my first move.
Maybe, things won't be that bad. Maybe you'll decide that; Yes the 4.10s were fun, but the (insert whatever you swapped in cheap), gears are adequate. And so, no trans swap will be required, nor any engine mods beyond what you already have done.
I couldda just said this yesterday, but would you have believed me?
But now you know the why of things, and can spend your money where it will do the most good.

and done

 

[junkyardhero]

i agree with the above, ditch the 4.10's for some 3.23's or 3.55's and either build your 904 to 999 spec or find a 999/998 to build on the side. that combo with a nice high stall converter will leave you saying 4.10 who?

it all bolts in, and if you get your ducks in a row you could knock that out over a weekend and not lay the car up for weeks on end.

 

[AJ/FormS]

What would you recommend I do transmission and rear gear wise? Could the a904 handle it? Would a shift kit make it less punchy out of first when I’m per say not on it hard?

Now to answer your questions;
The A904/998/999 even in stock configuration, can handle your street chassis with any tires that you can fit into the factory tubs.
The shift kit can be adjusted to make just about anyone happy. It does not have to be neck-snapping. That is mostly just a screwdriver adjustment away.
If I was in your pickle, I would keep the close ratio A904 that you already have, and
I would install a SureGrip with either 2.76s>3.23s ...... cuz I have at least one of each of those.
And if the 318 is a 9.2 engine pumping over 150 psi on the compression tester, I would NOT even touch the 318, beyond a 4bbl and free-flowing exhaust/ headers optional.
But, if I installed less than 3.23s, I would also opt for a higher stall.

Now, I gotta tell you something else.
I already installed a totally stock but freshened up ,LOW-compression 318 that pumped only 135 psi, into my 3650# Barracuda; with headers and dual 3s all the way to the bumper and a small-port cast-iron dual-plane with a TQ up top. I installed an A998 with a 2800TC, and 2.76 rear gears.
This was my Winter-engine one year .
It was no tire fryer on dry pavement, but I found it totally adequate for a DD, and with 2.76s she rocked 65=2234 at Zero-slip, somewhat more on the tach.
The 2800 Convertor, let the low-compression 318 spool up to about peak-torque, and then the TQ began it's roar.
I had installed a semi-auto shift kit into the VB, and what I used to do was get her into high gear as quick as she'd take WOT, and wait. That TQ carb would roar and roar and roar all the way to 70/75 mph, like 2800 rpm all the way; whatta hoot. I never missed the tire-frying business.
The 2.76s were also a hoot in first gear; with 5200= 50mph.
Why 5200? Well, firstly cuz it went there with the springs that I had installed, and secondly, cuz,you know, my HotRod summer engine went 7200, so sometimes I just had to let her rip, lol.
Oh, I forgot to mention, I live in the country and the nearest decent sized town where I found employment, was about 20 minutes away. So My mileage is probably 95% hiway, Ima guessing.

 

[273]

The whole idea of gearing/stall speed etc... is to keep engine around peak power much as possible at various speeds during acceleration, ideally at peak hp only would be optimal.
Gearing stall trades (multiply/divides) rpm and torque but not hp, same with displacement, if you pump eg.. 400 hp of fuel and air per minute at the same efficiencies different displacements will trade (multiply/divides) rpm and torque but not hp.

 

[273]

You can look at a 3 speed as a 2 speed powerglide with an od attached.
Say you only play around in town, could gear so second hits peak power at a reasonable mph.
So say 5000 rpm @ 80 mph in 2nd, 3.23 rear x 1.54 2nd x 80 mph x 336 / 27 tire = 4952 rpm

3 speed x 3.23 rear 1st-2.74, 2nd-1.54, 3rd-1.00 = 1st-8.85, 2nd-4.97, 3rd-3.23
2 speed od x 4.97 rear 1st-1.76, D-1.00, od-0.65 = 1st-8.75, D-4.97, od-3.23
or
3 speed x 3.55 rear 1st-2.45, 2nd-1.45, 3rd-1.00 = 1st-8.70, 2nd-5.15, 3rd-3.55

Many ways to look at this.

 

[Anthony Beauchamp]

Now to answer your questions;
The A904/998/999 even in stock configuration, can handle your street chassis with any tires that you can fit into the factory tubs.
The shift kit can be adjusted to make just about anyone happy. It does not have to be neck-snapping. That is mostly just a screwdriver adjustment away.
If I was in your pickle, I would keep the close ratio A904 that you already have, and
I would install a SureGrip with either 2.76s>3.23s ...... cuz I have at least one of each of those.
And if the 318 is a 9.2 engine pumping over 150 psi on the compression tester, I would NOT even touch the 318, beyond a 4bbl and free-flowing exhaust/ headers optional.
But, if I installed less than 3.23s, I would also opt for a higher stall.

Now, I gotta tell you something else.
I already installed a totally stock but freshened up ,LOW-compression 318 that pumped only 135 psi, into my 3650# Barracuda; with headers and dual 3s all the way to the bumper and a small-port cast-iron dual-plane with a TQ up top. I installed an A998 with a 2800TC, and 2.76 rear gears.
This was my Winter-engine one year .
It was no tire fryer on dry pavement, but I found it totally adequate for a DD, and with 2.76s she rocked 65=2234 at Zero-slip, somewhat more on the tach.
The 2800 Convertor, let the low-compression 318 spool up to about peak-torque, and then the TQ began it's roar.
I had installed a semi-auto shift kit into the VB, and what I used to do was get her into high gear as quick as she'd take WOT, and wait. That TQ carb would roar and roar and roar all the way to 70/75 mph, like 2800 rpm all the way; whatta hoot. I never missed the tire-frying business.
The 2.76s were also a hoot in first gear; with 5200= 50mph.
Why 5200? Well, firstly cuz it went there with the springs that I had installed, and secondly, cuz,you know, my HotRod summer engine went 7200, so sometimes I just had to let her rip, lol.
Oh, I forgot to mention, I live in the country and the nearest decent sized town where I found employment, was about 20 minutes away. So My mileage is probably 95% hiway, Ima guessing.

I haven’t stopped doing research and trying to figure out the best combo for me. Seriously thank you has been a giant eye opener. Tbh I’m not sure yet what I’m going to do I thought best I contact a & an about my 904 is a good start. You got a young hot rodder back into his hot rod.