Early 904 rebuild

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transman said:
No support of the front (pilot side)of the converter. Will shake like a dog passing razor blades.
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I ran one for 6 months with no vibes as the 4 bolts keeps it pretty dog gone centered but I ended up cracking 3 of 4 ears on the convertor! Didnt know of such mismatch until I started researching it.
 
AJ/FormS said:
Now, the long version;
If you were to install all the guts from an A998/999 hydraulically controlled loc-up,into your dual-cable case, so your push-button quadrant still works:You would end up with the equivalent of a 5-speed automatic. See below.
If not currently using the push-buttons, then just grab the A999.

The A999 will get you a new gearset of 2.74-1.54-1.00 ratios, Versus 2.45-1.45-1.00 of the standard A904 box. That would be ; plus 11.8% in low, and plus 6.2% in second. That would allow you to swap out the 3.22s for 2.94s for almost no loss in performance. After the swap the ratios are 8.06-4.53-2.94 versus 7.89-4.67-3.22; the second gears are practically the same. The only thing that changes is the lower hi-way rpm.So if not interested in fuel economy, then just use the A904 and 3.22s.
But here's the thing;
65mph with the 3.22s will be ~2763@ zero-slip, to as much as 2980 climbing a hill or such like. But locked up with 2.94s it will be 2523.. So that is like having an overdrive with a minimum ratio of .913 to as much as .847; Think about that!

Next; your stock stall in that 273, A904 trans, is probably less than 1800, so to get back the second gear 3.8% torque that the gear-swap gave up,it's gotta go. And my vote goes to a 2800. This will get you plus 8.1% back.
What's the point?
Well firstly,
the new starter gear is 2.74x2.94=8.06, versus the current 2.45x3.22=7.89, just 2% in favor of the A999. As for second gear; the A999 is 4.53 versus 4.67, the 3% nod going to the A904. These are the two gears you are gonna be using at WOT. You won't get into Drive at WOT until after 75 mph.
And secondly,
the reason I picked 2.94s is for the reduced cruise rpm. So if you are currently cruising at 65=2660@zero slip,(this number could be up to ~150/200 rpm either way depending on loading; terrain,wind,towing, etc), then your new cruise will be 2423 locked up. Period.
And the reason for the 2800TC, is for it's big torque multiplying advantage.

At the bottom of the post is a 318 Magnum graph to help illustrate the point. Your 340 would obviously have different numbers but this pic is especially nice to read. In the following examples I will use numbers off it.

The stock stall in that 273, A904 trans is probably less than 1800, per the graph, that is
270 ftlbs@1800
At 2800 the torque is 294 ftlbs , that's plus 8.9% right there.
and at 4400 it looks like 272

So at zero mph
A) with your current set up, this 5.2Magnum would put down;
270(@1800)x2.45x3.22=2130 ftlbs, times the TM(Torque Multiplication) in the TC estimated to be 1.8@ zero mph =3834@1800;
whooee that's smoke-the-tires territory.
B) With a 4-speed, this would be just
270(@1800)x2.66x3.22=2310@1800, maybe enough to spin skinny tires. That's a 40% loss.
A good street target is 2500ftlbs, so you might need to up the clutch rpm to ;
2500/(2.66x3.22)=292 ftlbs, which,per the graph is 2800 rpm. So now; 292x2.66x3.22=2501@2800rpm
C) Ok but how about your current A904x3.22s with a2800? Glad you asked.
294x2.45x3.22x1.8=4146 @2800
I could rest my case here, but

but, as the car begins to accelerate, the TM in the TC automatically diminishes as a function of torque input to to the load presented at the output side. So as the car accelerates, the TM will fall continuously from ~1.8 thru 1.7,1.6 1.5,and so on, to about 1.1 at the top of third gear. Somewhere in first gear, the ratio will be around 1.2, lets say it happens at 4400 rpm; So at this speed, the road-torque will have dropped to
294(@4400) x2.45x3.22x1.2=2783; still way better than the 4-speed's 2.94(4400) x2.66x3.22+2518.. In order for the MT to keep up, it would need more rear gear,namely;2783/(2.66x294)=3.56s

Roadgears
OK so lets line up the ratios; in road gears which will be, trans gear times rear gear, what the engine sees.
First the A833 with 3.22s; ....
C) 8.57-6.18-4.51-3.22 No multipliers
D) Next your current combo of;1800stall, A904,3.22s, and with the TC multipliers of 1.8 and 1.2 figured in; so
14.20-9.47-5.60-3.86; yeah, that's 4 ratios, the extra one being the 1.8 inside the TC.
E) Ok so lets see what the A999 can do with the lock-up, and say 2.94 rear gears;
14.50-9.67-5.43-3.53-2.94 ..........there they are ... all 5 of them; the first two are first gear, beginning and ending; then second and third, and last is the loc-up.
You can clearly see that the first three ratios are very similar, so you haven't lost nor gained performance yet. Even the "4th" ratio is fairly similar, but you won't get into that at WOT,until after 75 mph.
Let's put the torque numbers in there; and only the first two gears cuz you'll see it. And only the first two matter on the street.

OK, first gear only;
1) current combo with starter of 3.22x2.45=7.89, & 1800TC going to 4400;
270x7.89x1.8=3834 diminishing to; 272x7.89x1.2=2575 by 4400rpm
2) next the A999 with 2.74x2.94=8.06, and the 2800stall;
294x8.06x1.8=4263 diminishing to; 272x2.74x2.94x1.2=2630 by 4400
lookit that; top of first is about same roadtorque in both cases.
But the A999 is tops,with a killer plus 11.2%, off the line
3) Compare that to the 4-gear of
294 (@2800) x2.66 x3.22=2518 max and of 2299 with 2.94s; both@4400
Which would you rather have? I mean it's a personal choice and 2518 is plenty of take-off torque.
4) To be fair, here is what it looks like with the 3.22x2.45=7.89, and the 2800
294(2800)x7.89x1.8=4175,diminishing to; 272x7.89x1.2= 2575@4400
Compare this last combo to the first,

Now second gear
Again, first the current combo with the 1800stall and 3.22s
and lets get into it from 2800, which is from first gear revved to 4800 then shifted. So I estimate the TC ratios as 1.25 going in, and diminishing to 1.15 going out. It doesn't matter much if I get this wrong, cuz I will apply the same multipliers in all cases.
So
current combo, A904/1800TC/1.45x3.22=4.67;still ending at 4400
292(@2800)x4.67x1.25=1704,diminishing to 272x4.67x1.15=1460@4400
next the A999/2800TC/1.54x2.94=4.53
292(@2800) x4.53x1.25=1653 diminishing to 272 x4.53x1.15=1415@4400
next the A833;
292(@2800)x1.92x3.22=1805 diminishing to 272x1.92x3.22 =1682@4400
292(@2800)x1.92x2.94=1648 diminishing to 272x1.92x2.94 =1535@4400
Peruse the numbers
By top of second gear the A833/3.22 combo is spanking the automatic combos. But the autos have been killing it for most of the way there.
So, contemplate the value of these changes

Caveat
this is very important. Since I swapped rear gears between combos, the picture for the A999/2.94 actually looks a lil rosier than it is, in as much as the roadspeeds vary some between the 2800 and 4800shift-rpm numbers.
In first gear this won't much matter, because at WOT, the tires will be spinning most or all of the way thru it, and the A999/2.94s are gonna kill the other two combos any way.
Top of first at 4800 is 41.8mph,with 24.5 tires, in the A999/2.94 combo; with
the A904/3.22s; it is 42.7 mph. So there's that.
The A833 will hit..... 42.5 at 4800
Then;
60mph in second with;
the A999/2.94s will be ~4050, whereas the A904/3.22s will hit ~4002,lol, and the A833 is at 4896; finally making sense, for a 340.

BTW;
as you can see, with these autos and gears, and for just street duty, there is not much point in a 5500 rpm cam, for two reasons;
1) in first gear, the 4400 rpm cam should, in your lightweight 340 combo, be smoking thru first gear,; so in first gear the 4400 is enough.
2) in second,at 60mph,the Rs peak at just around 4000, so again, a 5500 rpm cam is gonna help you nothing............jus saying.
But the A833 is finally coming alive with the next bigger cam
Now, if you just want to smoke the tires to 60mph, well that sure is a lotta fun.

Ok remember, I used a 5.2 magnum graph from which to extract the torque numbers. Depending on what cam and cylinder pressure you have, your engine could have more or could have less. But the point is exactly the same.
Now; if you were not concerned about hiway fuel economy, then;
If you installed just the 2800TC, and kept the 3.22s then you wouldn't need the A999. And if you installed 3.73s, you could hit 60@4460ish, so again keep the 4400rpm cam.
But look at that graph; on the street, that 4400rpm cam is good to 4800. So; with 25.5 tall tires, that would take about 3.91s. The proof is 60x1056x3.91x1.45/80=4486@ zero slip, say 4800 @8%
With 3.91s, maybe you can spin to 60 on just the primaries,lol.
248 ftlbs(@4800) x3.91 x1.45(second)x1.08=1518 ftlbs; well maybe I exaggerated just a lil... lol.

anyway, fun with math.

Just to recap; with an automatic, there is a pretty good spread of Torque Multiplication going on inside the TC; from about 1.8 to 1.1, namely ~60%. This behaves sorta like a two speed automatic. Except;
1) the ratio is highest at zero mph, and
2) lowest at hi-speed, and
3) it is continuously varying it's ratio in response to the torque input, which is controlled by the gas pedal. Once moving, it cannot get back to 1.8. Once you are moving at an rpm that is higher than the stall rating, most of the TM is "used up".

I almost forgot; what about controlling that loc-up manually?
Great idea. Well it could be , if it wasn't just 9%. Say you're cruising along at a buzzy rpm, and you don't want to upshift. Well just hit the lock-up switch and see what happens. It's not gonna make a huge deal so I wouldn't hunt after it, but if one falls into your possession, then wth, grab it.

I better stop



View attachment 1715484665
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Wow, that’s some great info. How in the heck do you know all of that?
 
Tad said:
I did hear about the bushing but I never got one. Some people said you had to have them in other people said not a big deal. I have not had any issues
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IT. IS. A. BIG. DEAL. If it wasn't, there would be no reason to have ANY snout on the convertor. It's the same reasoning as a pilot bushing/bearing for a manual trans. IT NEEDS TO BE SUPPORTED and CENTERED. THAT IS HOW ITS DESIGNED. If it isn't properly centered, your balance can be out of whack causing all kinds of vibration, it could eat up your front pump (and more), it will eventually crack your flexplate, and then parts start flyin'. You don't want to be around when that happens, it can get ugly fast, both mechanically and physically.
Lots of guys say they've done it and not had an issue. Do you want to be the guy that does?
 
Murray said:
Should consider- a bolt on rear spragg and front pump conversion to later splines to allow bigger convertor selection.
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What is the part I am looking for to upgrade to use later TC? A Spragg? And pump conversion? Thanks!!
 
Tad said:
What is the part I am looking for to upgrade to use later TC? A Spragg? And pump conversion? Thanks!!
Click to expand...

Your 1965, 904 has a rear pump, as well as a front, pretty tricky... you can push start it if your starter dies.
To keep that trans, you will need a hybrid TC. to marry the trans to the 360 crank.
Or you can just install a later transmission with a floor-shifter. The later trans has a slip-joint driveshaft so you would need to do something with that.


AFAIK every 904 I ever built already had a bolt-in rear sprag. But the aftermarket does offer HD versions. Personally, In your car you can't install much tire so I don't see any real advantage. However, they are pretty cheap.
 
I think 64 was the last year for the rear pump. 65 still had cable shift and the Detroit rear u-joint, but no rear pump. 66-67 were rod shift and rear slip yoke, 68 and later had the larger converter. So both are one year only transmissions. If you want anything stronger than a basic factory rebuild, you'd be better off swapping in a later transmission.
 
Wow, I can't believe how much wrong info was posted in this thread. First:
A 65 down cable shifted 904 has a small crank pilot, a small input shaft, a rear pump, and a flange on the output shaft.
You can change the front internals of the trans to 1968 or later 904 "standard" ratio (non low ratio) non lockup parts, to get the larger input splines. The low first gear parts cannot be used in the 65 down 904.
The deep trans pan kit in the first post cannot be used on the 1965 and older 904, as the filter and deep spacer do not have the oil oil for the rear pump. The pan will fit, and you can put a second hole in the spacer, but will need to get a different filter. There is other wrong info.
Tad, if you have questions, send me a private message, and I will give you my phone number.
 
Why go to all that trouble to drop the filter? I installed a deep pan on my truck's 727 but I didn't extend the filter. No reason to do it. I don't want my filter down in the muck. It's not like the sump fluid won't be recirculated. The extra fluid is for cooling mostly and the only reasons to extend the filter is for 4wd or severe drag racing applications. If you have a leaky trans; then you might also have a use for the extension. Why can't the low gear parts be used in the 65 and older 904? I had a Jeep trans that I had to modify the sun gear shell to install new low gear parts when the original low gear parts were trashed.
 
One thing I learned is that you must not install A999 planetaries onto 904 output shafts. They physically fit but the splines are shaped different, and in a few
shift cycles the aluminum back planetary will have no splines left, and Zing! you will be walking.
 
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