904 vs 999

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318willrun

318willrun

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I'm no transmission expert.... with that said, this is what I "think" I know....
  • the A999 is like a 904 but has a lockup TC, usually a lower 1st gear ratio, more clutches and stronger bands.
  • However, the 904 usually has a "higher stall" in the converter from the factory.
I have found that even though the 999 has a lower 1st gear ratio, the 904 "feels" quicker because it seems to flash the converter a few more hundred RPM's taking off.
Am I correct?
Thanks in advance for knowledgeable responses.
 
Yes and no.
Either can win that discussion, it will depend on the WOT engine torque difference between the two stall-rpms.
Say you have a combo
with 3.23 rear gears, and a 318 that puts out a max of;
200.22 ftlbs at 1800, and 224 ftlbs@2400. I mean just say.
>the A904 has a low gear of 2.45, and the A999 comes in at 2.74

>The A904 stalls at 2400=224 ftlbs so this combo will put down and
224x 2.45 x 3.23 =1772 ftlbs into the rear axles.

>The A999 stalls at 1800=200.22 ftlbs, so this combo will put down;
200.22 x 2.74 x3.23= 1772 ftlbs
So it's a dead tie.

>Now, if the 318 has more torque @1800 than stated, then the A999 will pull ahead. Whereas if more torque at 2400 than stated, then the A904 will pull ahead.
> this assumes that both convertors have identical output ratios at both rpms.

Or so the theory goes.
 
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318willrun said:
I'm no transmission expert.... with that said, this is what I "think" I know....
  • the A999 is like a 904 but has a lockup TC, usually a lower 1st gear ratio, more clutches and stronger bands.
  • However, the 904 usually has a "higher stall" in the converter from the factory.
I have found that even though the 999 has a lower 1st gear ratio, the 904 "feels" quicker because it seems to flash the converter a few more hundred RPM's taking off.
Am I correct?
Thanks in advance for knowledgeable responses.
Click to expand...
Kinda depends on the year/version of the A999.
The early versions (starting in approx. 1978) did not have the lower 1st gearset, those started about 1980ish.
As far as stall speeds go, (and it may vary a bit year-to-year) the '68 FSM lists the A904 stall speed behind a stock 318 as being 2125-2425 RPM (stall if used behind a 340/360 would be a bit higher, maybe in the 3k range- the amount of available torque will increase the stall speed on the same convertor).
The '91 FSM lists the A999 stall speeds as being 1800-2100 RPM for units used behind the 3.9 V6, and 1700-2000 RPM for the 318/360 convertor. Using the V6 convertor behind a 318/360 would again increase your stall speed just like the 904 does.
I don't have the stall speeds handy for the early '78-'80 A999s, so I can't speak for those or if they use a higher stall speed to compensate for having a higher 1st gear...
Lots of variables to consider, so not the Y/N answer you were hoping for; but I've done my best to confuse the issue and muddy the waters...
:lol:
 
Professor Fate said:
Kinda depends on the year/version of the A999.
The early versions (starting in approx. 1978) did not have the lower 1st gearset, those started about 1980ish.
As far as stall speeds go, (and it may vary a bit year-to-year) the '68 FSM lists the A904 stall speed behind a stock 318 as being 2125-2425 RPM (stall if used behind a 340/360 would be a bit higher, maybe in the 3k range- the amount of available torque will increase the stall speed on the same convertor).
The '91 FSM lists the A999 stall speeds as being 1800-2100 RPM for units used behind the 3.9 V6, and 1700-2000 RPM for the 318/360 convertor. Using the V6 convertor behind a 318/360 would again increase your stall speed just like the 904 does.
I don't have the stall speeds handy for the early '78-'80 A999s, so I can't speak for those or if they use a higher stall speed to compensate for having a higher 1st gear...
Lots of variables to consider, so not the Y/N answer you were hoping for; but I've done my best to confuse the issue and muddy the waters...
:lol:
Click to expand...
But generalizing the statement, the 904 TC stalls higher than the lock ups.
 
Convertors do their thing, as a function of input torque, and resistance at the output shaft..
So as to
318willrun said:
But generalizing the statement, the 904 TC stalls higher than the lock ups.
Click to expand...
On the same engine and in the same car, with the same gears, the answer is Yes...... generally, lol
 
When introduced in 1974 behind the 360 2 bbl, the 999 till 1978 were non lockup. Starting in 1978 it came both ways LU and non-LU.. The low gear came along in the early to mid 80's and again, they didn't all get the low gears. That's what I know.
 
It's in a '82 D150, slant six. Not sure it the truck got a tighter converter, but two things I do not like about the truck lock ups:
  1. very unforgiving when going to reverse or drive, idle has to be low or it's more of a "bang" into gear rather than a "shift" into gear
  2. Once locked up around 45 mph, it lugs the engine on uphill's or such.
Transmission is in excellent working condition.
 
AJ/FormS said:
Yes and no.
Either can win that discussion, it will depend on the WOT engine torque difference between the two stall-rpms.
Say you have a combo
with 3.23 rear gears, and a 318 that puts out a max of;
200.22 ftlbs at 1800, and 224 ftlbs@2400. I mean just say.
>the A904 has a low gear of 2.45, and the A999 comes in at 2.74

>The A904 stalls at 2400=224 ftlbs so this combo will put down and
224x 2.45 x 3.23 =1772 ftlbs into the rear axles.

>The A999 stalls at 1800=200.22 ftlbs, so this combo will put down;
200.22 x 2.74 x3.23= 1772 ftlbs
So it's a dead tie.

>Now, if the 318 has more torque @1800 than stated, then the A999 will pull ahead. Whereas if more torque at 2400 than stated, then the A904 will pull ahead.
> this assumes that both convertors have identical output ratios at both rpms.

Or so the theory goes.
Click to expand...
Could a 1982 be a A998 ??
 
I think yes but IDK, the top of the bellhousing should have theA998/A999 designation cast into it with big ugly hand-drawn-type letters.
The PK numbers on the pan rail can also be used to identify it and the year. but I don't have such a decoder.
 
318willrun said:
It's in a '82 D150, slant six. Not sure it the truck got a tighter converter, but two things I do not like about the truck lock ups:
  1. very unforgiving when going to reverse or drive, idle has to be low or it's more of a "bang" into gear rather than a "shift" into gear
  2. Once locked up around 45 mph, it lugs the engine on uphill's or such.
Transmission is in excellent working condition.
Click to expand...
As to #1;
I'm gonna go out on a limb here and say, the engine has too much Idle Power is why it bangs. Take some Idle-Timing away, and see what happens. It could be other, but this is the easiest test.

As to #2
the trans should NOT be going into LU that early, the RPM is way too low.
Is the trans original to the truck? Or
Has the rear gear ratio been changed
or really tall tires installed,
cuz either of those are gonna affect the governor.
As will the KD adjustment and the line-pressure.
I would be hesitant to blame the one specific model or year for these annoying characteristics.
 
AJ/FormS said:
As to #1;
I'm gonna go out on a limb here and say, the engine has too much Idle Power is why it bangs. Take some Idle-Timing away, and see what happens. It could other but this is the easiest test.

As to #2
the trans should NOT be going into LU that early, the RPM is way too low. Has the rear gear ratio been changed or really tall tires installed, cuz either of those are gonna affect the governor.
As will the KD adjustment and the line-pressure. I would be hesitant to blame the one specific model or year for these annoying characteristics.
Click to expand...
  1. Initial timing is 2* BTC, so I will say I don't think it has too much timing.
  2. Almost all of these types of 3-speed lock ups I've owned have always locked up in 3rd gear around 45 mph. I don't know what anyone else has experienced, maybe they will chime in.
 
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An A999 will have a wire connecting for the lockup on the case just above the rear pan rail. I think on the drivers side, but I'll have to check later.
 
Garrett Ellison said:
An A999 will have a wire connecting for the lockup on the case just above the rear pan rail. I think on the drivers side, but I'll have to check later.
Click to expand...
I *think* the solenoid was added later on the 999s, or maybe it was dependent on the application? I've got (or rather, I had) a '78 LU 999 with no connector, pure hydraulic activation. Came out of a Fifth Avenue or Dippy, I believe.
Then I've got a '91 A999 (32RH) from a van that does have a solenoid connector that hooked into the tow/haul switch... don't know if the solenoid was dependent on the truck models or if it was phased in with the '88 computer controls for the TBI?
They did come both ways, though.
And somewhere along the line the cooler lines and fittings were upsized to 3/8, and reinforcement ribs were added to the tailhousing.
 
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Hmm....
My A999 is pretty snappy, HOWEVER. My A999 has a 3000 stall converter and is converted to non-LU with a Turbo action Cheetah Stage 2 valve body.
So basically the best of both worlds?
 
Professor Fate said:
I *think* the solenoid was added later on the 999s, or maybe it was dependent on the application? I've got (or rather, I had) a '78 LU 999 with no connector, pure hydraulic activation. Came out of a Fifth Avenue or Dippy, I believe.
Then I've got a '91 A999 (32RH) from a van that does have a solenoid connector that hooked into the tow/haul switch... don't know if the solenoid was dependent on the truck models or if it was phased in with the '88 computer controls for the TBI?
They did come both ways, though.
And somewhere along the line the cooler lines and fittings were upsized to 3/8, and reinforcement ribs were added to the tailhousing.
Click to expand...
Hey, thanks! I completely forgot about those fully hydraulic lockup units. IIRC, I think that I had read on AllPar that the later solenoid was primarily just an add on to that same hydraulic system to allow for an override off of the usual activation (I.E. tow haul, or other condition programmed into the computer, maybe cold loop mode for emissions).
 
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If it's the original transmission then it's a A904.
In 1982 the A904 was the only choice for trucks with 225 engine.
The 318 had the A999 transmission.
Both were lockup.

The A904 had 4 front clutch disc and the A999 had 5 front clutch disc.
Also they used different valve bodies and kickdown levers, rest of the gear train was the same.

Direct quote from 1982 Dodge truck parts catalog Torque Converter with A904 transmission - Lock Up High Stall #4293051.

Stall speed listed in the 1982 truck service manual is 1800-2100 rpm for the A904 with 225 engine. Of course many factors determine the actual numbers.
It would be nice if we had the PK numbers on the pan rail.
 
townsend said:
If it's the original transmission then it's a A904.
In 1982 the A904 was the only choice for trucks with 225 engine.
The 318 had the A999 transmission.
Both were lockup.

The A904 had 4 front clutch disc and the A999 had 5 front clutch disc.
Also they used different valve bodies and kickdown levers, rest of the gear train was the same.

Direct quote from 1982 Dodge truck parts catalog Torque Converter with A904 transmission - Lock Up High Stall #4293051.

Stall speed listed in the 1982 truck service manual is 1800-2100 rpm for the A904 with 225 engine. Of course many factors determine the actual numbers.
It would be nice if we had the PK numbers on the pan rail.
Click to expand...
Thanks! Great Info !!!
 
318willrun said:
I'm no transmission expert.... with that said, this is what I "think" I know....
  • the A999 is like a 904 but has a lockup TC, usually a lower 1st gear ratio, more clutches and stronger bands.
  • However, the 904 usually has a "higher stall" in the converter from the factory.
I have found that even though the 999 has a lower 1st gear ratio, the 904 "feels" quicker because it seems to flash the converter a few more hundred RPM's taking off.
Am I correct?
Thanks in advance for knowledgeable responses.
Click to expand...
From the factory, the bands for these transmissions are:
1961-1993 Kickdown band 1.4" Wide
1992-2003 Kickdown band 1.6" Wide This band is also used on all the A500 series of transmissions

1960-2003 Low and Reverse Band Single wrap, used with 6 cylinder and 273 engines
1968-2003 Low and Reverse Band Double wrap, used on V8 except 273 engines. This band also used on the A500 series of transmissions

Other bands might be available in the aftermarket, but from the information I have on factory bands, there are no other options that I can see.
 
The 360 999's part numbers are as follows: 74-75-PK3681844, 76-77-PK4028465, 78 NON LU- PK4028878, 78 LU-PK4028815, 78 LU-PK4058111, 79 LU-PK4130515 and 79 LU-PK4130645. These are all 360 only 999's. These part numbers were taken from the OLD Direct Connection Bible. After 79 I don't know.
 
I remember pulling out the lockup spring from the valve body, and stretching it to delay the lock up in the mid 1980's
 
318willrun said:
  1. Initial timing is 2* BTC, so I will say I don't think it has too much timing.
  2. Almost all of these types of 3-speed lock ups I've owned have always locked up in 3rd gear around 45 mph. I don't know what anyone else has experienced, maybe they will chime in.
Click to expand...
There was a bulletin way back where Chrysler recommended changing the solid front clutch retainer snap ring from the flat snap ring to the wavy snap ring to stop the hard reverse engagement. I’ve change a few. Kim
 
oldkimmer said:
There was a bulletin way back where Chrysler recommended changing the solid front clutch retainer snap ring from the flat snap ring to the wavy snap ring to stop the hard reverse engagement. I’ve change a few. Kim
Click to expand...
Good to know, thanks!!!
 
It's odd that you would have a bang as you describe it when going into reverse since you have a 1982 transmission. Chrysler made a change in 1978 to soften the engagement into reverse.
The following is a description of the change in reverse line pressure.

All automatic transmissions starting in 1978 are equipped with modulated reverse line pressure that provides controlled pressure in reverse gear.

Previously reverse line pressure was a constant 260 psi throughout the full range of throttle operation. This pressure is now modulated from 150 psi at idle speeds to 260 psi at full throttle operation.

This change reduces the pressure to which the front clutch seals and reaction shaft seals are subjected,providing a beneficial effect on transmission durability and reliability.

This improvement is accomplished by routing the reverse control fluid to the regulator valve, reducing the fluid pressure at closed throttle to 150 psi.
At wide open throttle , the regulator valve provides the 260 psi needed during heavy duty reverse operation such as backing up grades or parking a heavy trailer.
However, during normal reverse operation such as backing out of a parking space or driveway, the system is only subjected to a pressure of about 160 psi.

There are various ports on the transmission case where pressures can be checked with a simple 0-300 psi gauge.
Those numbers can be found in the service manual.
A good diagnostic tool to solve many problems,
 
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