A904 vs A999 vs A500

[88_AHB]

Hey guys,
Have been tossing around the idea of switching things up with rear end gearing and possibly a trans swap. I've done some research on these three transmissions. Right now in my 88 have either a 2.73 or 2.90 gear with a mild 318/904 2500 stall with a 225.70.15 tire.

I've read some posts in here about the A500 swap and it doesn't seem that difficult to do minus the fabbing to the trans cross member etc. So one of my questions has been how much of a RPM drop would you see on a 999 as opposed to a 904 when locked up at say freeway speeds etc? Next, with the A500 is the converter normally locked in all the gears or just 3rd and OD? Was there ever a A500 with a non lockup like the early years of the A518? I know most guys just run the lockup to a switch or something to manually control that. Is a 2500 stall for a M body a little too high? I know it depends on weight,gearing,tires,cam, driving conditions etc. Im spinning around 2300 rpm on the freeway now and not 100% sure if the trans is fully locked and hate to burn the 904 up.

 

[kkritsilas]

The overdrive/4th gear ratio on the A500 is .7 or.67, if I recall correctly. So the RPM drop would be about 30-33%. I'm pretty sure that the lower gears are pretty much the same. Top gear in the A904/A998/A999 is 1.0:1 (direct), which is the same as third gear in the A500. The above doesn't take into a account any torque converter slippage, which outside of the A904, shouldn't be happening as they are all using lock up converters. You wouldn't be "tearing it up" even on the A904, because they were made to work in top gear without problem, as were any three speed automatics since they came about, but you are losing some gas mileage (about5% is the number I have seen), and putting some added heat into the transmission fluid. As far as I know, the lock up only happens on third gear, under light load (i.e. cruising) for the A998/A999. I'm not sure if it happens in both 3rd gear and 4th gear on the A500.

I think the A904s were made without lockup converters only (somebody correct me if I am wrong). So even in high gear, the A904 will have some slippage due to the converter. You are therefore turning slight higher rpm due to that. Taking the typical 5% number quoted, that is about 115 rpm at your 2300 RPM. So just with a lockup converter, you would be turning 2185 RPM at 60. With the A500 it would drop to 1464-1530 RPM, call it around 1500 RPM, at the same 60 in overdrive.

I can't answer the rest of the questions because I don't know.

 

[AJ/FormS]

From your info, I see that if you have a rear gear around 2.90, and tires are~27.4 tall , then 65=2312 @zero slip is reading near that, then that would seem to indicate that you already have a loc-up. Altho the shift into lock up is only maybe 200rpm, you should be able to see that on your tach, by playing with the gas pedal.
IIRC the od ratio is .69 so your Rs will fall to 2300 x .69=1590
If you are going for fuel economy, there is no guarantee that your 1988 318 will get any better fuel mileage at that lower rpm, because there is no way to give the engine the timing that it needs, except if you build a timing computer. So then, I see no advantage for you in this swap.
But you are looking for a performance boost, you can gain quite a bit by swapping the 2.90 rear gear for one like 2.90/.69=4.10s. And your final drive will then be ;
4.10 x.69= 2.83,
which will drop your cruise rpm to 65=2260 And your 318 will blister thru the gears with those 4.10s. So then I do see an advantage.

Is a 2500 stall for a M body a little too high?

Not at all, in fact, I would run a 2800. But if you install an overdrive AND a 4.10 rear, then the 2500 will be just fine.

 

[Duke5A]

Hey guys,
Have been tossing around the idea of switching things up with rear end gearing and possibly a trans swap. I've done some research on these three transmissions. Right now in my 88 have either a 2.73 or 2.90 gear with a mild 318/904 2500 stall with a 225.70.15 tire.

I've read some posts in here about the A500 swap and it doesn't seem that difficult to do minus the fabbing to the trans cross member etc. So one of my questions has been how much of a RPM drop would you see on a 999 as opposed to a 904 when locked up at say freeway speeds etc? Next, with the A500 is the converter normally locked in all the gears or just 3rd and OD? Was there ever a A500 with a non lockup like the early years of the A518? I know most guys just run the lockup to a switch or something to manually control that. Is a 2500 stall for a M body a little too high? I know it depends on weight,gearing,tires,cam, driving conditions etc. Im spinning around 2300 rpm on the freeway now and not 100% sure if the trans is fully locked and hate to burn the 904 up.

This was the first major modification I ever made to my car. Drove around for a while with 318/500/8.75" with 3.55 gears.

The 500 only came in a lockup variety. Lockup and OD are both controlled electrically by a pair of solenoids by applying 12v to them, so a couple of toggle switches would work if you wanted to do it that way. It's a three pin plug facing upward somewhere next to the neutral safety plug. Lockup was only ever engaged in 4th gear by the computer. The right way to do it though is a couple of pressure switches and a vacuum switch to make it automatic.

Sometime in the run the 500 switched from a converter with slots to flats to engage the pump. The previous setup with slots was prone to cracking. This makes the converters between the two non-interchangeable. To be honest, whatever you pull a 500 from is going to be a 5.2L Magnum motor at most in a heavy chassis. The stall speck of the factory converter will be just fine. Don't overthink it and just run whatever you pull with the transmission as long as it's in working order. I would only start looking into aftermarket converters if you run anything hotter than your typical RV grind camshaft.

You don't necessarily need to go with a higher numerical gear in the axle, but to get the most out of the OD swap a 3.55 is nice.

 

[88_AHB]

What steps is there to take to beef up a A500? I'm sure there's a bunch of ways and money that can be sank into upgrading one.The obvious one I can think of is a shift kit and possibly Kevlar clutches etc. I've also heard some people using the drum from a A999 because it has 5 disc in it rather than the 4 disc in the A500 and 904? I know there's factors of how the cars gonna be driven and how much horsepower. But say for a mild 318 with a 3.55 or 3.73 gear for a driver.

 

[Duke5A]

What steps is there to take to beef up a A500? I'm sure there's a bunch of ways and money that can be sank into upgrading one.The obvious one I can think of is a shift kit and possibly Kevlar clutches etc. I've also heard some people using the drum from a A999 because it has 5 disc in it rather than the 4 disc in the A500 and 904? I know there's factors of how the cars gonna be driven and how much horsepower. But say for a mild 318 with a 3.55 or 3.73 gear for a driver.

When I ran the 500 behind a mild 360 it constantly smoked the high gear band. Replaced it twice before I swapped out to a 518. Never had any issues with clutches. If I remember correct the 500 is based off of the 999 and already has 5 clutches in it's pack.

For a docile 318 that puts out maybe 250 horse in a driver that doesn't see slicks, a factory build with a stacked plate cooler is probably all you need.

 

[SRTMirada]

In high gear both clutch packs are engaged. No bands. The kickdown band is used in second gear. To improve the life of the kickdown band try a higher ratio lever to increase the apply pressure. If you have a 3.8 then try a 4.2 or even a 5.0 ratio.To improve the apply in high gear increase the line pressure.

 

[Duke5A]

In high gear both clutch packs are engaged. No bands. The kickdown band is used in second gear. To improve the life of the kickdown band try a higher ratio lever to increase the apply pressure. If you have a 3.8 then try a 4.2 or even a 5.0 ratio.To improve the apply in high gear increase the line pressure.

You're right, I misspoke. Right before the band would brake it would slip shift the 1-2 and eventually I would lose second gear altogether. Been a long time.

 

[BudW]

The A518 (or 46RE/RH, 47RE/RH) has a lot more upgrade possibility's due to the diesel versions can be upgraded to handling 1,000+ Foot Pounds of torque.
The A500 or A518 don't really say much about torque capacity, per se, but when they went to new designations, later on, it did say capacity, by the series number.

Example:
A500 was renamed to 40RH (4-speed, “x” torque capacity, Rear drive and “H” for hydraulic or “E” for Electronic controlled).
Sense we want to the hydraulic versions “H” (and not “E”) for FMJ's, I won't mention the “E” series.
40RH, 42RH.and 44RH are all the same series, but 42 is stronger than 40 and 44 is stronger than 42.

Same goes for A518 which was renamed to 46RH (and 47RH/48RE for V10's and diesels).
Yes, more confusing numbers to keep up with, but at least looking at the model number, you get a good idea of what's inside.

One thing that sets the A999/A500/44RH transmissions apart from the A727/A518/46RH is the smaller transmission still has the better first gear ratio.
BudW