a999 modification questions

[turboking15]

I have been doing some research into what trans i want to run and i was looking to go with a 904 for the weight and parasitic loss factors. I then read some info about the a998 and a999 transmissions, mainly about the extra apply clutches and wider band, and also the gearing for 1st and second. These are all great features, however for performance a lockup converter is not ideal without spending a good bit on one. Now some will say to find a 999 out of a dippy cop car as they are non lockup, but they arent the easiest to find.

So this all got me thinking, can you just eliminate the lockup function of the trans and have a non lockup converter made to fit the lockup trans input shaft?

Will there be any downsides to doing this?
Is there anything else i would need to do?
Has anyone else done this?

Sorry for the long winded post just trying to gather as much info as i can.

This will be going behind a 450-550 hp sb in a 2800-3000 lb car.

Thanks

 

[fishy68]

A converter company can probably build you a special order converter but it may not be cheap. Might be just as cheap to build a lockup unit and just block the lockup function in the valve body. I haven't worked on the 904 series very much but wonder if it'd be possible to just replace the input shaft in the rear clutch carrier with a non lockup input shaft? 904-998-999 had some variances so you'd have to make sure and swap in a shaft that has the appropriate oiling holes.

 

[oldkimmer]

..........with that much torque/hp the short splines on the l u shaft will strip out the converter splines, the factory 1s did it..........kim.....

 

[Duane]

I have been doing some research into what trans i want to run and i was looking to go with a 904 for the weight and parasitic loss factors. I then read some info about the a998 and a999 transmissions, mainly about the extra apply clutches and wider band, and also the gearing for 1st and second. These are all great features, however for performance a lockup converter is not ideal without spending a good bit on one. Now some will say to find a 999 out of a dippy cop car as they are non lockup, but they arent the easiest to find.

So this all got me thinking, can you just eliminate the lockup function of the trans and have a non lockup converter made to fit the lockup trans input shaft?

Will there be any downsides to doing this?
Is there anything else i would need to do?
Has anyone else done this?



Sorry for the long winded post just trying to gather as much info as i can.

This will be going behind a 450-550 hp sb in a 2800-3000 lb car.

Thanks

Find yourself a non lock up slant six 904 at the junk yard and use that input shaft and the slant six oil pump the pump will need to be machined to match the diameter of the 999 forward clutch hub..
I have done this with success. The shafts press out of the hubs, but a 999 hub will not fit in the slant six pump. It will need to be machined to the larger diameter of the 999 pump. With 550 horse you may want to consider a billet input shaft from A&A transmission. Pm me if you need more detailed info.

Duane

 

[Woods74]

The best theory I've found to go about it is to use the 93+ flat hub pump and gears, the front half, bolted directly to the older stator/reaction shaft, with a 78+ 2 ring 27 spline input shaft. If the pump you have is lock-up, simply remove a checkball like below with a carbide dremel bit and a pick. Then you can use the pump you have. You can pick up the input shaft, front pump and gear for cheap at wittrans.com:

727:

904 Lock-up:

Non:

Then, get a converter company to cut you a nice, possibly 9.5" converter.

 

[RustyRatRod]

Doesn't matter. You can use any 904 variant. If it is a base 904 you can upgrade to the 998/999 parts easily and cheaply.

 

[Duane]

The best theory I've found to go about it is to use the 93+ flat hub pump and gears, the front half, bolted directly to the older stator/reaction shaft, with a 78+ 2 ring 27 spline input shaft. If the pump you have is lock-up, simply remove a checkball like below with a carbide dremel bit and a pick. Then you can use the pump you have. You can pick up the input shaft, front pump and gear for cheap at wittrans.com:

727:

904 Lock-up:

Non:

Then, get a converter company to cut you a nice, possibly 9.5" converter.

Yes this is what I was trying to explain. He needs a two ball instead of a three ball.
However when I build mine I used a lockup trans as a base because it comes with all the heavy duty planetary gears and the low first gear already in the tranny.
Then you would just need to get rid of the lockup feature.
What I found though was that the sealing ring diameter at least on a slant six pump is of a slightly smaller diameter and we had to machine it in a lathe to match the diameter of the pump. My terminology of some parts may be off.
Otherwise you made a very good post with the photos.

Duane

 

[Duane]

Doesn't matter. You can use any 904 variant. If it is a base 904 you can upgrade to the 998/999 parts easily and cheaply.

I may be mistaken but I don't, think that is quite right. There were certain versions of 904/999 that were specifically for the v8 engine. The op has already researched and identified certain heavy duty versions that have been made with wider bands etc. I noted small slight differences on the heavy duty v8 versions such as a thicker output shaft support, larger diameter servos.
The trans that he wants with the low gear, heavy duty v8 internals and non lockup, never really existed outside of a police car as he noted. It has to be made or converted if you will.
I called A&A trans about a tranny like this and they too identified to me that this type trans requires some pump modifications to be made.
To say it is easily or cheaply done is all relative. But it is not to my knowledge just a matter of swapping parts. But this trans can be built. I have done it my self personally including the machining of the pump.

Duane

 

[Woods74]

You could also just order the correct reaction shaft from wittrans for around $50... Whatever floats your boat, looks like the sealing ring sizes are the rub here. Always air test while building anyway.