Okay, so I've got an '88 Dakota (2WD, 3.9L V6, A998/A999 auto, 8-1/4" axle with 2.94 ratio (I think - the underhood sticker ain't in the best shape). The six-banger's really showin' its age and I think it's time to consider an engine swap. Instead of putting another six in it, I'm thinkin' it's time to 318-ify this thing.

So, I've done the appropriate Google-work and read the FAQs, and I think I've got a pretty good idea of what I'll need to make this project kick. However, I do have a few questions.

With the conservative axle ratio, I feel the wide-ratio A998/A999 auto should be a keeper. The question is, will it handle a stock-spec 318 2-bbl? I'm not planning any racing or major mods - no wild cams, no high-stall torque converters (I wouldn't be able to get one for that trans anyway), no six-grand redlines. The goal here is smooth, simple, strong, and dependable - and hopefully without spending a metric ton of cash. I might convert the 318 to the Dakota-style TBI setup eventually, but that's later on.

We're assuming, of course, that the trans is in good working order. If it's (natively) capable of handling a 318, I'll have it rebuilt before it goes back into the truck - but frankly, I'd do that even if I was replacing the engine with another six.

My next question is in regard to converter lock-up of the A998/A999 slush boxes. Is it controlled by computer or is it a purely-hydraulic thing? Obviously, with a 2-bbl carb, I won't be using the original ECM, and if converter lockup is computer controlled then I have to rethink this whole plan anyway.

This is all just in the 'brainstorming' stage right now. Nothing's actually been purchased yet - I want to get as much information as I can before I start laying out hard-won $$$$.

 

If you're going to upgrade to a 318, I would suggest going with the A-727 transmission because it's the heavy duty transmission designed for V8s. Back in the early 80's, Chrysler did use a mechanical lockup converter until 1986? I believe. You can always go with a non lockup converter the only downside to that is, your fuel mileage will suffer slightly.

 

I think you are OK to stay with the TF6/A904. Chrysler put this transmission behind the 318 for many years. The one advantage you will have is that it will sap less horsepower then a TF8\A727. The disadvantage is that it’s not as strong. Both the TF6 and TF8 in that year are hydraulic lockup systems. The converter you have in the unit now will work with a 318.
Having the Tranny rebuilt is a good idea. I’d also have them update it to a TF6\318 application. When the Tranny came stock behind a 318 it had more clutch plates in the forward and direct drums and 4 vs. 3 pinion planets. Used parts are pretty inexpensive for this transmission so it shouldn’t be an expensive upgrade to do.

Good luck

 

I gave you some wrong information. The A904 started using a lockup solenoid in 1987. If you are not using the computer you’ll have to get a pre 1987 lockup valve body that is a straight hydraulic lockup and put it on your transmission when you do the rebuild. Sorry about the misinformation.

 

Thanks for the input, fellas.

I knew the A727 was the 'bulletproof' answer, but it seemed like it'd be
overkill for a stocker 318. I'd heard that Mopar used A904s behind 318s
in the 1970s, and I'd also heard the A998/A999 automatics were derivatives
of the A904. I wanted to make sure the A998/A999 slushboxes weren't one
of those weak-kneed 'cost cutter' automatics like GM's TH200 and Ford's C3.

Okay, so I can't use the electrically-operated TC lockup. Is it really
that easy - just find the older hydraulic-locking valve body and install
it in the existing trans?

It almost seems too good to be true.

Any other suggestions or tips?

 

Yes it is that easy. I checked with two transmission rebuilders that have been doing this for about 30 years and they both said it’s a straight bolt on. I’ve never done it so I thought I should check. Upgrade the drums and planets and you should be good to go. The upgraded parts should run around 200.00 plus tax. That’s the forward and direct drums the front and rear planets, one hydraulic valve body and new thrust washers for the 4 pin planets. A rebuilt torque converter and overhaul kit with run about another 150.00. It’s still not as strong as a TF8 but it should stand up behind a stock 318 OK.

Very little in the A904/A999 has changed since the mid 1970’s. It’s a really good transmission as is the A727.