TF904 HOW DOES CONVERTOR LOCKUP WORK

Is the lockup for the tf904 electronicly controlled or just goes into lockup based on speed ? or hydraulicly controlled ? Is is a 86 4wd .tbi 2.5

The TorqueFlight 904 or 999 or LH30, has the torque convertor lock-up controlled by the PCM. It sends a signal to the connector on the trans that opens a hydrualic valve, and the hydrualic pressure from the valve actually locks-up the convertor. Everything else is hydrualically controlled internal to the trans.

You need a PCM for that m/y automatic optioned vehicle to properly control the tc lock-up.

I believe its different for the AW-4 automatic that has its own electronic control module that controls everything.

SO I MAY HAVE OVER HEAT PROBLEMS SWAPPING A LOCKUP 904 IN PLACE OF A NON LOCKUP 904 FROM 86 BACK TO 84 SINCE THE 84 DOES NOT HAVE A COMPUTER TO CONTROL THE LOCKUP, THANKS FOR THE REPLY

?? OK, you've confused me.

The vehicle came with a TF-904, that had NO TC Lock-Up? You want to swap in a later TF-904/999 that does have TC Lock-Up?

If this is the case, then yes, the TC will NOT lock-up in your vehicle.

Will it overheat? Not sure, the basically same trans did NOT overheat before without a TC Lock-Up, a newer one with a TC Lock-Up, that the TC Never Locks-Up should be the same as the earlier trans, except it has a valve and clutch in the TC that is never used.

BUT, maybe there were other changes that made the new trans less tolerant to heat and depended on the TC Lock-Up to keep it cool. I doubt it, there shouldn't be that many changes, but its possible.

I'd just add an extra auxilary trans cooler just to be safe, that should hold it.

People that have a vehicle that originally came with a TC Lock-Up, which the cooling system is lighter since there is less heat with a TC Lock-Up, are the ones the experience overheating and burned up trans when they do something to disable the TC Lock-Up, the existing cooling system is strong enough to handle the extra heat. They usually prevent any problems by adding an extra auxilary cooler.

I would think it wouldn't be a problem the other way around, your trans cooling system was designed to take a trans without a TC Lock-Up.

Chysler started using a lock-up 904 since the early 80's to save on gas. There were no computers in those cars. My 86' Cherokee 2.8L had a lock-up version, again, no computer.

Replacing a lock-up for a non-lockup should be no issue.
The radiator in the 2.5L is under used.

Ditto. And on a past mopar musclecar project where the lockup needed power, I just tied it in to 12v and a switch, and when I was going fast enough, flipped the switch, converter locked, rpm's dropped.

Zuki-Ron said:

Chysler started using a lock-up 904 since the early 80's to save on gas. There were no computers in those cars. My 86' Cherokee 2.8L had a lock-up version, again, no computer.

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So how did the trans lock itself up? Internal Hydrualic control obvously, I guess when load was low enough it just locked the torque converter?

How well did that work? I'm guessing not well, considering the number of kits I saw in the 80's for disabling the TC lock-ups because they were killing performance. As well, they went to a computer control as soon as they had computers, which I wouldn't think you'd go to the trouble or expense of doing so, if the internal hydrualic system performed adequately.

I like the idea of a switch and heard of others doing it before. That would be easy to wire up and when your cruising on the hi-way just switch it on, just have to remember to switch it off as you accellerate or come to a stop.

The converter locked up by hydraulics.

Worked rather well actually.

The lock-ups were designed to save fuel, which they did/do well for many folks. The folks who wanted to dissable them were folks who were looking for performance options. Non-lockup converters had a higher stall and were less efficient at low rpms than lock-up converters. Those hinderances are helpfull though if you have designed an engine which has marginal low end torque, but breaths well at higher rpms like street racers and performance enthusiasts tend to do.

Things are generaly designed with a purpose and just because folks try to subvert that purpose does not mean the design was bad.

The lockup on a 904 is controlled by vehicle speed and throttle position..there are absolutely no electronics involved. This is an extremely simple automatic transmission.

MudDawg said:

The lockup on a 904 is controlled by vehicle speed and throttle position..there are absolutely no electronics involved. This is an extremely simple automatic transmission.

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On earlier versions. But what about later versions? On the '95 Model, there is a different wireharness and PCM for the 2.5L automatic (31RH) and manual (AX-5). As well, there is a connector for the TC Lockup soldenoid/valve. Did I see the TC Lock-Up Soldenoid/Valve for a different application other than the XJ?

Or is it designations? TF-904 was purely internally controlled TC Lock-Up, the A-999/31RH was an external controlled TC Lock-Up from the PCM? I'm talking oranges and tangerines, and your just strictly speaking about oranges.

To my knowledge, all A-904 trans are a hydro-mechanical design...there are a few other trannies loosely based on the design...A-999 and A-998 come to mind...similar, but not the same. My '85 model Heep has a A-904...my two spare A-904s are from '86 models one came from behind a 2.5 and is exactly like my original...the other came from behind a 2.8 and is identical except the kickdown lever is reversed to operate with a pull cable instead of a push linkage.

If I am in error, please correct me so I may add to my database.

Dawg

I'm going to have to do some research. Before this discussion, I was positive that the A-999 is a A-904, except with a torque convertor lock-up.

If the A-904 has a Torque Convertor Lock-Up, but its purely hydro-mechanical, then I suspect the A-999 is the A-904 with an electronic TC Lock-Up, which the PCM would control that with turning 12V on to the soldenoid that opens the valve to apply the pressure to the lock-up. I'm guessing here, so I'll see if I can find some more info.

The 30RH is just the A-999 after Chrysler went to a new naming scheme for their trans. This would make sense, because the research I've done on my '95 XJ, to convert it over to a OEM Automatic setup, I got the distinct impression that the PCM turned on/off the TC Lock-Up on the 30RH, just like it does on the FWD model 3spd Hydraulic trannies, the A413 specifically.

There are probably more mods between the A-904 and A-999, because the old TF-904 I knew, could handle a lot more torque than a "0" rating in the 30RH designation, they gave the A-999. The TF-904 was on all the Chrysler small block V-8's, in big vehicles, it was often swapped in on big block drag cars, because it was tough enough to survive a whole season on a big block dragster, but smaller an lighter (in rotational mass) than the big TF-727, which translated into slightly better e.t.s.

Perhaps the A-999 is when Chrysler went to cheapo planetary gears and cages, that were much weaker than the older models guts, I'm not sure, but at one time Chrysler did trade off strength in there old RWD trans for cheaper parts because the new smaller cars didn't need the extra strength, at least for a few years.

THANKS , yall have basicly comfirmed what I thought , I have also found out through my local builder that a 999 gear train will swap into my 904 to give me a low gear 904 on the cheap assuming that I can find a 999 core to get the gears out of , thanks

Ask your builder, or inspect the parts yourself; agian I'm just guessing here, but I thought the A-999 is a A-904 with the different TC Lock-Up and maybe gear ratios. The other difference is the quality of the gears, that makes a A-999/30RH less strong than a A-904.

Things like the planetarey gears, a 904 would have 3 gears in set and a 999 would have 2 gears in the set. The cages for the gears in the planetary set for a 904 would be a solid milled piece, while the cages in a 999 would shaped plates welded together.

I could be very wrong on that, so ask that builder you know or it will be obvious if you replace the parts yourself and compare them.

Ok so I'm trying to figure out if my 85 XJ has a lockup in it or not? Are there any numbers on the tranny that would tell me this? Was a lockup converter an option or standard in 1985? Could i just swap in a lockup converter if its mechanical? HELP PLEASE!

Yes your 85 XJ has a A-904 three speed tranny with torque converter lock up..the lock-up is controlled by the lock up valve in the tranny...it will normally lock up at 45 MPH at normal part throttle cruise conditions. It is NOT electrically controlled. You will feel the 1-2 shift, the 2-3 shift and at 45 you MAY feel what seems to be another shift...nope..it's the lock-up.

can anyone help me? Iwant an 4.0 jeep with quadraloc,but am unable to determine which jeeps had this trans and what years? Thanks

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I'm guessing not well, considering the number of kits I saw in the 80's for disabling the TC lock-ups because they were killing performance.
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Many people used a kill switch on the TCL because when driving at lockup speed the converter would keep locking and unlocking. It drove some people nuts and shorten tranny life.
To fix this problem a delay in lockup was added to some systems (GMs for one). The unlock was never delayed but do to poor throttle response many believed it was.
A kill switch was often added by the badly misinformed in hope of improvement or just for bragging rights.

Didn't read it all, but I'll skip to the point. The 904 was hydraulically locked up till '93, but not all were lockups. As of @'83 Dodge made the cases with all the plumbing to lockup but unless it has the correct valvebody (one with the S shaped 5/16" tube on top) and input shaft (it has a hole in the middle that fluid passes through to the converter to lock it up) and of course the lockup converter itself (there's a bit more, but that's the basics)
Midway through '93 Mopar made the valvebody computer controlled (and also made it into an overdrive POS called the 42RE) just in time for the Grand Cherokees 2nd half of their first year of production.
There is a version of the AW4 for the 4 cyls as well, but I would probably go with a 700R4 (hydraulic version) intended for a Chev S10 4x4 with 2.8L V6. The tcase will probably even bolt up to the Jeep driveshafts.


Also, the 904 lockup has a kit available that boosts the lockup point to a higher speed.