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998 vs 904

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KLW View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KLW Quote  Post ReplyReply Direct Link To This Post Topic: 998 vs 904
    Posted: Jul/30/2021 at 3:04pm
does anyone know if the torque converters are the same between a 904 and a 998 assuming they are both lockup?

OR, do they even make a 904 with a lockup converter?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote WhatISit Quote  Post ReplyReply Direct Link To This Post Posted: Jul/30/2021 at 4:25pm
I believe 904 and 998 converters are the same. The AMC version does not have lockup. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KLW Quote  Post ReplyReply Direct Link To This Post Posted: Jul/30/2021 at 5:59pm
Are you sure about the lockup part? I was always told the 904 had a lockup version and the 998 was a lockup tranny.
I could be wrong.....
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ken_Parkman Quote  Post ReplyReply Direct Link To This Post Posted: Jul/30/2021 at 6:30pm
998 was always the heavier duty version of the 904, with 4 disc clutches packs instead of 3. AMC used the 998 version with the 304, mopar with the 318. IIRC the 999 version was initially used with 360 Mopar and has a 5 disc hi/reverse clutch pack. All of these bits are fairly interchangeable so a lot of people just call them 904's. Later stuff gets all confusing in applications, and the last ones went to the newer 30/1/2 rh nomenclature.

It's quite easy to build a strong 904 with factory parts.

Lock up converters are newer and have a different and hollow input shaft to feed the converter clutch.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Heavy 488 Quote  Post ReplyReply Direct Link To This Post Posted: Jul/30/2021 at 6:49pm
Originally posted by KLW KLW wrote:

Are you sure about the lockup part? I was always told the 904 had a lockup version and the 998 was a lockup tranny.
I could be wrong.....

At least in the AMC world, 998 came in 2 flavors. Lockup and non.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ken_Parkman Quote  Post ReplyReply Direct Link To This Post Posted: Jul/30/2021 at 7:08pm
A lot of these differences were year based. Lock up converters initially became available in 78 and were hydraulically (not computer) controlled. Also not all transmissions were lock up; often heavy duty applications did not include lock up.

The wide ratio 2.75 low gear set was a little later, 1980 I believe.

Some sites have this information wrong. The initial 999 was a HD 904, 5 hi/rev clutch discs, 4 direct clutch discs, standard 2.45 low, and no lock up converter.

The way to tell LU or not is the input shaft spline. The LU converter uses a 26 tooth spline, the non LU 27 teeth. This is not including the early (way before AMC used them) small input.


Edited by Ken_Parkman - Jul/30/2021 at 7:13pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote purple72Gremlin Quote  Post ReplyReply Direct Link To This Post Posted: Jul/31/2021 at 12:13pm
1979 998 was the first year for the lock up. 1980 904 haa lock up.  Later some did not..so it all depends. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KLW Quote  Post ReplyReply Direct Link To This Post Posted: Jul/31/2021 at 5:19pm
are the torque converters the same between the two (lockup to lockup, nonlockup to nonlockup)?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ken_Parkman Quote  Post ReplyReply Direct Link To This Post Posted: Aug/01/2021 at 8:52pm
Mostly I think. There are AMC/Dodge differences of course as Dodge put the ring gear on the converter. At some point they change the pump drive on the converter hub from slots to flats and I think that went with the bigger oil pump that went in about 93 on the OD trannies. Think that reads across on the 3 speeds, but not absolutely sure.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote FSJunkie Quote  Post ReplyReply Direct Link To This Post Posted: Aug/02/2021 at 1:19am
AMC 904 and 998 torque converters will interchange if the 998 is non-lockup. AMC 904's were never lockup. AMC 998's were lockup (and wide ratio) starting in 1982. 

I'm not sure if you can put a lockup converter in a non-lockup trans or vice-versa without bad things happening. Of course the lockup won't work. I wouldn't try it. 
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