How can I identify my transmission?.

Transmissions and Rear Ends

  1. Rustyroger

    Rustyroger Well-Known Member

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    I have a 1984 5th Avenue, as far as I know in original stock trim.
    I've always thought that Mopar rwd cars from the early 1960's thru late 1980's had either a 904 transmission behind slant sixes and LA blocks and a 727 behind big block engines.
    It seems there are several variants of the smaller transmissions, 904, 998, and 999. How can I tell which variant I have?.
    I intend to haul an 1800 lb trailer with this car, I will of course put in a transmission cooler, and get my transmission guy to give it an overhaul, I have been told a deep oil pan would be a good idea as well. Also I've been told a lower ratio diff would be very useful.
    I have a V6 fwd Oldsmobile 88 that does a good job of pulling the trailer, my wife's 2 liter turbo diesel Peugeot manages ok too, but is at the high end of what it can safely handle. I had thought the 5th Avenue would be an improvement on both of these right out of the box, but it seems the gearing is too tall.

    Thanks in anticipation;
    Roger.
     
  2. Aspen500

    Aspen500 Well-Known Member

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    The 318 could have a 904 (or 998, 999) or a 727. Majority were 904. The 340 was 727 and 360 could be 904/998/999 or 727 depending on equipment, model, etc. All BB are 727. There was also a 727 version for S6 but was mainly Police/Taxi.
    A 904/998/999 will have a basically square pan with a 45 degree angle cut off one corner, while a 727 has a "hump" on one corner of the pan. Chances are you don't have a 727 though.

    To identify between 904, 998 and 999? I'm not sure to be honest. They look identical externally. Probably a number code on the trans somewhere that i.d.'s it(?)
     
  3. AJ/FormS

    AJ/FormS Well-Known Member

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    The 904 has ratios of 2.45-1.45-1.00
    The 998/999 have ratios of 2.74-1.54-1.00
    The 999 has a loc up TC
    I think the 998 could be had with or without a loc-up TC, don't know for sure.I have one without.
    Each is progressively more heavy duty.
    The ratios can be determined by the rpm in first gear. But you need to know the rear gear ratio as well, and the tire size.
    The rear gear ratio can be determined by the rpm in third gear at 60 mph after lock-up has occurred
    Loc-up can be determined by seeing the loc-up shift on the tach. It is about a 150/200rpm drop at 60mph; a third shift. If you have that drop, then you do not have a 904.A tach is mandatory.In the A998/999,the 1-2 shift is a 44% drop, the 2-3 shift is a 35% drop, loc-up is about 6/7% drop.. This is the easy way.
    If the tranny is out,it is easy to see the loc-up feature. If it is apart, it is easy to see the ratios. The 4-pinion rear planetary gives the 999 away.

    The too-tall gearing is not in the transmission; It is in the rear-end. Those cars came with 2.45s or 2.21s, neither of which is suitable for towing much.
    You can identify your rear end like this;
    With 27"tires(205/75-15); 2.21s are 65=1784;and 2.45s are 65=1978
    A smaller tire will bump the rpm up. It works by %. There is only 6% difference from a 25.5 to a 27.

    A 2.73 is a very big improvement,65=2229
    2.94s will put the teener right at 65=2374 or about peak torque
    Towing in loc up, may not be a good idea.It is doable with a lightweight trailer. A transmission cooler and a deep pan is recommended.
     
    Last edited: Mar 5, 2017
  4. kkritsilas

    kkritsilas Well-Known Member

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    The differences between an A904 and the later A998/A999 are that the A904 had a 2.45 low gear whereas the A998/A999 had 2.74 low gear, and that the A904 had 3 friction plates, the A998 had 4 friction plates, and the A999 had 5 friction plates. Torque capacity increases with the number of friction plates. Not sure, but I think that the A998 and A999 could be had with or without a lock up clutch.

    I don't know if there are any markings on the case to show which of the 3 transmissions are installed. If the fender tags are still there, you can figure out the transmission from the option codes; same would work if you had the build sheet. I would guess that you have either an A998 or A999; there weren't many A904s built after 1979.

    My 1982 base Mirada had an A998 and was a 318 2BBL.My 1980 Cordoba Crown and 1981 Mirada CMX both have 318 4BBl, and both have A999s (from the codes on the fender tags).

    P.S. There are A727s with small block bolt patterns. The first year Miradas with the 360s (all 79 of them) had A727s behind the 360s, and the earlier 340s had A727s when they were automatics.
     
    Last edited: Mar 5, 2017
  5. 80mirada

    80mirada Well-Known Member

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    998s and 999s were built with both 2.45 and 2.74 first gears, and both lockup and non converters. There is a part number on the transmission housing that can be searched to tell you what you have. Yours SHOULD be a 998, lockup, 2.74 low gear based on model year.

    727 were built for A/LA series, B/RB series, G series (slant six), AMC V8 and I6. They stopped offering 727s in cars around 83 or 84.
     
  6. 80mirada

    80mirada Well-Known Member

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    I think the part number is on the bellhousing on a pad, not sure though
     
  7. AJ/FormS

    AJ/FormS Well-Known Member

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    I think I saw A998 cast on the top of the bellhouse on mine in fairly large letters;
     
  8. Rustyroger

    Rustyroger Well-Known Member

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    Thanks guys. The engine is coming out oer the next few weeks for some work, so I will take the transmission out as well, and send it off to be checked out and have any wear issues rectified.
    Guess I need to look out for a lower ratio diff as well, I understand this is a staightforward job?.

    Roger.
     
  9. AJ/FormS

    AJ/FormS Well-Known Member

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    It is if you swap out the complete rear end. We are talking everything but the brakes. Swapping ring and pinions is a whole nuther can of worms.
     
  10. BudW

    BudW Moderator Staff Member

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    I believe (but could be mistaken), the A904 was used until end of 1978 Model Year production (with a few versions in ’78 with lock-up converter).

    1979, the A998 came out, with the lower 1st gear drive set (the preferred gear set). Most (95%+) are with lock-up converter but a few are non-lockup.

    The only real difference between the A904 and A998 is the gear set.
    Also all A998’s have 4-disk direct clutch pack (A904’s mostly have 3-disk direct clutch packs except for a few that have 4).

    The A999 came out in 1980 and used until end of M-body production for police cars. For the most part, it is the same as the A998 but it has a 5-disk direct clutch pack and a slightly higher governor spring set (for higher shift points).

    I would see no reason why your A998 transmission would not work well for your intended purpose, as long as your transmission tech knows what your plans are and will use the appropriate parts.

    If wanted, it is not hard to find the 5-disk direct clutch pack parts and upgrade your A998 (also used in the A500 and other transmissions).

    Finding the police governor spring set is not easy to do.

    On an unrelated note: I happen to have an unneeded used A999 in my garage that came from a ’84 Gran Fury AHB (police car) that I keep tripping over. Shipping across the pond would not be cheap.
    BudW
     
  11. Rustyroger

    Rustyroger Well-Known Member

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    Thanks again Bud.
    My local transmission guy has a fine reputation as expensive but great long term value, and he helps me on many occasions in return for work putting transmissions in and out for him.
    Shipping from the USA, anything heavy is prohibitively expensive for the most part.
    I think my transmission is most probably a 998 with lock-up converter,I'll find out later this month when it's coming out along with the engine.

    Thanks once again;
    Roger.
     
  12. BudW

    BudW Moderator Staff Member

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    Very very few FMJ’s came with an A727.
    I would guess less than 1/100th of 1% and maybe closer to 1/1000th of 1%.

    I have only seen one FMJ with a 727 and I think it was added after the fact (not sure why, and it was a hack job).

    Note: I have physically worked on thousands of Chrysler transmissions, in my younger days.
    BudW
     
  13. kkritsilas

    kkritsilas Well-Known Member

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    From all iinformation that I have ever seen, the only J bodies that ever had a factory stock A727 are the 76 units made in 1980 as Mirada CMXs with the 360. I think they also had an 8 3/4" rear as well.
     
  14. 80mirada

    80mirada Well-Known Member

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    There were 318 J-bodies built with 727s, though rare. The 360 cars came with 8.25" rears, 8 3/4" rears ended production around 74-5. I nearly bought an 81 Mirada that was a 318, 727, 2.94:1 8.25" rear, Silver and Blue, power everything it was a beautiful car.