904 "braking" in 2nd gear

Transmission and Drivetrain Tech

  1. 68 A

    68 A Well-Known Member

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    Hi,
    As some of you may remember i had a problem with my 904 last summer due to not putting enough ATF in. I ended up getting the transmission rebuilt and put back in the car. Got about 120 miles on it, and now when the tranny shifts into 2nd gear, it feels like the brakes are put on. It is very clear that it is 2nd gear. it drives fine in first, shifts to second and feels like the brakes are on, then shifts to 3rd and it feels normal. I dont know what it is, possibly something internal?

    the guy that rebuilt it for me earlier this year told me i should have a 727, but everyone here says that a 904 is just fine for what i need. It was a stock rebuild, so if it does need to be rebuilt again, i would like to find one of the guys that makes these things "bulletproof".

    anyone know what is wrong?

    anyone know someone within 150 miles of auburn, ny that is a 904 mastermind?

    thanks,

    Steve
     
  2. ray79rt

    ray79rt Well-Known Member

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    Odd problems like yours is usually caused by the trans trying to shift into two gears at once. I would suspect that the rear band may be trying to apply when you are in second. (or maybe direct clutch pack appling instead of rear band, either one would cause your problem) Second gear should have the front band and the forward clutches applied only. The sprag should be free wheeling. If there is a oil passage in the valve body that is bleeding over to the rear servo while in second gear, the rear band will apply and try to stop the sprag. You need to connect a transmission pressure gage to the test port on the rear servo. There should be 0 psi on the gage except when in reverse and when in manuel low gear. If this is your problem a new valve body should fix it, Good luck, Ray
     
  3. djwhog

    djwhog Well-Known Member

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    That brake feeling is a shift timing issue. The 3rd clutch for high is applying while the 2nd intermediate band is still on.

    Call John Cope at Coperacing. He will get you fxed up.

    You can setup a 904 very strong, but if you need serious holding power and stronger internals you have to run a 727. Most times up to around 400 HP on a low weight car and under 400 or so ftlbs of torque you can build a nice 904.

    It sounds like you need a good trans guy, call John.
    http://www.coperacingtrans.com/

    Just an fyi, what car, make model, year and engine are you running, how is it built etc?
     
  4. 68 A

    68 A Well-Known Member

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    thanks for the info, i will see if a neighbor has a pressure guage, and then go from there.

    i did forget to tell that it has a shift kit in it, transgo tf-1 i believe (its been a while since i've thought about it), and a dynamic 3200 stall converter.

    the rest of the car is a 70 Swinger, 318 bored .060, 9.8 comp, J heads with 2.02 and 1.60s. comp 268XE cam, edelbrock performer rpm intake, 670 cfm street avenger, D.U.I. chrysler tri power ignition, headers. (i was following a mopar muscle build that resulted in 350 hp, 400 ft.lb. however they used stock 360 intake and ignition) also got a 8 3/4 with 3.91 suregrip.

    thanks for the help!

    Steve
     
  5. fishy68

    fishy68 Tyr Fryr's Inc. FABO Gold Member

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    Steve your 904 is just fine for your application and plenty strong. But it's got a definate shift overlap problem that is detrimental to your transmission. The rebuilder didn't do something right apparently or you wouldn't have this problem. He should've pressure tested each component (clutch packs and servos) during the rebuild. It's also possible that he mixed up the selective snap rings when rebuilding the clutch packs and didn't check the clearances, which should allways be checked and adjusted if necessary. Another possibility is he did something wrong when installing the shift kit and/or put a valve in wrong in the valvebody. Nevertheless the rebuilder should make it good. Have you talked to him about it?

    Whatever you do don't drive it until it's fixed or it will burn it up very fast!!
     
  6. dusterdon

    dusterdon Well-Known Member

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    Make sure that your shift linkage is adjusted correctly. I had a trans do that, readjusted the shifter (aftermarket B&M) and everything was fine.
     
  7. 68 A

    68 A Well-Known Member

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    i havne't talked to the guy that rebuilt it yet,thought maybe i could find some answers here first. He told me I needed a 727 so i thought maybe he would just tell me that again. But i'll give him a call to see what he says.

    right now its column shifted (will probably be switched in the next year), and i dont think that the linkage is adjusted wrong. If i put the car in drive, it will start in first, then second, then shift to third.


    Thanks,
    Steve
     
  8. fishy68

    fishy68 Tyr Fryr's Inc. FABO Gold Member

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    Yeah a lot of guys think a 727 is needed for any type of performance car but it really isn't. Especially if your running a light A-body. Their are tons of them running around with a 904 and just a good shift kit like the Trans-go running 12 second 1/4 miles (and faster sometimes) and they are holding up just fine.

    I've been thinking a lot about your problem and think that it has to be a valve body issue because if the rear band was applying when it shouldn't be it would mess up 3rd gear also, not just 2nd. Also if the front clutch was applying when it shouldn't be 1st gear wouldn't work right.

    The sequence of events for shifting are:

    Put it in forward and the rear clutch applies and stays applied throughout all the forward gears.

    In 1st gear only the rear clutch is applied unless you have it in manual low then the rear band is also applied.

    When it shifts to 2nd the rear clutch stays applied and the front band applies. If manual shifting it the rear band releases and the front band applies simultaneously.

    When it shifts to 3rd the front band releases and the front clutch apples simultaneously.

    I've seen guys mess up putting shift kits in several times. Seems they can't or don't read the instructions good. It's quite possible that is what happened.
     
  9. grumpuscreature

    grumpuscreature Resident Curmudgeon

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    This sounds like a problem I had once with a van after I put a shift kit in it. I cheated, I pulled the trans and took it to the dealer to have it fixed. The mechanic was nice enough to let me watch (Yeah, it's been that long ago) and when he started measuring the little steel balls from the valve body with a micrometer, I asked why he was doing that. He replied that there were two balls that were 5 thousandths of an inch different in diameter. The big one went in this hole and the smaller one went in that hole. If they were swapped, you had the problem you are describing and I had. Put 89,000 more miles on that van with zero tranny problems. Might be something to check into.
     
  10. 68 A

    68 A Well-Known Member

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    i called John Cope today, he gave me some more info on my problem. He didn't think it was a problem with the shift kit installation since i drove the car for 120 miles before i had any problems. Said to drop the pan and check that the screen is clean. Also drive it and see if the "braking" happens when manually shifting, automatic shifting, or both. Now i got some plans for this weekend. gotta get some fuel for the heater too, haven't been in the garage since its gotten cold out!

    Thanks,
    Steve
     
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