904 third gear flare

Transmissions and Rear Ends

  1. charlesvolare

    charlesvolare Active Member

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    I have a 904 behind a mild 360, probably around 350 hp and 325 ft/lbs I'm guessing. I built the trans with beefier clutches, and had it behind a stock 360 magnum for a bit as well. Has about 8,000 miles on it total, and I drive the thing hard. Stoplight to stoplight, there's never really much of a chance to get into third gear quick, but merging on the highways third gear has always been great. Second time I took the car to test & tune I noticed engine rpm would flare up on the 2-3 shift, so I messed with the kickdown cable (lokar cable, set up correctly as per instructions and internet for 7,000 miles prior) and it didn't do much so I put it back. A couple weeks later it started flaring on the street as well. Today, i discovered I can no longer drive on the highway due to the fact it won't stay in 3rd gear anymore.... there's a sweet spot in the pedal where it'll stay in gear, anymore and it'll downshift (not entirely onto second though, it's weird) any less and I'm just coasting. Not good for driving the highway with 3.55 gears. Whenever it would stay in gear, it'd hold. Pulled hard in third too. 65mph is right at the start of the good stuff at 3200 rpm, pulled to 90 in about .000001 seconds it felt like. The first 904 I built was for the original slant six, and that started doing the same thing; when I pulled that apart after the engine swap the front clutch pack was a disaster. I haven't touched the bands since I built it but every other gear is strong with hard shifts. Fluid is good. I'm just trying to come up with any reason it'd do this other than the front clutch pack is toast, any thoughts?

    Here's a video of a pass, notice the 2-3 shift where I let off the throttle for it to go into gear:



    It WAS like this, today is wouldn't even stay in gear...
     
  2. Aspen500

    Aspen500 Well-Known Member

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    You definitely have a forward clutch problem. My first guess would be the piston seal is failing. You also could have a cracked forward clutch piston that allows fluid pressure to bleed through. Have never seen it on a Mopar trans though (Ford's,,,,,yes). Either way, it's going to have to come apart as you already know.
    You didn't mention whether you modified the valve body or not. If not, highly recommended. Either "street" or "street/strip" version of the kit, which also has you adjust the line pressure regulator for higher pressure.

    With a 360 and 904, an aux. trans cooler is a must. Way back when, I had a '78 Cordoba with a 360 (2brl) and 904. It would start burning the trans fluid in 5,000 miles and,,,,,,,,,,the forward clutch would start failing a few thousand miles later, even if the fluid was changed. Only had the radiator trans cooler. Overhauled it twice (bone stock overhaul) and the third time replaced the trans with a 727, problem solved (in that case).
     
  3. Poly

    Poly Well-Known Member

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    With the 904 in our vehicle there was always a flare on the 2-3 shift. Of course the setup is nothing of the drag strip category. From the shop manual we increased the hydraulic line pressure one turn. The flare disappeared. The shift points were unbeliveable 1-2 @ 10 mph. 2-3 @ 18 mph with light throttle. Always lugging the engine around town. Got rid of that too but it's irrelevant to your circumstances. However, again, increasing the hydraulic line pressure did away with the 2-3 flare.
     
  4. charlesvolare

    charlesvolare Active Member

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    I haven't had time to mess with it much, but heres a few more things I've figured out that may or may not help:
    1) Shifts perfect when engine is cool. I can start the car in the morning and drive the few miles to class with no problems shifting into third.
    2) My allergies have cleared up enough for me to smell again. Fluid is so burnt it smells like a campfire.

    I'm no expert by any means, but bad fluid would result in loss of pressure/density of fluid, which is needed for shifts, and since it does fine cold (thicker) maybe a fluid change would fix it.

    If I remember correctly, reverse has higher line pressure than direct, so that's why reverse is fine. I can still break tires loose backing it up, cold and hot.

    When I can get the chance, I think I going to drop the pan and check it out. If it looks okay (aka not too much clutch material in it/metal in it) I'm thinking about just adjusting everything and doing a fluid flush, possibly a shift kit while I have the pan off. Does anyone recommend I do this first or does then bad trans fluid mean bad internals and necessitate pulling it apart?
     
  5. Aspen500

    Aspen500 Well-Known Member

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    If the fluid smells burnt, like a campfire, the damage is already done. The heat has more than likely turned the forward piston seal from pliable to solid. What you mentioned is worth a try but once the fluid is burnt, it rarely makes much improvement. Sorry...………..
     
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  6. Oldiron440

    Oldiron440 Well-Known Member

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    I would not bother with a shift kit in that trans
     
  7. 80mirada

    80mirada Well-Known Member

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    If it smells burnt, it will have to come apart
     
  8. Aspen500

    Aspen500 Well-Known Member

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    ............until the trans internals are repaired.
     
  9. 78VOLAREWAG

    78VOLAREWAG Well-Known Member

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    Usually if a transmission is still working but smells burnt, you will make it worse by putting fresh fluid in it.
     
  10. charlesvolare

    charlesvolare Active Member

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    Just pulled the tranny. Probably tear it apart this weekend and update with what I find.

    15392874732684540955552132454603.jpg
     
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  11. Aspen500

    Aspen500 Well-Known Member

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    Holy crap, you don't mess around or procrastinate, do you?:eek:
     
  12. Oldiron440

    Oldiron440 Well-Known Member

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  13. Aspen500

    Aspen500 Well-Known Member

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    I used to be like that, but the older I get, the longer things seem to take. Undercar work on the ground is even worse. Not so much the work itself but the standing back up after sliding out from under the car. That and trying to SEE WHAT THE BLEEP I'M DOING.:mad: Too close for either lens of the bifocals, too far away to see without glasses.........................Sigh. I really hate this getting old crap.:( Whine, grumble, complain.:cool:
     
  14. charlesvolare

    charlesvolare Active Member

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    Here's the direct clutch pack... The outside side of both end frictions are still red. Bits of metal in the pan.

    IMG_20181013_111108.jpg
     
    Last edited: Oct 13, 2018 at 11:24 AM
  15. Oldiron440

    Oldiron440 Well-Known Member

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    If I remember correctly were you manipulating the kick down linkage or not using it?
     
  16. Poly

    Poly Well-Known Member

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    If you have the clearance you might want to look at the deeper pans and a cooler. Many of them offered are used and a bargain. And an extra quart or so of fluid. You may already have these items. Can't tell from the photos.
     
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  17. BudW

    BudW Moderator Staff Member

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    The rubber lip seals for clutch piston (requires clutch drums taken apart even father) turn rock hard with heat, and sometimes shatter. When that happens, fluid rushes past the lip seals instead of holding pressure against the clutch.
    In some cases, the lip seal might roll over (or blow out) which causes a similar condition.

    Any time a transmission fluid smells burnt - STOP! Any additional driving will be causing additional damage! Those lip seals have to be replaced before things start to burn up (if not already in that condition)!

    20181013_111108.jpg
    The clutch disks (blue arrows), the top one looks OK/marginal, but the other three have discolored from heat (ie: burnt to a crisp).

    The clutch plates (pink arrows) and pressure plate (Red arrow) (all metal) also show signs excessive heat. These plates should be shiny (not darkened or in this pic, like are wavy).

    Clutch disks and plates normally come with a rebuild kit – but the clutch pressure plate (red arrow) does not.

    This type of damage is what I usually see on a transmission without the kickdown linkage hooked up (and I’m not saying this happened because of that, in your case).

    When complete, make sure you perform fluid pressure tests to make sure fluid pressures are in range. I don't think you want to perform this repair operation, again.

    Also, too much pressure can cause those lip seals to blow out (roll a lip) – so too much pressure is sometimes as bad as not enough pressure.

    Also check all metal (or Teflon) clutch sealing rings on the shafts – to make sure no broken sealing rings exist – as well as check for wear at those sealing rings on corresponding shafts/drums. A broken sealing ring or excessive ring sealing surface can cause this, as well. One sealing ring is indicated by gold oval.

    The kickdown band (green arrow) also looks overheated. This part “might be” reusable, but I sure wouldn’t want to. The clutch plates and bands use paper for frictional material. Once paper gets hot, it will usually crumble/disintegrate faster.

    Also (again not saying you have or do this), make sure you soak the transmission clutch plates and new bands in ATF for a while before usage. Dry clutches will also burn up really quick.


    When installing new seals (mainly lip seals), use plenty of fluid. I like to dip the seals into a bowl of ATF – but everyone has their preference. Also, this tool (or others similar) work great to make sure those lip seals are installed correctly. A feeler gauge will also work – but this type of dedicated (but generic) tool is quick. https://www.ebay.com/itm/Transmission-Lip-Seal-Tool-Installer-Power-Glide-TH350-TH400-4L80E-C4-727/132146838204?hash=item1ec490babc:g:5nYAAOSw3v5Ypz~Z:rk:5:pf:0
    Lip Seal Tool.jpg

    When placing the piston in place, run this tool (with a drop of ATF on it) around the area of the lip seal, before pushing it in and again mid-way down. If you find your lip seal has rolled, you will feel it with this tool, so you can remove piston and start over. To me, this tool has more than paid for itself for transmission lip seals as well as a lot of other items.

    I just rebuilt a lawn mower engine, and this tool worked great to make sure that both crank seals were on right. The bad news is my tool got left outside and is now rusty – so I need to get a replacement soon.


    Note: this information might be useful to you (or not). The main reason I go into detail is for the next person who might be in this situation, who doesn’t know all about these things.
    BudW
     
  18. Aspen500

    Aspen500 Well-Known Member

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    I concur with everything BudW said. He is 100% correct and has a much better way of explaining it all than I do.

    It also helps to have some sort of universal clutch spring compressor kit like the one in the photo. It makes getting the snap rings on MUCH easier. Of course, having all the trans specific special tools would be ideal but unless it's a dealership or trans shop, that's never going to happen, lol.

    Have you got the forward clutch apart yet? That would be the one responsible for drive and reverse.
    DSC00147.JPG
     
  19. Poly

    Poly Well-Known Member

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    002.JPG



    Noticed some noise around the 140's in the video with heavy throttle and was thinking oops, dropped a valve...then lost a tooth. My only transmission work has been through the factory books.

    002.JPG
     
  20. Aspen500

    Aspen500 Well-Known Member

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    I'm sure you know this already but, the throttle valve lever should be to it's rear stop when the throttle plate is wide open as far as it will go. Ideally they should both hit their limit at exactly the same time.