A833 Can't Downshift / Poor Performance

Transmission and Drivetrain Tech

  1. 440fury

    440fury Well-Known Member

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    Hey Guys,

    I am having a lot of trouble with a rebuilt ("rebuilt") transmission I bought. The trans shifts into gear just fine when idling in the driveway, and is marginal on upshifts (minor clash), but I can't for the life of me get this thing to downshift into gear while the car is moving.

    I read through a lot of posts on here, and so far I've:
    - Pulled the trans, inspected the clutch, cleaned/greased the input shaft,
    - Tried 3 different fluids; ATF, 75-90, and 85-140 (no real difference)
    - Checked the clutch disengagement (I can spin driveshaft by hand with clutch in, car in gear)
    - Ordered new shift rods and arms, installed, and adjusted the shifter perfectly.
    - Adjusted the stops on the shifter
    - Checked the pilot bushing for binding (it is perfect and new)
    - Checked the throwout bearing
    - Pulled the side cover - shift fork for 1-2 had some minor wear on it, and reverse gear was a bit chewed (not from me), but nothing absurd. Actuated the shift collars by hand and it all seems to jive just fine.

    Is there anything I am missing that I can try here?

    *** Not that it matters, but I did try to order a rebuilt one from Brewers, but unfortunately they were backed up until September (when I called in March) and I wanted to drive the car this summer.
     
  2. geardaddy

    geardaddy Member

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    put the back on jackstands and go through the driving motions with the wheels in the air and see what it does..
     
  3. 67Dart273

    67Dart273 FABO Gold Member FABO Gold Member

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    Possible it's a pilot bushing problem, bell misalighment, not enough clutch pp release even though "you think" otherwise, sure sounds like a release problem rather than an actual gearbox problem to me
     
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    • RustyRatRod

      RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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      What clutch have you got in it? If it's a diaphragm clutch, did you remove the over center spring? They are only used on the Borg and Beck three lever style and need to be removed for the diaphragm style. That can cause some issues too.
       
    • 440fury

      440fury Well-Known Member

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      Thanks, it's a diaphragm clutch and the over-center spring has been removed.

      Additional information: this transmission is replacing my old one, which shifted and operated just fine, but had a lot of miles and was worn-out. The pilot bushing, clutch, shifter, shift arms, shift rods, driveshaft, flywheel all have less than 1000 miles on them.

      @67Dart273 Thank you, I'll try adjusting it again tomorrow. I saw elsewhere (on another post on FABO) that if the driveshaft spins freely with the car in gear, clutch in, and tires in the air, it should be good, or at least very close. I'll crack out the Ye Olde feeler gauges and pull the inspection cover tomorrow to confirm.
       
    • RustyRatRod

      RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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      As detailed as your post was, I kinda figured you knew "all that" but had to ask to verify.
       
    • 440fury

      440fury Well-Known Member

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      I'll give that a go tomorrow! Thanks!
       
    • KosmicKuda

      KosmicKuda FABO Gold Member FABO Gold Member

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      I'll be the first to admit I know very little but you did NOT mention if you verified bellhousing bore alignment with a dial indicator. Seems to me that if the input shaft is off center, it may be getting enough side loading not allowing it to stop rotating.

      I've only rebuilt one 833 and haven't installed it yet, but I'm counting on it working because it's registered for Carlisle.
       
    • MOPAROFFICIAL

      MOPAROFFICIAL FABO Gold Member FABO Gold Member

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      Chance it's not really rebuilt and the synchro n sliders are junk.
       
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      • Dicer

        Dicer The past is practice. FABO Gold Member

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        I agree with the above statement, the synchronizer rings should have been replaced. And the gear cones should have been resurfaced as well, doing this will ensure the gear clusters would speed up or slow down while shifting.
        IMG_4362.JPG
         
      • 440fury

        440fury Well-Known Member

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        Very true, I did not test bellhousing bore alignment, but the bellhousing/clutch is the same as it was with the old trans. I did the standard ghetto engineering to confirm the pilot bushing wasn't dragging.

        Could be true - this seller has plenty of stuff listed on ebay, and seemed like an honest enough guy, but the countershaft reverse gear being chewed and the 1-2 shift fork showing a bit of abnormal wear has planted seeds of doubt.

        As an update to all this, when driving the car, it does feel like the synchro's aren't really grabbing the cones on the gear hard enough to spin up the gear set. You can hear the gears winding up a bit more if you apply some pressure.

        Almost all the gear oils I have tried thus far have been the GL5 type (I know now the errors of my ways..). To what margin this is grasping at straws, I'm not sure. I always got a giggle about the "I have a mechanic" type guys anguishing over the minutiae of each type of oil, but in this case GL4 vs GL5 may be the difference maker in the shifting.

        I'm going to try finding some GL4 or Redline MTL this weekend.
         
      • AJ/FormS

        AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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        Av you know, the synchronizers work by the brass grabbing the shiny smooth brake surfaces of the brake-cones.
        They gotta bite.
        In my experience;
        Full synthetic oil is TOO SLIPPERY and the brass just slips and slips and slips. But you tried three different fluids and all same.
        So next up is input shaft not stopping. So push the pedal down and have someone look. If it stops, and the car is stopped, and you still cannot engage a gear, this has nothing to do with the synchros.
        But if it slips into any gear as the input gear comes to a stop, perfect, that is working good. First will occasionally be a lil harder to get if the input comes to a complete stop, because the the clutch teeth could be butted up. Simply selecting second and then first may be enough to unlock them, but sometimes you gotta spin the input just a hair.

        More coming, supper time!
         
      • Early a body

        Early a body Well-Known Member

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        I have run into this problem before exactly as you described. I dealt with it because it would not downshift to second but would 4-3 . So after about 5 years of that nonsense I had another 833 rebuilt and replaced the one I had that would not downshift to second . Problem solved. I never opened up the old 833 just put it in the shed and forgot about it.

        Likely you are going to have to rebuild the trans again .
         
      • CRUZE 418

        CRUZE 418 FABO Gold Member FABO Gold Member

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        When you downshift, do you take the trans out of gear, let the clutch out and bring the engine up to the approximate speed of the lower gear and then finish your downshift?
        Sorry, old retired truck driver. Otherwise, sounds like brass blocker rings to me, maybe the gears too. Oil won't do that.
         
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        • 440fury

          440fury Well-Known Member

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          Here's an update - I checked the clutch release clearance today by pulling the inspection cover. With the clutch pedal in, there is an abundance of clearance, and I can spin the clutch disk with the tip of my finger, so I am thinking that's not it. I've got some Sta-Lube 80-90W GL4 on the way. I did conjure up a crackpot theory I wanted to run by everyone.

          First, some backstory - I actually installed this trans for the first time about 3 weeks ago. When I was driving it home, it still shifted awfully, but more critically, it got stuck in 4th gear. Removed the shifter - still stuck in 4th. Pulled the side cover, and the 4th gear syncro collar was past the shift keys, causing it to be locked in 4th. Pushed the keys back in, slid the collar back to the correct spot, and reinstalled side cover. Bada-bing, problem solved.

          Throughout this process, I have befriended a local transmission expert, and when I told him this he said that it's very odd that the collar went past the keys.

          Next, I'll describe my test:
          1. Put the car into neutral, clutch engaged
          2. Rev to 2000 RPM
          3. Press the clutch pedal
          4. Try to get into a forward gear

          ** Key point - During this test, for every forward gear (except 4th) the trans ground on its way into gear.

          Now, for the crackpot theory. Main question - why does the car go into 4th easily, but grinds every other gear? Next up - why did the shift collar go past the keys on my regular ol' drive home? I am thinking that, for some reason (bent shift fork?), the 4th gear synchro is ALWAYS partially engaged. When I try to shift into another gear, that synchro has to fight a friction battle against the 4th synchro, which leads to grinding. However, when I am going into 4th, no problems.

          ** Key point 2 - I am highly confident in the shifter adjustment. I've done it, read more about it, re-done it, ordered all new parts, checked it again, took everything out, put everything back in, then did it again.

          So, I am thinking there is something in the transmission that is causing the synchro collar to be slightly pushed in the direction of 4th, which is causing the synchro to always be a bit engaged, and is a possible reason for why I over-shifted 4th driving like a granny on my way home.

          ** Key point 3 - I have the shift stops installed and adjusted on the shifter. Like the shifter alignment, I did it while I had the trans out of the car.

          Has anyone here ever dealt with a slightly bent shift fork? What were the symptoms?
           
        • AJ/FormS

          AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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          Ok then, yur on yur own
           
        • harrisonm

          harrisonm Well-Known Member

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          Exactly what I was going to suggest. If you are very careful, you can actually upshift and downshift without using the clutch if you match RPMs as suggested above. I also agree that it sounds like synchros to me. Here is my version of the RPM explanation. This will be better on a less busy road. Drive along at about 40 MPH in 4th gear. Then do a normal downshift to third, but do it a little slower than normal and increase the RPMs by about 800 or so. That will allow the speed of the gears in third to more closely match the engine's RPM, and make the shift smoother. If there is an improvement if the downshift, my guess is that you have bad synchros. The transmission was supposedly rebuilt??? There is a big difference between what I consider a tranny rebuilt to be, and what others do. The previous owner could have replaced a few bearings and seals and gaskets and called it good.
           
        • oldkimmer

          oldkimmer FABO Gold Member FABO Gold Member

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          Exactly why I stopped replying to a lot of threads. Ppl don’t listen and a lot of bad advice. Kim
           
        • 66fs

          66fs FABO Gold Member FABO Gold Member

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          Could be a lot of things. It was definitely not "rebuilt" correctly. You should be able to downshift anytime anywhere as well as full on power shifts. If you are over travel on synchro assemblies, it needs to come apart and figure out what is wrong.
           
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          • mbaird

            mbaird mbaird

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            That wasn't the OP.

            Sincce you bought it on ebay and it was represented as rebuilt ask for your money back then file a complaint if seller refuses.
             
          • AJ/FormS

            AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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            there are exactly four reasons why a trans won't shift properly;
            1) input gear is spinning; there could be several reasons for this
            2) synchros not braking; there could be several reasons for this
            3) one of the mainshaft gears is dragging
            4) oil is too slippery or too thick, or will not vacate the brake
            As to;
            #3) this seldom happens,
            #4) I have had zero success with full-synthetics. Thick dyno oils are hard to squeeze out, and until the oil is squeezed out from between the brass and the brake cone..... NOTHING can happen. The brass has to make intimate contact with the brake.Intimate. This is why the brass has ridges and or channels, providing places for the oil to go. This is why I have modded my trans with channels ground right into the brake cones, to get rid of synthetic oil, which didn't work anyway, but worked awesome with dyno oil.
            I have had the best success with Dextron II ATF. But I worry about the cluster pin, so I run 50% ATF, 50% E/P oil.
            Some oils seem to bond to the metals in the trans . When this happens draining it will not make a difference. Even flushing it out with some type od solvent, will not . In this case the trans has to be taken apart and the brakes physically dressed to get it to shift again.
            #2) Lots of reasons for this;
            Wrong type oil;
            Brass worn out and sitting too low on the brake.
            Strut springs are weak, allowing the slider to pop over too early
            Struts worn too short. Forks worn out. Bearings with too much play. Parts moving in directions they have no business moving.
            #1) insufficient Clutch-departure;
            > could just be wrongly adjusted freeplay, but could be
            > 6-cylinder pedal ratio used on a 10.5 or bigger clutch.
            > bent or warped clutch disk
            > bad set-up of the Pressure plate
            > misalignment of the crank centerline to the trans centerline
            > broken Bellhouse
            > pilot bearing not releasing
            > flexing of the release-system
            broken or cracked TO pilot on the Retainer.

            Keep in mind that with the engine running and clutch clamped; EVERYTHING inside the box is spinning, unless the vehicle is stopped. At that time, the only things NOT spinning are the mainshaft and the two synchronizer assemblies. When you attempt to shift, whatever gear you are trying to get, has to be speed-matched to the mainshaft speed. Whether shifting up or down, the speed has to be matched very closely. That little tiny brass ring is the guy responsible for making this happen. But it depends on all the other synchronizer parts for support, and specifically the input gear has to be divorced from the spinning crank/flywheel/clutch assembly, so it can it's change speed! because the gear you are attempting to get into is spinning WITH the cluster, which is spinning WITH the input gear. So if you think about it, that brass ring has to speed match a fairly large mass, and the higher the speed difference, the more the mass grows.

            Ok now, just as an FWIW, my A833 shifts like lightning, all the way to my self-imposed redline of 7200...... because I tried everything I could think of to make it happen and after many many RnRs I finally got it figured out; see, I'm not particularly bright, but I am persistent, lol. In the end I was dropping that stinking box, and the GVod behind it and the mufflers/ front pipes ...... in 17 minutes. On a 4-post hoist mind you,lol.

            Gear clash is another topic;
             
            Last edited: May 22, 2021
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            • mbaird

              mbaird mbaird

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              6 cyl have different pedal ratios ?
              I never knew that .
               
            • AJ/FormS

              AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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              Hyup. the smaller clutch requires very little effort. But that same ratio works quite well with a diaphragm clutch with the O/C spring removed.
              But with a 3- finger performance clutch, you really need the V-8 peddle-ratio. Ok well, in a streeter, I need it, lol. I mean just count the number of times you push on the pedal during an afternoon's tooling around..... With a 3600# 3-finger, that would be real workout with the 6-banger pedal..
               
            • Johnny Dart

              Johnny Dart Well-Known Member

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              If there is an issue with the trans, obviously that needs to be fixed first.
              When you get it straightened out I wouldn't use anything but Red Line MT-90 or RED Line MTL.
              MT-90 is a thicker vicosity MTL is a lower viscosity.
              I put the MT-90 in my 833 and it was a game changer in regards to shifting. Really smoothed the shifts out.
              MT-90 is the recommended fluid at Brewers for an 833.
              Works for me.
               
            • 440fury

              440fury Well-Known Member

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              Thanks for the input everyone, I'll keep posting updates as I go along. I hope this could be helpful to someone in the future.

              That reality has set in, but this is really the first time I've had problems with one, so I wanted to make sure I had exhausted 100% of every possible thing I could be doing wrong before pissing and moaning to get the trans replaced. The one I pulled out from under a shelf in some guys garage had thousands of trouble free miles...

              At this point I've spent hours researching it, reading the rebuild book, and pulling this thing apart so I may just redo it myself. If it's rebuilt wrong, then the seller sucks, but the shortest path to me cruising may be fixing it myself.

              Do you have any pictures of the modifications you made to the cones? If it's all coming apart, I'm considering having some fun on the Bridgeport while I'm at it.

              17 minutes is impressive!

              I am still holding on to that. The MT-90 is my last ditch effort if I can't find anything wrong. It comes highly recommended from many.
               
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