Clunk noise on the 1/2 shift in an A999 trans.

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Clelan

Clelan

Inferno Red Duster
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74 Duster, 360/904/8 ¼” 3.23 SG

My transmission in my 74 Duster decided to stop shifting into second gear so I found a junk yard A999 from an 88 Dodge truck to keep me going till I get a chance to rebuild the 904 this winter. I purchased the TCI balanced flex plate since the Junk Yard transmission had a neutral balanced torque convertor.

The transmission shifts well both up and down except for a clunk noise on the 1/2 shift. It doesn’t clunk under light acceleration but even under regular acceleration from a stop light (like you would do with a cop behind you) the clunk is pretty bad. As the transmission warms up, it gets better but doesn’t go away. In the research I did on the forum prior to posting this, I saw it mentioned that it is likely too much line pressure causing this so I loosened off the kick down (cable type) to the point that it will no longer kick down to second when flooring it at 40 mph but still shifts good. I can now pull the cable about a ¼” further by hand than it gets pulled by the carb linkage at WOT. This helped marginally but the clunk is still there. There is also a slight whining sound in only 1st gear that I have never heard from an automatic transmission. This whine seems to all but go away at full normal operating temperature.

A couple things I should say, is that when I was cleaning up the transmission for installation I removed a heavy weight bolted to the back of the tail shaft because I could not see any use for it and found it to be useless added weight (was I wrong?). Also, this transmission does not have any wiring or control circuit yet hooked to the solenoid at the rear left corner of the trans pan which I believe actuates the lock up torque convertor. Also, there is a little more backlash in the rear end than there should be but it never clunked with the old 904.

I did drive it a little this weekend, and when accelerating down an off ramp, I floored it, kicking down into 1st gear and shifting up through all the gears super smooth and strong. Not sure why it didn’t clunk this time.

This weekend I plan to drop the oil, change the filter and fluid again, check the band adjustment (however I don’t think there is any problem there since it shifts so well otherwise) in hopes of correcting this problem. What else should I look for? What else could cause this?

Cley

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What year to what year do you find these in? Is the trans mount a direct bolt up to a A body. I may be interested in one.
 
They come in late 70s to late 80s trucks for sure (mine is from an 88 1/2 ton), maybe cars too. Mine was behind a 318, but the 360 versions have 1 more clutch pack in them from what I read. I like the lower 1st gear in the trans with my 3.23 rear. I just need to get it to stop that 1/2 clunk noise so I can drive it a little harder.

Cley
 
Cley, when you drop the pan loosen the valve body bolts (10 of them) drop the VB & check if the accumulator spring has been removed or the accumulator piston has been blocked with a blocker rod. One purpose of the accumulator is to cushion the 1-2 shift.
Here's a picture of a 727 but it is very similar to the 904/998.

30154089mj.jpg
 
89on35s said:
74 Duster, 360/904/8 ¼” 3.23 SG

My transmission in my 74 Duster decided to stop shifting into second gear so I found a junk yard A999 from an 88 Dodge truck to keep me going till I get a chance to rebuild the 904 this winter. I purchased the TCI balanced flex plate since the Junk Yard transmission had a neutral balanced torque convertor.

The transmission shifts well both up and down except for a clunk noise on the 1/2 shift. It doesn’t clunk under light acceleration but even under regular acceleration from a stop light (like you would do with a cop behind you) the clunk is pretty bad. As the transmission warms up, it gets better but doesn’t go away. In the research I did on the forum prior to posting this, I saw it mentioned that it is likely too much line pressure causing this so I loosened off the kick down (cable type) to the point that it will no longer kick down to second when flooring it at 40 mph but still shifts good. I can now pull the cable about a ¼” further by hand than it gets pulled by the carb linkage at WOT. This helped marginally but the clunk is still there. There is also a slight whining sound in only 1st gear that I have never heard from an automatic transmission. This whine seems to all but go away at full normal operating temperature.

A couple things I should say, is that when I was cleaning up the transmission for installation I removed a heavy weight bolted to the back of the tail shaft because I could not see any use for it and found it to be useless added weight (was I wrong?). Also, this transmission does not have any wiring or control circuit yet hooked to the solenoid at the rear left corner of the trans pan which I believe actuates the lock up torque convertor. Also, there is a little more backlash in the rear end than there should be but it never clunked with the old 904.

I did drive it a little this weekend, and when accelerating down an off ramp, I floored it, kicking down into 1st gear and shifting up through all the gears super smooth and strong. Not sure why it didn’t clunk this time.

This weekend I plan to drop the oil, change the filter and fluid again, check the band adjustment (however I don’t think there is any problem there since it shifts so well otherwise) in hopes of correcting this problem. What else should I look for? What else could cause this?

Cley

View attachment 1715084526 View attachment 1715084527 View attachment 1715084528
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My experience is that sometimes when you are accelerating at part throttle, that if the trans was just about to shift and just before it does you got off the throttle that the trans will make the shift with that clunk. My understanding is it is nothing to worry about.
That because we got off the throttle we momentarily screwed up the shift timing between 2nd and 3 gear.
 
I'm familiar with the clunk when letting off the gas at the wrong time. This is not that. It is when steadily accelerating from a stop. I will say that I have been driving it a little and it's getting better. I still need to pull the pan and look around. I'll look at the accumulator and spring now that I know about it. Is there anything else I should look for? Obviously I'll look for filings and friction material in the pan and valve body but I'm scared to do too much in the valvebody cause I have been having a recurring nightmare about springs and checkballs flying out of it and never being found again. :)
 
89on35s said:
I'm familiar with the clunk when letting off the gas at the wrong time. This is not that. It is when steadily accelerating from a stop. I will say that I have been driving it a little and it's getting better. I still need to pull the pan and look around. I'll look at the accumulator and spring now that I know about it. Is there anything else I should look for? Obviously I'll look for filings and friction material in the pan and valve body but I'm scared to do too much in the valvebody cause I have been having a recurring nightmare about springs and checkballs flying out of it and never being found again. :)
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The clunk may be a combination of shift overlap and the rear end play.
If it binds at all on the 1-2 shift the trans will try to stop the driveline and then the shift will slam it forward again causing the play to be taken back up and the clunk.
Try backing the front band off 1/2 turn and see what it does.
That will give it a second longer for 1st to let go before second applies.

Just a thought.
 
TrailBeast said:
The clunk may be a combination of shift overlap and the rear end play.
If it binds at all on the 1-2 shift the trans will try to stop the driveline and then the shift will slam it forward again causing the play to be taken back up and the clunk.
Try backing the front band off 1/2 turn and see what it does.
That will give it a second longer for 1st to let go before second applies.

Just a thought.
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D you not mean the 2-3 shift. There is not overlap from 1-2 normally.
 
Adjust the bands and kickdown when you're done.
 
Duane said:
D you not mean the 2-3 shift. There is not overlap from 1-2 normally.
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Yes, I do not mean the 2-3 shift.:D
If first has not quite let go before the second gear band takes hold it can bind for just a second and try to stop the driveline and therefore cause a backlash in the rear end that has play in it causing the clunk on the 1-2 upshift. (not necessarily enough to feel, but enough to jerk the driveline a little)
That was my thinking on it.
 
I think TB has nailed it.
There is nothing in the geartrain that can clunk. It has to be coming from the rear end and telegraphing up the driveshaft.
Before you do anything, tighten up the rear. It may be a crosspin getting ready to launch thru the fuel tank, Or it may just be the pinions are worn out. Sometimes extra washers here and there can tighten those up for another go round. Or it may be even simpler; just bad U-joints.
Then take her for a roadtest.
The clue for me, is that it doesn't clunk when under full power, cuz this tightens everything up.

On another note, I don't think the 2-3 has anything to do with it, cuz when direct comes in, it simultaneously deactivates the band using the same circuit; so all slack is taken up in those two mechanical lines. Except perhaps on a poorly timed lift-shift, as mentioned.
The 1-2 maybe.
The whining is in the planetaries, and is somewhat normal in high-mileage units. I've had some real screamers in 904s,..................................... in winter,lol.It didn't seem to affect the longevity of the trans tho.
 
TrailBeast said:
Yes, I do not mean the 2-3 shift.:D
If first has not quite let go before the second gear band takes hold it can bind for just a second and try to stop the driveline and therefore cause a backlash in the rear end that has play in it causing the clunk on the 1-2 upshift. (not necessarily enough to feel, but enough to jerk the driveline a little)
That was my thinking on it.
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What has to let go to make the 1-2 shift?
I have only taken apart a few 999s but all of them had a badly worn bushing in the 1st gear planetaries that could cause a whining noise.
Just replace a bushing in one a couple weeks ago , it was totally sloppy in there leaving only the planet gears to pilot the assembly.
 
Duane said:
What has to let go to make the 1-2 shift?
I have only taken apart a few 999s but all of them had a badly worn bushing in the 1st gear planetaries that could cause a whining noise.
Just replace a bushing in one a couple weeks ago , it was totally sloppy in there leaving only the planet gears to pilot the assembly.
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The low/rev servo and rear band.
That's why I suggested loosening the front band a little so it gives the rear servo/band more time to release before the front one takes hold.
 
Duane said:
What has to let go to make the 1-2 shift?
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The rear servo has 2 springs. The big outer and the small inner. They work against each other and when the trans is not modified it's not a problem. Mopar designed it to cushion the shift. When someone blocks the accumulator or adds a shift kit that doesn't come with a spacer to replace the inner spring 1-2 overlap can occur. If you notice all aftermarket servo's only use the outer spring and many shift kits (properly designed ones) come with a spacer to replace the inner spring.
 
fishy68 said:
The rear servo has 2 springs. The big outer and the small inner. They work against each other and when the trans is not modified it's not a problem. Mopar designed it to cushion the shift. When someone blocks the accumulator or adds a shift kit that doesn't come with a spacer to replace the inner spring 1-2 overlap can occur. If you notice all aftermarket servo's only use the outer spring and many shift kits (properly designed ones) come with a spacer to replace the inner spring.
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We would only be applying the rear band in manual low.
That's why I said normally. If in drive the rear band would not be on.
Or am I confused. I thought only the roller clutch is used in drive.
 
This is what I was thinking as well. In D 1st gear the rear band is not applied. The low/reverse drum is only held by the sprag. On the 1-2 shift the front band is applied & it is this action that causes the sprag to release & the low/reverse drum is free to turn in a clock wise direction. That is the reason why I asked if the accumulator piston had a blocker rod under it. One of the jobs the accumulator does is cushion the 1-2 shift, as the accumulator piston has to stop moving before full application of the front band is achieved.
 
KickDown said:
This is what I was thinking as well. In D 1st gear the rear band is not applied. The low/reverse drum is only held by the sprag. On the 1-2 shift the front band is applied & it is this action that causes the sprag to release & the low/reverse drum is free to turn in a clock wise direction. That is the reason why I asked if the accumulator piston had a blocker rod under it. One of the jobs the accumulator does is cushion the 1-2 shift, as the accumulator piston has to stop moving before full application of the front band is achieved.
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I totally agree, there is no release of anything to cause a bind up
Or timing issue from 1-2 in normal drive position. Now 2-3 is a different story.
 
Duane said:
I totally agree, there is no release of anything to cause a bind up
Or timing issue from 1-2 in normal drive position. Now 2-3 is a different story.
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That's kind of a trick statement since we know for a fact that 1-2 upshifts in D binds happen.
Technically it can be true, but a shift bind can be one part not releasing soon enough, or another applying too soon.
The later is much simpler and more common to solve the problem.

We could debate it for ten years and 300,000 posts or the OP could take 5 min to loosen the front band 1/2 turn and see what it does. :D
 
Duane said:
We would only be applying the rear band in manual low.
That's why I said normally. If in drive the rear band would not be on.
Or am I confused. I thought only the roller clutch is used in drive.
Click to expand...
You're correct. I was speaking as if the driver starts out in manual low
 
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