Low-speed "clunk" 1-2 shift, A-904

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MopaR&D

MopaR&D

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When my '70 Duster (318/904) was running, I would always have to drive funny at slow speeds (parking lots, etc.) because if I was accelerating really slowly (NOT when accelerating at a more brisk pace), the transmission would make a "clunk" when shifting from 1st to 2nd. Browsing through my FSM I saw the term "low/reverse band adjustment" and "kickdown band adjustment" and purely by the names of those parts I figured they might help me out. When I pulled the pan to replace the filter and fluid (BTW there were a couple tiny pieces of metal, smaller than fingernail size) I adjusted the low/reverse band just because I was under there and figured I might as well, but I haven't got a chance to adjust the kickdown band (and the low/reverse adjustment did almost nothing). Now that the engine is out of the car I figured I could pull the transmission to finally fix that damn fluid leak and adjust the kickdown band. Is this related to the "clunk"? Also, I have barely an inkling of how these (or any auto trans) work, so what exactly do these two "bands" do?
 
MOPEkidD-3 said:
When my '70 Duster (318/904) was running, I would always have to drive funny at slow speeds (parking lots, etc.) because if I was accelerating really slowly (NOT when accelerating at a more brisk pace), the transmission would make a "clunk" when shifting from 1st to 2nd. Browsing through my FSM I saw the term "low/reverse band adjustment" and "kickdown band adjustment" and purely by the names of those parts I figured they might help me out. When I pulled the pan to replace the filter and fluid (BTW there were a couple tiny pieces of metal, smaller than fingernail size) I adjusted the low/reverse band just because I was under there and figured I might as well, but I haven't got a chance to adjust the kickdown band (and the low/reverse adjustment did almost nothing). Now that the engine is out of the car I figured I could pull the transmission to finally fix that damn fluid leak and adjust the kickdown band. Is this related to the "clunk"? Also, I have barely an inkling of how these (or any auto trans) work, so what exactly do these two "bands" do?
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The 1-2 shift is made by the front band ( kick down) grabbing the front drum and stopping it from rotating if the transmission is shifting automaticly , the only thing INSIDE the trans that would make a clunk during that shift is the front drum being VERY loose in the sunshell OR the front planet being very loose on the sun gear or it's splines on the mainshaft .

The low reverse band is only applied if you shift the transmission into low or reverse so it not making a difference is not a surprise because it's not applied anyway .

check your u joints and the backlash in the rear end .
 
Something I also forgot to mention is that the car will shudder noticeably when backing up slowly (but not quickly). How do I check the u-joints and rear end backlash? It's the stock 7-1/4" rear end.
 
The trans operates via two clutches and two bands and an overrunning clutch. In D or L1, the rear clutch is applied. In L1, it is helped by the rear band. When the trans shifts to D(2nd) or L2, the front band is applied, holding the front drum. When shifting to D(3rd), the front clutch is applied, causing the front drum to spin. Simaltaneously, the band is forced to release. This means that pressure is holding the band applied, but a larger pressure is holding it released. The net effect is a faster "kickdown", producing the "snap" that you need when passing.

In reverse, the rear band and front clutch are applied, causing the output shaft to counter rotate.

All of this is accomplished using planetary gear sets. This allows the trans to have the gear ratios meshed at all times, so no "missed" shifts.
 
The backlash can be checked by opening the diff housing, and using a dial indicator to measure the slight amount of freeplay in the gear teeth. However, if you plan on any sort of power enhancements, plan to swap the rear to a 8 1/4".

U joints should have no slop in them at all.
 
I doubt that's the problem anyway. Wouldn't I also notice it when taking off quickly from a stop, or changing speeds at all?
 
I have heard the clunk you are talking about in a lot of mopars I've owned. And never really been able to clear it up, but have also never had anything fail in a car that I could blame that on. I had one one time that got on my nerves so bad that I would shift it manualy to keep this from happening. I think that mine were just high mile rears that had to much slop in the diff. as mentioned by someone else in this thread. Another way to get an idea if you have a lot of slop in the rear end is to take the drive shaft loose and just move the yoke back and forth to see how much play you have back and forth. Man My 8th grade would really jump on me about that run on sentence. LOL
 
Max340 said:
The trans operates via two clutches and two bands and an overrunning clutch. In D or L1, the rear clutch is applied. In L1, it is helped by the rear band. When the trans shifts to D(2nd) or L2, the front band is applied, holding the front drum. When shifting to D(3rd), the front clutch is applied, causing the front drum to spin. Simaltaneously, the band is forced to release. This means that pressure is holding the band applied, but a larger pressure is holding it released. The net effect is a faster "kickdown", producing the "snap" that you need when passing.

In reverse, the rear band and front clutch are applied, causing the output shaft to counter rotate.

All of this is accomplished using planetary gear sets. This allows the trans to have the gear ratios meshed at all times, so no "missed" shifts.
Click to expand...

Just to clarify the NORMAL position of the front band is RELEASED , the front servo is SPRING LOADED in the released position, it uses Fluid PRESSURE to APPLY the band , on the 2-3 shift the pressure is removed from the apply port and the spring in the apply servo releases the band naturally , it's not held open by fluid pressure .
 
MOPEkidD-3 said:
Something I also forgot to mention is that the car will shudder noticeably when backing up slowly (but not quickly). How do I check the u-joints and rear end backlash? It's the stock 7-1/4" rear end.
Click to expand...

the shudder could be the front clutch or the rear band slipping .

to check the backlash grab the driveshaft with the trans in neutral , apply the emergency brake and block a tire if the rear is on the ground and see how much playt there is and what is moving . the 78 lebaron I had made alot of noise when putting it in gear , higher fluid pressure and a stack up of clearance makes it loud when going in gear either reverse or forward ..
 
JohnRR said:
Just to clarify the NORMAL position of the front band is RELEASED , the front servo is SPRING LOADED in the released position, it uses Fluid PRESSURE to APPLY the band , on the 2-3 shift the pressure is removed from the apply port and the spring in the apply servo releases the band naturally , it's not held open by fluid pressure .
Click to expand...

That is incorrect. I'm sorry to say it that way, but there is no way around it. It is true that the servo is spring loaded in the released position. However, while in second and third gears, it is moved by hydraulic pressure. Second gear applies it, third gear uses pressure to counteract the apply pressure. This allows full pressure for apply to be already in place if a "kickdown" event occurs.
 
OK, all this talk is great, but most of it is just flying over my head. Does anyone know where I can find an article that explains the basic workings of a Torqueflite automatic transmission?

Just to give some more details, it acts fine when putting into gear and never misses a shift or slips. The shifts are also pretty firm and quick at WOT. The only issue I have with this transmission is that when accelerating slowly and then gradually letting off the gas(forgot to add that part), for example when driving through a full parking lot with a stop at the end, it will most of the time "clunk" into second gear as I start to coast. If I am accelerating at a constant rate, no matter how slowly, it usually won't "clunk" like that.
 
If its clunking as you coast or let off, its probably just the "nature of the beast". If you have the Factory Service Manual, it has more detail on how the 727 works than you'll want. But it also has drawings and theory, so you'll get a better understanding of how it does certain things, like kickdown.
 
Max340 said:
That is incorrect. I'm sorry to say it that way, but there is no way around it. It is true that the servo is spring loaded in the released position. However, while in second and third gears, it is moved by hydraulic pressure. Second gear applies it, third gear uses pressure to counteract the apply pressure. This allows full pressure for apply to be already in place if a "kickdown" event occurs.
Click to expand...

Now I have to look at the HYD. diagram as I don't see the need to pressure the release unless it's releasing too slow when the pressure gets removed ???.

As far as being SORRY for saying I'm incorrect , I would have just said WRONG not giving a rats arse if I hurt someones TENDER feelings :bootysha:
 
MOPEkidD-3 said:
OK, all this talk is great, but most of it is just flying over my head. Does anyone know where I can find an article that explains the basic workings of a Torqueflite automatic transmission?

Just to give some more details, it acts fine when putting into gear and never misses a shift or slips. The shifts are also pretty firm and quick at WOT. The only issue I have with this transmission is that when accelerating slowly and then gradually letting off the gas(forgot to add that part), for example when driving through a full parking lot with a stop at the end, it will most of the time "clunk" into second gear as I start to coast. If I am accelerating at a constant rate, no matter how slowly, it usually won't "clunk" like that.
Click to expand...

u joints or rear ...
 
All right then, I'll have to check those out some time. If it is one of those, how urgent would it be for me to fix it? Will it be just another excuse to upgrade yet another part (rear end)? BTW how much would an 8-1/4" cost?

I'll also adjust the kickdown band just to be on the safe side.
 
JohnRR said:
Now I have to look at the HYD. diagram as I don't see the need to pressure the release unless it's releasing too slow when the pressure gets removed ???.

As far as being SORRY for saying I'm incorrect , I would have just said WRONG not giving a rats arse if I hurt someones TENDER feelings :bootysha:
Click to expand...

The reason they use pressure to release the band is so the apply pressure stays present for a quicker kickdown.
 
Just exactly how much smaller than your fingernail? Nothing should be larger than a grain of sand in there.
 
Like, maybe 2-3 mm. long and 1 mm. wide. I saw only a couple too, maybe three or four.
 
MOPEkidD-3 said:
OK, all this talk is great, but most of it is just flying over my head. Does anyone know where I can find an article that explains the basic workings of a Torqueflite automatic transmission?

Just to give some more details, it acts fine when putting into gear and never misses a shift or slips. The shifts are also pretty firm and quick at WOT. The only issue I have with this transmission is that when accelerating slowly and then gradually letting off the gas(forgot to add that part), for example when driving through a full parking lot with a stop at the end, it will most of the time "clunk" into second gear as I start to coast. If I am accelerating at a constant rate, no matter how slowly, it usually won't "clunk" like that.
Click to expand...

Ahhh, I see... the "lift-throttle upshift". You're completely off the throttle when it happens. My /6 904 did that and it lasted forever. I ended up pulling the motor & trans before it ever broke. I wouldn't worry about it too much. You can do something about it when the transmission dies. If you find it a little embarrasing then just drop the car in 1st gear in parking lots.
 
autopar3000 said:
Ahhh, I see... the "lift-throttle upshift". You're completely off the throttle when it happens. My /6 904 did that and it lasted forever. I ended up pulling the motor & trans before it ever broke. I wouldn't worry about it too much. You can do something about it when the transmission dies. If you find it a little embarrasing then just drop the car in 1st gear in parking lots.
Click to expand...

Yeah, that's exactly what happens. I did usually keep it in first just so it wouldn't clunk and there was no use in having it upshift anyway.
 
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