518 Screech in neutral

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midnight340

midnight340

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Yesterday while running around town, when I put my 518 in neutral it (or converter?) responded with a very loud screech. (I had a similar quite disturbing sound once in the past, but it turned out the flex plate bolts were rubbing on my dust cover, removed it and left it off.) I pulled off to a parking lot and it still did this anytime in neutral. I got out to check the fluid, then realized I didn't want to sit there with it screeching like that if I put it in neutral. I had about 1/4 qt. of fluid with me, added that to see if it helped. Never made the sound again! Came home to other things going on, later when fairly cooled down, I started it, put it in neutral and checked and it read right at the full mark. (I don't know what else would have made the "neutral specific" noise?)
Any ideas???
(340 with a Cope Racing Transmissions build, 11" converter from PTC 2600 stall.)
 
IDK:
mustabin the low-oil warning system.......... Somebody had to say it, lol. Seriously IDK.

In neutral, there are only two regulator valves operational;
1) the main regulator, which reduces the line pressure down from whatever the pump is generating, down to about 55psi. and
2) the convertor charge valve, which takes the 55 down to something like 30psi at idle. All other circuits are shut off by the properly centered manual valve.

So then, the only one of those that you can change is/are
1) the manual valve, and only if it is not detenting properly. and
2) by varying the amount of air entering the pump, due to a low oil level, the bulk of which, will be going to the manual valve, and returning to the main regulator control valve; it can be seen that the regulator will be jumping back and forth from it's set point of perhaps 55psi, down in the direction of zero psi.
and this means that the convertor is seeing that change. Now, the convertor is designed to run at about 55% of that pressure, and so when it is jumping from 30 to zero and back IDK what that would sound like; but this I know;
Of that same convertor charge pressure, some of the fluid flow is redirected to the front clutch lubrication circuit. Which if you check it out, includes the entire lube circuit. and if it is alternating between being; oil, or air, or some mix of oil/air, yeah, I can see a screech happening there, lol.

So if it was mine,
the first thing I would do is:
check the oil in the proper specified way, which is;
1) in neutral
2) on level ground
3) with the oil warmed up
4) and that the oil is NOT foamy NOR burned
After that;

II) check the dipstick calibration; starting with;
is it the right stick, and matching tube? and
is the stopper at the top, properly located?
and; the liquid level in the trans, if you remove the tube, should be visible in the bottom of the hole and NOT running over the top, with the engine running, the trans in NEUTRAL, and the oil at "warmed up", being around 200*F. Y

III) and after that is to verify that the pump is sucking pure oil from the bottom of the pan. Which means that, if you have a deep pan, that you also have the extension installed, and that it is bolted on with gaskets, and "tight".

IV) of course if the pan is all scrunched up from hitting something, all bets are off.

If those are all 100%, then If it happens again, I'd be dropping the pan, looking for metal. It's one thing if the screeching is caused by air in the circuits, but another all-together, if it is caused by metal rubbing on metal. What is found/not found, in the pan would govern my next move.

Oh Yeah, I forgot
If you shift from Neutral to Park, the Manual valve dumps the line pressure which then falls to around 5psi, and the convertor runs as a function of line pressure, so it dumps to the same. You can use this information, maybe, to help in diagnoses.

Sorry man; I'm no auto-trans expert, so I'm just guessing here.
 
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Thanks AJ, good info, and as often, a bit beyond my knowledge, but thanks for the logical assessment.
I am now recalling (best of my memory..) that I may have briefly heard something similar coming down from OD/lock-up cruise to near stop and switching (toggles) out of OD/lock-up when I forgot to do it earlier. So maybe something in the OD/lock-up system was complaining???

At any rate, I will start checking things when I can get back to it. Younger members of my extended family seem to have plans around, St. Patty's!
 
Well yeah if you come to a stop with the lock-up still manually engaged, that clutch is gonna have to complain about it, and screeching would be the logical mode of complaint, as it was never designed to be powerful enough to stall the engine...........
 
Yeah, I've never done that one again!!! I'm running 4:11's and mostly drive around town, or runs on back country roads, only use the overdrive when on road trips on the highways. But what a blessing that is when I'm on the Interstate, to be able to drop the revs to 2700-2800 or so!
(Maybe it would be smart to double check the wiring for the lock-up switch...? But I hadn't been using the OD/lock-up, and since the screech only happened in neutral the lock-up clutch wouldn't be in the picture anyway, would it?)
 
AFAIK;
If your lock-up is coupled by an electrical switch, then it can only be decoupled by the same switch.
But
I do not have the hydraulic circuit map to prove it. But
It's easy enough to prove.

Just get the rear wheels up off the ground, get her up to 30/35 mph in Drive, and hit the lockup. Then let the engine return to idle, still in gear, and still in loc-up.
Obviously, still in drive and loc-up, the tires will continue to be powered up.
Next, stuff it into neutral, but leave the loc-up engaged, then see what happens.
If the loc-up decouples on it's own hydraulically, then the wheels will slow down, and you can stop them with the brakes.
But if the loc-up doesn't decouple and you try to stop the wheels with the brakes, something has to slip, and you can bet the convertor loc-up clutch is the weakest member
Listen for the screech, telling you the clutch is not happy! lol.

The wildcard here is the Forward clutch. If it is packed up it will cause trouble. Put the trans in reverse, and make sure the Loc-up is decoupled. This will be like putting it in two gears at once. it will take excessive throttle to turn the tires backwards.

Selecting reverse simultaneously activates the Hi drum and the L/R band. and everything in the trans spins easy in reverse. But if simultaneously the Forward clutch is dragging, the whole thing is likely to loc-up, depending on how bad the Forward clutch is bound up.
In any forward gear, the Forward clutch is activated, and if it holds, you might never know it is packed-up.
In neutral, all gears are uncoupled, so again, a packed-up Forward clutch is not discovered, except for the slight extra load on the crank.
A packed up forward clutch, is probably the number one cause of a burned up transmission. I am in no way suggesting that yours is packed up. At this point this information is only to be used to help diagnose the loc-up. Here's how;
With the engine running, put it in reverse and hold her there with the brakes. If the Forward clutch is packed up, then the guts of it are now locked up. Release the brakes, and if the car moves normally, then the F-clutch is off. That's a good thing.
Next, at idle, with the car still moving in reverse, engage the lock-up. If the loc-up engages then your trans is now operating like a manual trans. So if you step on the brakes, the engine will want to stall. To stop the car, something has to slip. Either the brakes will give up, or the engine will stall, or the loc-up clutch will slip. If the trans screeches, then you can know that the loc-up is complaining. release it ASAP!. lol.

I think that's how it will work, butum, I'm no auto-trans mechanic.
I can rebuild them, and I can install shift kits, and I know the A904 well enough to have reprogrammed one real nice, but that's all.
 
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Thanks again, AJ, that gives me some things to work with. I've sorta regretted not building the trans myself, as I've done everything else (engine, carb, headers, wiring, suspension, etc.) from front to rear myself. The trans the only thing I didn't, so that remains somewhat of a mystery. But when I check it out, I'll report back.
 
AJ/FormS said:
The wildcard here is the Forward clutch. If it is packed up it will cause trouble.

In any forward gear, the Forward clutch is activated, and if it holds, you might never know it is packed -up.

A packed up forward clutch, is probably the number one cause of a burned up transmission.
If the Forward clutch is packed up, then the guts of it are now locked up.
Click to expand...

What do you mean by "packed -up"?
I've overhauled a handful of transmissions over the years and never heard of that.
I have a 46re going back together right now that ate it's forward clutch. For those not familiar the "forward" clutch isn't the most forward clutch within the trans by position. It's actually the rear clutch, by position within the trans case.
The failure on mine was a quite sudden failure. It was fine, no sign of problem, it had sat a week or so while I had the dash out for a heater core and evaporator replacement, and the first time I drove it afterwards we went to the store, then stopped for gas. Upon leaving the gas station it started shuddering upon takeoff out of the blue. If I could baby it into 3rd or 4th/OD it pulled like expected. I probably put another 50 miles on it with scanner connected over 3-4 different drives before I pulled it (I was looking at the electronics/solenoids for the problem to start with)
My original gut - guess was that the sprag in the back of the case went out. I wasn't expecting to find the forward clutch fried. I had to hammer/pry it apart from the hi/reverse, and the plastic spacer between the snap ring and the Belleville spring was a melted glob.when i got to it, the sprag did fall apart as I pulled the gear train behind the clutch packs out. It's getting a new one of those too, I didn't even try to put the original one back together. Just swept it up and tossed it in the trash. I'm wondering if something stuck in the valve body as suddenly as this thing ate itself, I haven't gotten to pull that apart yet.
 
Packed up is when all the friction material of a certain clutch-pack, goes into the oilpan, and the resulting all steels, weld together in a "pack". Thus the clutch is no longer a clutch at all, but a "direct-drive".
I have also seen this happen when a builder drops the front stack into the case, and fails to engage the last clutch. So then when the pump is installed, it bends and traps that clutch, and the piston cannot compress the remaining stack adequately, and so it starts out slipping dragging from day one.

I am not a transmission guy, but I'm sortof known as the guy who figures stuff out. It's a talent I was born with. This God-given gift has always paid well. Now, in retirement, it looks like a few people still remember that, and bring me strange stuff to look at.
But I don't do electronics. I did not get that gift; just mechanical.
 
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AJ, you certainly have a knack for thinking things through! Many have benefitted here. Took some time tonight to see what I could find out. All seemed normal driving around the neighborhood. What I did find is that my switches only activate the OD and lock-up when in drive, and have no effect at all in low/2nd. But they work perfectly in drive, other than the fact that there is llttle to no seeming resistance to coming to a stop. Though I only checked that momentarily.

I'll give John Cope a call as he will likely be able to tell me what caused the screeching in neutral for that brief few times. (I saw on his web site Coperacingtrans.com that he is no longer building transmissions, focusing instead on parts/kits, etc.) Other than this little episode I've been very happy with this transmission.
 
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