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Suspected 727 problem

Ray70Chrg

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Scottsdale,Az.
I've suspected that the trans had some underlying problems for the last 1 1/2 years that I've had it registered and on the road. During street driving everything worked normally and there was nothing to worry about. the fastest I would go was 45-50, 2000-2250 rpm. When I took to the highway, at 2500rpm, loud noises began to develop and by 3000rpm- 65mph the noise was such I wanted to get off at the next exit. I did this on 2 occasions and decide not to do it anymore and just use it on the street and continue making progress on the rest of the project.
We had our 1st cold snap earlier in the week, temps 38-40 at night. I know you northern guys are laughing. Up to yesterday, the car started normally and went from hi idle to idle as the engine warmed up. However yesterday when it started the engine could hardly keep running and wanted to stall. It had only 5-600rpm, the engine was shaking quite a bit and loud noises from the torque converter area. I was able to keep the engine from stalling by playing with throttle and after about one minute or so this situation began to slowly allow the engine to build up to fast idle and the shaking stopped. As the engine warmed to normal everything was fine. I would shut down and restart and everything is fine. It seemed to me that something was trying to hold the engine from spinning freely when cold and then slowly releasing it's grip as things heated up. The engine would be in hi idle after about 3 minute of this incident and 5-7 minutes before normal temp. was reached. Today exactly the same situation.
I have read something in the forums here that makes me think that the torque converter and /or the fluid pump can produce a temporary condition that resolves itself as everything heats up. I guess what I'm looking for is some confirmation that I'm on the right track here. Thanks
 
Hmm, cool mornings without a choke can be like that anyway. Doesn’t seem too out of the normal. Noise on highway is a bit different, driveshaft ok?
 
Nate, thanks for replying. It has an electric choke and it is working properly. Sometimes it's hard to understand a situation without actually seeing it and being there. I've lived in the northeast for 40 years and had cold morning start problems and this is not that. This is more like a WTF moment.
 
Got it. Been there. It’s difficult to tell where people start sometimes. Art major having problems or 30 year automotive engineer having problems.

Seems like there are two issues, part 1 being the highway thing, part 2 being the cold start thing. Part 1: Does the problem track specifically with RPM or with vehicle speed? Can you hold it in first and get the same problem? Can you hold it in second and get the same problem?

Part 2 sounds more difficult. Kind of assuming the tranny was built properly (no excessive end play or anything). Sounds pretty awful, first thing I’d check is flex plate bolts. Outer ones are easy, inner ones by looking for backlash in the flex plate.
 
Before I answer the part 1 question let me give you some background on where I am in the restoration process. While fixing 5 leaks on the trans I installed a speedometer gear that will be right when I finally get the big wheels and tires I want some time in the future. The speedometer works, but shows me greater speeds than I'm actually doing so I have to use the tachometer to see my speed. I used a online computer to get actual speed/ given rpms.
part 1: @2500 rpm speed was about 55mph and that's when you become aware that more noise was now being generated and by 3000rpm (65mph) I would feel uncomfortable about going any faster or even continuing. I have a 383 magnum engine and if this is the original torque converter then this is the range where the converter stops slipping according to the service manual. (2350-2650). I have the car for 5 years now and have no history of replaced parts or not. When i changed trans filter it looked like a brand new trans on the inside even though the outside certainly did not. I didn't think to try 2500 rpm in 1st and 2nd but that's a good idea.
part 2: In trying to solve multiple noise problems under the hood I did find that the flex plate bolts were ticking against the dust shield down there but the bolts were tight so I reformed the dust shield. This stopped the ticking. I can't drop the trans because I'm not equipped to raise the car high enough to get it out so the inner bolts and the converter spacing is questionable. I truly believe that the trans has a problem and I'm hoping that someone that had this problem gets to read this. Thanks again
 
edit: Nate, after reading part 2 several times I realized I misunderstood your remark about checking the backlash on the flex plate. How is that done?
 
edit: Nate, after reading part 2 several times I realized I misunderstood your remark about checking the backlash on the flex plate. How is that done?
I’m thinking that with the dust plate off you could use a screwdriver to pith the torque converter one way, then the other. If it is tight to the crank it’ll resist motion evenly both ways. If it is loose there will be a tiny bit of free backlash. That of course would mean you need to drop the tranny to have a look and tighten things up.
 
One weird thing to consider may be you have the wrong converter bolts(flex plate to converter). Proper ones have a thin head compared to a standard bolt. For example my race converters have the larger thread bolts for the flex plate to converter. Same thread size as converter to crank. The flex to converter are a thinner head so I have ground the heads thinner to make them fit. I suspect the stock small thread bolts are the same, thinner head than a stock 5/16 bolt. Maybe??
Cold to warm does change many things, no idea where to look for that.
 
One weird thing to consider may be you have the wrong converter bolts(flex plate to converter). Proper ones have a thin head compared to a standard bolt. For example my race converters have the larger thread bolts for the flex plate to converter. Same thread size as converter to crank. The flex to converter are a thinner head so I have ground the heads thinner to make them fit. I suspect the stock small thread bolts are the same, thinner head than a stock 5/16 bolt. Maybe??
Cold to warm does change many things, no idea where to look for that.


I'm with you. There is nothing stated so far that would make me believe there is anything wrong with the torque converter itself.

The idle is simply a mis-adjusted choke.

Take a picture of the torque converter bolts and post. They should be thin heads with no lock washers. The noise created by the bolts hitting stuff will usually come and go based on rpm and load.
 
Went into garage this morning and pushed the throttle once to set the plate. looks good to me. Started engine and same condition as the 2 other previous mornings. But you guys got me thinking it's a tune problem and that got me back to the cam,lifters,chain,springs replacement this spring. All is well with that, however, since the new cam was quite a bit more aggressive I had to set initial timing to 20* btdc and tune from there. I'm running with the vac disconnected from carb, and for 4 months the engine ran great until the cold spell hit. I live in AZ. and the tune was set when it was probably 110*+. I brought the timing to 10* and tuned for best vac & idle. Will have to wait until next morning to see if anything changed. Will fill you in on progress then and thanks for keeping me in the ball park with it being a tune problem.
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There is more to how a properly adjusted choke works than just the choke plate closing.
 
You're right about the choke! When I rebuilt carb about a month ago, I set up the fast idle to the top detent and than adjusted choke spring pressure to get plate located. What I didn't recheck was when I reset the throttle was the fast idle position. I was only watching the choke plate position and what I realize now is that the fast idle cam is only returning to mid position. Tried adjusting spring to its fullest adjustment but no dice. Hunting down new choke, looks like it might be a day or two. Carb is carter, maybe edelbrocks will substitute. I guess when the cold snap hit last week the fast idle position became critical, while before it was close enough to get it started. Thanks again. If I didn't mention before, this is an electric choke. The original choke set-up was long gone when I got the car.
 
Also check the end play on the crankshaft, a worn thrust bearing can allow the converter bolts to contact the back of the block.
 
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