1983 1BBL Carter AOD Question

[Tooling17039]

Like many guys in the hobby I work on the truck when I have time then I test drive the truck and the process starts over. Let me explain what I have going on and hopefully with a little help I can narrow down on a practical place to move forward.

Theres quite a bit of unknowns with the truck I bought it with 160K miles and best I can tell everything is what it rolled out of the plant with. It's seen decent maintenance over the years but all the parts are going on 41 years old.

Now on to what I am noticing. When I'm driving particularly in overdrive around 55mph it's got 3:55 gears so let's say around 1600 RPM I notice the truck has a very notice low pitch constant sound rumble. It's not super loud but it's definitely noticeable. I also feel like there's a reduction in pedal feedback when the truck is rumbling. I wouldn't say it falls on its face but it's not what I would expect. (I have a 91 with a 300 and while that's fuel injected I can't imagine they would be drastically different). I cannot duplicate this in another gear.

Now on to additional observations or facts that may or may not be relevant. As someone who troubleshoots things for a living I recognize there's no such thing as too much information.

When I got the truck the EGR was seized and the previous owner had the timing retarded to 3 degrees. (I checked it a few times, yes it was 3) it didn't appear the manifold was plugged when I inspected it while the EGR was off but I did not remove the manifold and verify.

After I replaced the EGR and went to set the timing I noticed the timing mark dancing around on the flywheel. I believe I'm around 11 degrees advance which is what I found in my service manual. I'm wondering if the Distributor has slop in the bushings but would that manifest in this manner? I have verified the vacuum advance is operational. But I have to admit I have not verified the mechanical advance operation. Could that hanging up react in this manner. My 91 has an electronic distributor so I'm on a learning curve.

Not surprisingly the truck ran much better with more timing but the AOD is still a question. It seems to shift like the descriptions I've read of an AOD. 1st to 2nd fairly crisp, it doesn't hold second long with light pedal input fairly crisp into 3rd in that scenario. If your in it it holds second longer and is softer into 3rd. Same goes for 3rd into 4th fairly noticeable shifting light or no pedal input and softer with more pedal. Downshifting it holds onto gears pretty long, especially 3rd but that sounds like a trait of the AOD. I've never owned an automatic vehicle let alone a 41 year old one so I don't know if I'm experiencing issues with the AOD or not. For many years I drove an 84 with a C6 and 460 that belonged to a place I used to work but I never experienced what I'm seeing here. The AOD is also a learning curve.

I would also like to add the timing light I'm using I bought and used to set my 91s timing and it worked flawless with the timing mark being rock solid.

Last thing I should mention is I've not done anything with the carb since I got the truck. The truck seems a little rich at idle but I'm not sure that it is under load or not. Carburetors are new to me and I'm not the kind of person who just randomly starts adjusting things without knowing what I'm doing. Could a fuel delivery issue react the way I'm seeing? This two is a learning curve.

I like the learning curves but with so many I don't want to be hasty in a reaction. I'm a firm believer of you don't know what you don't know and it doesn't hurt to ask. Hopefully after your done you'll know exactly what's going on.

Sorry for the mini novel but I would greatly appreciate any theorys or advice which avenue to pursue. Maybe I should be looking somewhere different all together thats a ll part of what pulls me into this. Learning is always a lot of fun. Right now I believe I need to lubricate and verify my mechanical advance. Maybe I need to start looking into a new distributor but I'd like some more feedback before I start down that path.

[viven44]

I can only confirm one thing based on my experience.

I also had trouble starting my parts truck with a 460 after it had warmed up. The cranking was real slow. Using the timing gun, I saw that the timing mark was jumping around (10 BTC +/- 10 degrees easily). Replaced the distributor and that fixed it.  No more trouble starting the 460.

By "low pitch constant sound rumble", do you mean the engine is pinging ?

[FuzzFace2]

When you checked / set timing did you remove and plug the vacuum at the dist.
Also what was the idle speed set to?

Because the 300 uses timing gears and not a chain it will not have play in it that can make the timing jump also.

I also have not seen a electronic dist. wear out the upped bushing like the points dist. did as it dose not have the points pushing the shaft to 1 side.
But you can try and move the shaft and see if there is any movement.
Now that I think of it I dont know if there was shaft play if it would change the timing like it did with points?

You may want to check the plate the pick up coil is mounted to to see if it only moves to advance the timing with vacuum.

Last I might try a different DSII box. If you need to buyone buy top of the line one, you get what you pay for.
Dave ----

[mat in tn]

I agree that the description of low rumble seems odd. hearing or hearing and feeling? I'm trying to see in my mind what parts related to the aod could do this. if it were to do with anything "friction" I would expect a slipping gear or two. is the rumble happening differently by vehicle speed alone or does it vary by gear? have you tried running the vehicle in d only?  it is perfectly reasonable to do so. how about the universal joints. you might even look over the exhaust from front to rear. I had one 300 with an exhaust that crossed over the cross member close enough to vibrate against it under a little load yet let off otherwise.

[Tooling17039]

What you describe is about what I was seeing a 20 degree swing jumping randomly all around sounds about right.

Negative on the ping it's a constant low pitch rumble when on the accelerator only around the 55 to 60 MPH range. It's really odd. It does it less loud when you just rest your foot on the pedal in that speed range also. It won't do it at a higher speed nor a lower speed in any gear. If I could record it I would.

I originally thought it was a driveshaft or U-Joints I should have included that but the driveshaft is balanced and it's got brand new field lubricated U-Joints.

[Tooling17039]

Good thought on the exhaust I'll check that tomorrow. The truck will only rumble in OD mainly at 55 but it is less noticeable up to about 60. I feel like the pedal input isn't as noticeable while it's rumbling. It's also an audio sound the truck doesn't shake.

The only reason I'm dubious about the AOD is 55 to 60 is the speed it would have spent a lot of time with highway driving. It doesn't really feel like the trans is slipping but it's the only AOD I ever drove so I may not be picking up on a problem.

[mat in tn]

worse rumble at a near neutral load sounds more like motor mounts oddly enough. possibly a loose trans mount. when under accel or decel loads, the mounts are held one way or the other but near neutral can reveal a broken mount.

[Tooling17039]

I did indeed have the Vacuum advance disconnected and the vacuum line for it plugged when I set the timing. The idle currently hangs around 700ish. I never set it it's at the setting it was at when I got the truck.

Great advice on checking for slop in the distributor aswell as coils mounting. I did put a new cap rotor plugs and wires on the truck right when I bought it. I've put about 1k miles on it I will check to see if there's any abnormal wear on anything.

I'll save the duraspark 2 box for last, from what I hear they either work or they don't and I might be best to let that sleeping dog lie for the time being. I certainly won't rule it out but I'd like to confirm some of the other suggestions brought up first.

[Tooling17039]

Now that is very interesting. That is a great piece of advice. I can say visually they do have minor cracks noticeable.  I will gladly order brand new motor and trans mounts. Does anyone have a manufacturer they prefer for the 300s?

[mat in tn]

it's possible. it's not a diagnosis.  just something to check.  as much as I love these trucks and old cars in general. there is something that we deal with. NOTHING fits like the originals and so many modern replacements come from wherever, some things don't translate fully. just last week another here was dealing with mis fitting engine mounts.

[Tooling17039]

Understood. I just went through motor mounts on my 91 and am in the process of repairing the trans mount brace aswell as replacing the trans mount (weather and time are deciding that progress)

That being said my 91s replacement motor mounts required some modifications to make them work. That was the main reason I asked if there was a preferred manufacturer. I'll start shopping around. Motor mounts were on the list for the 83 so I might as well check that off to rule them out.

[mat in tn]

I have seen varied results even when staying with the same brands. in many cases I find the same import parts sold under many different brands. it's a bit discouraging.

[ratdude747]

Per a review of my 2020 Rockauto purchase history, I installed Anchor 2441 and 2442 mounts when I rebuilt my 300 and they've been great since then. Fit great.

The transmission mount is a Westar EM2448... bought at the same time but for reasons I can't fully remember (couldn't break bolts loose?) I didn't replace it until a lot later. No issues that I can remember either.

[Tooling17039]

Thank you very much for the information. Did you notice anything goofy prior to replacement of the mounts?

[ratdude747]

Old and cracked. Hadn't failed yet (at the time of the engine job) but no sense setting a refreshed engine on worn mounts.