I think I remember the owners manuals having recommended speed ranges for the various gears or am I mistaken ?
Short version
I have a customer with a 67 belevedere,
It has a stock smogger era 440, a 4 speed and 3.23 rear end gears with excessive backlash.
the car developed a noise ( which I first noted and made him aware of )
It is a knocking noise that appears to be coming from the transmission area.
The D/shaft has been checked, new u joints etc. It sounded like a cluster gear oscillating back and forth in the case. I pulled the trans and SURPRISE the front thrust washer cluster just flat wasn't there. Back together and all seemed well.

He called a few days later and said the noise was still there. I rode around with him for an hour and he could not reproduce the noise except for one time when he was down to10-15 MPH in 3rd gear. I told him to put it in first and the noise stopped.

I believe the remaining noise is the excess play in the R/E slopping back and forth due to his gear choice EDIT: and resonating up the D/shaft. I forgot to mention this noise appears only in a "NO LOAD" condition, IE: no accel or deccel but in between and at low RPM /Speeds using 2nd or 3rd gear

He seems to think it is OK to putz around at 15-20 MPH in 2nd or 3rd gear. Doing the RPM calculations at those speeds he is barely above idle speed, but I cannot convince him he should be using 1st gear at those speeds.
Any help is greatly appreciated

FYI: at 15mph with 3:23 RE gears
Transmission
Gear / ratio------ RPM w 25”Tire --------RPM w 26"

1st = 2.66:1---------- 1732 -------------------1665
2nd = 1.91:1--------- 1243 -------------------1195
3rd = 1.39:1------------905 ------------------- 870
4th = 1.0:1 ------------ 651 --------------------625

Grabbing at straws here: One other thing I have not verified is the "Phasing" of the U-Joints. The shaft was new a few years back and was done by a shop we normally use. If the phasing was slightly off I do not know if that could cause this issue ? No vibrations at higher speeds
TIA


[color:#CC0000][/color]

I generally drive my 4-spd RRs around between 2000-3000 RPM.
Good throttle response, nice part of the torque curve for a 383.
The Hemi car, I'd run it about 2500-3500, it was quite a bit more rowdy.
Does the car have a tach ?
I generally drive by the tach in everything.

hi

if he insist on driving like that he should install 4.10 gears !

Man, that's way too slow for those gears, does he think it's a diesel? I try to run at 2000 RPM minimum, cept of course starting from a stop. I've heard from people smarter than me that lugging an engine is very bad. It seems he's had at least a couple problems already lugging it around so far That'd be reason enough for me to change driving habits

If the torque demands on the engine are very light, it's not necessarily a problem to have low RPM... "Lugging" to me is a bucking feeling in the drivetrain where the power output is not smooth and the engine is letting you know it's unhappy It's also bad to place a heavy load on the bearings while the RPM is low (and therefore less oil pressure)

My 451 with 272@.050 cam, 4-speed, 3.91 gears, 26.7" tires, idles at 1100-1200... but I can also putt around town on level roads at 1600-1800 rpm without complaints from the drivetrain. I don't stomp the gas while doing that, of course.

I loaf along at 20-25 in 3rd all the time without clunking noises in my 51. 4.10 gears.

Did the same in my 64 300 and it did have 3.23's, yes it was a stick car. Heck,, I'd take off from an almost complete stop in third, three speed stick.

Doubt that is your issue

Ok, what do you think is the issue ?

No saying excessive back lash isn't the problem, but rather that loafing along in third at low road speeds isn't the cause.

Sorry for the confusion. You can test for excessive back lash by putting the rear on jack stands, hold the tire stationary and turn the driveshaft.

No worky

I know, I'm having trouble posting it . I had a previous post bay around May with a video attached but the search is only allowing me to go back to June ??? I can't remember how I posted the video ARRRGGGHHH

got it finally What a PITA, I have had the trans out , replaced a missing cluster gear thrust washer (NICE) and the rest all appeared fine. though i had it whipped with the trust washer The tailshaft bushing & yoke replaced, pinion yoke replaced (worn U joint cups) Driveshaft is fairly new as are ujoints. This is hard to duplicate and can only be heard at low speeds in 2 or 3rd gears. under no load conditions. If I drive the car as i normally drive a 4spd, no problem, no noise. But my driving style is a bit more aggressive (I keep the Rpms up a bit more by using the gears). IE: at 15-20 MPH in this car I'm in 1st gear. So a couple of videos for you to enjoy

thanks for the input so far

Wow, I have never heard that before. Almost sounds like something is hitting something else. I wonder if the pinion is climbing up the ring gear putting the rear u joint into or close to bind?

I would doubt it as it only happens at low speed in 2nd or 3rd with no load. Hit the gas, gone. Drop to 1st gear, gone.

Difficult to reproduce even at those low speeds and higher gears (2nd or 3rd). I thought for sure the missing thrust washer on the cluster was it. I feel it made a substantial difference but if driven the way he drives it the noise occurs from time to time. My guess at this point is the slop in the rear end coupled with the low RPM. Absolutely no noise when I drive it as I normally would.
I have contemplated trying to get him to put a tach in the car and keep the RPM's up a bit more but he says" I've been driving sticks for years" and it's not my driving. I hate to send the guy down the road but it's getting to that point
Anybody else ???

I had a 70 challenger that had a clunk from the exhaust being bent stupidly, hit the crossmember area. Only on bumps though, that one you have sounds like it changes as it spins. Have you checked all the mounts? Don’t see that one you list. Maybe moving things around randomly is hitting someplace.

I had a 68 charger four speed that had a sound something more like this now that I’m thinking back. It had a fubared Dana. Not sure the outcome on that as I traded a car for it and I brought the spare Dana I had and we swapped it out. He rebuilt that rear and stuck in the car I traded him.

Mounts have been checked as have the obvious clearances you mention. I'm beginning to wonder if the low rpm / gear choice is resulting in the motor "lugging" but is not being felt due to the excess play in the rear end + the normal play in a manual trans.

What I'm tryin to say is the lugging is being masked by the excess play and creating the noise as the gears (primarily rear end) slop back and forth against each other. That noise is then being transmitted up the hollow driveshaft to the rear of the trans.

Dunno, but it's a head scratcher Any other input is welcomed

What'd you figure out?

I haven't gotten back to it as I have had other priorities and the car is drivable. I still believe it's a combination of slop in the rear end and the owners driving habit's. Hope to get to it by spring. I am down to just myself doing the work and am semi retiring. I am flipping done tryin to finish raising other peoples children (employees)