Technical Muncie/quickchange pulsing noise only at cruise

Hi folks! New to the forum. I have a Frankland quick change rear end in my 1932 ford coupe and a Muncie 4 speed. I’m getting a pulsating noise from about 45mph on while maintaining a constant speed and not sure how normal this is for this type of rear end. The sound oddly enough goes away on decel or acceleration and is less around 70mph but gets louder again faster than that. I recently pulled the rear cover to inspect the straight cut spur gears and didn’t see anything abnormal. The gears looked new as did the bearings from what I could tell. Also, best I could tell with a bore scope camera the ring gear looked fine. The input shaft spun freely without play. No play in the pinion shaft either. The driveshaft u joints are new. Wheel bearings front and rear are new. I put 85w140 gear oil in and didn’t seem to really help. At least 7000 miles are on the rear end. In addition to the high pitch whine that directly correlates to speed which I know is normal for these rears, is the pulsing sound at part load also a normal characteristic of the straight cut gears? I’ve been thinking about replacing the spur gears with helical gears or at least a different set of spur gears to see if it makes a difference. There is no sound insulation so the coupe is practically riding along in a tin can. It sounds almost like a pulsing tire noise but wouldn’t think that would be load dependent. Thanks! Edit:…..here is a video link of it..
https://youtube.com/shorts/1g7VeJVLV2U?feature=share

 

I had straight cut gears in my Winters Champ rear end, replaced them with helical gears, massive difference in noise. Now if there was a quick fix for my wife's nagging about my driving.

 

If your Muncie is a M22, I would imagine that, along with the straight cut rear gears, to rattle pretty good at some speed, even with no other problems. If you suspect a problem, might double check the u-joints. Even though new, they could have a problem, something like the cap retainers too tight, squeezing the needle bearings or possibly a needle bearing fell out of the lineup and is now laying flat causing excessive space between the remaining bearings. Might check for proper phasing also. Good luck!

 

I should clarify on the u joints…when I took the rear cover off to inspect the gears I also pulled the driveshaft and put in two new*****er joints… the no name rear joint that was in it had a bit of slop…after I found this I was convinced that this was it…made no difference in noise though. I noticed the spur gears had a little slop on the shafts and a decent about of backlash. I can imagine them dancing around a bit under light load possibly causing this noise in conjunction with the trans…no weird noises from the trans otherwise at idle etc.

 

Possible your U joint angles aren't quite equal on both ends?

 

As said, ALL...straight cut gears WILL...whine. And yes, go away upon deceleration ! The ring gear vs the pinion gears teeth are working on different side of each others teeth ! Perfectly...normal.
Quick change rear axles "normally" have straight cut gears. YES...the rear end will...whine.

If your Muncie is an M22, it has straight cut gears. Another source for howling !

Its actually a "right of passage" to be driving a loud quickchange rear end.
But, if it bothers you, you can put helical cut gears in it to quiet it. But then you need to do it correctly, as the angled cut gears will try to push one of the gears out of the cover, and the other gear out of the case. You'll need proper thrust washers to protect the housing from gear damage.

Don't...whine about it, get used to it !

Mike

 

A "pulsating" noise is usually two different noises at slightly different frequencies, and when they combine they are sometimes "in phase" and other times "out of phase". When they are in phase, the sound is amplified, and when out of phase they tend to cancel each other. The noise you are hearing is likely a "harmonic".

 

It’s a cyclic wah wah wah or like a bad tire would do but is load dependent…accel or decel and it goes away. I’d think if it was a tire it would be mainly speed dependent. The sound in question is in addition to a constant steady gear whine that is clearly the spur gears (supercharger sound). The spur gear whine is of course mainly speed dependent…faster I go, the higher the pitch regardless of load. Anyhow, earplugs don’t really help much with the harmonic wah wah wah sound. Maybe it’s a harmonics thing between the Muncie, driveshaft, and quickchange under light steady load?

 

I’m not sure if the trans is an M22 or not btw.

 

In the olden days some times a drive shaft needed a****e fitting carboard tubr inside the driveshaft for a harmonic wah wah wah sound dampener.

 

There is a reason why QC rears are seldom used on street applications.

 

Cause there’s a lot of wussies out there.

I’d go searching at the ujoint angles first. Then balance the wheels. Then check all the “new “ bearings you said the car had - might not be working as designed. Then balance the driveshaft. Then last worry about the QC.

 

You might consider a video with good sound to help with the problem .
What you consider a pulsating sound might just be a normal sound from a hot rod .
Some of these older cars were just prone to a little mechanical road noise ,,,,,,where as today’s vehicles,,,,,,which most people are used to,,,,,,are whisper quiet .

It might even turn out to be tire noise,,,,,,I’ve had some tires that made crazy sounds until i replaced them with new .
Good luck .

Tommy

 

I have a video…it says it’s not an allowable extension when I try to upload it. I’m new to the forum and not a techie person. I’ve shortened a 10 second video up to 1 second and no luck. Just replaced tires on a daily that were making a crazy wah wah sound above 45 and a heck of a vibration that were just a few years old. New LTX tires and quiet as can be now. Will check the driveshaft angles with an angle finder…didn’t look out of line though.

 

Post the vid on Youtube and link to it.

Chris

 

Ok thanks….let’s try this…..https://youtube.com/shorts/1g7VeJVLV2U?feature=share

 

I don’t hear what you are talking about in that video. The very quick wha-wha’s?

 

Have you tried putting the trans in neutral and coasted to eliminate its input?

 

That noise is really obnoxious !!

 

Yes

 

Yes…it gets alot quieter but still there..likewise if I let off the gas or accelerate

 

Sounds like a bearing to me,,,,in the transmission .
But,,,I’ve been wrong before .

Tommy

 

I took the Chevrolet tech course on driveshaft problems and the rotating shaft made the same pulsating noise when the shaft was out of phase and also when the angles were wrong .

 

If that video is 45mph, the sound is repeating quick enough to be a bad bearing somewhere.

 

You said the rear had 7,000 miles on it. When did the noise start?

The noise gets louder at higher speeds, then quieter at 70 MPH and then increases again above that. Does the frequency of the wha, wha's increase with the speed being driven?

The fact that it makes noise at constant speed and quiets when under acceleration or deceleration tells me that the noise maker is being loaded at its travel limits during acceleration and deceleration and bouncing between them at constant speed. Have you taken someone with you to listen and feel around for an area of vibration? Have you tried to duplicate the noise on a lift and listen and feel for the noise?

Have you tried to gently swerve the car back and forth to see if that changes the noise?

As much noise as that is making, there should be a galled or shiny spot visible when you find it.

 

My biggest suspicion at the moment is the driveshaft and the angles…I’ll i investigate those more and possibly take it in to get the balance verified.

 

Sounds harmonic. Drive shaft out of phase???

 

Well darn I answered your questions but they show up inconspicuously in your quote x-cpe.

 

Vibrations you feel through the seat generally come from drivetrain or rear suspension.
The fact that the frequency increases with speed makes me lean toward drivetrain.

 

That's what I got out of it. Possibly 2 issues? That and an out of phase/drive angle thang going on.