MTFCA Forum

I am getting a noticeably loud growl coming from the rear end of my 24 touring when decelerating quickly or when using engine braking going down a hill. This has come about only recently. I can repeatably reproduce the growling with both rear wheels spinning on jack stands and then revving up and then backing off throttle quickly.

The U-joint, drive shaft and rear axle dope cups are all well greased and the differential
is full to the upper fill hole.

Any suggestions, other than a rear end tear down, are appreciated!

It appears to me as if you may still be using babbitt thrust bearings and that they're about to totally "let go". Or, maybe you have some bad pinion bearing issues. Given your last sentence, I have no suggestions.

Sounds like either a lost Babbitt thrust washer on the left side or the loss/destruction of the pinion bearing & race. The growling is the gear teeth slipping out of mesh. Lift the fear end up on both sides. Check the wheels for in & out movement. There should be very little to none.
Best to pull the wheels, since the brake drum bolts hitting the backing plate or perch nut would be limiting the movement.

"Any suggestions, other than a rear end tear down, are appreciated!"

Wish I could, but I dont see an answer outside of a tear down for what you describe.
If its the babbitt thrust washer only, theoretically the left side housing can be removed for access, however getting BOTH thrust washers changed with the proper gear mesh & clearances would be much more difficult & not worth the extra work. The ring & pinion gears are likely already damaged also.

"Open it up" before you see a wheel and axle fly out and pass you by!

Yup. Something is broken. Time to crack it open.

My guess? Pinion bearing inner sleeve.

Some repair history is in order here. Back in 2017 the rear end exploded due to a split pinion gear caused by disintegrated babbit thrust washers. I had a complete overhaul with new ring & pinion set, new BRONZE thrust washers, new driveshaft, and a new u-joint installed at that time.

There is NO in-out movement at the rear wheels, nice & tight. What could go wrong with those solid repairs after 10 years of use?

I had a rebuilt seize maybe 40 years ago. Inner pinion sleeve shattered. Hence, my guess. There were some bad ones around once.

mngreen wrote: ↑

Sat Aug 30, 2025 5:40 pm

Some repair history is in order here. Back in 2017 the rear end exploded due to a split pinion gear caused by disintegrated babbit thrust washers. I had a complete overhaul with new ring & pinion set, new BRONZE thrust washers, new driveshaft, and a new u-joint installed at that time.

There is NO in-out movement at the rear wheels, nice & tight. What could go wrong with those solid repairs after 10 years of use?

The new info does divert from thrust washers. Pinion gear bearing & inner sleeve still looks like it. Causing the gears to un mesh.
Can happen to some of the modern timkin conversions if a shaft collar moves. If a replacement solid roller bearing was used & the inner sleeve shatters easier than if an original bearing is used.

If the pinion skips on the ring gear you will definitely know it because that produces a loud, ratchet/banging noise and it will sound like it's coming from under the floor boards. I would not describe it as growling.

If the rear end is growling when accelerating, decelerating or going around corners, I believe that is due to wear but not from the pinion skipping over the ring gear.

Just thinking out loud which is neither here nor there.

The correct pinion to ring gear mesh is critical to quiet, smooth operation. If the pinion bearing or the thrust washer begins to fail, the running fit between the ring and pinion gear will change and noise will usually result well before total failure.

While your tearing the differential down replace your parts with this from Snyder’s. https://www.snydersantiqueauto.com/prod ... &cat=41857

mngreen wrote: ↑

Sat Aug 30, 2025 5:40 pm

Some repair history is in order here. Back in 2017 the rear end exploded due to a split pinion gear caused by disintegrated babbit thrust washers. I had a complete overhaul with new ring & pinion set, new BRONZE thrust washers, new driveshaft, and a new u-joint installed at that time.

There is NO in-out movement at the rear wheels, nice & tight. What could go wrong with those solid repairs after 10 years of use?

You didn't mention what, if anything, was done to the pinion bearing. Did it get the solid roller type Hyatt replacement bearing? The Fun Projects pinion bearing? Or???

A new pinion bearing was installed back in 2017. The part number on my service repair order says 2583/87B -- just says "Pinion brg". I don't know which particular bearing type was installed; back then it was priced at $121.

Bore scope thru the grease fill plug. Look @ the gear teeth.

John Karvaly---> I will do a careful look-see through the fill hole at the ring gear teeth and if they look good I intend to keep running it as is. If it matters, the overhaul in 2017 was done by Larry Blair at Tin Shed using new parts from Chaffins.

If the noise is coming from the rear axle, you have a very serious issue. But it could be in the u-joint or some other source in the drive line. I would NOT ignore it, since serious consequences can be expected to result from neglect. Do take a look at all the clamps and bolts related to the running gear and around the u joint housing and be sure the exhaust system or something like a loose motor mount bolt is not the source of the noise.

If the pinion bearing is the Fun Projects kit, the collar that is clamped onto the driveshaft may have slipped a little. That could allow too much driveshaft thrust. Remove the plug under the u-joint and see if you can pry the driveshaft fore-aft.

The appearance of the gear teeth may not indicate a problem. I would not depend on that alone.

Don't assume a good visual = no problem. My ring & pinion 'looked' fine....while ALL my internals were toast.
While I didn't notice any growl in motion, mine clunked (loud, & felt under the floorboard) in reverse. The DS spool bearing was badly worn causing pinion hop...among everything else that could go bad.

But, in generic (any/all, modern & otherwise) axle diagnostics, a noise in deceleration is a classic sign of worn pinion bearing or lash issues.

As for the set collar on modern spool bearing cartridges, after setting bearing pressure and torquing the heck out of the collar set screw, I also hit the collar ring/DS with two small welds 180 off. Easy to grind off if I ever have to go in again, but provided me with extra peace of mind of that collar ever letting loose.

It will only get worse then lock up. Not fun.

mngreen wrote: ↑

Sun Aug 31, 2025 8:13 am

John Karvaly---> I will do a careful look-see through the fill hole at the ring gear teeth and if they look good I intend to keep running it as is. If it matters, the overhaul in 2017 was done by Larry Blair at Tin Shed using new parts from Chaffins.

Larry is still around. Why not call him? He might remember the pinion bearing setup & have some ideas. If the bearing is set with a set screw & welded or not. Fixing it sooner than later will minimize the damage being/been done, if its not already too late.
What you described & a moved bearing collar I have seen before. The point of looking @ the gear teeth is to confirm skipping.
If there is skipping from a moving collar, eventually it will get worse to the point of loosing your motor braking. That could be disastrous. Maybe while trying to hold the car from rolling backwards.
Dont ignore this.

Mark Nunn wrote: ↑

Sun Aug 31, 2025 10:02 am

If the pinion bearing is the Fun Projects kit, the collar that is clamped onto the driveshaft may have slipped a little. That could allow too much driveshaft thrust. Remove the plug under the u-joint and see if you can pry the driveshaft fore-aft.

"Yes" on the possibility of the collar slipping. It happened to a friend of mine. Early instructions for the FP unit advised to leave out the pin connecting the u-joint to the driveshaft, (allowing it to float), and to remove the thrust flange from the torque tube bushing. Doing so takes away the ability of the u-joint to control driveshaft end thrust/play and places all of the load on the collar... which can slip.

As Mark suggested, remove the u-joint access plugs and inspect for excessive end play and/or a missing u-joint pin.

Of course, all of this assumes you have the FP bearing, but at $121.00, I'll bet that you do.

Jerry made a point I was about to make. If the adjustable pinion bearing collar comes loose the driveshaft, and consequently the pinion gear mesh can be affected. This is not the case if time is taken to face the drive shaft bush and also fit the rivet/pin when installing the U joint. This is good insurance against the collar becoming loose. I would not recommend leaving that pin out in any rebuild.

Allan from down under.