Pinion gear dinged a bit: reuse or replace?

O

oldmotorsguy

Senior Member
My 1919 Touring was starting to get loud in the rear end, and I put it up on jackstands, fired it up and BANG! Loud noise, and the rear wheels stopped turning. Oh crap.

Never having been inside the rear end of a Model T before, I feared the worst. Took it out, put it up on saw horses, split the differential housing and saw the pinion gear, castle nut and Woodruff key laying in the bottom relatively intact. No metal shavings, or evidence of a cotter pin.

The nut just came off. Plain and simple. When the nut finally fell off the last thread of the drive shaft, the pinion gear must have spun off with some velocity, hit the side of the housing and it left a little gouge in the key way on the gear, a tiny ding on the inside of the housing, and that's it, and the nut took a bit of a beating but it appears OK as well. Otherwise, everything looks and works fine inside the housing. I was expecting to find piles of shavings, broken teeth, and God knows whatelse. Nope. Everything looks good.

Here is my question for you guys: Although the ding in the pinion gear keyway can be smoothed out, it may allow for some minor movement of the key once I have bolted it back onto the shaft, OR NOT, I don't really know. DO I BUFF OUT THE DING AND REUSE THE GEAR, OR DO I REPLACE IT WITH A NEW GEAR?

Replacement costs are around $180 or so, for the gear, nut, key and gasket kit.

Reusing the gear, just a $3 gasket kit.

Sure, it's easy for some to say, just replace it while you have it apart. Others will chime in 'better be safe than sorry, replace everything, including the ring gear, pinion gear, left and right housing, differntial spider, etc, while you have it apart.

I say if it ain't broke, don't fix it.

What do you guys say?
 
If this were the mtfca, they'd tell you to replace EVERYTHING, down to the bolts that hold the ring gear on the carrier. Keep it in perspective; its a 20 hp car that goes 35 mph.
Honestly? Theres a few things to do while youre in there tho. Change out the babbit for bronze thrust washers, install inner oil seals by the outer axle bearings, and really consider using a FunProjects rear drive shaft bearing, Also get Chaffins' orange differential book.
Re-use the gear... that is if it REALLY passes a close inspection. They can crank and barely be noticeable. Used gears are pretty affordable and way beter on the quality than new chinaman stuff. IMHO... ws


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The funprojects bearing kit eliminates half of this stuff. Notice the busted pinion bearing... The other end has a bushing by the U joint thats probably gone as well...
 
You need to inspect the drive shaft pinion key way, if it's worn with a new key fitted then I would replace with a better one. What condition is the drive shaft sleeve in? Inspect for cracks in the notch area. Is it tight on the shaft (it's a press fit)? If it's not, find a better drive shaft. What condition is the roller bearing in? If it is loose but good shape you might re-stake the pins or get a new one.
I am in the process of doing a Ruckstell right now. The customer wanted me to check it out. I had to give him the good news, his wife and him weren't killed while driving the car. The pinion bearing sleeve was in chunks in the bottom of the case and that end of the drive shaft was bouncing around in the space no longer filled with the sleeve. The ring gear was not pretty ether! If You do not have the rear end rebuild book, GET IT!
 
Red: As I mentioned above, everything looks good, no wear or slop anywhere that I can see. It appears as though this rear end has either had an easy life, or has been rebuilt at some point in the past and little mileage has been put on it since. I suspect the latter, and the mechanic forgot to replace the cotter pin on the pinion gear nut.

And yes, Yachtsman, I am expecting to hear from lots of MTFCA members who would have me replace the entire rear axle/differential assembly, and while I have it apart, also replace the rear spring, spring hangars, all brake shoes, cam, springs, nuts, bolts, washers, gaskets, fenders, doors, seats,front end, tires and rims, wheel bearings, engine, frame, and replace all with new or OEM parts, never used.

One can't be too careful, right?
 
Yachtsman: after looking at the photo of your damaged pinion gear, I looked over my part a bit more closely. Sure enough, I saw a tiny crack on one of the teeth.

Not as long as the crack on yours, but a crack nonetheless.

Looks like this thread is over: new info necessitates replacing the gear. I have a Model T parts guy in Loves Park, IL, about 40 miles away, who has buckets of original used pinion gears.

I appreciate the info, Bill. As they say, a picture is worth a thousand words.
 
No problem... Bob will take care of you! Discuss the funprojects package with him too. John Regan (FP) will sell direct too. That kit greatly simplifies the whole job! You forgot the radiator cap gasket from the mtfca guys btw! ws
 
Went to Loves Park IL today, Bob B. sold me a new gear, made in USA, $150.00. I should be back on the road this afternoon, if I don't malinger and loaf around too long on other distractions.
 
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