3rd gear knock cause found (with videos)

[Brentwood Bob]

Can't get the farm out of the kid no matter how far away you go. Wish I had sound on this laptop. Bob

[Tom Endy]

I would like to offer my experience as to what can cause a pinion gear to fail such as seen in the video. The rear spring on a Model A can easily bounce the rear wheels off the ground when you travel at a good clip over railroad tracks or a rutted road (or a speed bump). The few seconds that the wheels are clear of the road will allow the rear wheels to spin up to a greater speed than the car is traveling if you keep your foot on the gas. When the wheels reconnect with the road a tremendous strain is put on the pinion gear and it can easily wipe it out. The moral to the story, take you foot off the gas going over railroad tracks and speed bumps, travel slow on rutted roads.

Another experience I encountered: I did a rear axle assembly rebuild for a local restoration shop. The differential had failed, but there was no information given to me how it had happened. When I got it apart I found a number of teeth knocked off the pinion gear.

When the rebuild was complete the shop owner picked it up and re-installed it in the car. The car has a Volvo overdrive installed. I did not see the overdrive, just the rear axle assembly with a stub shaft installed. Sometime later the shop owner called and said there was a load "clunk" coming out of the rear when shifted from forward to reverse. The shop owner was convinced I had somehow left a half inch of backlash in the differential gears. I went over to his shop and witnessed the "clunk". it sounded for all the world like the clunk was coming out of the back wheels.

I suggested he pull the rear axle assembly out of the car and examine the spline coupler to the overdrive. Sure enough, there was extreme wear to the spline teeth. The overdrive was a product of a cottage industry and the drive line elements were way out of alignment causing the spline coupler to wear. The overdrive was not a product of Mitch & Rich of Bakersfield, CA ,who produce an excellent overdrive, however the overdrive was taken there for repair and returned in excellent conditioned and properly aligned. The large amount of slop worn n the spline coupler was apparently the cause of the pinion gear to fail.

Tom Endy

[Tom Endy]

Originally Posted by Brentwood Bob

A lot can be said for the junior high, and high school shop classes that were then available.
We got exposure to great instruction, and hands on learning. Non-existent for the most part now. Bob

Very true:

I took auto shop all four years in high school. All the shops at my old school are now closed (Mark Keppel High School, Alhambra, CA). My teacher was Mr. White, who was in his early 20's at the time. Mr. White is an old car guy and is pushing 90 now. I see him occasionally at old car events, and even though we are both senior citizens I still address him as Mr. White.

Tom Endy

[Terry,NJ]

Tom, I hate to get "political"but here goes. It seems that the powers that be have condemned individual car ownership and are pushing mass transit.
If you question kids today, they seem to have little or no interest in cars of any age. Some even profess to hate cars. Someone is getting to them, as this is not natural. I have noticed this in my own grandchildren. They are lackluster in response to my offers to take them out for driving lessons. When we were kids, we would have killed to drive Granpa's new truck. kids today are ho hum about driving. Where's this coming from?
Terry

Originally Posted by Tom Endy

Very true:

I took auto shop all four years in high school. All the shops at my old school are now closed (Mark Keppel High School, Alhambra, CA). My teacher was Mr. White, who was in his early 20's at the time. Mr. White is an old car guy and is pushing 90 now. I see him occasionally at old car events, and even though we are both senior citizens I still address him as Mr. White.

Tom Endy