VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1929-1932 1931 Differential Highway gears

I did the Larry Jackson conversion from 4.11 to 3.55 about 5 years ago. Cost was about $1000 with spedo adapter to correct the spedo error. First thing I noticed upon assembly was the the tooth contact on the ring was not uniform. I used bluing dye to verify tooth contact to convince myself I had set lash correctly. I saw that I could only get partial tooth contact while rotating the pinion . It seems that the ring gear teeth on the 4:11 set are narrow at min diameter and wide at max diameter. Not so, on the Jackson 3.55 gear where the tooth width was constant from min to max diameter. I set up the lash at a compromise position and figured I don't make enough power to destroy the gears. I now have over 5000 miles on the gears with no obvious harm done. I have started using Luca Oil Mineral based oil stabilizer which has about an SAE 100+ viscosity rating as a 50-50 blend with the standard 90w140 multi-viscosity diff oil. Some schools of thought feel that the multi-vis differential oils have Sulfur additives which are harmful to yellow metals like brass, which for my '32, is the drive shaft pilot bearing.

Relative to performance: If you have many hills to climb, you may find that you need to downshift. My car won't pull a modest hill in high gear below 30 mph. The car has been chassis dyno'd and indicates about 32 HP on a sweep from 30 to 50 MPH. The car has an annoying drivetrain resonance between 34 and 40 mph which has me cruising in high gear above 40, or below 34. My target for level road is 50 MPH maximum.

OK, Now, all that said, I recently went looking for 3.55 gears for my '34 Plymouths which have a 4.11 ratio in coupes, and 4.37 in sedans. US Gear in Romulus, MI makes gears for hot rods with Ford 9 inch rear axles and other more modern cars, but could not make the spiral bevel gear set found in Plymouths. They directed my to B&R Machine and Gear in Sharon, TN. I sent photos of my spare Plymouth gears. They sent me a quote for $2500 for one set, $2000/set for 5 sets. 16 weeks lead time. I ordered 5 sets, sent them my spare gear set, and a 50% deposit in Feb. 2019. I'm sure most of you will have heart failure about the price, but remember, the Larry Jackson gears were made 10 years ago. Also, the price comes down if there are enough gears ordered to make forgings possible ( Maybe 50 sets ), rather than machining each set from a billet of steel. There are a lot of chips leftover from a billet.

One other item of note is that the Mid 30's Ford V8 suppliers are now selling Ford gears for about $400 - $500 per set. I'll bet we all can guess those gears are made by people across the western pond. Who knows the material and heat treating that goes into those parts?

About a month ago I posted a note that said I had probably the last set of highway gears Larry Jackson made, still wrapped up and in the box that he shipped them in. I will sell them for what I paid for them, $900, plus shipping. I will put a post in the "For Sale" section of this website. If I don't get quick results, I will put an ad in the G&D and also in Hemmings.

I will buy the gears. Have sent you a PM with direct contact information so I can send payment.

I responded to your P M over 3 weeks ago when you offered to sell them to me. I responded saying I would take the gears. Bobl, Check your P M s. for the last 3 weeks. I requested your address so I could send you the funds.

BeachVette,
Just an FYI, when I originally posted this thread, bobl was working with me to buy them. He has however been difficult to communicate with and I have yet not been able to get this deal done.

It would be nice whomever gets the gears if they would work with a gear shop to maybe reproduce a good quality repro of them for others.Figure get a group/lot order going. get an estimate of cost per set, then have people make a deposit to guarantee the maker $$. This way the make also KNOWS how may to make and he will get paid. should not be a hard task with all the modern technology out there. plus the simplicity of the gears themselves.