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Building a ’39 Ford Transmission with Lincoln-Zephyr Gears

by Dave on April 20, 2015

With few companies manufacturing speed parts, hot rodders in the ‘40’s and ‘50’s used junkyard ingenuity to coax more performance out of their cars. It didn’t take these guys long to discover that the taller ratios offered in the Lincoln-Zephyr gear clusters allowed them to wind out further in first and second gear, a definite advantage both on and off the track. The fact that a 26-tooth LZ cluster dropped right into a ’39 Ford transmission case made this conversion extremely popular.

Taller transmission ratios don’t automatically translate to better performance. Heavier cars with stock motors actually lug down under taller gears, but the kind of stripped-down, hopped-up soup jobs we drive definitely dig ‘em. Francis Bonamy’s ’36 five window falls into this latter category. With its hot flathead he has no trouble getting off the line in a hurry. We built one of our Banjo Pinion Seals for Francis. After it arrived he came back and asked if we could build him a transmission. What made the project especially cool was the fact that Francis lives in France.

The popularity of this conversion wiped out the supply of OEM 26 and even rarer 25 tooth LZ clusters years ago, but reproduction units are now available. We located one at a reputable supplier, and went off to hunt down a ’39 trans to build. Our buddy Brian Eakin had one available and, like all Brian’s stuff, it was in immaculate condition. The thrust washer faces were cherry as was the case and all the components we’d be using. ’39 transmissions come in two flavors: Standard and Deluxe. The Standard uses the old-style synchros and narrow shift fork. The Deluxe uses the later versions. While our new box was in great shape, it was a Standard. To be able to update the synchros, we’d need both a mainshaft and shift fork out of a Deluxe. We’d also need a ’36 style bearing retainer and rear mount so the trans would drop right into Francis’ chassis. Paul Jennings, one of the veteran Ford authorities in our area, came through with the parts.

We disassembled the trans, inspected and cleaned the stuff we’d be saving, then tanked, primered and painted the case, tower and mounts. The old cluster (below) was replaced with the new 26-tooth unit.

The new mainshaft enabled the use of the later synchros:
Here it is, reassembled and coated with assembly lube. We ran into one problem with the new bearings. Although well-manufactured, the rear bearing had a shoulder that was a little more square than the original Ford, which conflicted with our ability to set the end play. We opened the recess for the bearing on the retainer a bit on the lathe and everything fell into spec.

We also rebushed the cross-shaft for the clutch release and installed a new throwout bearing:

All finished. The second photo below shows the ’36-style rear mount. It includes a vulcanized rubber ring to isolate the trans from the chassis.

This will be the transmission’s home for the next couple of weeks. Everything is well-lubed and sealed in plastic – plus we added some big desiccant  packs, those keep-it-dry packages stenciled with “DO NOT EAT” – so the tranny would have a rust-free crossing on its sea cruise to Europe.

From → Past Projects

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