VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1912-1928 Overdrive Installers

Does anybody know of a shop near central Iowa who would be able to install a Laycock Type J style overdrive (out of an old Volvo) on a '26 chevy torque tube? I have the overdrive, cleaned it up, replaced the seals, etc. however, I'd prefer to have somebody with more experience than I to actually cut the torque tube, propeller shaft and weld on flanges, shaft couplers, etc. however, I am having trouble finding anybody willing to do it.

If you have any suggestions, please let me know!

-Tyler

Well, it's looking like I will be tackling this myself. My plan is cut the torque tube positioning the overdrive so the front flange is just under the back of the cab, this looks like the best spot from a clearance perspective and should allow full suspension travel without interference. It will require me to make new service and parking brake shafts so I can route them away from the new overdrive but this shouldn't be a problem.

The thing I'm most concerned with is coupling the cut shafts to the overdrive and keeping them good and straight. My plan is to machine steel sleeves with a tight slip fit, ~0.004" diametric clearance to the propeller shaft and the input shaft to the overdrive and braze the shaft/sleeve assembly once I get the shaft lengths correct. Based on my equipment and my skill set, this is likely going to give me the best chance of success. The input shaft into the overdrive is hardened, my guess is SAE4340 or similar steel so I feel more comfortable with brazing vs. welding. I don't have a tig or a mig welder, I typically weld with OA and I don't trust myself welding a hardened shaft with OA and keeping it from cracking or warping.

I probably won't start on this until winter but I'll let you know how it goes. If I'm totally nuts and this is the worst idea you've ever heard, feel free to let me know :)


-Tyler

Sounds like a cool project!
Please post pictures as you progress with this. It's an interesting project. I'd like to see more details on this overdrive unit.
You could always tack it and then have a shop do some of the specialized welding.

Here's an old thread that I think you'll find interesting: https://vccachat.org/ubbthreads.php...missions-for-1928-capitol-lp-4speed.html

I found it by using the Search Function with +install +overdrive search criteria in the 1912-1928 forum.

Being able to use the Search Function is one of the MANY benefits of being a VCCA member. ;-)

Cheers, Dean

Thanks Dean for that info. I had found Herbs site while researching installing one myself. Herb had a lifetime of research and info about various Chevrolet overdrives. Shortly after this he passed away. Since he was no longer paying for his server memory it was quickly purged. I contacted the server company and was told that they could not access it once it was gone. This is a classic example of backing up the info onto a permanent library. It was a shame his life work was thrown into the proverbial electronic trash so quickly, never to be seen again. Art

Art, thanks for the update, even though it is very sad.

A lesson learned for all of us.

Regards, Dean

Herb's old website has been captured and archived by Wayback Machine.

The webpage index can be seen here: https://web.archive.org/web/20030221050909/http://www.cybersurfers.net/~herb/

See the original post link here: https://web.archive.org/web/20030320172132/http://www.cybersurfers.net/~herb/overdrive.htm

More here: https://web.archive.org/web/20020605205341/http://www.cybersurfers.net/~herb/johnsn.htm

Some images are broken, but the text is there.

I tried that link. It wouldn't let me copy and paste so I typed it in both ways with the o in johnson, and without as shown. Neither worked for me, maybe it will for someone else. Art

I just tested all three links and they work. Try copy and past again.


https://web.archive.org/web/20030221050909/http://www.cybersurfers.net/~herb/

https://web.archive.org/web/20030320172132/http://www.cybersurfers.net/~herb/overdrive.htm

https://web.archive.org/web/20020605205341/http://www.cybersurfers.net/~herb/johnsn.htm

I am not familiar with the mechanics of the Volvo overdrive. One characteristic of some overdrives is that they are freewheeling in at least one of the two gears. This means that there will be no engine braking available to slow the car.

This creates more load on the brakes. In modern cars that is not as much of an issue. Older cars with mechanical brakes like yours require some more caution, especially if the overdrive allows you to drive at higher speeds.

Some overdrives may be freewheeling but the Laycock J-type is not one of them.

Wanted to give an update on this, I finally got the overdrive installed and working on my truck:



All and all, installation went went, after determining placement on the torque tube, I had flanges laser cut at a local sheet metal shop, cut the tube, cut the propeller shaft, had coupling sleeves machined, welded the flanges, brazed the coupling sleeves to the shafts, flame straightened the shafts within 0.002" TIR and crossed my fingers.

The first drive was a little disappointing, no bad noises or vibrations but the overdrive would not engage. I pulled apart the dashpot/relief valve assembly and found a seal that appeared to be the problem. After putting everything back together, the overdrive works great. I had the truck up to 46 MPH which is plenty fast with rear band brakes. Once the weather warms back up I'm excited to see what she'll do on a longer drive, I'm hoping to be able to cruise at ~40 MPH.

That looks great. Not really that big either. Very interesting project!

That looks a great piece of work, really impressive.

When these OD's were fitted as original equipment they would have had a mechanically operated switch on the transmission to ensure that you couldn't get reverse gear when the overdrive was operated (for anyone not familiar with Laycock OD's, reversing the input motion in overdrive mode wrecks the OD) did you fit anything like this?

IIRC, on the Volvo, the OD would only engage when the transmission was in top gear.

Hi Stuart,

I have not installed an interlock switch to lock out the overdrive when if reverse, yet. The hydraulic pressure does not get high enough to kick in the overdrive until the input shaft (into the overdrive) is spinning ~1,500 RPM. The max input shaft RPM in reverse is ~400 so I'm not sure if this switch is needed though it certainly would not hurt.

I have not had a lot of drive time with it yet but the overdrive will engage in 4th gear in the low-mid 20 MPH range. In 3rd gear, I tried to get the overdrive to kick in but it seemed to be right on the edge and didn't quite make it, if I really pushed the RPMs I might be able to get it to go but it's marginal. In 4th gear with overdrive engaged, I was able to downshift to 3rd gear and keep overdrive engaged, I'm curious if it would stay engaged indefinitely or if the pressure would drop enough for it to kick out over time.

-Tyler

Tyler,
That is a great looking installation. BE CAREFUL!! at 46 MPH you are on the verge of time travel. If you disappear into the past or future, we will never know the long term outcome of your overdrive experiment.

Mike