1940 56S Speedometer Update

[Daves1940Buick56S]

You all may remember about 3 years ago I ripped my dash apart and fixed the wiring and overhauled the instruments. I wrote it up in

and it was also put into the Bugle. (Thanks Pete!) Well, the speedometer worked a lot better but some things still annoyed me:

1. The plastic center piece that I put in is a little thicker than the original so the needle would stick near zero. Banging the panel would free it up but it was getting tiresome.

2. The odometer reads pretty low due to my current rear being 3.6 and the original was 4.44

3. Also, the speed readout was much lower than the theoretical difference of the rears would indicate.

 

So, about 2 weeks ago I unzippered the dash again and pulled the speedo. Testing of the speed confirmed that it was reading about 40% low. I disassembled the unit and basically determined the magnets were shot. I tried to remagnetize but no go. And in the middle of the testing the hairspring broke!

 

So on to Ebay! I found a 49 speedo, condx unknown for relatively cheap. Got it in, it tested pretty close to correct! My first thought was to move the speed cup over to the old frame but the magnet failure put the kibosh on that, so I had to move everything over to the "new" frame after cleaning all old grease, etc out and relubing. The numbers on the '49 unit (OD and trip) were all roached so I brought the ones over from the '40. There are a few minor differences but I was able to work around. All back together and tested excellent! So that takes care of #3.

 

HOWEVER, the needle on the speed cup is shorter than the original since the '49 has a metal plate center rather than plastic. So the question was how to modify the original pointer to work? Fortunately, on the '40 pointer the needle sits on a small collet that is in turned pressed into the pointer. I was able to extract the collet from the pointer. I was lucky that some 3/32" brass rod that I had was almost the exact diameter of the collet. So I cut a short piece off and matched drill size to the needle: #70.

 

Larry will like the next part: I chucked the brass piece and drill into my old Boley lathe and drilled out a nice hole!

I *gently* pressed this on to the speed cup needle and the gently placed the pointer with nice clearance so no more dragging, with a small bit of epoxy to stabilize it. Et voila, fixed and that takes care of #1.

 

The above pic shows the pointer, the new brass collet (blue arrow), and original collet (red arrow).

 

There are several firms that make translators to match changed rears to old speedo gearing. They attach at the transmission, and can be set to increase or decrease when manufactured. I needed an increase at a ratio of 1.23. I used Commercial Speedometer in Sacramento (916-371-5873) and they did a quick turnaround, I had it in 3 days and it was less than $100.

 

You can see the unit attached to my trans. Hopefully this solves the issues, I hope to get it all back together next week and test!

 

Cheers, Dave