The Stovebolt Site Forums The Shop Area The Electrical Bay '51 speedo after after diff. upgrade

I have just changed the differential to 3.55 and it was a great decision. I can now drive up to 60 kmp without feeling like the engine is going to blow up!

However, my speedo needle is not constant. It likes to flucturate back and forth about 3 mph and won't sit still.
I don't know if this was the condition before the switch or if it is new.
Any help?
Thanks
Peter

Changing the rear gears should not make the speedo jump around but will change the reading. You will be going faster then it shows. Remove the cable from the speedo head & pull out the core. Feed the core back in with some grease. Put a small amount of oil on the end of the speedo head where the cable goes. Make sure there is plenty of grease in the trans. This should make it work smoother. You may need to get a speedo gear with 1or 2 less teeth.

Thanks for the reply.
I followed the advice of another Stovebolter and took my GPS with me and was amazed at the difference the new diff may in my actual speed. I will make up a little chart so I know how fast I am really going. Not only do I have to correlate the new speed to the old speed, I have to convert to kilometers per hour (Canada, eh) - an awful lot for an old brain to do on the fly.

I should have twigged to the jumping speedo needle. Since taking over this old truck last year I am beginning to realize how much I have really forgetten from the old days when I bought cars for $30 and patched them up!
Sorry for the ramble.

I found the GPS quite handy too, for checking my speedometer. I made a new face for mine to correct for the rearend ratio change. Of course the odometer is not correct with the setup.

There's a guy in Flordia that advertises in the little ads in the back of car mags. He makes an adapter piece that goes between the end of your speedo cable and the tranny. All you give him is what your car is traveling at (MPH) ) and what your speedo is reading. He does the rest. Ir's a small gear reduction unit I think. Mine is off by .02 MPH (measured on a 100 mile Interstate trip). Close enough for me.

The adapter piece sounds very promising. I have not seen his ads in any of the mags we get here in Canada even though they are almost completely American in origin. Maybe they have region issues(?).
Is there any way you could give the name of one of the mags so I could track down a copy.
My speedo is so far off that I don't see any other way of doing it except by using an adapter.
Thanks for any info.
Peter

Peter, I faced he same situation when I changed the ratio in my '36 Chevy pickup to 3.55. A Canadian company, Mr. Speedometer, makes ratio correctors that go on the back of the speedometer head.

www.mrspeedometer.com

FOUND IT. Ad says, "Correct your mechanical speedometer with our ratio adapter. To order, tell us your speedometer reading at an actual speed. Install in 2 minutes. Call Ron anytime day or night. 727-410-6352." Hope this helps.

I was sure I posted a reply but, it seems to have vaporized(?).
So, here it is again.
Thanks for the replies.
I am going to call both and will post my results once I get a fix.
Many thanks.
Peter