Replacement Speedo Reads Low

Hi All

I have an XJ750 Seca, 1981. The needles on both the speedometer and the tachometer broke, and I picked up a replacement cluster for a bike of same year on eBay. Took me a while to get around to it, but, I finally swapped it for the old one. I think I probably have corroded contacts, as some of the idiot lights do not work (high beam indicator, neutral indicator, left turn signal indicator), the headlight warning lights up. I figure I will clean that up with contact cleaner and see how that changes.

Meanwhile, the bike starts, runs and drives fine, except for the minor detail that the speedometer reads very low. As in I can be moving 55, with the speedometer reading 40. Now, MAYBE that will get cleared up when I clean up the contacts for the computer, but, as the speedometer is mechanical, I am wondering just what the issue there may be. Thinking I am driving 55 and discovering I am doing 70 by the friendly local constabulary is not my definition of a fun commute to the office, so, open to suggestions on getting that sorted.

I have a laundry list of other stuff I want tot do to the bike to get it into better shape (transmission - dread second gear drop, repacking the muffler, and starter motor being high among them). It's a beautiful, and generally fun rider, and I am looking forward to making it even better.

 

Welcome , hmm sounds strange speedo are usually off by a slight margin I swear my truck is off by 25 miles per hr when I get on interstate 75 mph is what my speedo reads and I get the finger from SUV's that are running at least 95 ??? You may have a problem with your "new" speedo . Have you had someone run next you to check your speed in relation to their speed? you could mark it down and make a pattern to put on your cluster to correct for the difference might not look great but would save you having to buy another speedo.

 

find a speeding radar trailer that police park on side of road or one of the many new speed linit signs with speeding sensors to test your speed

 

The magnet that pulls the speedometer needle cup has gotten weak. It will need to be remagnetized and recalibrated. This is not an at-home job (i've done it. It's a pain and time consuming without the correct equipment).
The easy way is to use a label maker and print yourself some new numbers to lay on the glass. Speedometer calibration on the cheap.

The dead lights are likely just that; burned out bulbs.

 

Like K-Moe says.

 

Yep. Mine displays up to 125 mph now

 

Might not hurt to pull the speedo apart and clean out/lube the bushings inside. They might be gummed up preventing the spindle from spinning freely. When I was rebuilding mine, I had one parts speedo that was really gummed up. Brake cleaner works well just be careful not to get any on the speedo face or number dials, it will take the paint off instantly.

 

Actually there's a how-to on that.

speedo-and-tach-dissection-with-pics.15303

Brake cleaner is the wrong solvent for the job.
Mineral sprits is good, as is electical contact cleaner, or even just the lubricant that you'll be using.

 

Thanks kmoe, I was looking for that link.