Topic: Speedometer help!

[iFart]

So today I discovered that the speedometer wasn't working but it was still clocking miles. I hopped off and disconnected and reconnected the cable with no luck.

I got home and read some articles on here about the issue I was experienced and made sure the cable is moving freely inside it's housing, the blade from the gearbox on the front wheel was rotating properly. Everything seemed right. I tried spinning a small screwdriver over the end of the cable when the gauge was connected and it only had a tiny blip to it.

I then found an article that said to pour rubbing alcohol inside the light holes and shake it around and that will sometimes fix it and it won't mess up the paint of color or anything.

AHHHHHHH!! Not the case!!  My gauge face tuned a crazy color after the alcohol evaporated and black gunk got slung to the glass in the corner around 140mph and black spec on the needle.

So I've opened the gauge up to hopefully restore the gauge face back to where it was a couple hours ago and wanted to check with the folks here if what i'm seeing is normal and how I should proceed. I read something about filling up an oil tank, etc.

I'm wondering about the wire that is all around the center part; is that normal? I've never disassembled past the last pic and would like input on what to check.

[kerryb]

If it was still clocking miles, that means the drive mechanism is still working.  No need worry about the cable or wheel.  What is a problem is the easy movement of the needle, which is a shaft between the needle end and a bell at the other end which is driven through a MAGNETIC connection by a spinning magnet on the cable.  If the needle shafts has worn it's bearing enough for the bell to contact it's case, then that may require sanding/grinding the inside of the case to provide clearance for the follower to move the needle.  The drive case comes apart easily by removing the screws, but be very careful not to stretch or bend the spring which would be very difficult to fix.
I just went through this,  if pics would help I could take some tomorrow.

All part of the adventure.

[iFart]

I can wait a day for photos. It's not like I neeeed a speedometer, right?

 

[iFart]

I was able to get the discoloration off the face but it almost looks a bit dull now. Is there some type of oil or something I could wipe it down with?

Also, weren't the numbers an off white as opposed to a pure white? I ask based off a near pristine picture I found from Mecum auctions.

[pjlogue]

The numbers are white in "new" gages.  The small clock spring in your first photo looks like it broke and wound around the shaft for the speedometer.  That's probably why it doesn't register any speed.  That spring is spring steel and will rust and can rust through and break.  Not sure if there is a fix anyone knows of.  The spring force is specific for the gage so any old spring will not work.  If the spring force is not correct your speedometer will be WAY off.   You might be better off finding a working new one on fleabay and reconditioning it. 

-P.

[iFart]

Damn I hate to read that but it looked off 

Any idea what could of caused it? Maybe like something stupid like having the gear box on the wheel backwards or upside down?

If you say it's busted I guess I can't be any worse off seeing if I can open it and rewind it.

Sad day.

[pjlogue]

Damn I hate to read that but it looked off 

Any idea what could of caused it? Maybe like something stupid like having the gear box on the wheel backwards or upside down?

If you say it's busted I guess I can't be any worse off seeing if I can open it and rewind it.

Sad day.

 
Can't hurt to try.  If the spring broke then it will be shorter than when new and the spring tension will be more than the full length spring and the spedo will read lower mph than you are doing.

-P. 

[iFart]

I've successfully opened it up and pulled the spring out without breaking it and have straightened it out with some pliers.

Anyone have a picture of the spring? I find stuff on google but nothing specific to the CB750.

Now I'm just trying to find something appropriate to thread it around to try to wind it.

I found the following that have helped me; I'll take pics on re-assembly.

Yamaha - http://xjbikes.com/forums/threads/speedo-and-tach-dissection-with-pics.15303/

Beetle - https://www.thesamba.com/vw/forum/viewtopic.php?t=327535

Datsun - http://community.ratsun.net/topic/62098-datsun-320-speedometer-repair/

[iFart]

Well I put it back together and rewound the spring but no success; at least under what should be a 30mph tear.   

Defeat.

[iFart]

Correction! It did work! It helps if you connect the cable. =D I'll have to find a clocking street sign to see how accurate if at all it is.

In short; I pulled the spring wire straight up and out of that brass nut and then off that silver arm. I straightened it with pliers and tweezers. I wound it at first but I couldn't find an easy way to solder it coiled up. I straightened it out again and then I then took a little tang from where it was in the brass nut and soldered it to the nut where theres a vertical line through it.

I then put the needle on and held the wire and spun the needle around instead of the cup around and shaped the wire it till it looked like what I saw on the yamaha forum with mostly even gap spacing.

I forget the direction I had to spin it but I did it wrong at first. I had to re-wrap it because the spring was compressing instead of expanding when I simulated the rise of the needle.

Once I got the needle to return to the same position regularly while holding down the free end of the spring I soldered the end of the spring back to the arm.

Re-assembled and bada bing! Big bada boom.

If anyone is curious for more details let me know.

[PeWe]

Check with a GPS if you cannot find a clocking street sign
My CB750 speedo show rather accurate according to a clocking street sign. Better than my car that usually show +5%. Wheel + tires affect this.
CB750 K6 speedo showed around + 2-3% with fresh front tire. 100/90-19

[Nic]

Well done on the repair, hope it works n stays working.