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MG MGA - Speedometer accuracy

How accurate is my speedometer, it was rebuilt professionally 3 years ago, this is concerning a speeding offence from a fixed camera. 41 in a 30mph limit.

Dave
1500
Dave

Hi Dave - rather unfortunate - sounds as though you need to use a sat nav to check it -or have a friend drive in front of you at set speeds - cheers Cam
Cam Cunningham

Dave

Easiest way is to compare it against a sat nav. What was your speedo reading at the time of the offence?

Without knowing any specific details of your rebuild, a 5-10% overread is quite normal. i.e. you may have been doing an indicated 45mph.

Steve
Steve Gyles

I seem to remember that UK law says the speedometer can over read by 10% but zero under reading is allowed. So at 30mph a reading between 30 and 33 is permissible.

Malcolm
Malcolm Asquith

I think you will have a hard time convincing the authorities that your speedometer is 36% off. You would have noticed that large of an error long ago. I hope the fine isn't too large. The last speeding ticket I aquired was in 1964. I think I am running on borrowed time, but I do try to obey most of the rules.
Ed Bell

Ed

The trouble over here is that they put penalty points on your licence as well as the fine. 3 points is the normal. Gather 12 points in a 3 year period and you get disqualified from driving for a period, varying from say 3 to 12 months depending on the severity of the offences.

My only speeding fine so far was in a Fiat 500. It had a broken speedo and I had put a banner in the back window saying "supercharged". It had taken about a mile with a following wind to get up to speed and there was a speed cop at the end of the straight. The brakes were not too sharp either. He put his hand up to stop me and I went sailing past by about 50 yards!

Steve
Steve Gyles

Dave,
I think that you should be able to find a reputable speedometer repair facility that can check your speedometer on a dynamometer. I know that there are still a few of these places here in the states, although very few.
Could you go fight and offer to pay the fine without the courts placing the points on your license? They do this in the states.
Mike Parker

Steve, I once owned a Fiat 500, and a Fiat 600, so I know what you mean about taking a mile to get up to speed. I was humiliated many times by children on bikes out running me from a standing start,And once up to speed I was reluctant to slow down. They did go a long way on a gallon of gas. I hope that the authorities go easy with you on the points.
Ed Bell

Thanks all,
I am probably going to have to bite the bullet and pay the fine and take the 3 points, but I am asking the police to produce a current calibration certificate for the camera, if they can not give me this I am home free. I was not looking at my speedo at the time just enjoying the day.

Dave
Dave

Dave, Can I suggest you do a grease and oil change on your speedo - it could help save money in the long run! I went to Barneys site, ripped the speedo out, cleaned and oiled, and had it operating perfectly in half an hour. It really works!!
Barry
BM Gannon

Barry

I think I am going to have to do something similar or send my instrument back to Speedy Cables under guarantee. The needle was rock steady when I got it back from recalibration 6 weeks ago, but already it is fluctuating significantly above about 50 mph.

Steve
Steve Gyles

Spot on Barry.

Just changed my dash panel and while it was out I greased the speedo cable. It was pretty dry and my needle was fluctuating about 5 percent - very noticeable.

Just been for a spin and its hardly moving at all now (maybe 1-2 percent) - not noticeable.

Incidently the cables (speedo and tacho) should be removed and greased at 12,000 mile intervals according to the service instructions.

For other reasons I had taken the cable back through the bulkhead and did the inner cable removal/cleaning/greasing from the engine bay. I can thoroughly recommend doing it this way rather than from in the cockpit.

Neil
Neil McGurk

What type of grease is best to use on the cables? My speedo bounces +/- 3 or 4 mph at 70. BTW, I'm running 165/15 tires and the speedo is always about 10% high compared to my GPS. The speedo, xmission and rear end are all stock MkII.
- Ken
Ken Doris

Ken, Any light grease will do, just don't overdo it. A light coating is all that is needed. Clean all the grease 6 inches from end closest to the instrument to prevent any working its way up the cable into the speedo. Also I would strongly recommend you pull the speedo out and follow Barneys procedure for cleaning and lube - it will save you a costly rebuild later and you will also have an accurate, steady needle!!
Barry
BM Gannon

Barry - Yup, I think it's time to do that. I had the speedo apart during the restoration 3 years ago, but just did a basic cleaning. Time to do a more thorough job. Thanks,
- Ken
Ken Doris

Further to the above - at our Club garage tour last Saturday, Jim McKenzie said he pulls the inner cable from the speedo end, under the dash and rolls it on a piece of paper on the floor. If it jumps about this indicates the cable has been kinked at some stage and will cause trouble in the casing. If it rolls true then it can be re-installed. Just another test for efficiency. Thanks Jim for the tip.
Barry
BM Gannon

This thread was discussed between 13/06/2007 and 20/06/2007

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This thread is from the archive. The Live MG MGA BBS is active now.