Mechanics

SPEEDOMETER READS SLOW

Toyota Corolla

1997 Toyota Corolla DX automatic Overdive with 133,000 miles. The speedometer reads slow at highway speed. When it shows 60 actually gonig 55, when it shows around 73 actually going 65 and motor is really humming. Transmission shifts ok. Is this speedometer module, cable, or something within the transmission?
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Ohio Bob
March 12, 2007.




If you say that when the speedo reads 73 you are actually going 65, this is a fast reading speedo, not slow, if the speedo reads 25, and your actually going 65, this is a slow reading speedo. Slow reading speedo, is usually caused by the factory grease having been expended, over many miles of the cable rotating at high rpm the grease eventually dries up creating a high friction situation, and hence slowing the rotation of the cable end.A fast reading speedo on the other hand can be caused by three things: smaller than stock tires, a change in the transaxle gear ratio, or mechanical drag of the inticator's magnetic clutch OUTER DRIVE PORTION on the cable end INNER PORTION, hope this is helpful
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Tiny
Joemechanic
Mar 13, 2007.
Well yes, you're right, I had it backwards. The speedometer reads faster than I am actually going. That third item that you give as a possible cause (mechanical drag of the inticator's magnetic clutch OUTER DRIVE PORTION on the cable end INNER PORTION), is that part of the cable and will replacing the cable take care of the problem? Thanks for your insight. Bob

Tiny
Ohio Bob
Mar 13, 2007.
Unfortunately the magnetic clutch is a part of the actual speedometer assembly, failure of the magnetic clutch can be a reult of cable failure. Does the speedometer make any sound?

Tiny
Joemechanic
Mar 13, 2007.
The speedometer is quiet as a mouse. The only thing you notice is people passing you when you think you're driving the speed limit! I've had the car nearly 5 years and it's been this way since I bought it. Bottom line is I'm ready to sell it and move on. I just want to be able to assure any prospective buyer that there is nothing wrong with the transmission as it relates to the speedometer. If you think it's in the speedometer assembly I can tell them that. Otherwise this car's been a gem and I almost hate to part with it. Thanks much.

Tiny
Ohio Bob
Mar 13, 2007.
The mechanical assembly responsible for driving the speedometer cable is relatively simple. Regardless of weather your car has an automatic or a manual trans
It is Just a gear which is mounted on the final drive shaft
of the transmission, outside of the actual area of transmission operation, this gear drives a small gear mounted on the inside of the case(usually nylon). If this assembly fails, the speedometer simply won't work, and will be of no consequence to the transmission. The problem is more than likely in the speedometer itself, some of these speedometers can be calibrated, you might try contacting a speedometer specialist, and asking them if the unit on your perticular make/model is adjustable, hope this is helpful-Joe

Tiny
Joemechanic
Mar 14, 2007.
Well OK. That helps me know how to proceed, and we can wrap this one up. Thanks Joe so very much for your help. Take care.
Bob : D

Tiny
Ohio Bob
Mar 14, 2007.
Do you have the correct size tires?

Tiny
Bestbet777
Apr 18, 2007.

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