how can i synchronize speed ammeter after changing rear end in 88 Chevy van

Asked by Feb 02, 2017 at 12:30 AM about the 1988 Chevrolet Chevy Van 3 Dr G20 Cargo Van

Question type: Maintenance & Repair

1 Answer

101,915

Couple of ways, find out how far off it is using mile markers on the roadway, at 60 mph you should do a mile in one minute, once you find out how far off it is you change the driven gear on the end of the speedo cable drive, it is connected to the transmission where the speedometer cable attaches, it is help in place by 1 bolt and a hold down, count the number of teeth on the existing gear and depending on if the speedometer is fast or slow you decide on replacing the gear with more or less teeth, if it is fast you want too slow it down, so 1 tooth is approxmentally 6 mph, if it is slow you want to take away a tooth. Note if it is going to be more than one tooth in either direction you then will have to remove the transmissions tailshaft housing and replace the drive gear with another ratio depending on fast or slow speedo. The other way is to have the speedometer checked on a speed dyno at a shop that does this, then they can make an adapter that go's in between the cable and the transmission to bring it back to reading properly. This is a far eaiser way if you have to change the gear on the tailshaft, as the adapter can take up a lot more error than just changing the driven gear, plus it is way more accurate and also more expensive.

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