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| | | | Joined: Sep 2004 Posts: 93 Member | | Member Joined: Sep 2004 Posts: 93 | Wasn't sure where to post this question but since my 38 is a hot rod thought I would post my question here. Had my truck out on the road for first real test yesterday. Everything was good except I noticed that when I was doing about 45 MPH my speedometer was reading almost 60, that's a big difference. I have Stewart Warner gauges and a 350 transmission, 15 inch tires in rear. I know there are different speedometer gears, but have never had to deal with this situation before. Would appreciate some thoughts from some of you experts on how to get the speedo reading to be more accurate. Thanks for any help, Don. | | | | | Joined: Feb 2000 Posts: 5,193 'Bolter | | 'Bolter Joined: Feb 2000 Posts: 5,193 | | | | | | Joined: Dec 2001 Posts: 58 Member | | Member Joined: Dec 2001 Posts: 58 | Get down to your local Chevy dealer and find the oldest man in the parts room. Come armed with tire size and rear end ratio and he will be able to come very close to the right color gear for the transmission. Even if he misses chances are he will take it back and trade for another one. Good luck Richie Z | | | | | Joined: Jan 2001 Posts: 662 Shop Shark | | Shop Shark Joined: Jan 2001 Posts: 662 | That much off you might not correct with driven gear alone. The Speedometer Shop on the Links page has ratio adapters available. Mine works fine. | | | | | Joined: Sep 2004 Posts: 93 Member | | Member Joined: Sep 2004 Posts: 93 | Thanks Joe and Richie for your responses. I will check the TCI web site and Chevy dealer but probably will have additional questions later. Thanks again, Don | | | | | Joined: Sep 2004 Posts: 93 Member | | Member Joined: Sep 2004 Posts: 93 | Just saw your reply Chuck, thanks, will check out your suggestion. Don | | | | | Joined: Jun 2004 Posts: 8,597 Riding in the Passing Lane | | Riding in the Passing Lane Joined: Jun 2004 Posts: 8,597 | Pull the driven gear out of the trany where the speedo cable goes in. The number of teeth is written on it. Get a gear with 2-3 more teeth & install it. Run down the freeway & match the odometer reading with the mile markers. Change the gear with different teeth to get pretty close to the same tenth of a mile. 
They say money can't buy happiness. It can buy old Chevy trucks though. Same thing. 1972 Chevy c10 Cheyenne SuperIn the Gallery Forum | | | | | Joined: Sep 2004 Posts: 93 Member | | Member Joined: Sep 2004 Posts: 93 | I checked with The Speedometer Shop about a ratio adapter and they will build me one for about $90 + shipping. That would be the easiest way to go but I'm interested in what Wrenchbender suggested. After unscrewing the speedo cable how do you get the gear out?
Thanks, Don | | | | | Joined: Dec 2003 Posts: 1,554 Shop Shark | | Shop Shark Joined: Dec 2003 Posts: 1,554 | I had the same problem with my 55,and 700R4 tranny set up.It was showing 60 mph at 45 mph.I took the gear out,it was a 40 tooth.Installed a 42 tooth and its right on now. | | | | | Joined: Jun 2004 Posts: 8,597 Riding in the Passing Lane | | Riding in the Passing Lane Joined: Jun 2004 Posts: 8,597 | Take out the bolt that holds the clamp on. Pull the housing out. The gear will come out with the housing or will lay right inside. You probably will want to replace the seal inside the housing & the o-ring around the housing. There is a little ring holding the seal in it pulls out real easy with a hook tool.
They say money can't buy happiness. It can buy old Chevy trucks though. Same thing. 1972 Chevy c10 Cheyenne SuperIn the Gallery Forum | | | | | Joined: Sep 2004 Posts: 93 Member | | Member Joined: Sep 2004 Posts: 93 | Dale and Wrenchbender, thanks for the info. I will see if I can get the speedo gear out and check the number of teeth. I was thinking about this yesterday and I thought that the number of teeth on the gear would need to be increased by the same percentage that your speedo reading was off. In other words, if your reading was off by about 30% then the number of teeth on the gear would have to change by that same percentage, such as going from 40 teeth to 54 teeth. My thinking was sure screwed up on that one. Much thanks again for your responses. Don | | |
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