Rock Posted June 16, 2014 Share Posted June 16, 2014 Mine seems to be about 10mph fast. It said I was doing 75 and I was being passed by Toyota Prius. Is there a way to fix it? The speedometer is new aftermarket and the original was about the same. Is it in the cable or transmission? Not a huge deal but would like it to be a little more accurate. Quote Link to comment Share on other sites More sharing options...
70 Iron Posted June 16, 2014 Share Posted June 16, 2014 Try this Glen,they can give you the correct gears for your tranny,just call them and give them your tranny ,tire size,rear gears and they will figure out what you need. www.Transmissioncenter.com Ph #1 888-877-1008 Terry Quote Link to comment Share on other sites More sharing options...
Toppless72 Posted June 17, 2014 Share Posted June 17, 2014 When I'm going 65 MPH according to the GPS, the speedo reads 58 MPH. I go by the GPS Quote Link to comment Share on other sites More sharing options...
Rock Posted June 17, 2014 Author Share Posted June 17, 2014 Changing gears sounds like a pain. I will consult my mechanic(my son) and see what he thinks. A gps might be a cheaper alternative. Or topless and I could swap gears....we seem to have opposite problems! Quote Link to comment Share on other sites More sharing options...
70 Iron Posted June 17, 2014 Share Posted June 17, 2014 Its only the nylon speedometer gears,one is on the main shaft and the other is on the end of the speedo cable not too bad to change. Terry Quote Link to comment Share on other sites More sharing options...
Rock Posted June 17, 2014 Author Share Posted June 17, 2014 Is the gear in the transmission? I assume you just have to remove the housing for the cable to access the gears? Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted June 17, 2014 Share Posted June 17, 2014 "IF" you need to change the drive gear, the tailhousing and driveshaft have to be removed Quote Link to comment Share on other sites More sharing options...
Leghome Posted June 17, 2014 Share Posted June 17, 2014 I have a 700R4 and 3:73 gears and my speedo is right on with my GPS. My cruise will only hold 69MPH. I set it at 75 and it will drop back to 69 and stay there all day. Must be the downshift cable for the 700R4 putting to much pressure and the vacuum is not strong enough to hold it at the higher speed. I did put a lighter tension spring on the carb return and it increased 1 MPH over last year but a lighter spring than that and the car does not return to idle. Quote Link to comment Share on other sites More sharing options...
Daryl Posted June 17, 2014 Share Posted June 17, 2014 Some time ago I know I've seen a company that makes a little external gearbox that threads on where your speedometer cable goes on your tail shaft housing. Give them your tire size and gear ratios. I'll see if I can find the link for it. Quote Link to comment Share on other sites More sharing options...
Daryl Posted June 17, 2014 Share Posted June 17, 2014 Found one 62$ Ratio adaptor Quote Link to comment Share on other sites More sharing options...
Rock Posted June 17, 2014 Author Share Posted June 17, 2014 The things you learn here....awesome Daryl! Quote Link to comment Share on other sites More sharing options...
Murphy Posted June 17, 2014 Share Posted June 17, 2014 Which trans do you have? Quote Link to comment Share on other sites More sharing options...
Rock Posted June 17, 2014 Author Share Posted June 17, 2014 TH350. Nothing special and I am not sure the size of the tires. Is it possible for the wheels to throw it off by 10mph or more? Quote Link to comment Share on other sites More sharing options...
Murphy Posted June 17, 2014 Share Posted June 17, 2014 Try this site also.... http://www.laspeedometergear.com/TH350%20Driven%20Speedometer%20Gears.htm I've replaced mine several times in an attempt to get it correct, takes 5 minutes. Remove the speedometer cable from the trans, there is a small bolt holding a locking plate on the cable housing. Once the cable is removed, you'll see a plastic gear (pencil gear) about 3" long, as shown on this website, using their formula get the correct gear you need, their all color coded....I have a few spares but need to know which one you have?? Quote Link to comment Share on other sites More sharing options...
Rock Posted June 17, 2014 Author Share Posted June 17, 2014 I will climb under there tonight and see what I find. Thanks for the help. Quote Link to comment Share on other sites More sharing options...
Daryl Posted June 18, 2014 Share Posted June 18, 2014 This gear setup you're talking about is it only on the 350? How about the 400 ? Quote Link to comment Share on other sites More sharing options...
Murphy Posted June 18, 2014 Share Posted June 18, 2014 The 1st site recommended "transmissionCenter' has good info on the TH400 but you have to dig..... Quote Link to comment Share on other sites More sharing options...
John S Posted June 18, 2014 Share Posted June 18, 2014 When you replace the gear take note of which way the grooves in the shaft go. Either right twist or left twist. the grooves depending on the twist pull the trans fluid back up into trans or down out of trans and that can cause a leak. I had to change gears when I changed rear ends wasn't paying attention next thing I had was oil leak at speedo cable. when I compared gears I saw the difference, one had left thread other right hand threaded grooves. Put gear with correct twist and leak was gone. Made that way because some cables attach on left side and some on right side. John S Quote Link to comment Share on other sites More sharing options...
Rock Posted June 18, 2014 Author Share Posted June 18, 2014 My kid took my jack....It will have to wait till the weekend or later.....anniversary is Friday and we may be going to Vegas for the weekend. Quote Link to comment Share on other sites More sharing options...
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