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| | | | Joined: Jan 2016 Posts: 6 New Guy | | New Guy Joined: Jan 2016 Posts: 6 | I put a T5 transmission and a 4.11 rear on my '53 Chevy 3800 with a 261. Speedo reads about 35 when going 29, and I would guess when reading 60, I'm going about 50 mph. Any suggestions on how to make it read accurately?
Thanks! | | | | | Joined: Mar 2010 Posts: 10,272 Renaissance Man | | Renaissance Man Joined: Mar 2010 Posts: 10,272 | I use the math-on the-fly method. It exorcises the mind and helps kill time in traffic. A plus is that if I ever get a speeding ticket, I can get out of it when I have it calibrated.
1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission
| | | | | Joined: Sep 2001 Posts: 29,269 Bubba - Curmudgeon | | Bubba - Curmudgeon Joined: Sep 2001 Posts: 29,269 | Do your "higher" math on the fly with Carl, or get a ratio adapter that goes between the cable and the fitting on the transmission. However, exorcising the mind is a sometimes necessary practice/ritual. | | | | | Joined: Jun 2011 Posts: 5,096 Crusing in the Passing Lane | | Crusing in the Passing Lane Joined: Jun 2011 Posts: 5,096 | I use the math exercise method, too, my KB-5 speedo is 11% slow.
Ed
'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
'55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.
| | | | | Joined: Sep 2013 Posts: 1,361 'Bolter | | 'Bolter Joined: Sep 2013 Posts: 1,361 | You can....change the drive gear on the output shaft of the transmission along with the driven gear the the speedometer cable slides into for less than $10 or so. Google is your friend on the specifics. A couple years ago I did the research and had the necessary info at ready recall for about....Oh, 10 minutes. However with 4.10 rear gears (stock was 4.57) and a .72 5th gear T5 the speedometer in my 51, 3600 is pretty much accurate with the appropriate speedometer drive gears installed in the T5.
Lugnutz may step up and provide specifics, he is the Man on these issues.
Good Luck, Ron
RonR
1951 3600 with Clark flatbed, T5, 4.10 rear
1970 340 Duster
1990 5.0 V8 Miata (1990 Mustang Gt Drivetrain)
1964 CJ5
| | | | | Joined: Sep 2001 Posts: 29,269 Bubba - Curmudgeon | | Bubba - Curmudgeon Joined: Sep 2001 Posts: 29,269 | drive & driven gear for $10 - what a deal | | | | | Joined: May 2010 Posts: 74 'Bolter | | 'Bolter Joined: May 2010 Posts: 74 | there are sights that help you decide the necessary drive and driven gears. This is not a recommendation, but here is an example. I am sure you can find others with an appropriate search. drive and driven gear selection | | | | | Joined: Apr 2005 Posts: 2,832 'Bolter | | 'Bolter Joined: Apr 2005 Posts: 2,832 | On my old 37 Buick it had a 4.44 rear end from the factory and 8.25/15 tires. From there it went to a 2.73 rear and 28" tall radials and then to an overdrive transmission and 4.11 rear, same tires. Through all these changes the speedometer stayed dead accurate because I have a gps speedometer which I recommend as it does away with gears, cables, and inaccuracy. I had to have mine custom fit in the instrument cluster but as many AD's as there are someone most likely makes a ready to go unit.
Evan
| | | | | Joined: Jan 2016 Posts: 6 New Guy | | New Guy Joined: Jan 2016 Posts: 6 | Think I'll try the ratio adapter, exercising the mind technique gives me headaches. thanks for all the replies! | | | | | Joined: Jun 2004 Posts: 8,597 Riding in the Passing Lane | | Riding in the Passing Lane Joined: Jun 2004 Posts: 8,597 | First try changing the driven gear in the trans. Remove the bolt & retainer were the cable goes in. Pull the holder out of the trans. with the gear. Count the teeth on the gear. Get a gear with one tooth more then you have. That will get you close.
George
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: Jan 2002 Posts: 2,839 'Bolter | | 'Bolter Joined: Jan 2002 Posts: 2,839 | Forgot from whom, but when I installed Patrick's 3.55 gears in back, I got a very easily obtainable ratio adapter and bam! It now reads dead on. I used an app on my phone called speedbox to confirm how far off the speed was initially reading.
Craig My '50 Chevy 3100 5 window, '62-235cu, 3:55 rear My truck ....... Respect The Rust If I'm not working on my truck, '65 m00stang or VW camper, I'm fishing with the wife or smoking Salmon.
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