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Thread: Speedometer Accuracy with T50 transmission swap

  1. #1
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    Default Speedometer Accuracy with T50 transmission swap

    I've got a '73 TE21 powered by a mild 3TC. The previous owner removed the factory 4 speed transmission and upgraded to a T50 5 speed from an early 80's (USA models) Corolla/3TC. Does anyone have any experience with this type of upgrade from the perspective of --- will the speedometer read accurately?

    Also, I've verified that the gear drive in the transmission is working and that the cable is turning on the speedometer end. However, I'm becoming concerned that the speedometer itself has malfunctioned. Anyone with any experience with these old cable driven speedometers? Is failure of the speedo itself a common occurrence? Thanks.
    '16 Subaru Crosstrek; '17 Mazda3 Hatch; '82 Volvo 242 w/LS3 V8 power; '73 TE21 w/3TC power

  2. #2
    Forum Member Grease Monkey
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    Default Re: Speedometer Accuracy with T50 transmission swap

    Hi! I have done some swapping around with the T-gearboxes and the speedo gears. There are multiple ratios depending on what differential the original car were suited with.
    So the previous owner might have never switch the gears from the 4 speed to the 5 speed. With the right speedogear the speedo will read fairly accurate(like all old speedos).

    if the cabel is turning on the other hand it should be working, then i migth be on the backside of the speedometer where a small clip hold the cabel in place (might have fallen of) or in worst scenario the socket in the speedo is broken (which i dont see how it would happen if noone have been pulling the speedometer out without care).

    Good luck with getting it working

  3. #3
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    Default Re: Speedometer Accuracy with T50 transmission swap

    Thx for the reply! On mine, cable is held in place with threaded fasteners on both ends.

  4. #4
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    Default Re: Speedometer Accuracy with T50 transmission swap

    I had a 3TC in my RA21 with the T50. I'm swapping it for a 2TG/3T ("3TG" we used to call it in the 80's and 90's in cali). My speedo was not working. it was the cable but the speedo was kinda messed up anyway and cracked so I just bought a set of speedhut gauges. IT uses GPS and should be much more accurate esoecially since i run 15 inch wheels all around. Also it can clock your a 0-60 time and 1/4mile. Havent installed it yet since i have bigger projects with the car. but I cant wait to start playing around with the functions.

    www.speedhut.com


  5. #5
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    Default Re: Speedometer Accuracy with T50 transmission swap

    Thx Dragon - I run a GPS cable box on my LS powered Volvo. No more inaccuracies when playing with tire size and rear/trans changes. If my Corolla speedo ends up being shot, Iíll likely go the electric/gps speedo route. Thx for your response. Now I have to look up what an RA21 is....(embarrassed)

  6. #6
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    Default Re: Speedometer Accuracy with T50 transmission swap

    Quote Originally Posted by Michael Yount View Post
    Thx Dragon - I run a GPS cable box on my LS powered Volvo. No more inaccuracies when playing with tire size and rear/trans changes. If my Corolla speedo ends up being shot, Iíll likely go the electric/gps speedo route. Thx for your response. Now I have to look up what an RA21 is....(embarrassed)
    It's the chassis code for a 1st Gen celica in USA

    Sent from my SM-G975U using Tapatalk
    -1974 Celica GT (2TG/3T in the works)
    -2010 Lexus IS350 Luxury Edition
    -2013 Toyota Prius III
    -2004 Toyota Sienna LE

  7. #7
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    Default Re: Speedometer Accuracy with T50 transmission swap

    Thatís what I thought - and this was the hit on my first search - https://secretfactoryusa.com/2019/04...celica-update/

  8. #8
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    Default Re: Speedometer Accuracy with T50 transmission swap

    Quote Originally Posted by Michael Yount View Post
    Thatís what I thought - and this was the hit on my first search - https://secretfactoryusa.com/2019/04...celica-update/
    Those guys are cool at secret factory. I bought a set of watanabe's from them. Very good ppl to work with.

    Sent from my SM-G975U using Tapatalk
    -1974 Celica GT (2TG/3T in the works)
    -2010 Lexus IS350 Luxury Edition
    -2013 Toyota Prius III
    -2004 Toyota Sienna LE

  9. #9
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    Default Re: Speedometer Accuracy with T50 transmission swap

    Well - speedo does seem to indicate a speed that changes proportionally with road speed. But way off -- 55 mph or so indicates 35 mph. And when I come to a stop, the speedo won't return to zero -- stops at 10-15-20 mph. So looks like I'll have to pull the gauge cluster and either have it repaired/recalibrated or put something else in. Thanks for the help!
    '16 Subaru Crosstrek; '17 Mazda3 Hatch; '82 Volvo 242 w/LS3 V8 power; '73 TE21 w/3TC power

  10. #10
    Forum Member 1st year Apprentice
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    Default Re: Speedometer Accuracy with T50 transmission swap

    Quote Originally Posted by Michael Yount View Post
    Well - speedo does seem to indicate a speed that changes proportionally with road speed. But way off -- 55 mph or so indicates 35 mph. And when I come to a stop, the speedo won't return to zero -- stops at 10-15-20 mph. So looks like I'll have to pull the gauge cluster and either have it repaired/recalibrated or put something else in. Thanks for the help!
    After 30+ years the speedos can give up their ghosts.

    Hope you find a fix.

    Sent from my SM-G975U using Tapatalk
    -1974 Celica GT (2TG/3T in the works)
    -2010 Lexus IS350 Luxury Edition
    -2013 Toyota Prius III
    -2004 Toyota Sienna LE

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