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Apr 26th, 2026 | | AD Chevy Trucks  Over 6,000 pictures Brad Allen has an awesome collection of Chevrolet factory pictures that he has set up from film strips. Check them out!
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| | | | Joined: Jan 2020 Posts: 7 New Guy | | New Guy Joined: Jan 2020 Posts: 7 | I recently purchased a 1966 GMC 1500. The 1965 GMC I am restoring is down to the frame and will require many hrs of work. Not forgotten just needed a driver. The 1966 does not have the speedo connected. It has a turbo 400 in it but the transmission has an electric connection on the speedo drive. The rear end has a tag on it 4110/4:10. My question is how many tooth gear drive will I need? Also have connected a cordless drill to insure the speedo and cable are not locked up. Accelerated to 70 mph quickly. Yee haw Also what is the best way to lubricate the speedo cable? | | | | | Joined: Jun 2011 Posts: 5,096 Crusing in the Passing Lane | | Crusing in the Passing Lane Joined: Jun 2011 Posts: 5,096 | Slip the cable through regular grease in your hand as you insert it.
Dealer might have speedo worm gear info.
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: Apr 2005 Posts: 7,440 Bolter | | Bolter Joined: Apr 2005 Posts: 7,440 | I don’t think it is as simple as finding a gear drive. Your truck came with a manual speedometer. The transmission is for an electronic speedometer. There are adapters made but they are very expensive. You can change the transmission tail shaft to a manual speedometer but they are difficult to find.
Martin
'62 Chevy C-10 Stepside Shortbed (Restomod in progress)
'47 Chevy 3100 5 Window (long term project)
‘65 Chevy Biscayne (Emily)
‘39 Dodge Business Coupe (Clarence)
“I fought the law and the law won" now I are a retired one!
Support those brave men/women who stand the "Thin Blue Line"! Hug a cop!
USAF 1965-1969 Weather Observation Tech (I got paid to look at the clouds)
| | | | | Joined: Jul 2000 Posts: 2,188 Insomniac | | Insomniac Joined: Jul 2000 Posts: 2,188 | Are you sure that it is a TH400?
Gord 🇨🇦
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1954 1/2 ton 235 4 speed
| | | | | Joined: Feb 2000 Posts: 5,199 'Bolter | | 'Bolter Joined: Feb 2000 Posts: 5,199 | I thought all Turbo 400's used gear drive speedometers, better get a picture of what you have. A picture of the oil pan will tell. | | | | | Joined: Apr 2005 Posts: 2,832 'Bolter | | 'Bolter Joined: Apr 2005 Posts: 2,832 | Just do a search for "speedometer gear calculator" and several hits will come up. I used to use TCI but have since gone to gps speedometers where gear ratios and tire size have no bearing on getting a dead accurate speed reading. They are only about $60 so why mess with a caveman design.
Evan
| | | | | Joined: Feb 2004 Posts: 29,761 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,761 | Are you sure you've got a TH400? I don't think I've ever seen one with an electronic speedo drive. A 400 has an oddball-shaped pan with a bulge on the passenger's side. If the pan is square and there's no vacuum modulator, you probably have a TH 700R4 which can have either a gear drive on an electronic pulse type. You can convert the 700 to a gear drive by removing the tailshaft housing and swapping to a worm gear instead of the pulse ring.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: Sep 2011 Posts: 1,453 'Bolter | | 'Bolter Joined: Sep 2011 Posts: 1,453 | Picture worth a thousand words!
BC
1960 Chevy C10 driver 261 T5 4.10 dana 44 power loc
1949 GMC 250 project in waiting
1960 C60 pasture art
Retired GM dealer tech. 1980 - 2022
| | | | | Joined: Jan 2020 Posts: 7 New Guy | | New Guy Joined: Jan 2020 Posts: 7 | I have an appointment Monday at the tranny shop. Will advise results. A gps speedo wow. This opens a whole new frontier. Thanks for all the info. This site is a wealth of info. Just cause I don't post don't mean I ain't looking. | | | | | Joined: Jan 2020 Posts: 7 New Guy | | New Guy Joined: Jan 2020 Posts: 7 | The transmission repairman identified it as a 700. Have researched and believe I will go with a gps speedo. This site is great thanks for the ideas. | | | | | Joined: Sep 2011 Posts: 1,453 'Bolter | | 'Bolter Joined: Sep 2011 Posts: 1,453 | 700-R4 (later called 4L60) should have a mechanical speedo, would also have a T.V. (throttle valve) cable coming from near the fill tube to the throttle bracket & a governor cover on the left side near the rear of the case. 4L60E doesn't have either of these.
BC
1960 Chevy C10 driver 261 T5 4.10 dana 44 power loc
1949 GMC 250 project in waiting
1960 C60 pasture art
Retired GM dealer tech. 1980 - 2022
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