Speedocable problems - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Frijolito1988 · 02-12-2014, 08:20 PM

hey guys need some help.

I have a 72 GMC 2500 The speedo does not mark at any speed. I took off the speedo cable and it is not knicked, broken , and moves freely and good.

I hooked up 1 end to the speedo and the other end to a drill, put the drill in reverse and the speedo moves like its supposed to and also the mileage. When i put the drill going " forward " or clock wise the needle just fumbles around not going over 20 MPH.

If my speedo cable is good and not broken, and the gauge looks to be in good working condition , Should i be looking to replace the speedocable housing in the tranny ? or am i missing something ? It is a 402/400 combo.

Thanks in advance.

luvbowties · 02-12-2014, 08:51 PM

Quote:

Originally Posted by Frijolito1988

hey guys need some help.

I have a 72 GMC 2500 The speedo does not mark at any speed. I took off the speedo cable and it is not knicked, broken , and moves freely and good.

I hooked up 1 end to the speedo and the other end to a drill, put the drill in reverse and the speedo moves like its supposed to and also the mileage. When i put the drill going " forward " or clock wise the needle just fumbles around not going over 20 MPH.

If my speedo cable is good and not broken, and the gauge looks to be in good working condition , Should i be looking to replace the speedocable housing in the tranny ? or am i missing something ? It is a 402/400 combo.

Thanks in advance.

Sounds like cable(part you chucked into your drill) may be a tad short & not engaging speedo fully. I'd buy a new cable with housing--not just the cable, which usually comes in a universal length which you must shorten and install new tip. A new complete unit would just screw on with no mods to it. **Ensure cable housing is screwed all the way onto both trans and back of speedo. **CHECK THIS FIRST**
Sam

**LockDoc** · 02-12-2014, 09:09 PM

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Also make sure there is a gear in the trans gear housing. Look at the first picture at this web site. It will give you a good idea what everything looks like inside. This is a 700r4 trans but everything in basically the same....

http://www.transmissioncenter.net/sp...n_______va.htm

Maybe the end of the cable wasn't all the way into the speedometer or the trans gear as luv said. I would try assembling everything again and try it.

LockDoc

Frijolito1988 · 02-12-2014, 09:19 PM

Ok i had another speedo cable laying around from another c10. installed it on the tranny really tight, drove around without screwing the other side onto the speedo and the cable does not move at all. I am going to unscrew it and take a pic of it.

**LockDoc** · 02-12-2014, 09:30 PM

Quote:

Originally Posted by Frijolito1988

Ok i had another speedo cable laying around from another c10. installed it on the tranny really tight, drove around without screwing the other side onto the speedo and it does not move at all. I am going to unscrew it and take a pic of it.

Just because you have the housing screwed onto the transmission doesn't mean that the inside cable is inserted into the end of the transmission gear. It has to be connected to the speedometer also. That holds the inside cable into the transmission gear.

LockDoc

Frijolito1988 · 02-12-2014, 09:32 PM

Quote:

Originally Posted by LockDoc

Just because you have the housing screwed onto the transmission doesn't mean that the inside cable is inserted into the end of the transmission gear. It has to be connected to the speedometer also. That holds the inside cable into the transmission gear.

LockDoc

There is approximately 3/4 to 1'' cable going into the transmission

Frijolito1988 · 02-12-2014, 09:38 PM

**LockDoc** · 02-12-2014, 10:06 PM

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You might want to take the bolt out of the clamp and look inside the trans to make sure the gear on the tail shaft is in place. Another way you could check is to put a small screwdriver into the end of the transmission gear and gently try to turn it. It should not turn much at all. Do not force it.

LockDoc

Frijolito1988 · 02-17-2014, 08:37 PM

havent had much time to work on this, but quick question. is the drive gear ( gear inside the tranny ) supposed to only spin sideways ? Or is it supposed to go back and forth also ? mine is really loose and goes forward / backward and spins.

geezer#99 · 02-17-2014, 10:08 PM

THe drive gear spins with the output shaft and stays in one spot. The tang on the metal clip sits in a hole on the output shaft. Here's a link that shows a drive gear with the clip that holds it in place. This is for a t350 but is the same type for yours.
You need to pull the tailshaft to fix it.
http://www.ebay.com/itm/TH350-SPEEDO...c0129a&vxp=mtr

02-12-2014, 08:20 PM	#1
Frijolito1988 Registered User Join Date: Jul 2010 Location: So Cal Posts: 421	Speedocable problems hey guys need some help. I have a 72 GMC 2500 The speedo does not mark at any speed. I took off the speedo cable and it is not knicked, broken , and moves freely and good. I hooked up 1 end to the speedo and the other end to a drill, put the drill in reverse and the speedo moves like its supposed to and also the mileage. When i put the drill going " forward " or clock wise the needle just fumbles around not going over 20 MPH. If my speedo cable is good and not broken, and the gauge looks to be in good working condition , Should i be looking to replace the speedocable housing in the tranny ? or am i missing something ? It is a 402/400 combo. Thanks in advance.

02-12-2014, 09:09 PM	#3
LockDoc The Older Generation Join Date: Aug 2006 Location: Montezuma, Iowa Posts: 25,840	Re: Speedocable problems - Also make sure there is a gear in the trans gear housing. Look at the first picture at this web site. It will give you a good idea what everything looks like inside. This is a 700r4 trans but everything in basically the same.... http://www.transmissioncenter.net/sp...n_______va.htm Maybe the end of the cable wasn't all the way into the speedometer or the trans gear as luv said. I would try assembling everything again and try it. LockDoc __________________ Leon Locksmith, Specializing In Antique Trucks, Automobiles, & Motorcycles (My Dually Pickup Project Thread) http://67-72chevytrucks.com/vboard/s...d.php?t=829820 -

02-12-2014, 09:19 PM	#4
Frijolito1988 Registered User Join Date: Jul 2010 Location: So Cal Posts: 421	Re: Speedocable problems Ok i had another speedo cable laying around from another c10. installed it on the tranny really tight, drove around without screwing the other side onto the speedo and the cable does not move at all. I am going to unscrew it and take a pic of it. Last edited by Frijolito1988; 02-12-2014 at 09:35 PM.

02-12-2014, 09:38 PM	#7
Frijolito1988 Registered User Join Date: Jul 2010 Location: So Cal Posts: 421	Re: Speedocable problems

02-12-2014, 10:06 PM	#8
LockDoc The Older Generation Join Date: Aug 2006 Location: Montezuma, Iowa Posts: 25,840	Re: Speedocable problems - You might want to take the bolt out of the clamp and look inside the trans to make sure the gear on the tail shaft is in place. Another way you could check is to put a small screwdriver into the end of the transmission gear and gently try to turn it. It should not turn much at all. Do not force it. LockDoc __________________ Leon Locksmith, Specializing In Antique Trucks, Automobiles, & Motorcycles (My Dually Pickup Project Thread) http://67-72chevytrucks.com/vboard/s...d.php?t=829820 -

02-17-2014, 08:37 PM	#9
Frijolito1988 Registered User Join Date: Jul 2010 Location: So Cal Posts: 421	Re: Speedocable problems havent had much time to work on this, but quick question. is the drive gear ( gear inside the tranny ) supposed to only spin sideways ? Or is it supposed to go back and forth also ? mine is really loose and goes forward / backward and spins.

02-17-2014, 10:08 PM	#10
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,749	Re: Speedocable problems THe drive gear spins with the output shaft and stays in one spot. The tang on the metal clip sits in a hole on the output shaft. Here's a link that shows a drive gear with the clip that holds it in place. This is for a t350 but is the same type for yours. You need to pull the tailshaft to fix it. http://www.ebay.com/itm/TH350-SPEEDO...c0129a&vxp=mtr



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