Speedo gear box - The 1947 - Present Chevrolet & GMC Truck Message Board Network

*wolfthing2000* · 12-21-2005, 05:31 PM

Can anyone tell me what the purpose of the little gearbox that hooks to the transfercase on a 205 transfer is intended to do. I had to take one apart that was froze stuck and the gearing is 1:1 and the direction is not changed.?????????????????????????????????

Coleman · 12-21-2005, 09:22 PM

I'm guessing this little gear box is hooked up to your speedo cable. I'm getting one put on to adjust the indicated speed on the speedo vs my actual speed since I've changed my rear end from a 4.56 to a 3.73 gears. I have a Rockwell 221 transfercase but it's pretty much the same as a np205.

*wolfthing2000* · 12-21-2005, 11:18 PM

I thought the same thing. Like maybe a ratio change for different rear gears, but NO the thing is like a gear that drives an idler gear that drives another gear the same size as the first and because of that the 2 little gears are the same speed in and out, so no ratio change and no direction change. Could this be like some kinda shock absorbing accumulator for the speedo cable???? I just do not understand what the heck it's purpose is!!!!

*72longbed* · 12-22-2005, 11:07 AM

There's one on my NP205 also. Right now the speedo cable is too short to connect to it, but soon I should have the proper length cable and hook it back up. I think its a good thing to have because as you change tire size or gear ratios in the diffs., you can adjust for those changes with that little box. All you have to do is take the tire size info and diff. ratio info and that box to any qualified speedo repair shop and they can change out the internal little gears to make your speedo dead on.

It's a good item to hang onto.

72longbed

*wolfthing2000* · 12-22-2005, 01:05 PM

Please re-read the post. There is no gear change at all in this thing. What goes in comes out the same speed. The things are riveted shut and you have to grind the rivets off to get in.............not too easy of access.

*72longbed* · 12-22-2005, 01:47 PM

It's a Ratio Adapter Box, guaranteed. If a change is needed, the "rivits" will be ground off and different gearing can be installed. You should look closely at the cases, I doubt if they are really rivits, all of these that I have seen are screwed together with either Phillips head or slotted screws.

Either way its a Ratio Adapter Box. Now quit complaining and check how much your speedo is off, fast or slow, take the box and your driveline info to a speedo shop, and see if I'm right.

Just bustin' on ya,
72longbed

*wolfthing2000* · 12-22-2005, 03:02 PM

I don't seem to remember complaining. And they ARE rivets!

Bet you're right though. I just happen to have 1:1

4x4Poet · 02-11-2006, 06:35 PM

Doesn't two gears equal a direction of rotation change? Three gears would not change the direction. Granted, I'm easily confused by physics.

FWIW, my 4.11 K20 pickup has no box but my 3.73 K10 burb does.

12-21-2005, 05:31 PM	#1
wolfthing2000 Account Suspended Join Date: Oct 2004 Posts: 1,276	Speedo gear box Can anyone tell me what the purpose of the little gearbox that hooks to the transfercase on a 205 transfer is intended to do. I had to take one apart that was froze stuck and the gearing is 1:1 and the direction is not changed.?????????????????????????????????

12-21-2005, 09:22 PM	#2
Coleman Registered User Join Date: Nov 2005 Location: Tucson, AZ Posts: 50	Re: Speedo gear box I'm guessing this little gear box is hooked up to your speedo cable. I'm getting one put on to adjust the indicated speed on the speedo vs my actual speed since I've changed my rear end from a 4.56 to a 3.73 gears. I have a Rockwell 221 transfercase but it's pretty much the same as a np205. __________________ 68 Chevy K20 72 Chevy K20 (new) 2000 Silverado Z71

12-21-2005, 11:18 PM	#3
wolfthing2000 Account Suspended Join Date: Oct 2004 Posts: 1,276	Re: Speedo gear box I thought the same thing. Like maybe a ratio change for different rear gears, but NO the thing is like a gear that drives an idler gear that drives another gear the same size as the first and because of that the 2 little gears are the same speed in and out, so no ratio change and no direction change. Could this be like some kinda shock absorbing accumulator for the speedo cable???? I just do not understand what the heck it's purpose is!!!!

12-22-2005, 11:07 AM	#4
72longbed Account Suspended Join Date: Jun 2003 Location: PA Posts: 1,411	Re: Speedo gear box There's one on my NP205 also. Right now the speedo cable is too short to connect to it, but soon I should have the proper length cable and hook it back up. I think its a good thing to have because as you change tire size or gear ratios in the diffs., you can adjust for those changes with that little box. All you have to do is take the tire size info and diff. ratio info and that box to any qualified speedo repair shop and they can change out the internal little gears to make your speedo dead on. It's a good item to hang onto. 72longbed Last edited by 72longbed; 12-22-2005 at 01:48 PM.

12-22-2005, 01:05 PM	#5
wolfthing2000 Account Suspended Join Date: Oct 2004 Posts: 1,276	Re: Speedo gear box Please re-read the post. There is no gear change at all in this thing. What goes in comes out the same speed. The things are riveted shut and you have to grind the rivets off to get in.............not too easy of access.

12-22-2005, 01:47 PM	#6
72longbed Account Suspended Join Date: Jun 2003 Location: PA Posts: 1,411	Re: Speedo gear box It's a Ratio Adapter Box, guaranteed. If a change is needed, the "rivits" will be ground off and different gearing can be installed. You should look closely at the cases, I doubt if they are really rivits, all of these that I have seen are screwed together with either Phillips head or slotted screws. Either way its a Ratio Adapter Box. Now quit complaining and check how much your speedo is off, fast or slow, take the box and your driveline info to a speedo shop, and see if I'm right. Just bustin' on ya, 72longbed

12-22-2005, 03:02 PM	#7
wolfthing2000 Account Suspended Join Date: Oct 2004 Posts: 1,276	Re: Speedo gear box I don't seem to remember complaining. And they ARE rivets! Bet you're right though. I just happen to have 1:1

02-11-2006, 06:35 PM	#8
4x4Poet Registered User Join Date: Nov 2004 Location: "Under Montana skies." Posts: 1,836	Re: Speedo gear box Doesn't two gears equal a direction of rotation change? Three gears would not change the direction. Granted, I'm easily confused by physics. FWIW, my 4.11 K20 pickup has no box but my 3.73 K10 burb does. __________________ '71 GMC K20 Suburban, '71 GMC K10 Suburban, '72 Chevy C10 CST Suburban, '72 Chevy K20 clunker pickup.



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