89 2500 Transmission/Rear End Questions
 

Hi,

A couple of months ago I got my first truck. It's a 89 Chevy Silverado ext cab, 4x4, 350, 5 speed, with a flat bed. The engine was overhauled around 250,000 and a new/rebuilt transmission was put in it's place. I know from the pictures in the manual that this isn't the same 5 speed that came with the truck. Underneath all it says on the transmission is to make sure to refill it with a specific castrol oil. On the gear shifter knob it has a L-1-2-3-O-R. Does anyone know where I can find out what type of transmission I have?

I am not sure what ratio the rear end is. The codes in the glove box are all rubbed off so I can't see what it came with. Is there somewhere I can see the ratio?

The speedometer is off about 5 mph (so when I am going 55 it is really only 50 mph). I imagine that is because of the tires (The tires it is suppose to have is 245/75R16 but it has 235's). I did replace the speedometer gauge cluster and I heard that if you got the speedometer from a truck running a different ratio in the rear end it could be off, I never tested the old speedometer with a GPS before replacing it. In reality I just needed to fix the odometer since it was stuck so I could put in the old gauge set and just move the good odometer over. But I would like to know how I could get my speedometer working better

Re: 89 2500 Transmission/Rear End Questions
 

The VIN number may show what was OEM?

Re: 89 2500 Transmission/Rear End Questions
 

I think you have the 4:10 gears with a nv-4500 trans its extreamly rare for gm to put 4:56 gears behind a 350 motor but another kinda easy way to see what may be in it is by the design of the rear end is it a corpret 14bolt rear or a simi flow 14bolt rear
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Re: 89 2500 Transmission/Rear End Questions
 

So from what I have seen in the pictures it looks like I have a corporate rear end. I assume I also have 4:10. From what I saw on the pictures on the nv-4500 it looks exactly like it. Now I just need to find out if it was an earlier model that had trouble with the nut coming undone in 5th gear or if it has the longer splines so 5th gear will be fine.

I put the stock speedometer back in but I put all the newer gauges inside the older speedometer frame/electronic board and all is well now with my speedometer. It is now just -1 of what I really am going (Shows 70, going 69). I also put on the correct size of tires on the back so everything is working great. I assume the other speedometer I got was programmed for a different rear end ratio.

Re: 89 2500 Transmission/Rear End Questions
 

I am going to assume that when you were checking your speed you used a gps if so don't worry trust the truck 1mph off is nothing when I put bigger tires on my 95 gmc it threw the speedo off by like 8mph. But like I said just trust the truck gps is only acurate to a sertine point.
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