More WV Squarebodies

[HotRodPC]

But when the speeds are exponentially wrong, i.e. 2 mph at 30mph, 5 mph at 55 mph, 10 at 70, he would best benefit from getting the right gears for his speedo.

Tires are 33-12.50-15 Gears are 3.08s front and rear Trans is a TH400 Transfer case is an NP203 I would really rather do it the right way and never have to worry about it again. The PO did so many half ass things to this truck that have bit me in the ass already. I'm with Mike Holmes: "Do it Right!" No offense Burb, if it weren't so far off i probably would just move the needle. At least my cheat sheet got a laugh out of the guy who pulled me over.

Exactly. By moving the needle you are just splittin the lie. Instead of being off by 10 at 50 mph, now its accurate at 50, but then reading slow up to the 50mph, then past 50mph, its starts reading to fast again. It woudl never be accurate, just compensated for and off a little less. Its all mathematical. For purpose of making it easy, lets say you are off 5mph at 25mph, then 10mph off at 50, 15mph off at 75, the of course 20mph off at 100.

So your tire size make this one easy, we don't have to convert the tire size ti figure your height. You height is already given and its 33. Trans isn't going to matter cuz the Tcase is what will read the speed, so we need gears for a NP203 speedo driver, and gear ratio of 3.08 in the rear. I'll get busy looking for the info.

 

[HotRodPC]

To best I can figure out, is you'll need an 18 tooth driver gear on the output shaft, and 34 tooth driven gear in the speedo housing going to the speedo cable. This is provided your speed is 1000 RPM's per mile, which most are after 1965 accoring to speedo sites. Those gears are available for Th350, Th400 and 700r4/4L60-E. Now to find out if they exist for NP203. Oh, and you're using a Th400 so you should have a block off for the speedo since its in the case itself instead of tailshaft housing.

 

[HotRodPC]

Here is enough info to scare you and get you confused. I got to the formula, but didn't see if there was gears or what gear options are available for NP203.

http://www.transmissioncenter.net/speedometer_calibration_______va.htm

 

[89Suburban]

 

[crazy4offroad]

Here is enough info to scare you and get you confused. I got to the formula, but didn't see if there was gears or what gear options are available for NP203.

http://www.transmissioncenter.net/speedometer_calibration_______va.htm

NP203 is pretty simple, High range is 1:1, Low range is 2:1.

 

[HotRodPC]

NP203 is pretty simple, High range is 1:1, Low range is 2:1.

That part I knew. When doing the speedo calculation, that woudln't matter. I am reffering to what gears will fit the NP203 tcase.

 

[85k10383]

Well I'm scared shitless already LOL I would never have come up with that info on my own HRPC so I am once again in your debt. This driven gear on the speedp you speak of, does it require the speedo be disassembled? Or is the gear down on the trans end of the cable?

 

[HotRodPC]

Yep, at the the Tcase end. Your speedo is fine. You just want the gears correct so it reads correct. 2 plastic gears, usually about $10-$15 each. Just a matter of getting the right teeth combo and its possible one of your gears might already be correct, so you'd only need one gear.

 

[GreaseDog]

That speed chart thing is crazy, usually you are 5 mph or whatever off of the guage reading, but your's changes with speed? I don't get it. I took a handheld Garmin GPS to clock my truck and it was 5 mph too slow on the guage at all speeds, so I pulled the needle off tha guage and moved it 5 mph and stuck it back on and I have been on the money since, and I check it all the time on our local speed warning digital sign crap thingy's and it's right on.

generally it is varied by speed. since it is reading slower than actual, and the OP has obviously installed larger tires, its completely obvious that he didn't recalibrate the speedo.

just for information purposes, lets assume a truck with no OD and 4.10 gears...

with 33" tires
RPM SPEED
1000 23.9
1500 35.9
2000 47.9
2500 59.9
3000 71.8
3500 83.8
4000 95.8


with 35" tires
RPM SPEED DIFFERENCE
1000 25.4 1.5
1500 38.1 2.2
2000 50.8 2.9
2500 63.5 3.6
3000 76.2 4.4
3500 88.9 5.1
4000 101.6 5.8

as you can see it is not a set difference, it does in fact vary by speed.

 

[GreaseDog]

i'd say open it up and see what it has, and post a picture of your transfer case while you're at it. seeing as the truck in the pictures is an 81+ truck, it shouldn't have a 203 in it at all. it should be an NP208.

 

[HotRodPC]

GD is right if its OEM Tcase in it. But I understood it was swapped and pieced with a NP203 and Th400. Easy to tell for certain. NP203 and NP205 are cast iron Tcases, NP208 is alluminum. And if they gone even a little later in the Tcase, likely a NP241C. Might even be a round NP tag on the back of the Tcase, and it will tell you what it is. The NP208, and 241C will for sure. I'm uncertain about the NP203, I've avoided them cuz of Full Time 4x4 and lousy crawl ratio. But don't go throwing it away if that's what you got. They make good doublers with a NP205.

 

[85k10383]

My mistake it is a 208, I don't know what I was thinking. GD, thanks for that RPM/speed info, I never would have thought to look for that either. I'll be working on the truck this weekend, the left front brake has started making a horrible high pitched screeching noise in motion. I think i got some gravel sandwiched in the dust shield whilst playing around last weekend.

 

[HotRodPC]

Cool, that oughta make it easier to get the right gears to get your speedo corrected.
Now that you know for sure what model Tcase you have, need it figoure out what driver and driven gears are available and then get the right combo. Usually in the 208, whatever is available to the Th350 and 700r4 is avaiable for the NP208. So whatever is available then choose your combo from there. You might even look to see what gears you have now, and only have to replace one instead of both.

 

[WVscottsdale]

nice truck and nice motor. i drive thru glengary to go home