Speedometer and Gas Gauge

[T Col]

Follow up on speedometer specifics

Tire size / Rear axle ratio determines which driven gear to use

If they aren't STOCK tires and rims it will be more difficult to determine.

Please post all the pertinent info so we can get you the correct driven gear to use.

The original size of tire was L70R-15 - (approximately a 29.7 " tire)

Normally today a P235-R75-15 is the replacement

Mil1ion-

I have figured out with some confidence that I have a 4.10 rear end (out of 95 lightning per the previous owner and then my web research on the same)

The tire size is 31 x 10.50 R 15 LT

Automatic tranny

I am a little buffaloed as the calculators that I have been finding are coming up with more teeth needed than what is for sale

What do you think?

 

[Mil1ion]

10.50" ring gear ?

There should be a number like 75,78 or 80 meaning a %age of the tire tread width (255mm)

the 31 should be P255

so the tire size would be P255 78R-15

You know the ratio is 4.11:1 so the 10.5" ring gear size means nothing

Get me the TAG info from the C6 transmission in the truck

we need to know if it is a 6,8 or 9 spline drive gear in it

 

[T Col]

I just ran the calculator / converter here on FTF website and it says wit those numbers i gave you the metric conversion should be:

267/76 R15

Is that more what your looking for?

 

[5.0Flareside]

10.50" ring gear ?

There should be a number like 75,78 or 80 meaning a %age of the tire tread width (255mm)

the 31 should be P255

so the tire size would be P255 78R-15

You know the ratio is 4.11:1 so the 10.5" ring gear size means nothing

Get me the TAG info from the C6 transmission in the truck

we need to know if it is a 6,8 or 9 spline drive gear in it

31x10.5 is almost spot on to 265-75

 

[Mil1ion]

10.5" is the ring gear size and has nothing to do with the tire size

 

[Mil1ion]

I just ran the calculator / converter here on FTF website and it says wit those numbers i gave you the metric conversion should be:

267/76 R15

Is that more what your looking for?

P265/75R-15 is what you have
They don't make 267mm 76% tires

Now I need the Trans info so I know what spline drive gear is in it

 

[T Col]

I have viewed the bottom side of the tranny during the earlier discussions, is the tag your are speaking of top side or to the front or something as I did not note it on the rear portion of the tranny.

I got a little lost during some of the other posts, if it helps when I was researching the 95 lightning rear end it referred to it as 8.8 4:10.1 and the only one for that era (later models switched to 3.73)

 

[Mil1ion]

so where did the 10.5 number come from ?

 

[T Col]

The 10.5 is one of the numbers from the tire size that was on your list of needed items (31 x 10.50 R 15)

I just crawled under the truck, and from the location the diagram indicated I found:
D50P-7006-AA

Under this, there are two circles, the one toward the from is blocked and the top half of the one to the rear has a "78" visible inside of this circle at about the 2 o'clock position

Is this the information that I am hunting?

 

[T Col]

Just ran my iPhone up in the hole and was able to figure out that in the front circle that I could not see there is a "5" at about the 3 o'clock position

(sure will be handy when I figure out how to post a picture)

 

[T Col]

One more (sorry) after really looking that photo over, in the rear circle, across from the 78, at about the 7 o'clock position, there is either a 6 or a 9 (if you look at the circle in the same orientation you would to view the 78 it would be 6, if literally speaking it would be a 9

Again, as they say, a picture replaces a thousand words

 

[Mil1ion]

You're looking for a PJA-?? or PJA-??? type number

 

[T Col]

Still working on it- could not find that anywhere on the tranny and have been doing a lot of research (I now know how to decode the "d" number I sent you but does not convert into a pja anything (I am pretty sure it is a c4 now though))

Still looking

 

[DNFXDLI]

Look at post number 28 in this thread...that metal tag that is bolted on the servo cover is what you are looking for.

 

[T Col]

Thanks for connecting the dots between the two threads ---- I found in the diagram where the tag is supposed to be but found no tag which is why I threw out the other one hoping to catch someone's attention specific to transmission

Google provided me a lot of info really quick but not dice on the specific

 

[DNFXDLI]

If the servo cover was removed for any reason, it might not have been (the tag) put back.

 

[Mil1ion]

I don't see where you listed a engine size ?

Please provide

 

[T Col]

It is a 302 V8

 

[T Col]

Okay,let's back the thread up a bit, and think about this in another way

Earlier in the discussion and as I have been seeing there is 6 options for driven gears for the speedo cable, (unless anyone that was ever made will fit and if so this will kill the thought) since this 4.10.1 rear end is basically turning 4 to 1 is there any chance that the 16 tooth drive gear should be used????

Another thought, any of you that are good with the math, what if we just take a shot at which tooth count to try in the calculation - if I could with some confidence give it a try until something else could be figured out (since they are 6 dollars a piece)?

Right now it is about 30+ mph off at higher speeds which ain't gonna work for a teenage boy unknown how much at low speeds have not laced it, thought I could resolve it pretty simple but now finding things light the tranny ID tag I am having to rethink this.

Needing some educated theories

 

[DNFXDLI]

http://www.sccoa.com/faq/speedgr.html