Installed a tachometer learned something new

[oil pan 4]

I finely installed my ISSPRO tachometer on my diesel suburban using a magnetic pickup pulling a signal off the flexplate.
So I know its accurate.

After I looked up how many teeth the 6.2L diesel flex plate has (139) I programmed that into the tachometer.
As soon as I took it out for its first drive I realized I was turning a good number more RPMs than it should have been.
Also knowing how much my speedometer is off helped too (reads about 2 to 3mph slow at 60mph).

I found out that my suburban does not have 3.08 gears and a posi diff, like it should have according to its build sheet.
It appears to have 3.42 gears and an open diff.

Which makes sense for 2 reasons.

1 I have always had a feeling that the rear axle had been swapped.
2 When I bought my suburban it had a 2-5/16'' ball hitch on the back.

[Frank Lee]

Glad you did a fine job!

[justme1969]

Very common thing there Chevy and ford had a rash of delinquent rear axles in trucks from 82 -2002. many back yarders are scared to work on the rear gears and just pop one out and bolt whole axle into thiers. my suburban had special axles rated at 3/4 ton level but with 6 lug pattern found 2 separate gear ratios then much to my dismay found front axle was the weaker standard 28 splined replacement.
Regardless both got 4.11, with auburn gear limited slips, and 31 splined moser axles.
It balanced out the 38' tires and stock enging /trans operated at original performane levels again. was very costly!

[Frank Lee]

38 foot tires LORDY!