Another 3.08 to 3.42 swap question

[dmage]

Apologies if it's been posted, saw threads that came close but none addressed my exactly question so here goes:

Got a 1996 GMC c1500 4.3L 5 speed with maybe a billion miles on it. Noticing a lot of play when I turn the drive shaft before the rear gives resistance (e-break on, trans in neutral) - about 1/6th, 1/5th turn.

Thinking my rear is completely shot although there's no noise, clunking etc, but there was tons of noise when I bought the truck because the diff was basically dry. I don't have the tools/skills/time to do my own rebuild kit, I bet i'd screw up the lash too, etc. I can however do a swap, only issue is all the junkyards only have the 3.42. I don't really mind the 3.08, I know it's a slug but I'd swap that in to limit headaches. Here's the big question, if I do swap the 3.42, do I have to do a tune? If so (ugh), any advice there? Find a shop, find a program, etc - seems to be the only real gotcha with this job though if there are more please don't keep it to yourself

Thanks in advance everyone!

Edit: well actually I took a vid (took a gif?) of the play - would this cause any alarm to you good folks? No clunking, no noise since I filled the thing with gear oil https://media.giphy.com/media/a3hqIboWAZRvmXtfbk/giphy-downsized-large.gif

 

[PlayingWithTBI]

if I do swap the 3.42, do I have to do a tune?

A tune isn't really necessary but a good thing to do. You will have to calibrate your speedometer for the different gears.

 

[kennythewelder]

A tune isn't really necessary but a good thing to do. You will have to calibrate your speedometer for the different gears.

X-2

 

[dmage]

Thank you folks! Can you flash yourself or its only dealership.

 

[Supercharged111]

In my '88 C1500, the slop ended up being entirely from the spider gears and cross shaft being worn into each other.

 

[kennythewelder]

Thank you folks! Can you flash yourself or its only dealership.

I use one of these. It works grate, but once you use it, it's locked to that vehicle. Summit racing has them. They are a little under $350

You must be registered for see images attach

 

[dmage]

I use one of these. It works grate, but once you use it, it's locked to that vehicle. Summit racing has them. They are a little under $350

You must be registered for see images attach

thank you!!

Moses, it's $450

 

[kennythewelder]

thank you!!

Moses, it's $450

What I like about the Jet, is that it is also a live data code reader. You can reset your CEL. Look at live data, on things like your 02 sensors, ECT. Just go to Summit's site and put in your info. I think it's $337, if I remember rite. I have been having mine for maybe 8 years. I have adjusted tire size, rear end gear ratio, set the tune to premium gas, set the top speed to 225 MPH, and in the passed, I have used it to trace down issues with the CEL more than once. Sure, an in person tune is more effective, but I like the fact that I can reset things any time I want to. When I rebuilt my rear end, I put an Eaton truetrac in, and I went from 342s to 373s. All new bearings, and seals, ECT. I just broke out my Jet programmer, and reset things. There are some videos on the jet programmer, on YouTube.

 

[dmage]

What I like about the Jet, is that it is also a live data code reader. You can reset your CEL. Look at live data, on things like your 02 sensors, ECT. Just go to Summit's site and put in your info. I think it's $337, if I remember write. I have been having mine for maybe 8 years. I have adjusted tire size, rear end gear ratio, set the tune to premium gas, set the top speed to 225 MPH, and in the passed, I have used it to trace down issues with the CEL more than once. Sure, an in person tune is more effective, but I like the fact that I can reset things any time I want to. When I rebuilt my rear end, I put an Eaton truetrac in, and I went from 342s to 373s. All new bearings, and seals, ECT. I just broke out my Jet programmer, and reset things. There are some videos on the jet programmer, on YouTube.

Thanks again sir, really appreciate these details. found it way cheaper on amazon and summit like you said.

 

[sewlow]

I use one of these. It works grate, but once you use it, it's locked to that vehicle. Summit racing has them. They are a little under $350

You must be registered for see images attach

Actually, there is a way to use that on multiple vehicles which are within the years of the tuner's parameters.
Plug it into a laptop or desktop.
There should be a port on it somewhere. Mine came with a USB cable but it's...where? (Doh!)
The cable for my camera happened to be the same! Once the 'puter recognizes, go to the manufacturer's website & hit 'update'.
Not only will you get the latest software updates, but it will also zero-out the programmed vin.
Now you can use it on another vehicle to set whatever. Tire size, fuel grade, rev limiter, etc. etc.
Once that's done, go back & repeat that 'update' process in order to remove the second vehicle's vin.