Another OD swap.....

[inthedirt]

My first Chevy, so forgive the general lack of knowledge on what the heck I'm driving.

I have a 1987 3/4 ton with the 350TBI and TH400.  Just put new 265/75/16 tires (32in?) and the rest of the truck is all stock and original.  Not sure on the ring and pinion, but I tack around 2900rpm at 60mph.  Obviously, I'd like that lower.  I asked my local mechanic on OD options and he stopped adding up the price after he hit $3k assuming that I didn't want to get that deep into it.  That was for a reman 700R4, various t-case adapters, and blah blah blah.

Since I don't know which rear axle is in this, or T-case, is his pricing that far off or is there a cheaper way to do this?  I'm no stranger to turning wrenches, but I don't have a lift in my shop yet, nor do I have the time. I've looked into Gear Vendors and other similar "add a gear" devices and they, too, are wickledly expensive (>$3000).  Figured that if I needed to spend that kind of money, I would sell it and pick up something a little newer with the OD already in it.  But.......my wife wants me to keep it and I'm already into it for $1800 in tires and a complete front end job.  That's not including the $1500 I paid for last June.  Thoughts? Comments? Suggestions?

[inthedirt]

Found some info in the glove box and decoded.  It appears that I have 4.10 axles, a 66A alternator, GVW of 8600 lbs.  All other codes seemed to match the equipment my truck has on it.  Also found a code for "Reactor System Air Injection," whatever that means.

[hwh]

you dont have really any cheaper options. change trans or gear vendor. or change gears to 3.73

[inthedirt]

Since GM offered so many options back then, including the 700R4, I thought for sure something would bolt up.  I was prepared for different driveshaft lengths or something else fairly easy, but my mechanics list of parts was quite long.  And his price didn't include labor.....

[1967KaiserM715]

Transmission(700r4) $2,000
Transfer case(can do input shaft swap-but typically isn't that much cheaper) $500

Driveshafts (front may work, but the rear will likely need to be shortened) figure $200 for that.

Depending on the transmission crossmember, that may need to be swapped out as well.

Then a couple little things like the TV cable and bracket, so figure another $100.

I figure around $5-6000 all said and done by a mechanic.

Also, the TH400 should be a 32 spline input, the 700r4 is 27, hence the transfer case swap.

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[Dr_Snooz]

If it were mine, I'd swap out the diff. You can get a scrapper for next to nothing, or buy something new for not much more. Better yet, you have the option of putting in an LSD or locker or something to really improve traction. You aren't going to save enough gas with a trans swap to ever break even on the expense of it.

[1967KaiserM715]

Do you plan on using the truck as a truck, or is it just a toy?


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[Stewart G Griffin]

If it were mine, I'd swap out the diff. You can get a scrapper for next to nothing, or buy something new for not much more. Better yet, you have the option of putting in an LSD or locker or something to really improve traction. You aren't going to save enough gas with a trans swap to ever break even on the expense of it.

If you can manage to find a rear axle at the salvage yard, i think 3.21 is the highest you can get that would fit a 3/4----a 14 bolt.

OR you could get any rear out of any truck---say a 10 or 12 bolt out of a 1/2 ton and go as high as 2.56, but then you may have to weld new spring perches on.  Still much easier/cheaper than the trans swap.

Maybe the cheapest/easiest way is to go with a taller tire----if that's possible at this point?

[Dr_Snooz]

From OP's first post, I'd guess he's got a 4.10 rear end. So he has some room to improve.

[inthedirt]

It's used to haul my boat to the lake,  haul my dirtbikes or sleds to the mountain, and for commuting to work.  Its definitely no show truck, and I'm ok with that.  Would rather not have to waste an entire tank of fuel to get somewhere, that's all.  Thought for sure there would be an easier/cheaper alternative to paying my mechanic's mortgage payment, but I'm finding otherwise.  It will remain my farm truck and be available when my boys learn to drive, but I'd rather spend that kind of money on something newer.  Guess I'm done spending anything real on this thing.  No big deal. Thanks for the help and advice.

[Stewart G Griffin]

But first, research:

1) Are there tires taller than 32"?

2) Can you take a rear out of a 1/2 ton and simply bolt it in a 3/4?

[1967KaiserM715]

First off guys, I am assuming he has 4wd, since he mentioned a transfercase, so he would need 2 matching axles, a re-gear on one would require a re-gear on the other, figure parts for that in the $3-400 range, then proper install by a mechanic would put each axle at around $1000. If he could do it himself, then it's not bad, but at the moment it seems like that is option is out for now.


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[fitz]

How many miles do you drive a year?
GM engineers designed your truck to drive on the highway with the gears it has.
An overdrive trans may make it more efficient, but how long would it take to save $3000 in gas?

[1967KaiserM715]

Assuming an increase of 3 mpg that could mean $400 saved of he travels 5,000 miles a year. So it would take over 7 minimum years to recoup the cost.




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[fitz]

Assuming an increase of 3 mpg that could mean $400 saved of he travels 5,000 miles a year. So it would take over 7 minimum years to recoup the cost.
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  Thanks 67kaiser for running the numbers.
   While I would never discourage someone from spending money building a square body into a dream truck, I hate to see someone waste money that they don't need to.
  Inthedirt said he had about $3300 into the truck as it sits. If it's a reliable  & trustworthy rig that gets the job done, I say run it as is.
  When I bought my first M1028 years ago. I have to admit I didn't do my homework (long story). I have to say I was a little disappointed to find out it had 4.56 gears and was noisy on the highway.
  I looked into regearing & trans swaps. Unless you use parts from a parts truck, both option would easily cost $3,000.  A Gear Vendors overdrive can cost close to $5000 by the time your done. For me it didn't make sense to do that on a $1500 truck.
  A few M1028's have come & gone since that truck. My current truck runs 285/75R16 tires (33") and they brought my highway speed up to about 60mph.  If I need more then that, I drive another vehicle.