Cruising Under Stall RPM- TH350

[kenny78]

I just refuse to pay any one for something I can learn to do myself. I don't blame you tho and to set up gears that isn't a bad price.

I usually agree but have to compromise somewhere.

 

[Honky Kong jr]

I usually agree but have to compromise somewhere.

I compromise when I need something painted nicely. But it n all my projects it was only twice. My 67 Chevelle and one of my 64 Impalas. Me and shiny paint don't mix. Lol

 

[74 Shortbed]

Me and shiny paint don't mix. Lol

That makes two of us, lol..

 

[Splandman]

I'm not overly knowledgeable on the 10 bolt vs. 12 bolt deal, but like you, I had read a lot on the internet about the 10 bolt being way inferior. I destroyed a 10 bolt in my K10 recently, but it was the original, stock rear end, with 2.73 gears (I think), and it just didn't hold up to the bigger wheels/tires and increased power.

When I went to have it rebuilt and do a gear change I was prepared to be told I needed to upgrade to a 12 bolt. The guys that did the rebuild were pretty adamant that I did not need to change the rear end, just rebuild the 10 bolt with a good posi unit and gears and I would be fine. I now have 4.10 gears and the truck feels pretty good. No problems so far.

 

[Honky Kong jr]

Hey all you guys can send me all your 10 bolt 89-91 K5 and Burb axles.........front and rear.

 

[SHOTROD81]

Thanks for all the tips! This will probably be my next improvement. I spent all last winter rewiring the entire truck after an electrical meltdown, so this will give me something to do next winter. If this is normally a 2 day project, rest assured that it will take me an entire season.

I will be checking out the threads here for more info on gear swaps. If anyone has recommendations on brands, posi configurations, axles, etc..., please let me know.

 

[Honky Kong jr]

I'm not overly knowledgeable on the 10 bolt vs. 12 bolt deal, but like you, I had read a lot on the internet about the 10 bolt being way inferior. I destroyed a 10 bolt in my K10 recently, but it was the original, stock rear end, with 2.73 gears (I think), and it just didn't hold up to the bigger wheels/tires and increased power.

When I went to have it rebuilt and do a gear change I was prepared to be told I needed to upgrade to a 12 bolt. The guys that did the rebuild were pretty adamant that I did not need to change the rear end, just rebuild the 10 bolt with a good posi unit and gears and I would be fine. I now have 4.10 gears and the truck feels pretty good. No problems so far.

10 bolts got a bad wrap because they often get lumped in with the 8.2 and 7.5/7.625. The 8.5 replaced the 12 in 1/2ton trucks.

 

[bucket]

10 bolts got a bad wrap because they often get lumped in with the 8.2 and 7.5/7.625. The 8.5 replaced the 12 in 1/2ton trucks.

Eh, they get a bad wrap because they tend to blow carriers under the rear of a heavy truck, IMHO. They are fine for light use in a 4x4 or most any 2wd pickup, but I would never trust one under a Burb or any 4x4 with larger than stock tires and a heavy right foot. I've just seen too many of them puke their guts out.

 

[SHOTROD81]

Came across a 12-bolt today with an Eaton posi in an 87 Suburban with 3.73 gears. About 51K on the rebuild. Would this be a fairly straightforward swap? I'm a little apprehensive about trying to put new gears, posi, etc.. in my current 10 bolt, and the price seems fair. Anything to look or listen for if I go check it out? Or is this not a good idea?

 

[Honky Kong jr]

Came across a 12-bolt today with an Eaton posi in an 87 Suburban with 3.73 gears. About 51K on the rebuild. Would this be a fairly straightforward swap? I'm a little apprehensive about trying to put new gears, posi, etc.. in my current 10 bolt, and the price seems fair. Anything to look or listen for if I go check it out? Or is this not a good idea?

If it in fact it is a 12 bolt that was already swapped where a 10 bolt was. I have a 12 bolt in where a 10 bolt was easy swap bolts right in. Just be sure to get new U bolts

 

[SHOTROD81]

If it in fact it is a 12 bolt that was already swapped where a 10 bolt was. I have a 12 bolt in where a 10 bolt was easy swap bolts right in. Just be sure to get new U bolts

Thanks for the tip. I think they are asking around 900 for it, does this seem fair? I just posted this in the driveline/differential section in case anyone had any other advice. Thanks again.

 

[Honky Kong jr]

Thanks for the tip. I think they are asking around 900 for it, does this seem fair? I just posted this in the driveline/differential section in case anyone had any other advice. Thanks again.

I paid 80 for mine..... is this a car or truck 12 bolt? Car 12 bolt that's a decent price truck not so much. You could regear your 10 bolt and find a posi for that price tho.

 

[SHOTROD81]

I paid 80 for mine..... is this a car or truck 12 bolt? Car 12 bolt that's a decent price truck not so much. You could regear your 10 bolt and find a posi for that price tho.

The rear differential pursuit was put on hold by an engine failure, but I'm pretty close to having that resolved. The rear I was describing is a truck 12 bolt. For cost comparison, unless I'm looking in the wrong place, it seems that parts alone would run around 1200 for my 8.5 bolt, plus labor if I don't tackle it myself. (around $475 for Eaton posi, $300 for axles, $400 for ring/pinion and other installation parts). Is there a better place to look than the usuals (Summit/Jegs)? I suppose it's probably better, though, to go with new components even if it is a little more expensive since I don't know how much abuse a "pre-owned" unit has endured.

 

[HotRodPC]

If it in fact it is a 12 bolt that was already swapped where a 10 bolt was. I have a 12 bolt in where a 10 bolt was easy swap bolts right in. Just be sure to get new U bolts

Isn't there a difference in the pinion length between 10 and 12 bolt? So although they bolt right in where each other was, isn't the driveshaft lengths different?

I know for a fact on the 14b Semi Float and 14b Full Float there is a difference. The 14b Semi Float is about an inch and a half longer so the driveshaft needs to be shorter. Now if you're going from a 14b Semi Float to a 14b Full Float, there is probably enough slip on the 2pc driveshaft that you can use the same driveshaft, but going from 14b FF to SF, then the driveshaft is to long and will need to be trimmed about an inch to an inch and a half.

 

[SHOTROD81]

I have been working on an associates project with a similar setup. The vehicle is 4k lbs, 383 10.8 238/246 duration with 700r4 and 3.08 gears. The owner wanted a racecar that got good gas mileage. He got a mismatched pig that is not good at anything. The builder used a 1200rpm towing converter!
The owner had a set of 3.73 gears installed and the car gets better gas mileage, has better street and cruise manners, and pulls like a freight train above 2500 rpm. The cam card even recommends a 2200-2800 stall.
It still tries to die when put in gear and rattles horribly at idle but that is beyond my desire to help tjat guy any further.
Go with the gears and don't be overly concerned about the 10 bolt vs 12 bolt stuff. I have been 10s on an 8.5 10 bolt.

Finally got the rear end completely rebuilt and am loving it so far. Went with AAM 3.73s and a Detroit Truetrac. I sidestepped my pride and had it done by someone who knows what they're doing. The guy who did it recommended putting on at least 500 miles before any hard launches, so I'm patiently racking up the miles with restraint. I'm not missing the 2.56 or the mini-spool at all. Thanks to everyone for their advice.