help with transmission.

[Meir]

That makes it the same length as a 700R4. No driveshaft work when they did the swap.

So with the power that you are wanting to shoot for, and the possible tire size, are you still leaning towards the 400?
And then solid axle swap with better gears to go with 37" tires?
I think that you should!!!

If to be honest, I'm starting to have second thoughts about the transmission.
I think I'm pretty much down to the 400 or the beefed up 700.
https://www.geareduptransmissions.c...issions/products/g-2-700r4?variant=6023605829
Didn't consider a solid axle swap, but hi, I'm just in the beginning of my way. Still have a lot to learn, and you just gave me some more homework to do.
I plan on dropping the transfer this weekend, and the transmission on the next.
I'm not in a rush, but I hope to take a desiscion and order a new transmission and the parts I will need, by the next weekend.
Will appreciate if you could put your vote on the top. You guys rock
I love this forum.

 

[skunked]

you need to decide if you want overdrive or not. If not, you should be comparing a th350 to a th400. If you want OD look at the 700R or 4L80E

Your comparing apples to oranges looking at the 700 and 400.

 

[Blue85]

It would be silly to run a TH400 in a truck with a 10-bolt rear axle.

 

[mrk5]

The military blazers did tho. 6.2L/TH400/NP208 with 10 bolt axles.

 

[dyeager535]

The military blazers did tho. 6.2L/TH400/NP208 with 10 bolt axles.

They also had 3.08's, and the 400 was common throughout the fleet, so logistically that makes sense. From anecdotes I've heard, as the 1009's were loaded down, the axles were most definitely the failure point.

Still, I can see the reason to run the 700R4 with 10 bolts, a well-built (and properly cooled) 700 is probably more likely to stand up to abuse than the 10 bolts are.

Hmm...now I want to see the MPG on a 6.2 K5 with 700 and 3.08's.

 

[mrk5]

I was thinking my M1009 had 3.73 gears. I remember we could get 19mpg no matter what we were doing. Add OD and maybe you could get into the 20's.

 

[dyeager535]

I was thinking my M1009 had 3.73 gears. I remember we could get 19mpg no matter what we were doing. Add OD and maybe you could get into the 20's.

Made me second guess myself, been a long time since I had to deal with them, but this says 3.08's as well: http://olive-drab.com/idphoto/id_photos_m1009.php

They also say 27 gallon fuel tank (I thought they were 25?) but even with a 25 gallon tank and 19MPG, that's 475 miles of range. 589 with the 31 gallon. 25MPG with the manual has been documented...775 miles on a fill pretty much negates the need for additional fuel IMO...that would be amazing for long times off pavement.

Ugh. Way off track. But that said, I don't see a reason to use anything but a 700R4 unless you know the trans is going to be subject to a lot of abuse, such as heavy towing. IIRC, 1st ratio is pretty good, and if you don't need overdrive all the time, it's not like you can't drop it into 3rd. I guess if you knew you were never going to change ratio, and would never need OD, simpler is better, so TH350, but realistically, you'd need probably 2.73's with 31's to be in the situation where you could never use OD. It's hilly out here, and even with the 305, 700, 3.08's and 31's, I was able to use overdrive. Mainly on the freeway, but nothing wrong with having it.

 

[mrk5]

I've had an unknown condition 700r4 in my K5 for 4 years and the crew cab for 5 years. 10 trips to Moab which usually nets about 1000 miles each time. Not really any towing but the crew cab weighs 7700lbs. I haven't had any trouble but I use a big cooler and keep an eye on temps.

 

[Meir]

Hi guys.
I cannot believe it has been more then 3 months since my last post.
Was mostly busy at work, but also spent tremendous amount of time readin and learning about the truck.
The more I read, I understand I have more to learn.
I have decided what is the general rout I’m going to take with my build, and decided to go at this point with the 700r4.
I found a local transmission guy that sourced a k case and fully rebuild it for me.
I’m about to start with the project today.
The plan is to drop the old transmission today, clean the undercarriage of the truck, replace the transmission fluid lines with flexible AN6 braided lines, install new oil cooler and external filter, flush the radiator, and install the new transmission tomorrow. At the same time, I will replace the rear main seal and the oil pan gasket.
I cannot thank enough to all of you for chiming in, and sharing your knowledge.
I will update the thread with my progress, as I’m sure I will have some question to ask.
Thanks in advance.
Meir.

 

[diesel4me]

GM used TH400's in a lot of big land yachts with highway gears in the 60's and 70's,they mostly had only 10 bolt diffs too..
It is puzzling to me why an old beast like a big Caddy or Buick that weighed 3 tons ,just like a pickup truck,didn't seem to have many rear diff problems ,despite them only being a 10 bolt,taking a lot of abuse--burnouts,lots of torque from big blocks,etc..yet in a pickup or K5 a 10 bolt seems to pop pretty easily..

The 700R4 tranny's main advantage is the lower first gear,and overdrive...
I never liked them much myself due to the fact they seemed weak and failure prone,until they were rebuilt with some expensive beefed up parts like the sun shell...also the throttle valve cable can kill one in a matter of minutes if it goes out of adjustment or broke..

As for better fuel mileage with a 6.2 & a 700R4,and 3:08 gears,that may not always improve it,having it lugging at highway speeds--if your in hilly terrain the engine will be struggling to maintain speed and that will probably reduce your fuel mileage--maybe a 1/2 ton 2wd "light" truck would tolerate over-gearing it better,but in a heavier rig it will probably get less mpg..

My van got 3-4 mpg more when it had 3:08's compared to the 2:73 diff I had to swap in it after the diff case got hogged out on the 3:08..
I bet the 307 V8 & TH350 would get slightly better mpg if it had 3:42's or 3:73's,that engine likes to wind up some ,rather than pull at lower rpms..its a dog on takeoffs with the 2:73's in it..

 

[Hogback Fabrication]

GM used TH400's in a lot of big land yachts with highway gears in the 60's and 70's,they mostly had only 10 bolt diffs too..
It is puzzling to me why an old beast like a big Caddy or Buick that weighed 3 tons ,just like a pickup truck,didn't seem to have many rear diff problems ,despite them only being a 10 bolt,taking a lot of abuse--burnouts,lots of torque from big blocks,etc..yet in a pickup or K5 a 10 bolt seems to pop pretty easily..

Terrain and use. Like you said, you'll see 800 horsepower cars make a 700R4 and 10 bolt work fine, but a 4x4 with 150 hp can easily break both.

The 10 bolt rear in a street application sees really consistent loading. Launching at a drag strip seem like it would be hard on parts, but both axle shafts are loaded pretty equally and smoothly. The little 7.625" 10 bolt in my Camaro has lived through ~550hp and wide tires without failure.

4x4's load the rear end heavier when climbing, tires can spin fast and then catch when climbing through mud/rocks, bouncing, etc. Horsepower isn't the big killer for rear axles, weight and use are. Guys run 10 second 1/4 miles on 10 bolt rear ends in cars, and break them on 33's offroad.

 

[76zimmer]

700 w full manual v/b

 

[JT88K5]

I snapped a 10 bolt in my 76 cutlass w stock 350 motor, pulling out just a little heavy on the go pedal. Wife happened to be going the other way, saw me on the side of the road and ran into someone changing lanes. That’s was a shitty day.