Rear axle gear ratio?

[jarrodscot]

The truck is a 1970 c10 short box. The vin code identifies it was a inline six motor. It now has a 350 with turbo 350 trans and currently winds up to 3000 rpms at roughly 60 65 mph.The code on the top side of the passenger tube of the axle says TDA 0226w2 the the front side of the pumpkin says NF3896838 and GM56. The webbing on rear says con1 and 1234567890. Also looking for suggestions on how to remedy this. I assume 700r4 is one option but what other options are there.

[Wrenchbender Ret]

Get a 3.08 rear end from a similar truck.

[Barba Negro]

200r4 works great in place of th350. Crossmember needs to be moved back or mount adjusted. Driveshaft is the same yoke and length. Best part is the .67 overdrive. Fairly simple kits available to take care of lock up convertor.

[jocko]

Welcome to the forum Jarrod! Cold up in Sioux Falls yet? I wore shorts this morning to walk the dog. Then again, it's 115 here all summer long... Anyway, you didn't mention tire diameter, and that's kind of important here. So, for the sake of discussion, I'll assume an approx. 28" dia tire. Here are some numbers:

At 60 mph with a TH350 (and 28" dia tire):
4.10 rear = 2952 rpm
3.73 rear = 2686 rpm
3.08 rear = 2218 rpm

Wrenchbender is correct, one way to skin the cat is to install a 3.08 rear from another truck. The tradeoff is your ability to do a burnout, if that is important to you - it kinda goes away because you lose a bunch of torque multiplication in all gears with a 3.08.

A 700R4 (or better yet, in my opinion, a 2004R) would give you the best of both worlds - a bit more torque multi in 1st, but also an o/d gear for hwy use.

At 60 mph with a 700R4 (and 28" dia tire):
4.10 rear = 2066 rpm (but, note, you'll have almost TOO much torque multi in 1st - will want to shift to 2nd before you cross the intersection...)
3.73 rear = 1880 rpm
3.08 rear = 1552 rpm (bad combo, 700R4 and 3.08, unless you're gonna be cruising over 100 mph...)

At 60 mph with a 2004R (and 28" dia tire):
4.10 rear = 1978 rpm (same note as above)
3.73 rear = 1799 rpm
3.08 rear = 1486 rpm (same note as above)

The factory often pairs a 3.73 with an o/d trans - for good reason, great combo of off the line perf and highway cruising rpm mildness.

The other options available are to change tire diameter, but if you like what you've got, then you should keep what you've got. (hmmm...) Or, you could keep the TH350 and install a Gear Vendors over/under drive and use it as a tack-on overdrive. Not cheap, but bulletproof, with approx. the same results as a 700R4 swap (just the o/d gear part, not the low-end toque multiplication).

Recommendation: 3.08 if off the line perf not hugely important. If you like acceleration(!), or if you plan to tow/haul anything: 2004R.
Hope that helps. And, again, welcome to the forum.

[Already Gone]

If your truck was an original automatic it shoukd have a 3:73 final drive ratio with the 6 cylinder engine. From what I've read and heard on this site a 3:73 with a 700r4 trans gives yiu the best of both worlds. The other factor is the cost if the 700r4. You are probably looking at a minimum 2000. to buy and install a 700r4 properly.

[jarrodscot]

I am pretty sure it was a inline 6 with a manual. Not sure the tire hieght but they wheels and tires will be changing soon. Currently has 225 50 17s. And yes todays high was 30 yesterdays was 15. Little chilly thanks for the welcoming.

[LockDoc]

Originally Posted by jarrodscot

The truck is a 1970 c10 short box. The vin code identifies it was a inline six motor. It now has a 350 with turbo 350 trans and currently winds up to 3000 rpms at roughly 60 65 mph.The code on the top side of the passenger tube of the axle says TDA 0226w2 the the front side of the pumpkin says NF3896838 and GM56. The webbing on rear says con1 and 1234567890. Also looking for suggestions on how to remedy this. I assume 700r4 is one option but what other options are there.

According to the charts I posted a while back 1970 TDA would be 3.73:1. I changed the rear in my White '67 from a 3.73 to a 3.08 and it worked like a champ. I also put a 2004r trans in my Suburban and had to go from a 3.08 to a 3.73....

http://67-72chevytrucks.com/vboard/s...d.php?t=578793

Oh, and to the board.

LockDoc

[jarrodscot]

So with the information I listed its also a non posi rear? thanks again everyone.

[LockDoc]

Originally Posted by jarrodscot

So with the information I listed its also a non posi rear? thanks again everyone.

It is not a positraction.

LockDoc

[jarrodscot]

Does any one know with this 1970 c10 2wd 12 bolt tda 373 open differential would it be 30 spline axles? Looking to purchase a mini spool for it.

[jarrodscot]

Got my Rallies on with these tires are little taller and its a little easier on Rpms on highway. But i think that the plan will be to swap my turbo 350 for a 700r4 or a 4l60e.

[SS Tim]

Originally Posted by jarrodscot

Does any one know with this 1970 c10 2wd 12 bolt tda 373 open differential would it be 30 spline axles? Looking to purchase a mini spool for it.

A mini spool really does not belong on the street. A posi or even a locker sure, but a spool is last choice. If you are playing with it hard enough to be thinking spool you might want to think about a "C" clip eliminator kit too. Better yet a Dana 60 from a Big Block 4-speed manual C10/C1500.

Here is the original 70 powertrain chart, most are at a link in my signature.

[jarrodscot]

Its not a truck thats drive daily just driven ocasionally. Might see a few passes at the track next year not sure. I have been looking for a posi rear end for it but havent had a lot of luck with that. So would my axles be 30 spline?

[SS Tim]

5 or 6 lug is going to be 30 spline from the factory for a 3500lb (HO35) 12-bolt rear end.
If you are having trouble finding a posi axle you could always install a lunch box locker that reuses the existing case. Not the best of solutions but better than running a spool.

[frank69]

never heard of a lunchbox locker please enlighten me thanks frank69

[SS Tim]

Originally Posted by frank69

never heard of a lunchbox locker please enlighten me thanks frank69

Like I said earlier. It is a locker that reuses the existing differential case (the part the ring gear spins containing the differential side gears). Basically everything inside the case is replaced by the locker assembly. While not the strongest solution vs a dedicated design it is easy to install compared to setting up a replacement differential.

http://www.ringpinion.com/b2c/Produc...Spartan_Locker