Rear Gear Install for C10 with TH350

[plckidd]

I have a Goodwrench 350 with 290HP. I am replacing the cam with a 480 lift / 107 degrees separation, roller rockers and adding 64cc/180cc heads.

I want to add a torque converter around the 2,000 - 2,400 range to compensate the cam, but would like to replace the rear 2.73 gear with something different first. Maybe something between a 3.23 - 3.73

I have a TH350 (stock) tranny and the axle is the stock 10 bolt.

The tire sizes are 295/45/20 (30.45" tall)

My plans for this c10 is to drive it on nice days and to events from time to time... around 1,000 miles per year at best. If there is any highway driving, it would be close to 40 miles one way at a time.

Does anyone have any suggestions for the rear gear that would be ideal for this build? Basically looking for something with more low/midrange torque and a nice cruiser.

Thanks, Shawn

 

[Keith Seymore]

Yep - I always go 3.42 with a non-overdrive trans; 3.73 with an overdrive.

It's a really nice balance between fuel economy and off the line performance. Been very happy with that strategy for about 45 years now.

K

 

[Ricko1966]

I'd suggest you go 3.73 and overdrive. Since you're planning on running stall you'll want the lockup converter.And your low-end will be incredible.

 

[plckidd]

I like the idea of running a 3.42 gear especially with the lower RPM's around 2400 at 60MPH.

What transmission would be a nice swap with the TH350? I read that a 200r4 would be pretty much plug n play except the crossmember would need to relocate about 6' closer towards the engine. I don't have the 6" without redoing my exhaust.

 

[Ricko1966]

There are 3 lengths of th350 transmissions,so depending on which th350 you have that will determine what changes need to be made,mount and drive shaft wise. I do not have the dimensions memorized. Check the overall length or tailshaft housing length of your th350. Post it up.More than likely you have a 9 inch tailshaft 350 which would swap easiest to 700r4. A 6 inch 350 would swap more easily to a 200r4.

 

[Grit dog]

3.42 for cruiser. 3.73 to make it the quickest and still somewhat driveable at highway spee
I’d go 3.42s. 300hp will still do burnouts and it’s not a drag racer but a small block at 2700 rpm’s at 70 mph is ok.
If I was driving it on road trips I’d probably be in the 3.08 camp.

 

[Matt69olds]

If you have no plans to swap transmissions, go 3:42.

If a 700 trans is in the budget, go 4:10.

A 2004R properly built will handle far more power than a 700, regardless of the reputation they have. While a 700 is stronger in stock form, the 2004R has far more potential, assuming your pockets are deep enough. The 2004R has stamped steel carriers and other parts that can be easily replaced with stronger components. The weak point in a 700 will always be the input housing.

I don’t think a 2004R would be an easy swap in a truck. There is no long shaft version, meaning the driveshaft would have to be pretty long.

Of course, if your making the power that requires expensive transmission upgrades, go 4L80 and be done with it.

 

[Ricko1966]

Yea, not likely to be anything other than a 9inch but on a 40 some year old truck I think he should measure the transmission who knows what has been done in the past. If it is a 9inch 350 a 700 almost installs itself,if it's a 6inch 350 the 200 would be the better choice and if by some chance it's a 12 inch 350 well it's a blank slate.

 

[plckidd]

Thanks guys, I'll be back home this weekend and I'll get those measurements. I have not dropped the tranny out of the truck, so I can get an overall measurement. Does the tranny have to come down to measure the tailshaft? My headers are long tubes and I wouldn't have any room to move the crossmember, unless it moved away from the headers. I can get my hands on a 700r4 tranny from a buddy.

 

[82sbshortbed]

GM Chevy 8.5" Chevy 10-Bolt Rearend TrueTrac - 28 Spline, Gear, Bearing Kit Package - 3.73 Ratio https://a.co/d/4tQyZgk















This is what I have behind a 700r4 with a 2,200 tc andi28 inch tires. It's quick and runs 2,200 rpm at 65. I like this set up.

 

[DoubleDingo]

I like 3.54 with 30 inch diameter tire, it'll run 70 at 2,600. Trouble is, 3.54 are not an option last time I checked, but 3.42 would be a good alternative.

 

[Ricko1966]

Thanks guys, I'll be back home this weekend and I'll get those measurements. I have not dropped the tranny out of the truck, so I can get an overall measurement. Does the tranny have to come down to measure the tailshaft? My headers are long tubes and I wouldn't have any room to move the crossmember, unless it moved away from the headers. I can get my hands on a 700r4 tranny from a buddy.

No you don't have to drop the transmission. I'll see if I can get you some pics. Most likely it's a 9 inch but better to check and know for sure.The green one is a 6inch the grey one is a 9inch so now you can picture the difference and see what to measure.

 

[MikeB]

My 82 square body had a mild 350, TH350, and 29.5" tires. Call me an exception to the rule, but I thought its 2.73 axle was ideal on the highway, and the engine would still spin the tires in low gear.

I now have a 69 C10 with essentially the same engine, trans, and tire height, but with 3.08 gears. The engine is happy at 60-65 mph, but is a bit busy running with 70-75 mph traffic. I'm just sayin' you might be shocked on that 40 mile highway trip if you go from 2.73 to 3.42 or even 3.23 gears. And a higher stall converter will make it even worse, unless you invest in a quality (expensive) model.

On another note, if that's the 290hp/350 Goodwrench engine, the actual static compression ratio is quite low (less than 8.0:1), and the heads are pretty crappy. So your plans to install modern 64cc heads will help a lot. But don't spring for the cheapest pair. Do some research first. Even a head with a decent casting won't be worth a darn if it uses low-bidder valves, guides, and springs.

 

[75gmck25]

The original compression ratio on the Goodwrench 350/290 is definitely only around 8-8.2. I swapped to aluminum heads with 64cc chambers, and also used the thin .026 head gasket, so I estimate I’m now up to about 9.2-9.4. That’s good enough for a mid-range cam, but not enough compression for any radical duration. Big cams like high compression.

You mentioned a few specs for your new cam, but not the duration at .050. The low 107 LSA is also kind of unusual for a street cam. It makes it sound agressive, but may reduce power for a mild build. Exactly what cam are you using?






Exactly what cam see you using?

 

[AuroraGirl]

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a quality4l60e, 700r4, or a 200r4 would indeed be good uses. but the 2.74 first and 2.07 reverse would not be as ideal in a truck id think.
And the minor difference in 4th.. I would think thats negligible