Cruising Under Stall RPM- TH350

[SHOTROD81]

Hello! First time poster. My basic question: does cruising under the torque converter stall RPM damage the transmission? I bought my 81 C10 about year ago for a home-project hauler and for a little fun. The price was right for a solid, but ragged looking, C10 with a freshly rebulit engine and transmission. The rear end is somewhat mismatched to the engine and transmission, but I chose to buy it as-is anyway. Engine is a 372 with a TH350 and a 2.56 (approximate) rear end with a mini-spool. The converter is a 2800 RPM stall, but due to the high geared rear end, I rarely hit stall RPM during in-town driving, even when held in first gear. My budget doesn't really allow for a rear-end swap right now, but I am concerned that this under-stall condition may burn up the transmission prematurely. Any advice would be appreciated. Thanks!

 

[Honky Kong jr]

Welcome and put a trans cooler on it and look to regear that rear.

 

[SHOTROD81]

Thanks for the response. It does have a Tru-Cool trans cooler in it, so hopefully this will keep the temp down while I save up for a rear end upgrade. Would it be best just to find an entire 12 bolt with the right gearing rather than rework the 10 bolt? I don't plan on drag racing it, but I am concerned that I might tear up the 10, or at least the flimsy mini-spool, during an occasional outburst of fun.

 

[Honky Kong jr]

Thanks for the response. It does have a Tru-Cool trans cooler in it, so hopefully this will keep the temp down while I save up for a rear end upgrade. Would it be best just to find an entire 12 bolt with the right gearing rather than rework the 10 bolt? I don't plan on drag racing it, but I am concerned that I might tear up the 10, or at least the flimsy mini-spool, during an occasional outburst of fun.

There isn't anything wrong with a 10 bolt. What gears are you looking for? If I get hadn't found the 12 bolt I have in my truck that had better gearing and a posi I'd have a 10 bolt in the rear just with 30 spline axles on 36s and a big block.

 

[SHOTROD81]

I'm thinking around 3.73, or whatever is available in the mid 3s. At 6 mpg, I'm probably not going to be taking it on any highway trips, so I might as well gear it toward city speeds. Can the 10 bolt be built to tolerate a few extra hp? I am learning a lot after re-entering the world of car projects after a 25 year break, so please forgive the newbie-ish questions.

 

[Honky Kong jr]

I'm thinking around 3.73, or whatever is available in the mid 3s. At 6 mpg, I'm probably not going to be taking it on any highway trips, so I might as well gear it toward city speeds. Can the 10 bolt be built to tolerate a few extra hp? I am learning a lot after re-entering the world of car projects after a 25 year break, so please forgive the newbie-ish questions.

There are cars regularly running in the 9 second range with 10 bolts. The rear in your truck is an 8.5" the 12 bolt is 8.875" not a whole big difference. The pinion shaft on a 10 bolt is bigger then that of a 12 bolt as is the inner bearing. The outer bearing is the same 10 or 12. The 12 bolt has 30 spline axles the 10 has 28 but 12 bolt axles can be used in a 10 bolt with a 30 spline carrier. In 89 10 bolts got 30 spline axles front and rear in the 10 bolts that's the K5 and Suburban any way. I could go on forever.lol

 

[HotRodPC]

Is this pretty much a stock engine? Are you drag racing? There's no reason for a 2800 stall converter if it's stock and you're not drag racing. Just a loss of power to the wheels being absorbed in the stall converter, as well as running hotter than needed due to all the slippage and friction in the converter. No reason for anything over about 1800 stall in a stock cam small or big block for that matter.

 

[SHOTROD81]

I don't plan on drag racing, but it might be fun to try a pass or two on junker day at the local strip. Engine isn't stock. The build sheet I got from the seller was a few pages long, but here are the highlights:

-.04 over 350, 3.625 stroke crank
-Bullet 262/272 @.05 solid roller cam, 107 LSA, .618/.628 gross lift
-10.8:1 compression
-616HP, 536TQ on engine dyno
-Built by NVR Racing in Butler, Wisconsin

It makes trips to the dump a little more fun.

 

[twinturbo427]

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.

 

[twinturbo427]

And.... sell that mini spool when you change the gears and put any other kind of posi in it. You will be much happier later on.

 

[SHOTROD81]

Thanks for the advice. I'm glad I checked in here rather than just Googling it. Many google searches pretty much deemed the 10 bolt as far inferior to the 12, but seemed to lack real knowledge backing up the opinion. I wasn't looking forward to an entire rear swap, which I have only done once, 25 years ago. I've never messed with gear changes. Would this best be done by someone with experience, or can a shadetree pull it off? Also, any recommendations on what kind of posi to use? My last square had a "lunchbox locker", but I've heard they are the weakest of all the choices. The telltale chirps of the current spool earn me a few weird looks at the grocery store. As ratty as the truck looks, I think most people just assume something is wrong with it.

 

[crazy4offroad]

If you got a dial indicator with a stand, caliper micrometer, high-torque impact, access to a press and a ****-ton of patience you can set up gears. There's a couple writeups here on the forum about it.

 

[Honky Kong jr]

Also if you get a set out of a rear with all the bearings spacers and shims that were used with it it's not that bad. I've done it a lot like that to great success.

 

[kenny78]

A trusted local shop quoted me $100 dollars plus parts per axle. I'm not going to teach myself and possibly ruin some parts for that. Maybe if I run out of hobbies but I will let a pro do gears and transmissions for now

 

[Honky Kong jr]

A trusted local shop quoted me $100 dollars plus parts per axle. I'm not going to teach myself and possibly ruin some parts for that. Maybe if I run out of hobbies but I will let a pro do gears and transmissions for now

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.