Turbo 350 transmission question

[Red69stepside]

Ok, here's yet another rookie question. I just got this 69 stepside and the PO tells me it's got a arebuilt TH 350 tranny and rebuilt 327 engine.

is this a good configuration? What kind of performance should I expect from it? How does it compare to other trannys and why would someone install a 350 instead of anything else? how about potential problems, and what should I do to take proper care? -- any warning sings of problems?

Thanks to all.

[shuttermutt]

Originally Posted by Red69stepside

Ok, here's yet another rookie question. I just got this 69 stepside and the PO tells me it's got a arebuilt TH 350 tranny and rebuilt 327 engine.

is this a good configuration? What kind of performance should I expect from it? How does it compare to other trannys and why would someone install a 350 instead of anything else? how about potential problems, and what should I do to take proper care? -- any warning sings of problems?

Thanks to all.

The TH350 is probably the most common automatic transmission you'll run across for a GM. They're a good, basic 3-speed automatic that should serve you well. They'll easily take all the horsepower your 327 is likely to throw at it. I'd never turn down a good TH350.

Heat kills automatic transmissions. Make sure there's a transmission cooler hooked up and functioning. Be sure you check the transmission fluid level on a regular basis. If you're so inclined, you might want to replace the transmission filter. Be aware this requires dropping the pan. If you're not comfortable with that, take it to a reputable shop.

As for performance, as long as it's not slipping or generally acting funky then you're all set. I'd say run it for a while. You can put in shift kits, tweak the modulator, swap out the converter, and other fun stuff once you figure out exactly what you want the tranny to do.

[Red69stepside]

'Mutt:

thanks for the info...and the reassurraance. I'll check it out as much as I can.

Are the gear ratios in the 350 set up rigtht for highway speeds? I've read that stock trucks --especially older ones --are geared pretty low and rev too high on the open road.

I'm also wondering about the differential? Is ther e any benefit to upgrading this--especially for higher speeds?

Thanks again.

[toddtheodd]

A TH350 is not an overdrive transmission. This means that final drive is 1:1, just like every other non-overdrive transmission. If the truck revs high on the road, this will be due more to the rear differential than the transmission. 3.08 rear gear would not be that bad on the highway, about 2600 rpms @ 70mph. 4.56 rear gear would sound like a screaming banshee, 70mph at about 4000 rpms. To find out how streetable your truck is you'll need to find out what the rear gear is.
Todd

[Red69stepside]

Todd:

That's great info, thanks. Please excuse me for some more rookie questions.

Are you saying the differential doesn't always run at 1:1?

So a 3.08 rear gear would have the engine/drive shaft turning once for every 3.08 turns of the rear axle?

Finally, how do I find out what my differential is?

thanks again.

Tim

And which of those would be going at 2600 rpms at 70 mph--the drive shaft or the axle?

[toddtheodd]

No, the drive shaft would spin 3.08 times for every 1 spin of the rear wheel.

[toddtheodd]

The driveshaft would be spinning at 2600 at 70mph with 28inch tires and a 3.08 rear gear.

[toddtheodd]

You can use this site to find out your rear gear.
Just enter in your rpms, your final drive (with a th350 that would be 1) and your tire diameter.
Hit computer and it will tell you how fast you would be going with a selection of different gears.

[shuttermutt]

Take for example, Todd, that my truck has a TH400 transmission with a 3.73:1 differential. When I'm in 3rd gear and I'm travelling 70 mph with my 28.9" tall tires then all of the following is happening:

- My engine speed is about 3035 rpm
- My transmission is spinning 1:1
- My driveshaft is turning 3.73 times for every complete rotation of my tires

To do the math yourself, you'll need a Tire Height Calculator and a Potential Engine Speed Calculator. You'll also need to know that your TH350 will be 1:1 in 3rd gear.

Hope this helps!

[toddtheodd]

I think you were referring to red69stepside.
And you can do the math without fancy calculators and so forth. You just have to know the conversions and formulas. I know I know. That's too much to ask of today's kids since they have everything handed to them on a calculator.
I didn't even know those sites were out there (by the way, the second one isn't working for me) and to make sure I wasn't incorrect I was checking my math before I posted the previous numbers for red. I've got a whole piece of paper covered over here. Not too bad though, I like math , and it was kinda relaxing.

[Red69stepside]

Thanx guys. great info.

I'm gonna get all this stuff covered pretty soon

[shuttermutt]

Originally Posted by toddtheodd

I think you were referring to red69stepside.
And you can do the math without fancy calculators and so forth. You just have to know the conversions and formulas. I know I know. That's too much to ask of today's kids since they have everything handed to them on a calculator.
I didn't even know those sites were out there (by the way, the second one isn't working for me) and to make sure I wasn't incorrect I was checking my math before I posted the previous numbers for red. I've got a whole piece of paper covered over here. Not too bad though, I like math , and it was kinda relaxing.

Yep, you're right. Sorry 'bout that. Oh, and I'm very aware that it's possible to do the math without a calculator. In fact, a person can do any math without a calculator. Of course, I could chisel a reply to this thread on a stone tablet and carry it by hand, too. But, why not take advantage of the tools that are available?

PS: Not sure why that second one isn't working for you. Works a treat on this end.

[Red69stepside]

I finally got to check this out, and my tach says that at 70 mph, i'm revving at about 2600 rpm, and I got 28" tires.

Its great when this stuff works out.

Thanks for the help.

[smitty62]

The first thing to do, if you haven't already is to change the fluid in the tranny. This is one of the most neglected maintenance chores and it's important!!

[Red69stepside]

Originally Posted by smitty62

The first thing to do, if you haven't already is to change the fluid in the tranny. This is one of the most neglected maintenance chores and it's important!!

Smitty:

My mechanic said the fluid was clear and smelled ok, but I think I'll change it anyway. Thansk for the heads up.