keeping stock rear with a sbc & th350?

[1-ton of fun]

has anybody kept the stock rear when they swapped motors to a v8 with an auto?

we are thinking about keeping the stock rear but we are switching out the motor soon. trying to figure out the driveshaft

[OrrieG]

How many miles on the original rear end? you can get a junkyard lower miles replacement for less than rebuild cost. And probably get a posi and disc brakes in the process. Any good drive line shop can sort out the drive line as long as you have the spline end for the trans you want.

[_Ogre]

does your 36 have a 4 speed with parking brake on the rear of the trans?
a 32 or 34 with the standard 3 speed could use the stock driveshaft without any mods
the 4 speed will need to be shortened and a different yolk to slide in the trans
the 36 rearend is (approx) 4.90 open spool one wheel wonder (can someone confirm a ratio)
good if you want to pull stumps, not so good if you want more than 8 miles per gallon

[1-ton of fun]

Sorry this is on my sons '55 3100, not my 36. It already has a 10-bolt from a nova.

[1-ton of fun]

I was starting to think about just changing the rear, because of the rear disc conversion price. I want to get moving on the front end and if the rear is changing to a 5x4.75" pattern, the front needs to match, so that's a different front brake kit.

[mr48chev]

That stock rear is probably going to have 4.11 gears in it and if he is going to drive it on the freeway and do some distance driving the engine will be running at a lot higher rpm level than is desirable for both good engine life and any sort of fuel mileage. I think there are some ring and pinion sets out there that are sold to give 3.5 or better road gears that would help.

Over the years a lot of guys have swapped in V8 engines and run the stock open drive rear end the main issue being gas mileage. My 57 Panel with a hot 327 that was pushing around 400 hp got about 4mpg.

[1-ton of fun]

yeah i think my '71 chevelle ss454 did about 4 mpg with the th400 also

[_Ogre]

go with a 200r4 it will be the same length as the original 3 speed and it has the overdrive to get better highway speeds

[octanejunkie]

That 10-bolt is either an 8.2 or 8.5" ring gear, it's unlikely to have come from the factory with 4.10 gears, but you can easily check the current ratio by jacking up the rear, marking the drive shaft and rotating the tires, counting revolutions.

Depending on your tire size, you may want to consider 3.23, 3.42, or 3.73 gears max, without OD.

Check out a calculator like this one: http://www.coastdriveline.com/htmlfo...lculator2.html

You want to put the vehicle in the RPM range that gives you best performance from your engine - gotta know your cam and having a dyno curve wouldn't hurt.

I like this chart for reviewing RPM and gearing based on tire size

Originally Posted by _Ogre

go with a 200r4 it will be the same length as the original 3 speed and it has the overdrive to get better highway speeds

X2

[1-ton of fun]

Originally Posted by _Ogre

go with a 200r4 it will be the same length as the original 3 speed and it has the overdrive to get better highway speeds

Already have the th350...I'm sure we will upgrade later.

It's going to be my sons truck and he's 15 now. Mechanically limited to 70 mph is ok with me for now for his truck, lol.

[1-ton of fun]

Originally Posted by octanejunkie

That 10-bolt is either an 8.2 or 8.5" ring gear, it's unlikely to have come from the factory with 4.10 gears, but you can easily check the current ratio by jacking up the rear, marking the drive shaft and rotating the tires, counting revolutions.

Depending on your tire size, you may want to consider 3.23, 3.42, or 3.73 gears max, without OD.

Check out a calculator like this one: http://www.coastdriveline.com/htmlfo...lculator2.html

You want to put the vehicle in the RPM range that gives you best performance from your engine - gotta know your cam and having a dyno curve wouldn't hurt.

I like this chart for reviewing RPM and gearing based on tire size



X2

The 10-bolt is an 8.5" ring gear and in my '59. It might be getting a 6l80e since I gave my kid my sbc385/th350 setup for his truck. That project got sent to storage to get his '55 done first. Found a local yard with an s10 4x4 rear with 3.42 gears but haven't had a chance to call them yet

[_Ogre]

the stock 3 speed, 200r4 and th350 are all the same length and will use the same stock drive shaft without a problem
nice thing about building a chevy, they stuck with the same stuff over many many years
octanejunkies chart is strange... i have what i consider a big tire on truk at 28''; his chart starts at 28''

[octanejunkie]

Originally Posted by _Ogre

octanejunkies chart is strange... i have what i consider a big tire on truk at 28''; his chart starts at 28''

Here's one for the little tire guys

http://www.4x4community.co.za/forum/...9&d=1241897367