Rear end question

[dubie]

I have 3:73 non posi in my truck right now. I also have 2 parts truck that each have 3:08 (i believe) non posi in them. Would it gain me much on highway travelling to swap out the entire rear end to the 3:08 ? At 60 mph my engine has to be running at about 2800 rpm or higher right now. I am running the original saginaw 3 speed as well. I plan on swapping out the tranny in a couple years, but was wondering about the rear end swap for now

[junkyardjohn]

YES IT WILL.... YOU SHOULD SEE A LITTLE BETTER THAN 20% REDUCTION IN YOUR R.P.M.s AT HIWAY SPEEDS. JOHN

[Joe67]

You should see an increase in MPG going from the 3.73 to a 3.08
If you tow anything of size frequently, I'd stick with teh 3.73.

[dubie]

I don't haul much with this truck, so this looks to be a good swap for me. I just want something that doesn't run so high on RPM's when we go to other surrounding towns for shows and making runs to the cabin on weekends. Looks like I may have to set aside a weekend to swap out the rear, install the lowering blocks and cut the coils up front. I have 500 sq ft of laminate flooring to lay this weekend so I won't have time for truck play time

[Longhorn Man]

How does that sound to you?
350/TH350 non lock up, 3.07 rear gears, ans 28-ish inch tall rear tires.

[dubie]

I can actually hear myself fart in the cab at those rpm's Andy Right now tho, she's damn loud

[gr8scott51]

Andy, buy some gas, man. Hey Tim, maybe Shawna doesn't want to hear you fart.

[piecesparts]

Let me tell you a story about a little truck that we own. The truck is an 86 chevy, with a 350 engine, a 700 R4 tranny and 3:73 gears. It used to have 3:08 gears and the rpms were around 1900 on the highway. Sounds good doesn't it? Well the problem was that the truck's gas mileage was lousy with the 3:08 gears (12.5 mpg MAYBE) and the performance with the truck at 1900 was sluggish. The cruise control was constantly kicking down when you got into any kind of hills. I guess if you live on the flatlands---no problem. We put a 12 bolt 3:73 posi unit under the truck and the gas mileage went up to 15 mpg and the engine performs great, even when the cruise control is engaged. The 350 engine has a power curve that is predominant around 2100 to 2700 RPM and that is where the engine will become really efficient. The truck now runs at 2500 RPM at 70 mph and pulls real strong to get into traffic. Every person for their own choice, but a little kick is worth the fuel to me. I really do hate an anemic truck that couldn't get it's a$$ out of a peterbuilt's way. I also have an 84 GMC pickup with a 383 stroker and the same tranny and rear end. It is getting a good 15 mpg with a 400 hp motor, that is why we did the 86 with the 3:73 gears.

[Longhorn Man]

Very good points there...however, we are dealing with non overdrive vehicles here, so that is a non-issue.

Tim...if you can't hear your fart on a vinal seat...even at 3000 RPM, then you ain't pushing hard enough.
No joke, I made one audible on the freeway with open headers. My passenger was about to punch me.

[junkyardjohn]

ANDY ... I KNEW A GUY WITH A V.W. DIESEL RABBIT THAT GOT 50 MPG. (I'M NOT SURE WHAT GEARS HE HAD) BUT I GUESS THIS ISN'T AN ISSUE EITHER. JOHN

[Longhorn Man]

LOL! Very good point.
I had a hopped up 86 civic Si that got about 46 - 48 on the open road...only if I kept it below 80 though.
That too...is probably a non-issue.

[Slams_58]

Originally Posted by gr8scott51

Andy, buy some gas, man. Hey Tim, maybe Shawna doesn't want to hear you fart.

I think you're right Scott!!! That's one exhaust leak I can't fix tho!

[Longhorn Man]

Now Shawna...I'm sure you could find something to plug up the leak.

[dubie]

yeah but then I'd build up to much back pressure and take out a window

[Dean]

I don't think that swap would be worth the effort to me. Will lower your rpms, but don't expect miracles on the fuel mileage. Just my two cents.....

[Longhorn Man]

Dean...I kinda agree with you on that. What ever you do save on the open road, you'll burn in town trying to get her rolling.
Onless you fly on the freeway more often than the surface roads.

[Tx Firefighter]

Dubie, my 454 truck had 3.73 gears in it. I could not make myself drive at speed on the freeway. 70 miles per hour was too much.

I traded a board member straight across for a 3.08 rear. My mileage increased 5 miles per gallon (up to 12) on highway driving.

I have actually experienced what pieceparts has on an overdrive vehicle though. My 83 truck came with 2.73 gears and an overdrive. The mileage was horrible. When the 700 went bad, I replaced it with a non overdrive Th350 trans. The mileage actually increased without the overdrive because the engine didn't have to work as hard at highway speeds.

For your 3 speed truck though, 3.08 will make you a happy man.

[Canadian694x4]

Originally Posted by Longhorn Man

Very good points there...however, we are dealing with non overdrive vehicles here, so that is a non-issue.

Tim...if you can't hear your fart on a vinal seat...even at 3000 RPM, then you ain't pushing hard enough.
No joke, I made one audible on the freeway with open headers. My passenger was about to punch me.

This Thread is amazing...I damn near pissed myself laughing this morning! LMFAO!!!

[70c10]

Tim, I would personally stay with 3:73's for the fun factor!. If you really plan to do ALOT of highway driving then that's a reason to consider. If you had a torquey Big block then it might not be as noticeable, but with the current 350 the launchability will probably be felt. My 2 cents.

[Longhorn Man]

I damn near pissed myself laughing

Well then...my work here is done.

[dubie]

Originally Posted by 70c10

Tim, I would personally stay with 3:73's for the fun factor!. If you really plan to do ALOT of highway driving then that's a reason to consider. If you had a torquey Big block then it might not be as noticeable, but with the current 350 the launchability will probably be felt. My 2 cents.

Yeah this truck can really launch when you dump the clutch on it and i kinda like that feeling. I am toying with the idea of a T5 tranny swap so I gain some OD and that in turn would help get the rpms down. But seeing how my budget is spent on the truck, I kinda have to wait. Just thought if the rear end swap was worth it, I would do that for the short term. The truck is mainly used for around town cruising so the 3:73's work great for that. I'll just have to decide whether all the work involved in swapping the rear end out is gonna be worth it for me right now. And seeing how the truck is going to be rolled into the sister in laws garage in 3 or 4 weeks for the winter, I may run out of time for big jobs like this. It's gonna hurt to have to put the truck away until May 2005

[Longhorn Man]

I wouldn't use the T5. The strongest version in stock form can only handle 305 foot pounds of torque. Your 350 should be there...or at least close. When you add in the factor of a heavy truck, that just ups the scatter factor.

Yeah this truck can really launch when you dump the clutch on it and i kinda like that feeling.

And it defenately wouldn't hold up to that.
There is a reason the T5 was never offered behind anything bigger than a 305.

[dubie]

maybe time to search for a Muncie 4 speed then??