OD and 3.08 rear end

[Howitzer]

Ole Greenie,

I've been doing a lot of research the last couple weeks on doing a 4L80E swap. Looks like the biggest single expense (after the tranny) is going to be the controller.

There are a few brands out there, if i do the swap i am leaning towards a Performance Automatic PA99104 controller and for your TPS concerns, a Performance Automatic PA99111 TPS for carb units.

After that if you want to keep your stock speedo setup you'll be looking at either a cast tail house with provisions for a mechanical speedo drive (at a ridiculous cost of around $650) or going with a cable-x box for around $350 which converts the electronic VSS signal to a mechanical output. The cable-x box allows you to change tire sizes or ratios in the rear end and be calibrated with dip switches.

[Boog]

Originally Posted by Ole Greenie

Okay, here goes my experience:

I have aBBC LS6 with a Bowtie Overdrive Level II and 3.08 gears.

What I like about this is the low RPM at hwy cruise speed. I tend to cruise at 75 most of the time and the motor is at 1800 rpm...not quite the sweet spot for the motor as the LS6 likes RPM.

What I don't like about the 700R4 is that the convertor locks up at 40 mph and at hwy speeds it a bear to get it into kickdown. It has a corvette governor and the TV cable is adjusted properly. Lastly, it is not quite as crisp off the line, partially due to the open rear gear and partially due to the length of the gear.

I am thinking about changing to a 4L80E but I have not done enough research to adapt a TPS to a carburator.

Any other thoughts?

God Bless!

That's a great example right there John. A 3.42 gear or better yet a 3.73 gear might put that engine about right where you want it where it would run easier. A lower gear to get it moving easier and the od to cruise easier.
You can use calculators like one from Richmondgear.com/streetcalculators to play with ratios to see what rpm you would see with different gear ratio and tire diameters.

[LockDoc]

Originally Posted by Howitzer

Ole Greenie,

I've been doing a lot of research the last couple weeks on doing a 4L80E swap. Looks like the biggest single expense (after the tranny) is going to be the controller.

There are a few brands out there, if i do the swap i am leaning towards a Performance Automatic PA99104 controller and for your TPS concerns, a Performance Automatic PA99111 TPS for carb units.

After that if you want to keep your stock speedo setup you'll be looking at either a cast tail house with provisions for a mechanical speedo drive (at a ridiculous cost of around $650) or going with a cable-x box for around $350 which converts the electronic VSS signal to a mechanical output. The cable-x box allows you to change tire sizes or ratios in the rear end and be calibrated with dip switches.

If you aren't real concerned about keeping the stock speedo here are a couple of links to another option.

http://67-72chevytrucks.com/vboard/s...d.php?t=421745

http://67-72chevytrucks.com/vboard/s...d.php?t=453615



LockDoc

[Ole Greenie]

Howitzer and Boog,

I appreciate the replies. Since I'm fixin' to PCS to Ft. Eustis in May, I'll have to wait till after then to be serious about a gear swap. I'm pretty handy, but I fear that a gear swap may be above my capability. I'd sure hate to get the gear install a bit off and burn them up. Definitely going with a 3.42...the largest gear set I can put into the 3.08 pumpkin. I think it will be perfect ratio given the BBC. Of course I'll install a limited slip too to make sure it gets off like it should.

I am kind of torn between the limited slip manufacturers out there, although I am focusing on an Auburn unit. Before I go to a 4L80E the new gear will go in...but then again I am also thinking about a newer 6L tranny.

Do ya'll have any suggestions concerning which LS manufacturer I should go with?

All the best,

John

Ecclesiastes 4:9 & 10

[69GWC]

Might look at a Detroit TruTrac Locker for it, no clutches to wear out and are really tuff.
Posted via Mobile Device

[Ole Greenie]

I had thought about one of those but I don't have 4WD where it could really be used. Eaton too is a possibility. Heck if I could find a good rebuilt factory unit, that would be acceptable too.

My research indicates about $600 for the parts (shipping included) but I still believe I can get the matched gear set and the LSD for under $500. There will be a bit more burn in the pocket for the install too.

Of course I'll remove the whole rear end and take it to a shop but what do ya'll think is a fair asking price to install the gears and the LSD?

P.S: Now going to Ft. Knox, KY. Any good shops up that way?

[BrutonLS1]

I've got a 5.3 bored to a 5.7 with a 700r4. The 700r4 is in the shop right now being rebuilt with all performance "stage 2" parts with a 2500 stall. I'm very curious on what my highway cruising rpms will look like with a stock rear end. The guy told me I'd be better off with a 3:55 or 3:73 rear end. As soon as I get it in I'll let everyone know what the numbers look like. I'd definitely like to learn more about all this.

[BrianV]

I have a 700r and 3.08 gears behind my mild small block and I run 80 at 2100 rpm although I only have 15" tires but I am very happy with how it runs down the highway. The guys at bowtie overdrives are very knowlegable and with their TV cable kit it is very easy to do and seems very reliable so far

Just my 2 cents

[AustinScott]

I have a 2004r and had an open 3.08 rear... boy was that painful. My tranny would also shift into OD around 40 and lock the converter up... this would send my truck into shock..
It did not like cruising at 1000 RPM in OD locked up.....
On the freeway my truck was a dog at speeds under 75 in OD.. around 1800 RPM. (My little 327 just didn't have the torque down that low to keep the truck moving.

Here are the numbers with the 2004r and 3.08





My cure was to rebuild the rear with a Eaton posi and 3.73 gears..... Boy did this fix the problem.
Not only did it fix the issue I was facing, but it brought life to my truck...

Here are the numbers with the 2004r and 3.73



The 2004r still likes to shift a bit early into 4th and lock the convert, but I have added a toggle switch right before my brake pedal switch.
This way I can keep the converter unlocked while driving around town & locked up on the freeway with braking release.

My experience says 3.08 & Overdrives do not mix well with our trucks, unless you are ready to drive in 3rd everywhere and use OD only on the freeway & even then you better be ready to go fast or die trying

Hope this helps..

Scott

[71meangreenc10]

350/700r4 and 3.42 with 275-60-15's,

Great combo for me.

Smitty

[Boog]

Now that's a great grid there Scott. Your experience with a high gear'd rear and OD is similar to one I had. My 88 GMC rcsb 2 wd had a wimpy 305/700R4 and a 2.73 rear from factory. You mention how doggy your 327 was with the OD and 3.08s. Mine was totally gutless. The slightest incline at 70 mph had it downshifting back and forth or even a headwind for that matter. And it didn't get great mileage either. I know it was spec'd for economy but they missed the mark. They put too high a gear ratio for the low horse engine in it. 3.42 would have been much better in that truck.
I've always thought that a small block is most effecient in the 1800 to 2200 rpm range at highway speeds. They seem to run easier and more effecient there.