4:77's & 35's...some stats...

[Ldub]

Since getting my 4:77's & locker finally wrenched into the machine, I have had to re-calibrate all the associated numbers so that I can evaluate changes in mileage, odometer etc.

First, I borrowed a GPS unit from my Boss & put a small dot on the lens of the speedo corresponding to 55-60-65-70 & 75 mph.

OK, now I know how fast I'm really going.

Next, I took a little 30 mile cruise, while my co-pilot, Hunny Girl, wrote down the beginning & ending mile markers, & the corresponding trip odo values.

Then, crunched the numbers & came up with nearly 7% (6.94) margin of error.

My old margin of error, figured the same way, was about 16% with the stock (4:30) gearing.

My current rpm @75 mph is 2800.

I will be updating this with my findings regarding mpg in the future, but my initial guess is that my mileage is getting better. As the fuel ga is moving to the left @ a slower rate @ previously known mileage values...
Also, while maintaining a cruising velocity of 75 mph, I am experiencing neutral intake pressures, sometimes even slight vacuum, where before at the same speed, I was always under 3-4 psi boost. That's gotta help.

For those trying to make sense of these convoluted calculations:

The mileage on the trip odo will be multiplied by .07, that number is added to the miles on the trip odo, then that total (actual miles driven) is divided by the number of gallons used.

[LittleBeast]

THANKS!!!!!

I will be getting the 35's as soon as my 33's wear out (they have already lasted over 2 years and 60k miles), and since I already have 4.78's in front and rear this will help a lot!

Do you still get the driveline vibrations? I have ordered the Indy4x lower links to correct the pinion angle after lifting to see if this fixes this. Thanks again for the info :-)

[Ldub]

Do you still get the driveline vibrations? I have ordered the Indy4x lower links to correct the pinion angle after lifting to see if this fixes this.

Yep, I'm experiencing some DL vibe, especially @ 55mph.
I know it's coming from the rear, because it was noticeable before I installed the front axle/driveline.
I'll be very interested to hear your results.

[samneil2000]

You guys make me jealous. How are your CV boots holding up with maximum lift? Other than that, and some high angles on them, there's really nothing major going on. I wonder if the rear axle shafts are strong enough for the 35's and offroading - not to mention supercharging.
Are your A-arms resting on the bottom stops or do you have a little space left for down-travel?

Edit - Yall both have diff drop brackets, so your angles probably aren't any worse than mine... Crap, I need a bonus so I can go shopping for VX parts. haha

[Ebenezr]

Your driveshaft and universal rotation is now faster at 55 (not that you didn't know this) so was there vibe before at 65??? oops you said it was noticable

[Ldub]

I wonder if the rear axle shafts are strong enough for the 35's and offroading - not to mention supercharging.
Are your A-arms resting on the bottom stops or do you have a little space left for down-travel?

There is some down travel left in the front because of the ball joint flip & the addition of low pro bumps from Indy4x.

I've seen more than a few posts here & there on the web that indicate the Isuzu corp 12 bolt compares in brawn to a Dana 44.

[Ldub]

Your driveshaft and universal rotation is now faster at 55 (not that you didn't know this) so was there vibe before at 65???

Yep.
Also, I re indexed the drive shaft/third member connection 180 deg, on the chance that it would help, but alas, not so much...

The funny part of that is:
I had backed into my parking spot (on a slight incline) & was about to proceed with the "laying on of the wrenches", when Marlins experience flashed into my brain.
I then pressed the wheel chocks into service...

[Ebenezr]

Yep.
Also, I re indexed the drive shaft/third member connection 180 deg, on the chance that it would help, but alas, not so much...

The funny part of that is:
I had backed into my parking spot (on a slight incline) & was about to proceed with the "laying on of the wrenches", when Marlins experience flashed into my brain.
I then pressed the wheel chocks into service...

YES understood. You do not want to be a human wheel chock. but U joints are noted for singing at 55 MPH.

[Triathlete]

Our 12 bolt rears are actually stronger than a 44 and pretty close to a dana 60 iirc. They are getting popular with the dark side (jeep guys).

[LittleBeast]

My first thought was u joints with the vibration, but after having the driveshaft professionally rebuilt with new u joints and all and seeing no real lasting improvement, I am convinced most of the dl vibration after lifting is due to the new different angle of the pinion in the 3rd member side.

As far as down travel goes I am the same with ldub with the ball joint flip and ultra low bumps on the front, so i do have some down travel left at rest, but you would be surprised to note that the first thing to make contact now is the bolts that connect the front cross member to the frame.

[Ebenezr]

My first thought was u joints with the vibration, but after having the driveshaft professionally rebuilt with new u joints and all and seeing no real lasting improvement, I am convinced most of the dl vibration after lifting is due to the new different angle of the pinion in the 3rd member side.

As far as down travel goes I am the same with ldub with the ball joint flip and ultra low bumps on the front, so i do have some down travel left at rest, but you would be surprised to note that the first thing to make contact now is the bolts that connect the front cross member to the frame.

When you say "professionally rebuilt" was your driveshaft rebalanced??

[VXorado]

After a good conversation with Matt from indy4x yesterday, I am reducing that extra lift I added last weekend for my new 35s and installing a 3" body lift to make up the difference. I have ball joints flipped, low profile bump stops & a 2" drop but to get the appropriate height you need to get close to max ifs down travel (about 4"). The body lift should give me some room in the wheel wells for 35s while leaving the suspension with some room to move. I'll let ya know how it goes.

Oh and I'm jealous of those 4.77s dub & littlebeast. I just bought a 12 bolt with an arb locker & 4.56 gearing so I guess I'm giving up on finding those mythical 4.77s.

[samneil2000]

What about those really low 5.xx something gears that were being sold here a while back. They might be a good match for 35's...

[LittleBeast]

What about those really low 5.xx something gears that were being sold here a while back. They might be a good match for 35's...

Yes but the fronts 5.38's are near impossible to find. You can get the rears pretty easily though. Those that have the 5.38 fronts tend to know that they can get a lot for them :-(

And yes they did the high speed balancing when they rebuilt the driveshaft. Nice shop here in Houston.

[VXorado]

Yes but the fronts 5.38's are near impossible to find. You can get the rears pretty easily though. Those that have the 5.38 fronts tend to know that they can get a lot for them :-(

Right unless you do a SAS. Probably less work to do a SAS than to source these rare Isuzu gears...

Its too bad that 4.56 is the lowest readily available gearing option, its really the only downfall to the Isuzu 12 bolt. IMO if gearing wasn't an issue, I would take a 12 bolt over a D44 anyday, the strength is comparable (as Billy said) & 3rd member axles are much easier to work on.