Super Chief

[Smokeyyank]

Nice, I got the same truss. Havent burned it in yet but got it fitted. I thought you could use the bigger k20 brakes and keep the same bolt pattern but I honestly can't remember. 

[derf]

40 minutes ago, Smokeyyank said:

Nice, I got the same truss. Havent burned it in yet but got it fitted. I thought you could use the bigger k20 brakes and keep the same bolt pattern but I honestly can't remember. 

You can Frankenstein the build to get bigger rotors.  But really, with a 97+ booster and standard half ton calipers and rotors, I should be able to stop a Comanche on 35s just fine.

[derf]

I do have to say  having the right tools at hand makes working on 50 year old axles so much nicer...

 

[derf]

Outers are disassembled.  Everything from the ball joints out were going to be replaced anyway.  

 

The knuckles for the drum brake Ford are different than for disc brakes.  But I am upgrading to Reid high steer knuckles anyway.  The spindles are different too.  I would have kept the originals but that wasn't an option.

 

Time to finish cleaning off the tubes.  I need to get the rest of the slag ground down and remove the track bar bracket.

 

 

I did confirm it is factory 4.09 gears.  Not quite enough gear for 35s.  So they will get bumped up when I install the locker.

 

[derf]

Some things are just easier with a plasma cutter...

 

[derf]

And then a couple hours with a grinder...

 

[derf]

The truss basically fits.

 

 

But there's a minor problem with the breather...

 

 

[neohic]

Looking great so far!

[Smokeyyank]

I had to do some minor trimming on my housing to get the truss to fit. My housing had this extra rib on the back and then the leaf spring pad. Excited to see how it turns out! 

[derf]

19 minutes ago, Smokeyyank said:

I had to do some minor trimming on my housing to get the truss to fit. My housing had this extra rib on the back and then the leaf spring pad. Excited to see how it turns out! 

I expect that I will need to trim somewhere.

 

There is another hole in the top of the housing.  It had a bolt that held on the brake line tee.  I'm going to see if I can hijack that for the locker line.

 

[derf]

I am having a bit of a moment of indecisiveness right now.

 

A stock manual transmission MJ with 215/75R15 tires has 3.08 gears.

 

Do the math stepping up to 35x12.5/15 and you get 3.84 to keep the stock ratio.  Step up to 4.10 to account for rolling resistance and weight.

 

With 4.10s and 35s (602 revs per mile), I get 2437 RPM at 75 on the freeway.  That's not terrible.  And with the Atlas transfer case with the 4.3:1 low range, I get a respectable 67.52:1 crawl ratio (first gear, low range)

 

I have 4.56 gears to swap in.  That bumps me to 2711 RPM at 75.  My crawl ratio drops to 75.10:1.

 

Both would be decent overall.

 

If I had 3.73s in the axles now, I wouldn't bother keeping them.  But I have 4.10s.  It would be easy to keep them.  And it would make setup easy since the pinion shims would just go back in.  The carrier is changing to a locker but that's not a huge deal.

 

The 4.10s would be a little more friendly on the freeways around here that get up to 75MPH (80 on the way out to Moab).

 

But this isn't a daily driver.  So I would only be driving to the trails most of the time.

 

4.56s are a jump but not huge.  The freeway RPMs aren't horrible.  And I get a hair better crawling on the rocks.

 

I'm just waffling back and forth right before installing the lockers.  And wondering WWCCD?

 

For reference, 4.10s and 35s is close to having 3.31s on stock tires.  4.56s are close to 3.55s on stock tires.  And this Jeep is getting an AX15 to replace the Peugeot manual.

[89 MJ]

I'm seeing a 33.5 having 602 revs/mile and a 35 having 576 revs/mile on your site. Did you use the actual measurement of a particular 35?

 

At 33.5s, I think I'd stick with 4.10s. For a 35, 4.56s would be my vote. 

[Eagle_SX4]

I have 4.10's and 33's with an AX15. Sometimes I wish I had 4.56's. My vote with 35's is go to 4.56's.

 

Also keep in mind that bigger tires means more weight to move so lower gears will help there as well.

[neohic]

At least 4.56s. I don’t out freeway speeds into the equation unless it’s. Vehicle that primarily sees them. Getting to and from the destination in a modified vehicle is absolutely part of the journey. 

[Smokeyyank]

4.56 would be my vote. 

[derf]

1 hour ago, 89 MJ said:

I'm seeing a 33.5 having 602 revs/mile and a 35 having 576 revs/mile on your site. Did you use the actual measurement of a particular 35?

 

At 33.5s, I think I'd stick with 4.10s. For a 35, 4.56s would be my vote. 

Nearly every "35 inch" tire is never truly 35 inches in diameter.  And the advertised outside diameter is the tire in the air with no weight on it.  And, frequently, even that is smaller.

 

Most tires have in their specs "revolutions per mile".  That tends to accurately reflect the real rolling diameter.  Using that in your calculations gives you usually very accurate numbers that match your real world performance.

 

The spec for the 35x12.5/15 BFG A/T and M/T both is 602 revs per mile.

 

Both list 34.5" advertised outside diameter.  33.5" true rolling diameter is typical for most "35 inch" tires.

[Eagle_SX4]

My tires are Toyo Open Country AT3's 285/70r17. They are spec'd at 634 revs/mile. So they are smaller than what you will be running. I would definitely go with 4.56 gears based on that alone.

 

I got better gas milage with my old 31's and 4.10 gears. So don't be afraid of the RPM while cruising it could actually help with better gas milage.

[derf]

I'm sensing a pattern here...

[Eagle_SX4]

2 hours ago, derf said:

 

For reference, 4.10s and 35s is close to having 3.31s on stock tires.  4.56s are close to 3.55s on stock tires.  And this Jeep is getting an AX15 to replace the Peugeot manual.

I will also say I have 3.55's with my T5 in my Eagle with 215/75r15 and it feels great and would never want 3.07s. I never understood why that was the standard gear ratio with the manual transmission.

[derf]

15 minutes ago, Eagle_SX4 said:

I will also say I have 3.55's with my T5 in my Eagle with 215/75r15 and it feels great and would never want 3.07s. I never understood why that was the standard gear ratio with the manual transmission.

Fuel economy standards.

[89 MJ]

1 hour ago, derf said:

Nearly every "35 inch" tire is never truly 35 inches in diameter.  And the advertised outside diameter is the tire in the air with no weight on it.  And, frequently, even that is smaller.

 

Most tires have in their specs "revolutions per mile".  That tends to accurately reflect the real rolling diameter.  Using that in your calculations gives you usually very accurate numbers that match your real world performance.

 

The spec for the 35x12.5/15 BFG A/T and M/T both is 602 revs per mile.

 

Both list 34.5" advertised outside diameter.  33.5" true rolling diameter is typical for most "35 inch" tires.

I figured that was probably the case, thanks for confirming

[ghetdjc320]

4.56 gears would be my vote. I run 4.56 with metric 33’s that run almost a perfect actual 33” diameter.