99 Suburban c1500 gearing

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bravocharlie

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highway speeds, RPM only increased to about 2,200 to reach 70 mph. I am curious what kind of mileage it currently gets on the highway.
 

bravocharlie

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Confirmed 3 or 4 inch spindle lift and rear block. Rear sits lower & softer than i would like it to. Returns me to the question on the rear end. New shoes as the old Michelin lower rated tires where DOT 2014. These cooper E-load rated tires are quite, stiffer, aggressive and taller set up. Happy with the results.

That 14 bolt from a light 2500 seems to be the route to take. I think a complete rear end would meet my criteria. Leaf springs along with the drive axle. Really not a fan on how the rear sits and handles.

Also, had a chance to put some miles on it over the holidays. She gets 10mpg. Does fine once your cruising at highway speeds, still feels like a slugger getting up to speed.

So far, just did an oil change with 5w30 conventional. Trans oil looks immaculate, not dark in color. Air filter can use a clean and oiling.

I am convinced this tire size and increase in rational mass is not ideal for factory gearing. I would be skeptical if a higher gear would make milage worse. I think it would only help put more power down, ease off the throttle. Input appreciated.
 
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bravocharlie

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Good name for it.

Scrap that weak ten-bolt, step up to a 14-bolt semi-float axle from a light-duty (6-lug) C2500.

3.73 will be very common, 4.10 somewhat less-so; but probably still "find-able" if you're willing to drive a ways to get one from a friendly Treasure Yard. You'll need the u-bolt mounting plates from the 14-bolt axle donor vehicle, a conversion U-joint, new U-bolts 'n' nuts, and whatever repairs the brake need. Pop the cover off, inspect the guts, re-fill with fresh axle lube. New axle seals recommended.

The only real issue is that you'd need 5-lug axle shafts to fit the 14-bolt SF. Available in the aftermarket, probably discontinued through GM.

That, or replace the wheels with 6-lug units, and front hubs to match.


I'll just stick with the 6 lug. I like the 17" ZL1 Tahoe wheels anyway. And they are priced well.

Any links for the u-bolt conversion?
I read on other post, a 6 lug disc brake fits the front bearing of a 1500. Can anyone else confirm?
 

Schurkey

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That 14 bolt from a light 2500 seems to be the route to take.
Removing 10-bolts in favor of the "14 bolt semi-float" is nearly always a good idea--depending on the condition of the 14-bolt.

Air filter can use a clean and oiling.
Oiled-gauze air filter? Cleaning them before they NEED to be cleaned is the WORST thing that most folks do to them.

If your air filter restriction indicator isn't showing restriction...leave the filter alone.

No air filter restriction indicator? K&N used to recommend cleaning when there was 1/8-inch of crud built-up on the outside of the element. Basically, if you can still see pleats, it shouldn't be cleaned. K&N also said that with substantial dirt build-up, you might want to add a few drops of filter oil to the CLEAN side of the filter--to replace what's been absorbed by the dirt. But all that has been scrubbed from the web site, in favor of the restriction indicator.

Oiled-gauze filters filter BEST when they've got dirt build-up on them. The dirt becomes a functional part of the air filter, making it more effective.

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Found these two rear ends. What y'all think?
If they're not 9.5" ring gear units, you're wasting time, money, effort, and enthusiasm. In particular, the one that's specifically listed as a "1500" is probably a weak 8.5" ring gear job, although being from a Suburban, it might be a weak axle with the better, 11.x Duo-Servo brakes.

No promises on the width being right. At least on the pickups, the C rear axle housing is different width than the K axle housing. I don't know about Suburbans.

Re-gearing a 10-bolt is a waste.
 
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shovelbill

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Is gas mileage the main reason for the gearing change? How will the rig be driven 90% of the time? What is the GR now? Are the new tires you want for looks or the ply rating...do you need an E-rated (heavier) tire? What kind of weather will you be driving in on the left coast?

Typically, the all-around 'standard' was 3.73 for 31s, 4.10 for 33s, and 4.56 for 35s for what folks call a "stocklike" truck, whatever that is. My guess is it has a 3.42 ratio, possibly a 3.08, since she is sluggish, "specifically getting up to highway speeds."

First, I would jack up the rear, mark the driveshaft and spin the tire one full rotation. Count the shaft rotations to see what your effective GR is right now before making a decision.
 
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