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Which tire/gear combo would you run?

AaronJen

AaronJen

1/2 ton status
Joined
Jul 22, 2009
Posts
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Location
Georgia
So I'm at a crossroads. My '90 has the stock 350 TBI with a 700R4 and NP241. I swapped in a NOS CUCV D60 loaded with 4.56s in the front. The 3/4 ton 14BFF I put in the back has 4.10s currently. I've got a brand new set of Yukon 5.38s in the garage (without the gouges on the pinion snout:rolleyes:) for the 14BFF.

The original plan was to get a matching set of 5.38s for the D60, add a big tranny cooler, and run ~39-40" tires with the stock motor/tranny combo until it dies. After thinking a little more about it, and considering the money to swap gears in both axles versus one, I am wondering if the logical course of action wouldn't be to get a set of thick 4.56s for the back to match the front, and run ~35-36" tires.

I've got the DIY4X shackle flip on the back with X-tied 6" shackles and zero rates, and plan to run some 4" TCs up front with zero rates there too. Possibly add a 1" BL for a little extra clearance. I have already trimmed the driver side front fender (looks about like the gray/white CK5 UA Vehicle), and will be matching the passenger side soon.

I won't be doing any rock crawling, so the flex part of it doesn't scare me away from the bigger tires in terms of sheet metal/tire carnage, but I wanted LTBs, and those are apparently unobtanium these days. I considered PB Rockers, but they are almost too wide for my taste and I've seen mixed reviews on performance in sticky GA clay. Either way, I can't run either one unless I regear both ends, which is significantly more $$$$.

So with all of the blabbering out of the way, what would you do if you were me? Buy one set of 4.56s and run a smaller tire, or regear everything and run a set of tires that in reality is only about 4-5" taller but looks a helluva lot better (to me), and offers a little more ground clearance? :dunno:
 
You already have the gears and a D60 will hold up just fine to a 40" tire. aslong as you have the clearance you want then go big or go home.

Im not real sure how long your 700R4 will last, but since you got the gears, you should be alright for a long while depending on the condition before the change over
 
I hear what you're saying on the go big or go home, which is what my original plan was. On the gear side, though, the dilemma I'm having is that if I just match the front, I only have to pay somebody to set up one set of gears. If I use the 5.38s I have, I will need to buy another set for the front, and have both axles done.

I guess I'm just ready to get the thing back on the road, and I'm trying to convince myself to alter my original plan just to be able to drive it. You're probably right though. I should just do it all or leave it alone. I won't be happy until its like I really want it.
 
With a 700 if I had to drive I would go 5.38s no question. Makes it easier on the trans.

The 4.56s would work just fine but I think they will stress the 700 alot more than the deeper gears.

So I would do 5.38s do the rear setup yourself its super easy on a 14 bolt except for pinion preload.

Not too hard on the 60 either but some special tools make it easier
 
So if the conventional wisdom is to use the 5.38s in conjunction with the 700, what size tire would you run if it were yours?

Are the 39s/40s with 5.38s gonna be too much for the 700?
 
AaronJen said:
So if the conventional wisdom is to use the 5.38s in conjunction with the 700, what size tire would you run if it were yours?

Are the 39s/40s with 5.38s gonna be too much for the 700?
Click to expand...

This is a question I should never be asked :D

In all seriousness, I give that recommendation on the fact that you would be running 40s, remember that your 40s aren't going to measure 40" tall more than likely, and in fact their static loaded radius ( measurement taken from the center of the hub to the ground with the tire mounted on the truck with normal air pressure in it) won't even be close to 40, on most 40s ( I just say 40s but include anything advertised as a 39.5) your actual tire measurement would be closer to 38 maybe even 37 depending on tire.

So keep that in mind.

There are several on this board running 5.13s with 37s and a 700 and they like the combo.

Whatever you decide the huge trans cooler is a perquisite

The biggest thing to remember when trying to figure out RPM is the actual size of the tire, not the advertised size of the tire.

The thing you want to prevent with a 700 is hunting, not even sure 5.38s will do that. If your 700 is hunting at speed in top gear, you are going to lose the trans quick or you will have to shift to 3rd
 
Thanks for the links. I've definitely read up on everything here and on Pirate, as well as played with the gear calculators, and that's a lot of the reasoning behind my original question.

From what everybody says, 35s are about perfect with 4.56s and OD. To get in the same basic RPM range, 39s or 40s looked about right with 5.38s. My big hangup I guess is a combination of (lack of) tire availability in the larger sizes, taken together with the cost of setting up gears in one axle versus two.

I have read the 14 Bolt Bible until I could just about quote it as scripture, but I'm just not confident enough to be certain I won't fry my brand new gears. I've never done a set and I don't have all the tools it would take. From what I can tell, the D60 is a good bit more involved which = out of the question. Too many shims and too much math.

And since you bring up things that have been covered a lot, what's your take on the 5.38s themselves? I remember reading in several places something about less than optimal tooth contact (I believe Kert was mentioning it when he chose 4.88s for his caddy powered K5). Is that a real concern, or more of an "opinion + severity of intended use" consideration?
 
Good point blazinzuk. I keep batting it back and forth, and almost decided to toss the 700 for a 400 and go 4.56 with 40s, but I may drive home to FL some with it, so the OD and current gas prices kind of dictate staying with the 700 if I want to avoid more electrical wiring with the 4L80E.

Add to my confusion, I've got a 400 mated to an NP205 at my folks house in FL just sitting there asking to be used. This crap drives me crazy and never seems to end. Decisions decisions :doah:
 
also 14ff needs little machine work / grinding inside to fit the 5.38 in there.

and dont put the motor back to stock rpm also if bigger tires and or you know the working power band put it up a little more for bigger tires and or match the working power band to rpm at spec mph you are going to run.

my pic was 5.13 gears as bolt in and go no machine work needed. but havent finished truck yet. but all my calc's from that site and tires size and overdrive with my motor's power it will be 300-400 rpm or so abouve stock rpm was. should make it a good driver and play toy. and if i need more low end i also have a 203/205 tcase setup. :whistle:

and if you have a tbi setup now and want hd over drive like 4l80-e look here for 3 wire hook up controler with LOTS of options for adjustment and extra's offered in it. http://www.optishift.com/index.shtml few guys here have it and LOVE it . i am tossed up on it or my stock ecm swaped and rewired for 4l80. i think optishift will be for me also.

and if you go away from 700r4 you ill loose DEEP first gear. and 4l80-e is same ratios as 400 but lock conv and overdrive added.
 
Grinding/machine work? That one must have slipped right by me, or I would definitely have gone with the 5.13s. I'm not looking for all that action. What is involved, and are you sure it is required for the Yukon 5.38 thick gears? If so, these might be made available to the highest bidder and a couple of sets of 5.13s ordered up.
 
AaronJen said:
Good point blazinzuk. I keep batting it back and forth, and almost decided to toss the 700 for a 400 and go 4.56 with 40s, but I may drive home to FL some with it, so the OD and current gas prices kind of dictate staying with the 700 if I want to avoid more electrical wiring with the 4L80E.

Add to my confusion, I've got a 400 mated to an NP205 at my folks house in FL just sitting there asking to be used. This crap drives me crazy and never seems to end. Decisions decisions :doah:
Click to expand...

I love the 700 not because of its overdrive, and lets face it, it needs to be built up to handle large tires/power, but because of its 1st gear.

My Jimmys crawl ratio is 38:1

Hortons crawl ration with a doubler is 45:1

considering I am running 42s on Horton and 35s on the Jimmy the Jimmy has a pretty darn fine crawl ratio. I like the 700 for its first gear ratio

Your truck would have 44:1 with a 700/241/5.38s

With the 400/205 you would be 25:1

44:1 is way better than 25:1

the 700 241 combo is a great combo
 
its not that bad . just a little here and there inside to clear the teeth . any good axle gear setup guy can do it easy.
 
I run a 37" tire with 5.13 gears and 700r4. And the tire is 37" tall.

The blazer has a good jump off the line and it doesn't hunt gears.

If I wanted I could run a 38" tall tire and still have good rpms without the trans hunting. So 5.38s should work great for 40"s.

If money is not an issue then go with the 5.38 regear and bigger tires. The extra clearance is a bonus. :waytogo:

wheels
 
The BTO unit is definitely the plan for when the current trans bites the dust. I know Ryoken was planning on going that route too, albeit with a helluva lot more motor than I have.

Getting back to these damn 5.38s. You've got me gun shy now. I did a quick search and a few Pirate threads I turned up seem to say you basically have to remove so much metal from the pinion support that it doesn't even offer enough strength to justify it being there at all. Seriously re-thinking the approach now.
 
I have done a couple 5.38 setups one did not require any clearance at all, of course that one had the marks ( that made no difference at all) in the pinion snout.

The other one it took a couple minutes, big deal, I think not

Its not a big deal at all.
 
Wheels, I might end up with what you've got. I sure as hell didn't know anything about machining the housing itself. I've heard of turning down the outside of the ring gear to clear diff housings, but this sounds a good bit more involved. Don't think I want to want to get into that.
 
I guess in the interest of not beating the hell out of a horse I don't even have yet, I'll go with everybody's suggestion and do the 5.38s and see what I get into. Hopefully I'll get lucky and there will be room without hacking on the housing.

Between the crawl ratio and easing the pain for my bone stock 700R4, plus the fact that I've already got them, I guess it's worth a shot.

Thanks to all of you for the insight. Now, if anybody's around northwest GA in the near future and wants to put in a set of gears while consuming all the free beer and pizza they can hold...............:whistle:
 
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