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Gear ratios...

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Mudslutk51984

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So here's another question... I have an 84 k5. 6" lift 35" tires. I'm pretty sure I have 3:73 in the rear and 2:73 in the front so the 4x4 can't be used ... I like the 3:73 and I want to keep it. How close do the front and rear ratios have to match?

P.S: I jacked up all 4 tires off the ground and put it in 4x4 all tires spun just fine but on the ground the bind up.. is that cause the mismatched ratios?
 
The ratios need to be the same. For some with mechanical skills who has not done gears, find a front axle with 3.73:1 ratio. If not, new gears for the front.
 
ktmoutfront said:
The ratios need to be the same. For some with mechanical skills who has not done gears, find a front axle with 3.73:1 ratio. If not, new gears for the front.
Click to expand...
I was planning on puting in new gears but I don't do much pulling with it at all.. I spend more time in the mud and dirt than on the road. Is 3:73 a good half way gear for 2 lane highway (sometimes I hit it) and off road?
 
I liked 3:73 gears with a 3 speed non overdrive transmission (automatic)--it gives good acceleration and you can still cruise at highway speeds without the engine going 3500+ rpms,especially if you run larger than stock tires...with overdrive you could go even lower ,like 4:10 or 4:56 ratio..

Personally I would rather swap in a complete"good used" front or rear axle,than try to set up gears myself...its a rather involved process that involves a lot of precision ,not a job for someone who hasn't had experience --like me!--though it can be done..its often cheaper to buy a whole axle than have a shop install gears in your existing one..
 
I do not know much about mud racing. But I have heard of running higher gears in the front to pull. But I did not think that far apart.

What trsnsmission is in the truck?
 
The front and rear gears don't have to be identical but should be close. For example 4.09 vs. 4.11 is close and won't cause any issues. On the other hand 2.73 vs. 3.73 is way too far apart. If you were stuck in 2wd you could put it in 4wd long enough to get out of the situation but as mentioned it would really start to bind up shortly after getting back on ground with some traction to it.

3.73 gears aren't ideal if you have an OD transmission with 35" tires but are OK. As mentioned above I would just go buy a fairly common complete front axle with 3.73 gears and bolt it in. This should be cheaper and easier than setting up a new gear set in the existing axle.

But first things first.........you really need to 100% verify what gear ratios you currently have before doing anything as it does not sound like you are 100% positive what you currently have.
 
I'll point out that even apart from binding up on pavement, spinning tires at different speeds turns your truck into a trencher. At least one of your axles will always be slipping at all times. So you may find you're digging a hole instead of digging yourself out.
 
I've told here how I had a '71 K5 I bought for 300 bucks,it had a 3:73 front axle,and a 3:08 rear axle--hence the cheap price!..
(I was not aware of this when I bought it,but it was a CST in otherwise decent shape,with a factory SM465..

I couldn't even drive it 5 mph down my driveway with the hubs locked,the frame started twisting up and a loud "BANG" was made by the hub when it let it "slip" ,the binding was that severe..it felt like the transfer case was going to blow apart..

I tried driving it around the yard in 4wd after it snowed,the rear end just wanted to slide sideways instead of going forward !..it did great donuts,but if you tried going straight,it crab walked sideways as it went forward..

I eventually found a 3:73 rear axle for it,but never got around to installing it--I just used it in 2wd during the summer and drove my more rusty '72 K5 in winter..
When I sold the truck I gave the guy the rear axle with it--he never put it in either--instead he put much larger tires up front (like 35" ones) and left the 235-75-15's in the back--this allowed it to be driven on slick surfaces fairly well,but was far from perfect..

He moved to TX and drove the truck there the way it was!--his father called me about 6 months later and asked me if I wanted the axle back,he had left it in his yard..I ended up selling it to someone for what I paid,75 bucks..

I guess its not uncommon to find 4x4 trucks that had a mismatched axle swapped into it..most buyers eithe take the previous owners word the 4x4 works ok,or dont find out it doesn't till it snows,or they try taking it wheeling..
 
diesel4me said:
I've told here how I had a '71 K5 I bought for 300 bucks,it had a 3:73 front axle,and a 3:08 rear axle--hence the cheap price!..
(I was not aware of this when I bought it,but it was a CST in otherwise decent shape,with a factory SM465..

I couldn't even drive it 5 mph down my driveway with the hubs locked,the frame started twisting up and a loud "BANG" was made by the hub when it let it "slip" ,the binding was that severe..it felt like the transfer case was going to blow apart..

I tried driving it around the yard in 4wd after it snowed,the rear end just wanted to slide sideways instead of going forward !..it did great donuts,but if you tried going straight,it crab walked sideways as it went forward..

I eventually found a 3:73 rear axle for it,but never got around to installing it--I just used it in 2wd during the summer and drove my more rusty '72 K5 in winter..
When I sold the truck I gave the guy the rear axle with it--he never put it in either--instead he put much larger tires up front (like 35" ones) and left the 235-75-15's in the back--this allowed it to be driven on slick surfaces fairly well,but was far from perfect..

He moved to TX and drove the truck there the way it was!--his father called me about 6 months later and asked me if I wanted the axle back,he had left it in his yard..I ended up selling it to someone for what I paid,75 bucks..

I guess its not uncommon to find 4x4 trucks that had a mismatched axle swapped into it..most buyers eithe take the previous owners word the 4x4 works ok,or dont find out it doesn't till it snows,or they try taking it wheeling..
Click to expand...

My blazer went into typical G80 failure, and rather than repair it the P.O. decided to install an 8-lug 4.10 axle from a C30. While leaving the 6-lug 3.08 axle up front. He didn't try to hide it from me, but it still seemed like a fairly crummy solution.
 
9 replies and nobody has suggested ditching 1/2-tons yet? A CK5 record?

I've found that even with matched gears, just having new tires on one axle and worn on the other is enough to make it drive weird on icy roads. Best to not force things to slip at all.
 
Blue85 said:
9 replies and nobody has suggested ditching 1/2-tons yet? A CK5 record?

I've found that even with matched gears, just having new tires on one axle and worn on the other is enough to make it drive weird on icy roads. Best to not force things to slip at all.
Click to expand...

I did mention it, but it was subtle and veiled, hidden inside my story. :pimp:
 
Oh well--at least you were halfway through an 8 lug upgrade,with no effort on your part,all you had to do was find an 8 lug front 4:10 axle and you'd be golden..:D..

I had a friend who bought a 1976 2wd K5 many years ago,it was sitting up on cinder blocks in the backyard of the owner--and he called and asked me if he could borrow 4 rims with junk tires just to load it on his trailer...it was pretty nice,had a 400 small block and a TH400 in it..not much rust either..paid 600 for it.

I had several sets of rims & tires hanging around,I said "Sure--but that truck has 5 lugs ,right ?...he goes and looks,and says "Yeah,5 lugs"...
So,I grabbed 4 stock steel rims and tires I had off my '66 Buicks after I got 4 factory rally wheels for them,same bolt pattern,and headed over to the guys house where the K5 was..

We put the front rims on no sweat--but when my friend went to put one of the rears on,he says "oh-oh--the rim wont fit"...

I said "You mean the center hole is too small" ?..
"No--there is SIX lugs on the rear !..:eek:..

Evidently someone either swapped a 4x4 axle in it,or just the axle shafts...had to drive 15 miles back to my house,to get two more 6 lug rims with bald tires ,to get the thing loaded up...

He later found out after we got the truck to run,it did awesome smoke shows..first trip down the highway after it was registered,he said to me "gee,I think the tranny is stuck in second gear,it wont go over 70 without screaming"...

I listened to it shift through the gears--1-2-3...nope,its going into third OK...we took the rear diff cover off after we got back to his house,and found out it had 4:56's in it.!...with 205/75-15" tires,it had great take offs,but top speed was about 60 or so,anything faster the engine sounded like it was going 5,000 rpms!..it got about 6 mpg too..but few cars could beat that truck off the line at red lights!..
 
diesel4me said:
Oh well--at least you were halfway through an 8 lug upgrade,with no effort on your part,all you had to do was find an 8 lug front 4:10 axle and you'd be golden..:D..
Click to expand...

Nice story, Bob. Yours usually are. :thumb: As for my truck, I didn't want 4.10 gears, they wind the diesel up too fast with 31" tires. And aside from being loosely U-bolted into place, the axle wasn't attached to the truck in any other form. So I did a gear swap and then had to tighten up the bolts and do driveshaft, shocks, brakes, etc. And then I had to swap out the front, too!

If he hadn't "messed it up" half-heartedly, I would have just kept on rocking the 3.08s.

Now that it's on the road, I still think that 3.73 is too much gear for a 6.2 truck on 31s. 33s would be better, IMO.
 
Your truck doesn't have overdrive ?..

My '85 K10 Suburban has 3:73's supposedly,it has a 12 bolt rear too though--I hope it matches the front !..never had it registered,and I only drove it around a mile loop where I bought it in 2wd..
But I have locked the hubs in my driveway and it seemed OK when I tried the plow out a few times...
It has a 700R4,which is dying according to the PO,it loses reverse when hot and wont shift into OD...but reverse works in my driveway fine (so far)..

Everyone tells me I'd hate it if I swap a TH400 into it,but I dont think so...sure,it might rev higher on the interstate without OD,but all the trucks prior to the early 80's had only 3 speeds and still got us everywhere OK..I dont go very far or very often if I did,so I wouldn't care if it loses a few mpg,and the extra revs might come in handy in the hilly areas around here..I could put taller tires on it too..
Rate I'm going the thing will rot into flakes and never be put on the road again...let it sit since '09 and its looking pretty rough..:(
 
diesel4me said:
Your truck doesn't have overdrive ?..

My '85 K10 Suburban has 3:73's supposedly,it has a 12 bolt rear too though--I hope it matches the front !..never had it registered,and I only drove it around a mile loop where I bought it in 2wd..
But I have locked the hubs in my driveway and it seemed OK when I tried the plow out a few times...
It has a 700R4,which is dying according to the PO,it loses reverse when hot and wont shift into OD...but reverse works in my driveway fine (so far)..

Everyone tells me I'd hate it if I swap a TH400 into it,but I dont think so...sure,it might rev higher on the interstate without OD,but all the trucks prior to the early 80's had only 3 speeds and still got us everywhere OK..I dont go very far or very often if I did,so I wouldn't care if it loses a few mpg,and the extra revs might come in handy in the hilly areas around here..I could put taller tires on it too..
Rate I'm going the thing will rot into flakes and never be put on the road again...let it sit since '09 and its looking pretty rough..:(
Click to expand...

Yes, I have O/D. Yes, I know that plenty of gas rigs (and even some 6.2 rigs) have such gearing. I still don't like it. 3.73 with 700R4 is exactly what my Suburban runs. Running in 3rd on the highway (no T/C lockup) is painful to listen to. It needs 33s to get the engine speed down to where it belongs.

For putzing around town, it's less of an issue. But my goal is long-haul road trips.
 
Bump. Any idea what gear ratio this '89 Suburban with 700r4 might have in it (stock)? It's just a 6 lug but that's all I need. I have 4:56 in my K5 now (700R4 and 33" tires) and it's just fine, I might not like anything too much higher. It's the last day of the Pick and Pull half price sale ($75 per axle) and I'm debating getting them but not if they are very high ratio. It's a fairly long drive to get there.. 6 lug axles are fairly common aren't they, from guys upgrading, maybe it's not even worth it.. thanks..

bYxRPUF.jpg
 
A 6 lug 10 bolt is what most guys here throw away in favor of an 8 lug SF or FF diff...most of the 10 bolt 1/2 tons had highway gears like 3:08's or 3:42's,3:73's...rarely a 4:11....they are not noted for durability ,they are OK for daily driver duty,but anything beyond that they usually break fairly easy,especially if it has a gov-loc diff..
 
If anything id snag the 241 transfer case out of that 89.
Axles likely don't have desirable ratios.
 
Thanks guys. I grabbed the t case Friday :), OK, nix on the axles, didn't feel like another Pick and Pull day anyway. For some reason the previous owner of my K5 put 4:56s in the 10 bolts, with gov lock, probably the 35" tires it had on it. Spent a bunch on that I'll bet. Seems to work OK, I only use 4WD to get up the steep muddy driveway to my cabin, no real bashing.

FhTQTGK.jpg
 
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