Gears front /back

[Big Blue]

Building my k5 rear. I am putting in 3.73 in the rear. Question is do I put the same gear type in the front?? Since I am putting 3.73 in the rear.
thank you, John

[kipps]

The only time the front and rear should be mismatched, is for some extreme mud-racing situations. I think they usually overdrive the front axle a little, to keep the vehicle tracking straight under full-power runs in deep mud.

For anything else, you definitely want them to match. If you're trying to spread out the cost, you can leave the old gears in the front for now, but you should remove the front driveshaft to avoid any risk of engaging the front axle.

[sweetk30]

i have a question for the o.p.

what size tires ? and trans and you planning ?

doing all the work i hate to see you do it for the wrong ratio .

[kipps]

Originally Posted by sweetk30

doing all the work i hate to see you do it for the wrong ratio .

Second this. I'd be interested to specs you're working with.

I'm building the truck in my signature with 4.10 gears and 33" tires. I think this combo(engine/trans/gears/tires/truck-weight/intended-usage) will work well together. I expect to do a bit of gooseneck towing with this truck. I doubt I'll use overdrive at all when towing, unless I reach 65+ mph. There's a good chance as well, that I'll be skipping first gear when driving empty.

[mongocanfly]

My IH build with the LS/nv4500 and 33in tires got a set of 4.56s..
My C30 with LS/nv4500 and 31in tires has a set of 4.10s..
Kipps..I'm betting you use 1st more than you think..

[kipps]

Originally Posted by mongocanfly

My IH build with the LS/nv4500 and 33in tires got a set of 4.56s..
My C30 with LS/nv4500 and 31in tires has a set of 4.10s..
Kipps..I'm betting you use 1st more than you think..

Could be. I've just never had a very deep first that wasn't a non-synchronized granny-low.

What engines are in your trucks? 6.0, turbo-4.8, etc? For my build, would you have recommended 4.10 or 4.56, considering my VVT 5.3, nv4500, 33" tires, and combination of run-around usage and heavy stock-trailer towing?

Part of my reasoning was that I'm largely duplicating what GM was building in the early 2000's. Same gearing, similar engine, same transmission, etc.

[mongocanfly]

Yeah kipps..your setup will probably be just fine...i had a 99 z71,5.3/4l60 that had 31s and 3 73s..i used to tow with it and it did just fine..
1st in a nv4500 isnt real low..not like a sm465 anyway...my C30 has a stock LQ9 6.0 with headers and a dyno tune..I regularly pull 10k loads with it...it will cruise all day at 75-80 mph with this setup...I love the way it works...at 65mph its turning just over 2000rpm...i really like the way it is..
The IH hasn't been driven but I tried to duplicate my C30 setup on it...only diff is it is a 5.3...but with the little taller tire I think the 4,56s will be fine..

[Big Blue]

Thanks everyone for chiming in. To answer The size of the tires, they are 31 x 10.5. As far as the trans, I do not really know much about transmissions except it is the standard type that you would fine in a k5 blazer. Again thanks, John

[mongocanfly]

What yr model blazer...I'm guessing maybe a t350 trans...

[Big Blue]

Its a 1979 BLAZER frame with a truck cab on it. I think it is a th350.

[mongocanfly]

If it's a t350 itll have a final ratio of 1:0
So with 3.73s ,and 31in tires , and a 1.0 trans, you'll be turning 2628 rpm at 65mph..
http://www.csgnetwork.com/multirpmcalc.html

[kipps]

Those rpms won't be bad at all for a LS engine. They're a tad high for a SBC.

Here's my favorite gear ratio calculator --

http://www.grimmjeeper.com/gears.html

[4u2nv]

I see what you guys are running here and mine is a 87 c10 4x4 350,350 and 342 rear gears and at 50 miles per hour mine is tacking at 3000 .
WHY ?????
And she is a pig on gas.

[kipps]

@Big Blue, is that frame painted silver, or did you by any chance galvanize the frame?

[kipps]

Originally Posted by 4u2nv

I see what you guys are running here and mine is a 87 c10 4x4 350,350 and 342 rear gears and at 50 miles per hour mine is tacking at 3000 .
WHY ?????
And she is a pig on gas.

You're right, the 3000 rpm doesn't make sense. What tire size? Is your convertor locking up or not? Have you double checked the tach and speedo accuracy? Check the tach with a timing light, and check the speedo with a phone GPS.

[Mathew21]

Originally Posted by 4u2nv

I see what you guys are running here and mine is a 87 c10 4x4 350,350 and 342 rear gears and at 50 miles per hour mine is tacking at 3000 .
WHY ?????
And she is a pig on gas.

That don't make since, it sounds like your truck is in second gear. What size tire do you have?

[mongocanfly]

4u2...something sure ain't right...I just guessed at what size tire you might have...and like Matthew stated..in 2nd gear would be close to 3k rpm...
Like asked ..what size tire are you running?...and double check rpm and mph...

[Big Blue]

thanks kipps, Painted silver. though I'd be different.

John

[kipps]

Originally Posted by Big Blue

thanks kipps, Painted silver. though I'd be different.

John

Thought I'd ask. I'm seriously considering hot-dipping a frame. I was quoted $450 to dip a sandblasted full-size truck frame. The Land Rover guys do it frequently, due to the bad rust problems they have with their frames. As I see it, hot-dipping is about the same price as using a proper three-stage chassis paint from Eastwood. It should be much better protection.

[sweetk30]

4u2nv your in 2nd gear via the calculator at 50mph and 3k rpm .

you have the vacuum modulator hooked up ? or maybe another problem .

can you start off and count 2 up shifts . first is a given then bump 1 = 2nd and bump 2 = 3rd .

[4u2nv]

Originally Posted by kipps

You're right, the 3000 rpm doesn't make sense. What tire size? Is your convertor locking up or not? Have you double checked the tach and speedo accuracy? Check the tach with a timing light, and check the speedo with a phone GPS.

35"s for tires, i think i should check the converter,tach and speedo are good

[4u2nv]

Originally Posted by sweetk30

4u2nv your in 2nd gear via the calculator at 50mph and 3k rpm .

you have the vacuum modulator hooked up ? or maybe another problem .

can you start off and count 2 up shifts . first is a given then bump 1 = 2nd and bump 2 = 3rd .

It's shifting all gears

[mongocanfly]

4u2...you've got some serious issues going on...with the numbers you stated you should be turning 1642rpm...
are you sure your tach is right?...I know some older tachs had dip switches for 4,6, or 8 cyl

[4u2nv]

Originally Posted by mongocanfly

4u2...you've got some serious issues going on...with the numbers you stated you should be turning 1642rpm...
are you sure your tach is right?...I know some older tachs had dip switches for 4,6, or 8 cyl

It's a aftermarket tach (Bocsh)
You can tell going down the highway that it is reving that high .
Truck shifts good , has all kinds of throttle response .
At 65 mph it tachs at 4000 .
I'm puzzled .

[kipps]

Your numbers do line up perfectly with it staying in second gear.

Try putting the truck on a lift, and run it up to speed. With no load, see if the tach and speedo act the same as they do while driving.

Also, while still on the lift, use a timing light on the engine and the driveshaft. The two should be exactly the same speed if the converter is locking in on 3rd gear.