Hi everyone,
I'm new to the forum and new to 4x4s as well but I hope this will become a regular hangout for me.

I'm looking at buying a 73 K5 Blazer 4x4. It's in great shape and has a rebuilt transmission and transfer case. It also has a stall converter.

It has 38.5" X 11" X 15" Boggers and has Warren front locking hubs.

Most importantly it has front and rear 4:10 matching gears. I understand the owner installed them because he used the truck for hunting and was usually off-road.

In contrast I hope to street drive it on weekends, take it camping to our state park and only rarely off-road.

I've been told for example that the 4:10 gears are not designed for highway driving (60-70 mph) for any extended amount of time. That the engine at that speed is working too hard to maintain that rpm. That it will prematurely wear out the engine.

Well our state park where we camp/hunt in is over an hour away. The owner told me he used to take the truck on a trailer when he went hunting...I want to drive it not tow it.

Can you guys confirm, shoot down, advice etc. on this information?

Here's some additional questions I have.

1. If I choose to swap out the gears with other gears which won't be an issue for highway driving, what's it going to cost to swap them out? Any rough ideas? New Gears, labor, etc.
2. If I choose to swap out the 4:10 gears do they have any resale value?

Thanks
Devildog67

 

I'm not sure where the owner was getting his information from. True, the engine will work harder to get you down the road at 60-70MPH, but that is because of the 38" tires on it more than it is the gearing. 4.10 gears are helping to correct the overall gear ratio back closer to stock. 4.56 gears would be better with 38's, but I wouldn't do anything until you get it and see how it does.

Costs to swap gears can vary greatly. A local guy here will happily charge you $1500 to rebuild a rear end (parts included) and I would imagine that it would be near $1000 for him to replace the gears.

For prices, that depends on what it has under it for axles. With 38's, I would hope it has a Dana-60 front and a 14-bolt full floater in the rear.

Used gears always have resale value. I picked up a set of Dana-44 4.10's for $80 and a set of 14-bolt 3.73's for $90; both in very good condition. My truck currently has 3.73's in it and the 14BFF I have has 4.10's so I wanted options when it came to gear ratio depending on the tires I went with. Currently with 3.73's and 33's, things aren't too bad. But if I go to 35's, the 4.10's will go in. Anything larger and I will be getting a Dana-60 and swapping in 4.56's.

 

Hi swartlkk,
Thanks for the great information. I think I understand what you're saying about the gear ratio in regards to the larger tires...do you think it would be better to swap the tires out for 35s? To be honest the 38s seem a bit larger than I actually want.

So you wouldn't have any concern driving on the highway at 60-70 mph for a couple of hours each way with this gear ratio/tire combo?

I've asked the owner about the axles and I'll post with his reply.

Thanks
Devildog

 

As long as the truck drives fine you won't have any issue. I assume it has a 350 so you should have enough power. I have a 4.3 and I am currently running 4:10s with 37" tires and I can drive 70 pretty easily. That being said my fuel mileage is horrible lol! I wa going to re-gear down to 5:13 but decided against it with the moor swap I have planned so for now it's 4:10s and all is well! If you don't need/want that much tire dropping to a 35 would be about perfect.

 

I am assuming that the truck has the original TH350 3-speed transmission or 4-speed manual which means that the high gear is 1:1. Your engine RPM should be somewhere in the range of 2300RPM at 65MPH (engine RPM = gear ratio * MPH * 336 / tire diameter -- does not include slip in a torque converter without lockup). If it were down around 1500RPM, then I would be concerned, but that isn't too bad.

 

i ran my 38s with 373 gears for years and they did fine, werent really that great offroad but the engine had enough power to spin them tires. but yeah going down the highway was fine the few times i did it

 

Not a fullsize, but my blazer has 4.10's and I drive it on the highway every day (70+) going to work and back. Haven't had any issues...

IMO, If the ratio is too steep Id be worried more about killing fuel mileage than wearing anything out.

 

KM346, what size tires do you have on your Blazer?

 

They're metric 285/75/r16... but basically a 33".