Front Diff (posi) Locking Question

[AZ79K5Project]

I'm very late to the conversation. I ran lunchbox lockers front and rear on 33's in rocks for about 6 - 8 years. I did that at the beginning of wheeling with this truck. 10 bolt front / 12 bolt rear with Yukon shafts. Some will say I wasted my money and polished a turd with the Yukon shafts but I got them dirt cheap and it was peace of mind. Horsepower and weight will snap the weakest point. Finesse and throttle control goes a long way. I never had any breakage running an under powered 350 with a TBI conversion and saved money I didn't really have. I also had disc rear brakes on the 12 bolt that I picked up for dirt cheap too. I did this in case I broke an axle shaft or c-clip. The disc brakes would help keep the axle from leaving the chat.

I knew I was going to go to bigger tires and a better engine but the issue that forced my hand was driving on a sweeping curve on the freeway as I began to accelerate. The rear locker pushed me into the next lane and I about shat myself. It only happened once, but once was enough for me. I knew not to accelerate and do stuff like that, but I was tired after a long run had a mental slip. I knew the mannerisms of those lockers and I drove around them. Learn those mannerisms and you'll be fine with lunchbox lockers.

The lunchbox lockers are easy to install, have great operational benefits but when locked, like to go straight. I never had an issue on the trail or road with them, with that one exception, and they helped so much while 4-wheeling. I never had an issue where I couldn't turn or turning was ever an issue, unlike the true selectable lockers.

I eventually went to the D60/14bb with air lockers front and rear on 37's with an LS swap after the 350 decided to polish itself from the inside out. I sold each axle and some pretty good money back. I do have to unlock the front on some really tight turns. I normally keep the front open and the rear locked when wheeling. The K5 behaves pretty well when doing that.

These guys know what they are talking about and provided some great information.

 

[jimmyleetn]

I am late to the convo as well, but in my '88 on 33in tires I have an Eaton TruTrac in the rear and a Spartan Lock (lunchbox locker) up front. I did not do hardly any wheeling with that truck but did get some experience with it on the trail before I started my frame off rebuild. If you're on a budget and don't think you'll offroad much, the spartan lock isn't too bad, but you do have to learn how to use the throttle in turns or you'll notice difficulty steering. It will take some practice. You can also only lock in one hub. If you think you're going to end up doing some wheeling, get the TruTrac up front. It's stronger and way more user friendly. In the rear, TruTrac hands down. That thing is all beef.

 

[Aegis43]

@AZ79K5Project @jimmyleetn Thank you both for your insight. Yes, I'm not going to go with lunchbox type lockers. I'm not willing to deal with the unfavorable characteristics. TruTracs are clearly the best choice and their expense is just the price to pay

 

[jimmyleetn]

@AZ79K5Project @jimmyleetn Thank you both for your insight. Yes, I'm not going to go with lunchbox type lockers. I'm not willing to deal with the unfavorable characteristics. TruTracs are clearly the best choice and their expense is just the price to pay

The major downside (depending on your time and money) to the TruTrac install will be that you will need to reset or replace your ring and pinion. It is not a drop in. In the case of my '88, I regeared to 4:11s when I did the differential swap. Even if you keep OE gears, which I would recommend against, you're still going to have reset the gears and get a good pattern and backlash.

 

[Stephen]

I’ll throw another vote in for the Eaton tru-trac up front. 2wd hubs unlocked and you don’t know it’s in there. The tru-trac has been awesome for me off road, dirt, rocks or snow.

The only time I’ve run into any odd handling was coming back from a snow run in the mountains. On the road coming home there was patches of snow and dry pavement. At speed I hit a patch of snow with one tire while the other was on dry road and it torque steered to the side with traction. It was actually pretty startling the first couple of times it did it. I wised up quick and shoved the t-case back into 2hi.

One time out of countless snow runs would not make me want to swap it for anything else. If the road is completely snow covered it’s never done it. Same if it’s dry. But that day taught me quick to take it out of 4hi if the road is patchy with snow.

Mixed patchy ice is problematic for anything that drives off the wheel with the most traction. Limited slip or locker, you'll feel it when the traction side changes from one side to the other. This is one of the points that an auto locker (grizzly, detroit) is at it's worst.

If the hubs are unlocked and the T-case is in 2WD, it doesn't matter what differential you have up front or even what gear ratio. Everything is free-wheeling.

If you're really going down the rabbit hole, it will be mentioned that the front driveshaft does sometimes turn a bit when you're in 2WD/unlocked hubs, but no appreciable torque can be transferred, so nothing bad is going to happen.

I think the interesting part of the discussion is what happens with various types of front differentials when in 2WD but hubs locked.

I've definitely been in situations (tight icy hairpin corners mostly) where the torque required to unlock a front automatic locker made funny things happen with front wheel traction. This is with hubs locked but front driveshaft not powered.

In the end, I boiled down to the following for snow an ice conditions:
open front or selectable, always. Even an LS diff will make you miserable if you have to run 4wd on the road.
In a burb or K5 or truck with weight in the back, a detroit is OK. A selectable is better. In something light and short, anything locking the axles together is a problem.

All that said, I've never run a true trac in the rear because I want a locker when I want it. But, I can interpolate that in something with good rear weight it'll be pretty friendly. In something light and short, it'll have problems.

 

[Aegis43]

The major downside (depending on your time and money) to the TruTrac install will be that you will need to reset or replace your ring and pinion. It is not a drop in. In the case of my '88, I regeared to 4:11s when I did the differential swap. Even if you keep OE gears, which I would recommend against, you're still going to have reset the gears and get a good pattern and backlash.

Got it. That was also always part of the upgrade plan because it has 3.42s in it and I have 33x12.50 KO2s. The plan is 4.10s.