chevy diffs

z71MudDog · March 16, 2012

i bought my1984 k5 blazer from a guy who rebuilt it and put two types of diffs in it it has posi trac and the 4x4 works but if i go too fast(above 5mph) or use it for too long it will grenade either the fromt or rear diff.i need the fectory differentail details if anyone knows.much obliged

AirForceAngler · March 16, 2012

Not sure what you're trying to say? The only thing that would cause this problem is if it has different gear ratios front and rear. Pick which ratio you want and have that installed in the other end.

ChevyTech77 · March 16, 2012

Even if the gear ratio's are different, you'll be fine if it's only ever put in 4WD, off road. Dry pavement would for sure cause problems in a hurry, with split gear sets. We use to split gear ratio's all the time for sand and mud drag racing vehicles back in the day. If done correctly, it works like a charm.

z71MudDog · March 17, 2012

it does have two sets of gear ratios the two arent the same.i have a rear end its a 307 i can buy but im not sure what the front ratio is so if i put that rear in im back at square one not knowing what the front is..the guy i bought it from said if i use the 4x4 for too long even in mud or snow the gears will bind up...the posi is 3.73.i just need to know what the factory front ratio is.i cant really get a hold of the fella i bought it from to ask him an i acant find anything on the net..

Ape0r · March 17, 2012

put it on jackstands and spin the driveshaft by hand to figure it out. not rocket science.

brainpause · March 18, 2012

it does have two sets of gear ratios the two arent the same.i have a rear end its a 307 i can buy but im not sure what the front ratio is so if i put that rear in im back at square one not knowing what the front is..the guy i bought it from said if i use the 4x4 for too long even in mud or snow the gears will bind up...the posi is 3.73.i just need to know what the factory front ratio is.i cant really get a hold of the fella i bought it from to ask him an i acant find anything on the net..

If the front is original, look in the glovebox or door or somewhere for the 3-digit RPO codes. Look them up at http://www.gm-trucks.com/rpo-code-lookup/ and you'll know what it has if front diff hasn't been changed.

z71MudDog · March 18, 2012

ill do that..just wonderin might be easier if the differentials are matching ratios,are the inspector covers the same shape front and back?

ChevyTech77 · March 19, 2012

More than likely, your front ratio is either a 3.08 or 3.42 as those are the most popular ratio's in those years.

The front and rear diff covers are not identical, no.

kstruckcountry · March 19, 2012

I wouldn't worry about what the factory ratios are, if you're looking to offroad it you want gears in the 4's at least.

ChevyTech77 · March 19, 2012

Do yourself a REAL favor and shitcan the 1/2 ton axles altogether if you plan to keep the truck for serious off road use. 14 bolt full float GM rear and Dana 60 front. < I miss mine.

z71MudDog · March 19, 2012

thats what i wanna do like the diffs off an old suburban

kstruckcountry · March 20, 2012

You can do junkyard axles, or custom built. Either way, you'd have to sink some money in gears and lockers.

AirForceAngler · March 20, 2012

thats what i wanna do like the diffs off an old suburban

Unless you find a 3/4 ton Suburban, you'll end up with the same axles you have now. At least if you get them out of the same truck they should have the same ratios!

z71MudDog · March 20, 2012

thats what i been looking for a 3/2 ton sub to swap

ChevyTech77 · March 21, 2012

thats what i wanna do like the diffs off an old suburban

3/4 ton Suburban wil not have a Dana 60 front unless it was installed by a previous owner. Matter of fact, the factory 3/4 ton front Suburban axles are no diferrent than the one you have except they have 8 lug brake rotors on them. Plus, unless you get an 1980 and older or 1980 and newer with a diesel or big block equipped 'Burb, you'll get the wimpy 9.5" semi-floating 3/4 ton rear axle as well.

Again, if you're going to spend some serious time off road in this Blazer, start looking for the 1 ton drivetrain pieces that are nearly indestructible. One last thing you'll have to worry about breaking when you're off road having fun.