72 Posi Traction Problems - The 1947 - Present Chevrolet & GMC Truck Message Board Network

72BlazerJOE · 07-24-2004, 10:22 PM

I recently purchased a 1972 Blazer with posi traction and seem to be having a problem with it. Going around a corner it both rear wheels appear to be locked then something will snap and it will be free. Sometimes it doesn't happen at all, sometimes several times while turning a corner. It will also do it going down the highway and the release is sufficient enough to move the back end of the vehicle over to the point you need to correct the steering. Has anyone else ever had this problem before?
i was considering just taking it out and rebuilding it. Does anyone know if a manual is available for this?

Jimmy72custom · 07-25-2004, 12:25 AM

What kind of posi is it? Or is it a locker?

skid · 07-25-2004, 02:31 AM

If it is stock, it is an Eaton posi. These are excellent units. I would drain the existing oil by pulling the cover off and inspect things to make sure everything looks ok, then refill with gear oil AND GM posi fluid additive. This is a must, and not having it gives symptoms just like you describe.

72BlazerJOE · 07-26-2004, 09:04 AM

Sorry about the ignorance but could you tell me the difference between a posi and a locker?

Jimmy72custom · 07-26-2004, 12:29 PM

If it is posi unit it will most likely have clutches in it to make it slip smoothly when bound up (limited slip). As Skid said the proper fluid an or additive is very important for it to work correctly. If it is a locker it locks the axle mechanically. The most common after market add on locker for your 12 bolt is Lock-Rite. This unit uses coupler gears that are spring loaded to lock the axles. They replace your side and pinion gears in an open rear end. When you turn they make noise. If they are under a lot of pressure and slip they make a lot of noise. If they are making noise on a straight road, some times uneven tire size or inflation will make them make noise. Hope this helps.

skid · 07-26-2004, 02:59 PM

For more information on Eaton posi's, go to www.tomsdifferentials.com Go to the car 12 bolt section. If anyone is interested, I have an old article from Tom's which describes how to rebuild/bulletproof the posi without the pre-load springs and a few other hot rod tricks to strengthen it. I did this to the posi in my Vette which I drag race occasionally, and it launches like a spool, yet still acts like a open differential on the street. I can fax it to anyone who is interested, or, if someone can tell me how to scan and post it on the forum, I will.

I use Red Line and Royal Purple synthetic gear oil which comes with a posi additive as part of the formulation.

72BlazerJOE · 08-18-2004, 03:16 PM

I found out that it is a posi, not a locker. we did a couple of things and cleared it up. One, we changed out the lube and put in the additive. secondly, we put a new set of tires on the rear thinking that if there was a difference in diameter between the back tires, one axle would try to spin faster than the other. It works great now, thanks for all your help!

07-24-2004, 10:22 PM	#1
72BlazerJOE Registered User Join Date: Jul 2004 Location: Michigan Posts: 8	72 Posi Traction Problems I recently purchased a 1972 Blazer with posi traction and seem to be having a problem with it. Going around a corner it both rear wheels appear to be locked then something will snap and it will be free. Sometimes it doesn't happen at all, sometimes several times while turning a corner. It will also do it going down the highway and the release is sufficient enough to move the back end of the vehicle over to the point you need to correct the steering. Has anyone else ever had this problem before? i was considering just taking it out and rebuilding it. Does anyone know if a manual is available for this?

07-25-2004, 02:31 AM	#3
skid Registered User Join Date: Dec 2003 Location: Left Coast Posts: 254	If it is stock, it is an Eaton posi. These are excellent units. I would drain the existing oil by pulling the cover off and inspect things to make sure everything looks ok, then refill with gear oil AND GM posi fluid additive. This is a must, and not having it gives symptoms just like you describe. __________________ Toys: 72 K5 Blazer 74 Vette

07-26-2004, 02:59 PM	#6
skid Registered User Join Date: Dec 2003 Location: Left Coast Posts: 254	For more information on Eaton posi's, go to www.tomsdifferentials.com Go to the car 12 bolt section. If anyone is interested, I have an old article from Tom's which describes how to rebuild/bulletproof the posi without the pre-load springs and a few other hot rod tricks to strengthen it. I did this to the posi in my Vette which I drag race occasionally, and it launches like a spool, yet still acts like a open differential on the street. I can fax it to anyone who is interested, or, if someone can tell me how to scan and post it on the forum, I will. I use Red Line and Royal Purple synthetic gear oil which comes with a posi additive as part of the formulation. __________________ Toys: 72 K5 Blazer 74 Vette Last edited by skid; 07-26-2004 at 03:03 PM.

07-25-2004, 12:25 AM	#2
Jimmy72custom Registered User Join Date: Apr 2004 Location: Willits Ca Posts: 261	What kind of posi is it? Or is it a locker?

07-26-2004, 09:04 AM	#4
72BlazerJOE Registered User Join Date: Jul 2004 Location: Michigan Posts: 8	Sorry about the ignorance but could you tell me the difference between a posi and a locker?

07-26-2004, 12:29 PM	#5
Jimmy72custom Registered User Join Date: Apr 2004 Location: Willits Ca Posts: 261	If it is posi unit it will most likely have clutches in it to make it slip smoothly when bound up (limited slip). As Skid said the proper fluid an or additive is very important for it to work correctly. If it is a locker it locks the axle mechanically. The most common after market add on locker for your 12 bolt is Lock-Rite. This unit uses coupler gears that are spring loaded to lock the axles. They replace your side and pinion gears in an open rear end. When you turn they make noise. If they are under a lot of pressure and slip they make a lot of noise. If they are making noise on a straight road, some times uneven tire size or inflation will make them make noise. Hope this helps.

08-18-2004, 03:16 PM	#7
72BlazerJOE Registered User Join Date: Jul 2004 Location: Michigan Posts: 8	I found out that it is a posi, not a locker. we did a couple of things and cleared it up. One, we changed out the lube and put in the additive. secondly, we put a new set of tires on the rear thinking that if there was a difference in diameter between the back tires, one axle would try to spin faster than the other. It works great now, thanks for all your help!



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