I have been curious as to what type of differentials that were in one of my parts K5 Blazers so I pulled the cover and took photos. I will be selling the entire vehicle shortly but may reconsider because of this great find. I am not sure if the differential bolts into an M1009 without modification though and that is my question at this point. Also pulled the cover off of the front differential and nothing special in there; will also post photos of that as well. The front cover was really made solid though! Very heavy and thick metal; just a 10 bolt in the front. This K5 has the manual hubs also which is another great plus!
That is the typical "Gov Lock" differential. It's known to be fairly unreliable and does not deal with any sort of abuse. A normal clutch type limited slip would be considered a huge leap forward in reliability. If you just use ti for a daily driver, you should be ok. If you intend to work the truck, use it off road or do anything that you would normally consider a locker ideal for, be prepared to find all the little fly-weights in a pile in the bottom of the housing.
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~Elwenil~
Lanty A. Clemons Mopar Parts Advisor
1988 Dodge Ramcharger AW450 Project
318TBI - NP435 4 speed - NP205 - Front & Rear Dana 60s
"I am the voice of reason, in an unreasonable world."
"Ya know, offroading is for people who have more sense than money. Not the other way around." - Maddawg308
Looks like there was water in the gear oil. Water will settle to the bottom and can rust the gears like that as well as the rust on the bottom of the housing while the upper portion appears to have little to no rust.
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~Elwenil~
Lanty A. Clemons Mopar Parts Advisor
1988 Dodge Ramcharger AW450 Project
318TBI - NP435 4 speed - NP205 - Front & Rear Dana 60s
"I am the voice of reason, in an unreasonable world."
"Ya know, offroading is for people who have more sense than money. Not the other way around." - Maddawg308
Steve, The spring perches are on top of the axle if you are talking about the "nut ends" of the U-Bolts; the U portion is under the axle. Is this good?
Thanks for all the replies regarding this axle - even though it is a 12 bolt I guess it is no more beefy than the 10 bolt of the same type. There was water in the fluid that I drained out of the rear differential for sure and it was kinda nasty looking stuff too - not clear like the stuff I drained out of the front. I was considering using this in one or more future projects and still might do so. There has to be some heavier-duty parts in this as compared to the 10 bolt. If nothing else, it was great to see what I had sitting in my lower yard for years! This thing also has the SM465 transmission and 205 transfer case so I will part it on out very shortly!
That's a standard GM 12 bolt. Unless the gears are something nice there's nothing terribly special about it and as you discovered the Grenade Lock isn't a plus and the strength isn't terribly much greater than a 10 bolt rear. Not even 20%. A 12 bolt is mostly bolt in, the differences can be found over on www.ColoradoK5.com pretty easily. It's an upgrade but not much of one and would only really be worth it if you had to regear or rebuild a 1/2 ton rear and had a 12 bolt available instead of a 10 bolt.
Also as mentioned I'd be a bit worried about the rust myself. I bet the gears are fine but I'd worry more about the bearings and races, seals, etc in the diff. That said I know folks who have run "chocolate milkshake" filled diffs for years or taken junkyard diffs, busted the rust off with wire brushes, hosed it out with brake cleaner, and then filled it up and ran it with success...and then folks who had minor imperfections cost them over a grand in axle work.
Oh yeah, to figure out the gear ratio just count the number of teeth on the ring and then divide by the number of teeth on the pinion.
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89 Chevy K5 Blazer. 6.2L diesel, stockish, and clean.
These opinions and thoughts moderated with your sensibilities in mind.
Sold my CUCV and won't likely be around much. If you want a good forum with excellent knowledge of 73-87 GM trucks where folks won't judge you for modifying YOUR vehicle, please join us at www.ColoradoK5.com .
Oh, and don't EVER buy anything from Alfa Heaven. Do a search.
AJM Blazer, thank you so much for the information about the differential that I have. I still want to use it as one of the components in a 60's era dune buggy that I used to make when we could legally drive on the beach here in Brevard County; basically a shortened truck frame, bucket seats, roll bar and whatever motor/transmission you want. I'll go to the Colorado K5 site, which I am a member of already and see what they say about this rear chunk and go from there. I have three more rear differentials to inspect here at the house (10 bolts each) because I have no idea what is in each of them (all civilian K5s).
12 bolt limited slip/Gov Lock rear
