'59 Plymouth Forum

In looking for extraneous items in my garage, I came aceross a Sure-Grip Posi.
This item is stamped 2070742. These posi's were manufactured from 1961-1969.
According to an article in Hemmings Oct 1, 2004, it is a decent, dependable 8 3/4" unit.
I bought this from Mike Waller in Idaho. The ID tag is missing, so if you want to know its' ratio, you will need to guide me on how to figure that out.
I do not ever expect to put it on my car, so it is available for purchase.

Roger, on the outer edge of the larger ring gear it should have the ratio stamped into the metal. Or at least the mid 60's versions I have shows the ratio. I believe it should be on yours.

John Q.

Hey John Q,
According to an article I found, the early Posi units were for tapered axles, then after 1964, they switched to flanged axles. If this unit is for tapered axles, you also have to have the correct length tapered axles. Non-Posi tapered axles, such as are in my car now, can't be shortened to accomodate a Posi.
The stamping seems to hint that it was built in 1966, so maybe it is for flanged axles, which are easier to find (and to work with), plus, standard flanged axles can be modified to fit. How can I tell if it is a flanged axle unit?
Am I making sense?

Actually thats not a Sure-grip posi, It's a Spicer Trac-lok, which is better because you can put new clutches in it when they wear out. Sure-grips are a cone style, when they wear out you throw them away!

Roger, The 8 3/4 Pumpkin/Center Chunk should work for the flanged style being a 1966 machining. A 3.23 geared Sure Grip, (Mopar called all there Posi units (Chevy term) Sure Grips regadless if they are the cone shapped or the clutch pack style.) Auburn or Spicer vendor units

Clutch pack style can be re-built whis is correct statement by 59$avoy. I have heard of a few people attempting a re-build on the cone shape versions with mixed results.Lots of machining...

A 12-1-66 date on the ring gear would actually be for a 1967 Model year car. 3.23 was one of the most popular in B and E bodies with 340, 383 and 440 motors.C bodies going for the 2.76 (Highway Gears)

The one I took a picture of today for Roger came from my cell phone and it was a blurry 3.55 open style with no sure grip. But can be added. I took that one out of truck 15 years ago.

John Q.

Nice chunk, the unit is known as a sure grip, and the unit is also known as a power lock, with clutches. these are desirable but cause some concern with a 59 axle system because the sure grip units used slightly shorter axles. Early 742 cases has a S and the gear ratio stamped into the flat pad on the lower rear of the dropout case. Example: S 3.23 Hope this helps. The S stands for sure grip.I have worked and rebuilt several of these units, Yes parts are readily available from direct connection.

P.S. Early axles can be machined to shorten them. I also have the floating centering buttons for these units in stock.

I sold this Sure-Grip to Jeff Carter for $100.

For him or me? (I assume for him, as I heard these go for $200 minimum).
Well, beggars can't be choosers.

ForJeff: I have pulled these from the axle housings, at the local automotive recycle and paid more. And I have sold them for as little as $35. when I needed funds. Not a good business practice. But I love the hobby.

he got a great deal.... i've personally paid anywhere from nothing right up to the $589 tag for a brand new unit depending on the build. a friend just scored a complete b-body rear at carlisle for $400... drum to drum... good considering the cheapest "suregrip" of any ratio in a crate seemed ot be 350 [carlisle swap pricing]

i hold onto these things like they were gold... always can use one! as for the spicer unit- the 4 spider clutch type is literally indestructible... one in particular to note is a '65 300 unit that i removed from my 300 when it had 170xxx miles- the engine went one way, trans another, rear to my 59 eventually, and interior to a 64 galaxie.. anyway- the center section first was put in my 62 880 'vert for maybe 20xxx miles, then in a 71 duster with a 440 that saw severe abuse on the street and track, then back into its c-body housing in my 59... to this day, it still give a little tire squel in turns, and with a sweet burnout- no less than 200' evenly laid down tracks!