67 Belvedere Convertible - 489 Case - want to go to Posi

conv67bdere · Oct 5, 2014

I have got a 1967 Belvedere Convertible II, with a welded up free carrier and would like to convert it to a Posi . . . not for racing, this will be a driver.

Summit sells an Auburn Gear pro series differential - http://www.summitracing.com/parts/aub-542051/overview/year/1967/make/plymouth/model/belvedere-ii

The other option is to look for an original posi for the 8 3/4 - 489 case . . .

Questions:

Does the posi fit all cases ( 741, 742, and 489 ) - or do you need to find the posi for the 489 case ?

Which is the best way to go - stick with an original unit or buy the new Auburn gear from Summit ?

Other options for posi besides the original unit and Aururn ?

Any and all suggestions / advice would be greatly appreciated . . . Thanks in advace

twinscrew698 · Oct 6, 2014

It is called a suregrip for Mopars and yes they all are interchangeable for the 8 3/4 diffs.

HT413 · Oct 6, 2014

I used the auburn unit from summit. I think it's a great unit, new steel as opposed to 40-45 year old metal, contrary to popular thought, they can be rebuilt, but honestly, we'll all be dead before that is needed.

I run mine with 30"x12.5" street slicks and it operates great, though I don't have many miles on mine yet and haven't raced it.

Dr diff has a clutch type unit for sale for less than that unit, but have never used it.

conv67bdere · Oct 6, 2014

twinscrew698 said:
It is called a suregrip for Mopars and yes they all are interchangeable for the 8 3/4 diffs.

Thanks for the information twinscrew698 . . . now to try and track down my suregrip . . . wooohoooo ! !

HT413 said:
I used the auburn unit from summit. I think it's a great unit, new steel as opposed to 40-45 year old metal, contrary to popular thought, they can be rebuilt, but honestly, we'll all be dead before that is needed.

I run mine with 30"x12.5" street slicks and it operates great, though I don't have many miles on mine yet and haven't raced it.

Dr diff has a clutch type unit for sale for less than that unit, but have never used it.

Thanks HT413 . . . my thoughts exactly about the New metal vs 45 year old metal . . . really appreciate the product review . . .

might just need to pick me up a new unit from Summit too ! ! !

747mopar · Oct 6, 2014

I agree, If it's going to cost $500.00 for a used set and a new set is $500.00ish then it's a no brainer (I just don't have any experience with the new ones to offer an opinion). Dealing with Summit also gives you some confidence that you'll be taken care of (unlike American Powertrain).

5.7 hemi · Oct 6, 2014

Just keep in mind, the older clutch style sure grip is a forged unit and can be rebuilt.

conv67bdere · Oct 7, 2014

5.7 hemi said:
Just keep in mind, the older clutch style sure grip is a forged unit and can be rebuilt.

Thanks 5.7Hemi . . . that is the reason that I'm posting this question - I really need others knowledge and expertise on this . . . I do not know much about them.

So my question to you is . . . if you had to choose, which way would you go - new or old style ? ? The car is a daily driver, not a race car . . .

And HT413 indicated that the Auburn unit can be rebuilt too - but I may never need it in my lifetime.

5.7 hemi · Oct 7, 2014

For me, I use the clutch style. Money always dictates what I can afford and picking up a used clutch sure grip is reasonable. Clutches are around 75 bucks if they are needed and the internals are available from Dr. Diff (aka Cass) for 175 and they are a 1 piece design side gear which is way better than the factory 2 piece, plus when you install those internals there is no need to line up the splines with the axles in. you can pick a used unit (clutch) for about 250-500, 500 being the high end for those sellers on the crack pipe. So say you bet one for 300, and tear it apart (mark the case halves before hand) and see the clutches are worn out, 75 for the new ones, and say you decide to replace the internals (totally up to you unless there is chipped or broken parts) for 175, you will have a strong clutch style sure grip for about 525, and the price could be more or less depending on how/what of deal you get on the sure grip to start with. I did not included bearings as I would replace those anyway.

kb67mopar · Oct 7, 2014

I plan to run a new auburn unit eventually unless somebody gives me a great deal on a used "sure grip". If i am spending 500 plus bucks it will be for a new unit. if I can get a good working used unit with 3.23 gears already installed I am all for that too. I have no intention of rebuilding an old unit though...these things were used for drag racing WAAY to often not to have fatigue built into them by now. If it was way cheap I'd consider doing it though.

Also for those who get caught up on terms....Posi, Suregrip, Traclock....it doesn't matter it all means the same thing to a gear head....two equal length black lines and a smile that opens legs

5.7 hemi · Oct 8, 2014

I don't think that you will find a "good used working unit for under 500". Not to say it can't or wont happen, just don't see it happening. Also, I'm referring to just the "sure grip", no case, no gears, no yoke, just the sure grip.

conv67bdere · Oct 8, 2014

5.7 hemi said:
I don't think that you will find a "good used working unit for under 500". Not to say it can't or wont happen, just don't see it happening. Also, I'm referring to just the "sure grip", no case, no gears, no yoke, just the sure grip.

Agreed 5.7Hemi . . . when I was the Mopar Nationals I saw 3-4 of them in the AM for the $500-600 price range, figured I go back later and pick them up and hopefully barter them down on the price . . . when I went back, I could not find any of them. Looks like they all got scarfed up . . . oh well . . .

I guess I am leaning toward the NEW Auburn unit myself . . . still giving it some thought . . .

mikefryezinnger · Jan 18, 2015

Of the original MOPAR posi units both the clutch type or the cone type carriers will fit all of the three 8 3/4 carriers.
The earlier clutch type is stronger and rebuildable. The later cone type units will hold up well unless raced in high horse
power cars with slicks.

67 Belvedere Convertible - 489 Case - want to go to Posi

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