I am looking into upgrading the rear end on my 72 Cutlass Supreme. factory 350 2 barrel car with i believe open 2.73. Would like to go with 3.42 or similar rear gear and posi to not make driving on the highway unbearable. automatic 350 transmission.
What are the options for posi units? I am confused as it seems some olds rear ends dont have many options?
72 Cutlass Posi Options
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aggrorider1
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Re: 72 Cutlass Posi Options
Wow, Sorry we missed this post.
The gear options for the 10 bolt 8.5 (which should be your factory optioned rear for this car)
are as follows.
2.93 (very hard and expensive to find) In 8.5 rears this was in the wagons in the early 90's)
3.08 (should be fairly easy and reasonable to find in used GM condition) This ratio will be a slight upgrade and still get you done the freeway quite well.
3.23 (again a harder to find ratio in the used market) This ratio will be a noticeable bump and you will start to hear your RPM noise level increase at 60-70 rpm for sure. But with larger rear tires is still acceptable for freeway driving.
3.42 (Very popular gear in GM and should be get-able in yard used condition still) This ratio from 2.73 will be about the last ratio before freeway becomes unbearable for MOST swaps that go from 2.73 range Pop out of the hole is pretty snappy can still be driven on the freeway ...long trips can get noisy and long with th e RPM range being quite high especially with stock size tires 25" to 26" diameter.
3.73 (Most popular tire in this era we are in and has been pretty popular since the GRand National too the seen. ) The freeway time with a 3 speed auto or a 4 speed manual is really not to FUN you can do it for about 10 - 20 mins and your about done with the amount of RPM and engine noise and being an old car you are going to feel ALL the flaws of your OLD muscle car....lol. Shaking, vibrations, shimmy, etc. even with larger than stock tires freeway is not so cool.
YOU will notice a great increase in torque out of the hole and if your just hanging around town it is great FUN.
DO remember this is only MY personal options to help other try to make a decision and I am only trying to help you understand what the ratios do and you have to understand THIS IS THE FELLING going from 2.73 (stock GM ratio ) to any other gear steeper.
Hope it helps.
Thanks for reading.
Jim
JD Race
The gear options for the 10 bolt 8.5 (which should be your factory optioned rear for this car)
are as follows.
2.93 (very hard and expensive to find) In 8.5 rears this was in the wagons in the early 90's)
3.08 (should be fairly easy and reasonable to find in used GM condition) This ratio will be a slight upgrade and still get you done the freeway quite well.
3.23 (again a harder to find ratio in the used market) This ratio will be a noticeable bump and you will start to hear your RPM noise level increase at 60-70 rpm for sure. But with larger rear tires is still acceptable for freeway driving.
3.42 (Very popular gear in GM and should be get-able in yard used condition still) This ratio from 2.73 will be about the last ratio before freeway becomes unbearable for MOST swaps that go from 2.73 range Pop out of the hole is pretty snappy can still be driven on the freeway ...long trips can get noisy and long with th e RPM range being quite high especially with stock size tires 25" to 26" diameter.
3.73 (Most popular tire in this era we are in and has been pretty popular since the GRand National too the seen. ) The freeway time with a 3 speed auto or a 4 speed manual is really not to FUN you can do it for about 10 - 20 mins and your about done with the amount of RPM and engine noise and being an old car you are going to feel ALL the flaws of your OLD muscle car....lol. Shaking, vibrations, shimmy, etc. even with larger than stock tires freeway is not so cool.
YOU will notice a great increase in torque out of the hole and if your just hanging around town it is great FUN.
DO remember this is only MY personal options to help other try to make a decision and I am only trying to help you understand what the ratios do and you have to understand THIS IS THE FELLING going from 2.73 (stock GM ratio ) to any other gear steeper.
Hope it helps.
Thanks for reading.
Jim
JD Race
J D Race
Re: 72 Cutlass Posi Options
Posi units
8.5 10 bolt has some of the best optional posi units out on the market.
EATON tradition performance LSD clutch type is the most popular choice anbd a good one
- the posi has been re-manufactured by many copies now so be careful on the brand name you get.
-there are Summit brand, Jegs Brand, Everyone in the Internet has repoped them. so they are assemble by anything and everything....lol. BE CAREFUL
stick with a good brand name...We use Yukon for all our build and come with a 1 year manufactures Warranty and I think in 20-25 years we used warranty ONCE...lol. Good stuff. CAn not usually go wrong with Actual EATON brand name the inventor and designer of the unit...
AUBURN Again a traditional friction base posi unit.
-were Originally used in Muscle car era cars like Buick Olds and Pontiac...Mopar even had them in the 8.75 popular MUSCLE car rears from 69-78 era.
-Cone unit hook very well ...done side they usually are NOT rebuildable with out machine work that a regular back yard guy can not do with out VERY expensive machinery.
These and Eaton unit still should last many years of driving like 15- 20 years with out issues.
TRUE Trac - Torsen Worm gear posi units
-Becoming very popular these days ...most Foreign and imports come with these forms of initial Helical gear to gear type multi biasing units.
-People like they because generally there is not maintenance to the unit...BUT I guarantee they WILL WEAR out like any other unit...Just might be in the more violent total LOCK up way when it finally does happen. TRUE TRAC has a hardened case as the WORM gears need a strong hole that will not oblong over years of use. This give the unit a strong ability to plant power to the ground and torque sensing ability to delivery the power as much as it can in turns until friction is lost between the tire and ground. True trac will also give you another slight side to to slide gear contact point again for strength.
Auburn had this also with the 4 pinion posi unit which was and great increase from the traditional 2 pinion spider gear unit.
GM AUTO LOCKER (also nick named the GOV LOCKER)
This is a great unit for a everyday none performance driving car or truck....IT IS NOT A PERFORMANCE UNIT.
Meaning for burn outs and cornering spirited driving muscle car...IT IS NOT A GOOD CHOICE. It is a low speed operational unit ...30 MPH and under is the lock up point of these units. OVER 30mph it does not lock. Best not to make this choice for a Burn out or drag race machine.
DETROIT LOCKER Legendary locker...extreme application unit...Not street friendly,. Clunky around corners...normally used for OFF ROAD machines not drag racing and corner carving up mountain hills on the pavement. EXPENSIVE and all heck too.
LUNCH BOX LOCKERS (power trax, lock right, Spartan locker, maxx traxx, ) All are posi unit derived from the Detroit locker design but easy install with out gear ratio or carrier swap makes this unit convenient, easy, fun, strong unit AS LONG AS YOU READ THE DIRECTIONS and install correctly. This unit has one of the worst records for WRONG install by customer just plain getting them install wrong...lol they do work well and can be great money spent.... We have used and installed many for weekend warriors here in Ohio The unit will have a tapping noise in turns and hooks hard in straight aways. Follow the instructions to the T and you will love it. DO NOT you will have headaches!
SPOOL MINI SPOOL Well these I would say are for either DRAG RACE ONLY or VERY low buck application where you rolling the dice...lol.
Full spool will require BOLT IN AXLES (factory BOP or C-clip eliminator for chevy c-clip rears.
Mini Spool can be used in either or... BUT really is not supposed to be a street driven unit as it is just blocks that stack in the place of the open spider gear cavity when spiders are removed. MINI SPOOL is dangerous and I personally HAVE used them on the street in my younger days...and did not have any issues. They do not last for ever the blocks will beat them selves and the case up after a while 3-4 years of street driving if you do not break something else first...lol axle shafts tire wear etc. high strain on axles around corners. Terrible in weather like rain and snow...lol. NO sensing of traction at all IT IS ALL or nothing...
Any way those are some of the different designs out there just read and google people opinion and be smart...try to pick something that fits your price range and driving techniques / terrains / conditions your going to see when driving .
Again some of the info is opinion and not all fact... I am just trying to help you the buyer make a good decision from my personal experiences too.
Safe driving to you and your families.
Jim
JD Race
8.5 10 bolt has some of the best optional posi units out on the market.
EATON tradition performance LSD clutch type is the most popular choice anbd a good one
- the posi has been re-manufactured by many copies now so be careful on the brand name you get.
-there are Summit brand, Jegs Brand, Everyone in the Internet has repoped them. so they are assemble by anything and everything....lol. BE CAREFUL
stick with a good brand name...We use Yukon for all our build and come with a 1 year manufactures Warranty and I think in 20-25 years we used warranty ONCE...lol. Good stuff. CAn not usually go wrong with Actual EATON brand name the inventor and designer of the unit...
AUBURN Again a traditional friction base posi unit.
-were Originally used in Muscle car era cars like Buick Olds and Pontiac...Mopar even had them in the 8.75 popular MUSCLE car rears from 69-78 era.
-Cone unit hook very well ...done side they usually are NOT rebuildable with out machine work that a regular back yard guy can not do with out VERY expensive machinery.
These and Eaton unit still should last many years of driving like 15- 20 years with out issues.
TRUE Trac - Torsen Worm gear posi units
-Becoming very popular these days ...most Foreign and imports come with these forms of initial Helical gear to gear type multi biasing units.
-People like they because generally there is not maintenance to the unit...BUT I guarantee they WILL WEAR out like any other unit...Just might be in the more violent total LOCK up way when it finally does happen. TRUE TRAC has a hardened case as the WORM gears need a strong hole that will not oblong over years of use. This give the unit a strong ability to plant power to the ground and torque sensing ability to delivery the power as much as it can in turns until friction is lost between the tire and ground. True trac will also give you another slight side to to slide gear contact point again for strength.
Auburn had this also with the 4 pinion posi unit which was and great increase from the traditional 2 pinion spider gear unit.
GM AUTO LOCKER (also nick named the GOV LOCKER)
This is a great unit for a everyday none performance driving car or truck....IT IS NOT A PERFORMANCE UNIT.
Meaning for burn outs and cornering spirited driving muscle car...IT IS NOT A GOOD CHOICE. It is a low speed operational unit ...30 MPH and under is the lock up point of these units. OVER 30mph it does not lock. Best not to make this choice for a Burn out or drag race machine.
DETROIT LOCKER Legendary locker...extreme application unit...Not street friendly,. Clunky around corners...normally used for OFF ROAD machines not drag racing and corner carving up mountain hills on the pavement. EXPENSIVE and all heck too.
LUNCH BOX LOCKERS (power trax, lock right, Spartan locker, maxx traxx, ) All are posi unit derived from the Detroit locker design but easy install with out gear ratio or carrier swap makes this unit convenient, easy, fun, strong unit AS LONG AS YOU READ THE DIRECTIONS and install correctly. This unit has one of the worst records for WRONG install by customer just plain getting them install wrong...lol they do work well and can be great money spent.... We have used and installed many for weekend warriors here in Ohio The unit will have a tapping noise in turns and hooks hard in straight aways. Follow the instructions to the T and you will love it. DO NOT you will have headaches!
SPOOL MINI SPOOL Well these I would say are for either DRAG RACE ONLY or VERY low buck application where you rolling the dice...lol.
Full spool will require BOLT IN AXLES (factory BOP or C-clip eliminator for chevy c-clip rears.
Mini Spool can be used in either or... BUT really is not supposed to be a street driven unit as it is just blocks that stack in the place of the open spider gear cavity when spiders are removed. MINI SPOOL is dangerous and I personally HAVE used them on the street in my younger days...and did not have any issues. They do not last for ever the blocks will beat them selves and the case up after a while 3-4 years of street driving if you do not break something else first...lol axle shafts tire wear etc. high strain on axles around corners. Terrible in weather like rain and snow...lol. NO sensing of traction at all IT IS ALL or nothing...
Any way those are some of the different designs out there just read and google people opinion and be smart...try to pick something that fits your price range and driving techniques / terrains / conditions your going to see when driving .
Again some of the info is opinion and not all fact... I am just trying to help you the buyer make a good decision from my personal experiences too.
Safe driving to you and your families.
Jim
JD Race
J D Race