rear ends explained please

[Bruceynz]

Hi Guys,

Ok I feel a bit stupid here I don't really know much about rear ends. Can someone please fill in the rest and how they work differently?

You have:

Open - Stock on most cars I know that much
Posi - ?
Suregrip - ?
trac lok - ?
Lockers - ?
LSD - Limited slip - locks both wheels together when one spins

Also I have an 8.25" open diff 3.21 rear end I am thinking I might change to a LSD, because of the year of mine (1976) it makes it a 27 spline so does anyone have for sale the bits I would need to change my 8.25" to a LSD?

Thanks
Bruce

 

[kkritsilas]

There are really only two types of differentials: open (sometimes referred to as "one legger"), and limited slip, as you said in your original post. Posi (or Positraction, to give it its full name) is a Chevy/GM term for the limited slip differential, Suregrip is the Chrysler/Mopar name for the same thing, and this is where it gets a little fuzzy for me, but I think Trac Lok is the Ford or maybe American Motors name for the limited slip. Detroit Lockers are what one company calls their limited slip differentials. Yhere are multiple companies making limited slip differentials (Eaton, Dana, Moser, etc.) Some of them use plates, some of them use cones, but they essentially do the same thing with differing characteristics. There are are also Torsen (TORque SENsing) differentials which only use gears, but they are also limited slip differentials.

Lastly, there are spools, or locked (not locking) differentials in which the differential action has been eliminated to maximize the strength of the differential. They are unusable on the street, but are used on drag strip only cars. Can be thought of as a straight axle from wheel to wheel, with a ring gear on it,

 

[Bruceynz]

So if I was to buy something like this it would bolt right in and give me the LSD


from eBay add

"Dodge 8.25 sure grip / trac lok (posi) 27 spline unit with 3.55 (11-39) gears. Gears have a nice wear pattern and unit is nice and tight. Includes adjusters, races, c clips, abs reluctor ring and used bearings that could be used as is or replace to your liking. Should fit many different years and models with the 27 spline 8.25 rearend (1997 and older 10 bolt) so do your research. Any questions? Ships to the lower 48 US states only. Thanks"

Dodge Plymouth Mopar 8.25 8 1/4 Sure Grip Trac Lok Posi 3.55 Gears 27 spline

 

[Bruceynz]

and here is the grenade looking thing

Chrysler 8.25" Yukon Spartan Locker - 27 Spline - SL C8.25-27 - Posi Locker Axle

whats better?

 

[80mirada]

Stay away from the second one, those ratchet lockers suck in a street car, they are noisy and are hard on the axel ends. a brand new Mopar limited -slip is only a little more

http://www.summitracing.com/parts/dcc-4529273/overview/

you would need a set of ring gear bolts and new carrier bearings,

http://www.summitracing.com/parts/rat-1304/overview/
http://www.summitracing.com/parts/rat-9001/overview/

you will be much happier. I had a buddy that put one of those ratchet type lockers in a barracuda. It was noisy, rough and it had a tendency to not unlock around corners. The police were not amused.

 

[bremereric]

Sure Grip

 

[Monkeyed]

from what I understand a Detroit Locker is an open differential that you can lock with air pressure to form a type of spool.

 

[Aspen500]

An air locker is similar to a Detroit Locker except the Detroit is pure mechanical that works (or doesn't work as the case may be) on it's own. The air locker needs a compressor (obviously) and you flip a switch inside the car to engage it. Mostly used on trucks and Jeeps that are used off road frequently.

I'm not positive the SureGrip you mentioned would bolt in to your housing. It mentions a reluctor ring for ABS so it's from a newer axle. You should do some careful research on it before buying.

 

[Bruceynz]

Can I use my 3.21:1 ring and pinion in my current open rear end with the with the summit mopar limited slip unit?

And I bought this the other day, I think it will have everything I need, ring gear bolts and carrier bearings.

http://www.summitracing.com/int/parts/rat-3022k

 

[Bruceynz]

By the way mucking with rear ends is expensive! You guys in the USA are so lucky, I get stiffed with a weak dollar against the USD and a hefty USPS bill to pay Just to give you an idea $325USD + $100 USPS and then I get stuck tax of 15% ends up costing me about $760NZD now you see why when I buy something I got to get it right, bit hard to send anything back to Summit from here, why do I live so far away from the USA So your guys advice is so awesome, many thanks to all you who reply and help me out.

 

[7T8 Custom]

Don`t feel all alone. If your Canadian like I am you live much closer to the U.S. but still have a terrible exchange rate due to a weak dollar, still have to order most parts from the U.S., and still get shafted with shipping costs from USPS.

 

[Bruceynz]

On eBay which one looks the best buy, I like the idea of the 3.55 ratio

This one

8.25 3.55 gears 27 spline posi trac lok dodge chrysler plymouth mopar dakota

Or

Dodge Plymouth Mopar 8.25 8 1/4 Sure Grip Trac Lok Posi 3.55 Gears 27 spline

Thanks
Bruce

 

[80mirada]

Your stock gears will work with the mopar unit, and you wouldn't have to setup the pinion, you just have to set gear lash. If you change gear sets you have to setup pinion depth which can be a pain in the ass

 

[Bruceynz]

So best to buy the new LSD from summit and use my existing stuff? That way I would have a new reliable LSD

The car that my rear end came out of had 116,000 miles on it. So should be all good inside, turns over ok with no nasty bumps.

any idea what the Summit LSD part would way, just trying to get an idea if I can USPS to NZ and how much it would cost.

 

[Bruceynz]

So before I buy one this unit from summit will turn my open rear end into an LSD rear end with no extra parts required. The only reason I ask is because I see this written about them on ebay.

"Chrysler 8.25 limited slip 27 spline Works on 96 and older rear ends. This is a factory OEM unit that Chrysler sells and came in the 8.25 if it had limited slip."

Does that mean it replaces an existing LSD or will upgrade my open rear end to an LSD?

 

[80mirada]

It will replace a worn LSD, or an open Ring gear carrier. New carrier bearings, and ring gear bolts are recommended.

Ring gear bolts http://www.summitracing.com/parts/rat-1304/overview/

Carrier bearings http://www.summitracing.com/parts/rat-9001/overview/

You will need a torque wrench, Loctite, and a dial indicator with stand. The ring gear bolts are left hand threaded. The hardest part will be setting the backlash. I made an adjuster tool for the bearings by grinding the head of a large bolt to fit and welded a 1/2' drive socket to it. a simple spanner could be made from some round stock, or a large pin spanner works if you can find one in a size that is close.

 

[80mirada]

My bearing adjuster tool was a 1 1/2' bolt that I ground the sides down to 1.4-1.42" (36.1mm). I added a nut under the head to act as a stop to keep it from sliding through the adjuster, and welded a 15/16" 1/2" drive socket.

If you can find one, a 36mm headed bolt would be even better

 

[aspen77rt]

Nit noid question. If you're replacing the rear end and springs, isn't it easier to remove the old rearend/springs as one unit?

 

[Bruceynz]

My rear end is a 7.25" I am upgrading the car to the 360 mild performance, I have an open 8.25" rear end to bolt in, but before I bolt it in it is easier to do all the work now well it is out of the car.

 

[aspen77rt]

Ill be doing the same in a few months. 7.25/springs will be coming out. 8.25 and New epso 5 leaf fmj packs will be going in. It would seem easier to just remove the old 7 1/4 and old springs as one unit if you're replacing everything. Once the brake lines and other stuff are disconnected, it's only six bolts per side to remove the rearend/springs as a unit. Like the pic for example.