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BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(6468 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Posi units
Posted by: BlownMGB-V8
Date: November 26, 2008 12:24AM

Which one do you think is the most suitable for a LBC swap and why?
Jim


Bill Young
Bill Young
Kansas City, MO
(1337 posts)

Registered:
10/23/2007 09:23AM

Main British Car:
'73 MG Midget V6 , '59 MGA I6 2.8 GM, 4.0 Jeep

authors avatar
Re: Posi units
Posted by: Bill Young
Date: November 26, 2008 08:28AM

Jim, I like the older style posi using a spring pack and plates. They are not as "locked" as some of the other designs, but don't have to have any slip in order to lock up like the newer Eaton styles which use a "govenor" weight. The main reason I like the older style is that they are more linear in their action so don't seem to lock and unlock when in a turn making the handling "twitchy". Locker types with the dog clutches are very good for race cars, but really rough in operation. We were pushing Jessie Prather's Miata onto the trailer after the run offs this year and every time the rear locker clicked to slip you could feel the rear of the car shudder. That's a little rough for a street car for my tastes. Probably the best is the completely gear driven type, but they're expensive and I've heard a bit weak for the higher torque and horsepower cars, and yours should qualify there. I'm not a fan of the Auburn cone style posi, got one of those out of a Firebird rear at the salvage yard when I bought the gears and found it badly worn. Direct metal to metal wear surface isn't my idea of a good high performance locking rear, I'll take some type of fiber and steel clutch plates any day. Here's an interesting article from Hot Rod on the Eaton and Auburn types. [www.hotrod.com]


MGBV8
Carl Floyd
Kingsport, TN
(4511 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
1979 MGB Buick 215

authors avatar
Re: Posi units
Posted by: MGBV8
Date: November 26, 2008 11:35AM

If it's good enough for Jessie Prather, it's good enough for me!


Bill Young
Bill Young
Kansas City, MO
(1337 posts)

Registered:
10/23/2007 09:23AM

Main British Car:
'73 MG Midget V6 , '59 MGA I6 2.8 GM, 4.0 Jeep

authors avatar
Re: Posi units
Posted by: Bill Young
Date: November 26, 2008 12:32PM

I can't agree more Carl, but remember that smooth action and great tire wear are not high on the list of priorities for the race car. I'd prefer a little less aggresive action for a street car. When you're under power on the auto cross circuit the locker is nice, when you're trying to parallel park then they're a pain in the rear so to speak.


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(6468 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: Posi units
Posted by: BlownMGB-V8
Date: November 26, 2008 07:36PM

Well here's what I was thinking. I've used TracLoc units in the past and it always seemed like they lost their edge right quick, or in other words the clutches wore pretty fast, and after maybe 20,000 miles they really needed to be shimmed up. But who wants to go in there every 20K?

I've never run a PowerLok but that was what came in the axle so I have all the right internals if I just get the right case. These look to me like a better design with pressure ramps and steel clutch plates that shouldn't wear as fast but I have no experience with them.

Then there's the TrueTrac which looks to be an effective design that should give consistent performance throughout it's lifetime, but is strength a real issue?

It seems most of the other ones are either expensive, complex, or jerky in their actions, but again I don't have experience with them. That's why I started this thread.

Jim


WedgeWorks1
Mike Perkins
Ellicott City, Maryland
(460 posts)

Registered:
07/06/2008 08:07AM

Main British Car:
1980 Triumph TR8 3.5 Litre Rover V8

authors avatar
Re: Posi units
Posted by: WedgeWorks1
Date: November 26, 2008 10:45PM

Jim-
I have the TracLoc in my Jeep Wrngler housed in a dana 44 that had 97K on it. Besides chaning the fluid and adding the clutch lube it has not missed a tick. I would say that the one draw back is in wet or snow conditions it is not a fun drive with the rear only. When it breaks loose you can only hope when it locks your not pointing towards trees or gaurd rails!

The best rears I have seen used is either the Ford 7.5 or 8.8s from the mid-80ies to early-90ies. The posi units already come with disc brakes and you can choose any gearing from tall to revy.

One more thing is a company called phantom grip has a limited slip spring type insert that runs about $300 to $400 for various rear axles.


t.lay
Tom Lay
Grayslake, IL
(93 posts)

Registered:
05/13/2008 09:53PM

Main British Car:
72 mg b gt

Re: Posi units
Posted by: t.lay
Date: November 27, 2008 12:14AM

With more torque, I'd want a tougher unit. MAE racing sells a few different rebuilt units on e-bay - from trak-lok to some other designs. Might be worthwhile getting in touch with them.



BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(6468 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: Posi units
Posted by: BlownMGB-V8
Date: November 27, 2008 01:09AM

I could use a TracLoc but I'd have to get side gears to fit the Jag stub axles, and based on past experience with three different units I would not be satisfied with their performance. It may well be that better friction clutches are available that could change that, I don't know. But by the time I buy all those parts I've just about paid for a new unit.

Does anyone have any actual experience with the TrueTrac? I like the design which has no wear parts and smooth action. The one report I've seen questioning it's strength referred to trail use and recommended a maximum tire diameter of 33 inches. Considering those rigs would typically have 4:10 gears, about 2:1 reduction in the transfer case and a 3:1 reduction in 1st gear, along with a 4000 lb weight and 300 hp/torque I would think my application would be a bit less demanding. The cost would be more than a case for the PowerLok or internals for the TracLoc, but since I could offset that some by selling those two units it still sort of makes sense. I'll have to do some more research on it, but does anyone have any other recommendations?

Jim


t.lay
Tom Lay
Grayslake, IL
(93 posts)

Registered:
05/13/2008 09:53PM

Main British Car:
72 mg b gt

Re: Posi units
Posted by: t.lay
Date: November 29, 2008 01:44AM

my experience is more with the offroad crowd. It works pretty well on snow/ice with something closer to a stock 4x4 set up like my wife's jeep with a dana 35 and 33" tires. Going more extreme you see more selectable lockers or spools (not so good on the street). As the use gets more extreme they get less reliable - even then, u-joints and axles tend to break first. There are some reports of bolts backing out of them on some bigger toyotas. I think your tires are more of a traction limiter than a true track. If one wheel gets spinning though, you usually have to slow it down/hit the brakes to get the speed down for the unit to engage.


bplus
Tracy Moore
Jacksonville, Fl
(40 posts)

Registered:
11/24/2008 06:36PM

Main British Car:
71' MGB GT 350 Chevrolet

Re: Posi units
Posted by: bplus
Date: March 24, 2009 10:08PM

Kinda in love with the double black marks I've
left on the pavement from the standard posi
units underneath the big block chevelles and
el caminos I've owned over the years. Got one
hanging around the garage, just in case.


castlesid
Kevin Jackson
Sidcup UK
(361 posts)

Registered:
11/18/2007 10:38AM

Main British Car:
1975 MGB GT Rover V8 4.35L

Re: Posi units
Posted by: castlesid
Date: March 26, 2009 06:37AM

Jim,

Many years ago I had a Jaguar XJC V12 coupe that had a powerlock diff, it was quiet a very effective in operation.

At that time we lived in a valley and that winter we had heavy snow, I was the only one to get up the hill!
not bad for 2WD.

Regards,

Kevin.


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