Who is satisfied with open Diff?

[DaveR]

I've read all the threads debating types of limited slip differentials, and I understand that the on and off track drag racers need this, but before I plunk down more cash, I thought it might be educational to ask the question in reverse. Is there anybody that has an open differential who is perfectly happy with it? Would also like to hear from some road racers on this topic.

[Ron61]

Dave,

I am not a drag racer but used to road race and a limited slip is a real plus. I still remember when I broke one coming out of a corner and turned the car sideways. If you don't plan to use the car as a drag car or do any road racing then I see no reason you would need a locker or limited slip. I am sure there are many who will disagree with me but how many of your daily drivers have limited slip, excepting the off road SUVs and such. If you do decide to have one put in get a good one.

Ron

[wilf leek]

I like my car with an open diff. IMHO it makes for a sweeter-handling Cobra for road use.

On a track I hate it - inner rear spends most of it's time spinning away the power.

Since the balance of my usage of the car veers significantly towards road rather than track, I will stick with it as it stands.

[DaveR]

Ron61,

Thanks for the road race input. My real problem is that I want to road race a few times a year but I know that 90% of my driving will be on the street. What do you classify as "a good one".

Wilf,

I assume that when you say "inner wheel" and "on track" you are talking about road racing?

[Ron61]

Dave,

I have an Eaton unit built up with the 31 spline axel. You will never get enough traction to break it. I don't know about the newer soft lockers as no one around here is using them. But Cranky and some of the guys still racing can really tell you what the newer stuff is as they are always looking into it. If your roiad racing is just as a hobby and not serious then you could most likely go with a cheaper trac-loc unit and never have a problem.

Ron

[wilf leek]

Dave - yes, please forgive the "english" terms. What I mean is that for road racing, the lack of a slippy diff is a negative.

For pure road (highway) use I much prefer the open diff. And I have tried both.

[Jahred]

Dave R.

I have a 514 and was advised in no uncertain terms that a "locker" was critical. I went with a "Protrac", which I think some above are referring to as a "soft" locker. I believe this refers to the fact that they "disengage" more quietly than a "Detroit" Locker or similar. I don't believe it implies they are any less efficient traction wise, as once engaged they are still metal to metal with no clutches. My big concern was that I'd have to slow or be cautious in turns during "locking" and "unlocking"...........the Protrac is very seemless. Unless your turning full radius at a few miles an hour you will never feel it.

I understand Shell Valley now used them as standard hardware on their BB applications.

[Ron61]

Jahred,

The Protrac was what I was trying to think of. I also have a little tire lock in a slow tight turn with the built Eaton unit but at speed it is great. I could adjust that out but it isn't enough to worry about and I like the hard lock. I only notice it occasionaly when I am at a stop sign and am making a hard slow turn. But I would be happy with an open diff. if I were only driving it on the highway as I just can't see why you really need a locker to drive down a freeway. Not to start an argument as I like having the locker but really don't need it now for my type of driving.

Ron

[Jahred]

Ron, I agree. I think its a great unit. I am guessing they make some progress year to year. I don't think I would ever feel mine in a right or left turn in city driving. I have only experienced it with the wheel cramped when doing an unusual parking maneuver. I have a 4 Wheel drive truck and wanted to avoid that feeling in the Cobra........have no regrets on this end........its not an issue.

[Zderf]

I was perfectly happy with my open diff for road use. It really makes for a more contolled drive, as one rear wheel is always hanging on to the pavement regardless of throttle.

But one day I snapped one of my 28 tooth spline axles during a hard 2nd gear shift... the subsequent findings inside the Ford 9" diff were catastrophic. So I went with all new innards including 31 tooth spline axles and the Detriot TruTrac limited slip. It has no clutches, and I feel no gripping during low speed tight radius turns.

I did however, have to learn how to "power drive" again. Once both rears light up, things get kind of squirrely.

If I had not trashed the open diff, I would not have felt the need to go with limited slip... and never with a locking set up.

Respectfully Submitted,

Zderf

[Mr.Fixit]

Doesn't every cobra owner need a posi so they won't do huge burnouts every time they touch the throttle? My litle chevy couldn't go anywhere in a hury when it had an open diff. The right tire would just smoke and the car would sit still. I remember my father coming home one day when I was 17, I had just finished removing the whole rear end out of my chevy. He got pissed, thought I was in over my head. I was replacing a 10 bolt, open diffed, 3.23 ratio; with a 12 bolt posi with 3.73's. When I told him that, he stared back with a blank face, he just didn't understand. His buddy laughed and said that makes sense. Best thing I did for the car. Even though it had more gear ratio after, the posi allowed the car to actually accelerate away from a stoplight, instead of doing a pegleg tire roast.

[ls1ac]

Terms
Spool:: both wheels turn together. When you turn one wheel drags around the corner. Very poor for street but very good at the drags.
Locking differential: Can be run open or locked up. Good for in the mud and on the street.
Limited slip: operates, as an open differential until there is a difference in rear wheel rotation rates, then it will lock up.
Possitraction: Uses clutches to limit the wheel slip at all times. The normal choice for road tracks.
Torque distributing: Uses the torque differential between axels to distribute the load.
Traction control: uses speed sensors to distribute the load by electric cluthes.
Open diff. Original style used in most road cars.
And combinations of the above

[DaveR]

Wilf,

There's nothing wrong with "your english". I just wanted to make sure you weren't talking about drag racing when you said "on the track".

[DaveR]

Jahred,

Do you know who makes the Protrac? I just got off the phone with Bill Thomas High Performance in San Bernardino and he used the same term "soft locker" but he was talking about a Detroit Locker. He says that they have changed a lot over the years and can now be tuned thru the use of differential strength engagement springs to suit your application, from street to race.

Ron61,
Is your Eaton a locker or disk type? Why did you quit road racing? What do you know that I need to know?

Zderf,
You broke a 28 spline axle! Is this common for Cobra's? I am on the verge of buying some 28 spline axles. I didn't think a car this light would need anything bigger. Now I have to re-think my entire rear end.

[Ken Greene]

Are air lockers like one from ARB anygood for this type of car?
they are an open diff until you "lock" it?

[Zderf]

You broke a 28 spline axle! Is this common for Cobra's?

I can't say for sure. We think the machined axle was cut to too small of a diameter, and may not have been properly heat treated. Its hard to say... I'd buy the extra insurance of a 31 tooth spline if had that choice.

How bout the twist??? Boy it SNAPPED!!

Zderf

[B. SMITH]

THAT MUST HAVE BEEN ONE TERRIFIC SHIFT.

YIKES, B.SMITH

[Ron61]

Dave R,

I quit racing because I feel that I am getting to old and I don't have the reaction for it any more. I still like to go to an open track day with the street tires and just run around for fun. I also enjoy going to the high performance driving schools as it seems every instructor can teach me something different.

My Eaton unit is a clutch type posi-trac that a guy who builds the rear ends for a lot of the local racers did for me and he quaranteed me it would stand up to anything that I could put on it with this light car. As for me knowing anything that you need to know, you probably already know more than I do. Zderf breaking his like that on a shift is rather rare on a road course I think but if he was drag racing then it wouldn't be quite so rare. I have the 31 tooth axels in both cars and thay have stood up to a lot of down shifting which is hard on arear end too. Just remember the Cobras don't have a lot of weight in the rear end. I have my battery and some other weights that I used to use at times but now just have the battery in the trunk and a small plastic tool box strapped on the other side.

Ron