How does changing the springs in a Detroit effect its drivability and handling?

[JavmanBBG]

I know there is a lot of discussion on this and this was originally a PM to Ron Sutton but I was asked to make it a new topic.

I was reading through an old thread about lockers vs torson style difs and had a question for you about lockers. the cars I have or have had all used a clutch style LDS or my new DD car has a torsen dif.

Do the lighter springs in a Detroit change how it acts under partial acceleration say mid corner? I don't have any experience with lockers and was told that as soon as you get back on the gas they act like a spool and you want to be pointed strait before you accelerate at all. My uncles experience with a stock unit in a street capable drag car was it would actually push through the skinnys on the front under acceleration even if you turned the wheels and if you where in a corner and got on the gas at all it would break the rear end loose.

I am asking as I have a 9" with an aluminum center and 35 spline axles already setup from a drag car and want to just change over the gears and dif. and us it in a street car that I will also auto X and may hopefully run an open road race or two in so I am trying to figure out what is best. Originally I was looking at the Wavetrac but I keep seeing the G Force Detroits for $200-250 setup for 35 spline axles or with the option of using 35 spline axles witch is pretty tempting if there isn't a huge sacrifice in drivability.

Roughness is probably the least of my issues as I already have an Emco 44t 4 speed for it but I don't want it to be too big of a hand full (like snap over steer) to drive spiritedly around town or on a road trip.

Thanks
David

[Ron Sutton]

Hi David,


I know there is a lot of discussion on this and this was originally a PM to Ron Sutton but I was asked to make it a new topic.

I was reading through an old thread about lockers vs torson style difs and had a question for you about lockers. the cars I have or have had all used a clutch style LDS or my new DD car has a torsen dif.

Do the lighter springs in a Detroit change how it acts under partial acceleration say mid corner?
No. Under acceleration the locker locks ... as it should. There is no "slip" like clutches do in a posi. A Detroit Locker is either locked or unlocked. The rate of the two springs inside determine how easy ... or how hard ... it is to get the locker to unlock when turning.

But lighter springs do affect how the car handles mid-corner on track.

This is simple: If the spring rate is too stiff and won't unlock as you turn into the corner ... meaning it stays locked ... then both rear tires are locked together like a spool. So the inside tire can not turn at a slower speed than the outside tire ... as it needs to ... and as the locker was designed to do. So with both rear tires locked ... it makes the car push mid-corner ... and will continue pushing on exit.

The cure is simple too: Install the correct rate springs for the application ... so the locker unlocks on corner turn in.



I don't have any experience with lockers and was told that as soon as you get back on the gas they act like a spool and you want to be pointed strait before you accelerate at all.
That's not accurate.

My uncles experience with a stock unit in a street capable drag car was it would actually push through the skinnys on the front under acceleration even if you turned the wheels and if you where in a corner and got on the gas at all it would break the rear end loose.
I can see that happening. But the cause is wide soft slicks in the rear & hard skinnys in the front. It should push with any diff except an open carrier or a worn out limited slip.


I am asking as I have a 9" with an aluminum center and 35 spline axles already setup from a drag car and want to just change over the gears and dif. and us it in a street car that I will also auto X and may hopefully run an open road race or two in so I am trying to figure out what is best.
For track performance, nothing beats a Detroit Locker. The challenge with buying a used Drag Race or NASCAR locker is you don't know what springs are in it. But they are easy enough to take apart & see ... or replace the springs.

Note: Even new stock, off the shelf Detroit Lockers come with too stiff of springs (78#) for what we do.

In racing, we tune the lockers with different spring rates from 25# to 125#. The softer the spring the easier it releases when turning. The stiffer the spring, the more it takes to get it to release. On big tracks like Daytona & Talladega the last thing you want is for the locker to release. So they run the 110# to 125# springs. If you bought a used locker with that much spring rate, it would be a bear to get it to unlock. With street tires, I don't think the tires have enough grip to force those 110# to 125# springs to unlock consistently ... if ever ... and would on occasion/often simply slide the tires instead.

Drag racers typically leave the stock 78# spring in, which is still too much spring rate for what we do here. For road racing & autoX, the hot ticket is softer springs. The key to picking locker springs is based on rear tire grip. The less you have the softer the spring needs to be.

From my experience, this is what I recommend …

25# ... Street cars with 8" or smaller tread width street tires and TW200 or harder.

40# ... Street, autoX & track cars with 10"+ TW200 street tires.

55# ... Track cars on 10”+ slicks & race cars.


As a rule of thumb, you can go softer 1 step, but don’t go stiffer. The key to making lockers work well is getting them to disengage in tight corners. Of course they need to re-engage too. So you wouldn’t want to run way too soft of a spring.

Having said that ... there is no disadvantage to running a 40# spring with slicks on road courses. In my new Warrior cars, they come with 40# springs in the locker, so they perform just as well on TW200 tires as they do on slicks.


Originally I was looking at the Wavetrac but I keep seeing the G Force Detroits for $200-250 setup for 35 spline axles or with the option of using 35 spline axles witch is pretty tempting if there isn't a huge sacrifice in drivability.

Roughness is probably the least of my issues as I already have an Emco 44t 4 speed for it but I don't want it to be too big of a hand full (like snap over steer) to drive spiritedly around town or on a road trip.

Thanks
David

Detroit Lockers are not as civilized as limited slip diffs. But with a limited slip "posi" on track ... the degree of grip/slip posi clutches have ... changes with heat. And that does affect the handling of the car in corners. So on track days, the corner exit handling changes as the rear end heats up. This is one of many reasons posi's are not commonly used in racing. For all their clunks & pops ... the oil temperature does not affect how Detroit Lockers work ... which is one of several reasons why they common in racing.

If the Detroit Locker has the correct rate of springs in them ... for the rear tire grip the car has ... they behave ok. Except when you turn while backing up ... like getting out of a parking spot. They will clunk & pop ... and civilians walking by in the parking lot will ask you if your rear end just broke. The correct answer is, "OMG ! It did break. Can you give me a ride home?" I do that just for the interesting looks on their faces before I tell them I'm just kidding.

If you don't have the correct rate of spring to make the DL unlock when making tight corners ... parking lot, driveway, city street, etc. ... and both rear tires stay "locked" ... it will squeal the tires as either the fronts or rears slide on the pavement. IMHO ... most of the problems experienced with Detroit Lockers are simply the wrong rate of spring in it for the tires they have. If you have the correct rate of springs, the diff will ALWAYS unlock as you turn.

:cheers:

[sam 74]

i have a locker in my car, i use the factory springs at the moment, its not all that bad for my setup but my car is heavy and i currently don't have the tires on the rear i want to run, so no point in changing the springs until i get the correct tire im going to use. all that said its a little roungh especially backing up but i've gotten used to it and can drive it fairly well now, it took a while to get used to it.

[JavmanBBG]

So, from what I see here is too soft and even under acceleration it will not want to lock up, too stiff and it will not unlock or will lock up too soon and cause wheel spin and just right it will act as an open diff throughout the corner. Is that even if you are accelerating through the corner? Will it stay unlocked then also?

If so that begs the question of I would you be able to put more power down with a gleson style unit as it is always torque biasing and would allow for a twice the contact patch?

Sorry for all the questions I just want to get it right the first time.

As far as tires go being a stock body car I know 275 tires will fit up to 27" tall and 295s (from the measurements I took) look possible with minimal massaging .

[Ron Sutton]

Hi Javman,


So, from what I see here if it is too soft and even under acceleration it will not want to lock up
That's not an accurate statement. You would need to be WAY too soft for a Detroit Locker to not engage when you apply the throttle. That is what they were designed to do ... engage when you apply power ... so you have grip to both rear tires.


too stiff and it will not unlock
This is accurate. If the springs inside are too stiff in relationship to how much rear tire grip you have, they can stay locked through the corner, which makes the car want to be tight or push.


or will lock up too soon and cause wheel spin
Not accurate. A Detroit Locker will lock when you roll the power on (or unwind the steering) ... and provide power to both rear tires ... which is what you want it to do.

and just right it will act as an open diff throughout the corner.
You want it to act as an open diff after initial corner "turn-in" and through the "roll through zone". This allows the inside tire to roll at the speed it needs to for the smaller radius it is running. This allows both rear tires to have optimum grip ... turn well ... and not want to cause the car to push the front end. Then you want it to lock on throttle roll on.

Is that even if you are accelerating through the corner? Will it stay unlocked then also?
We do not want to be accelerating through the corner. I only see rookie drivers do that when they lift too early or brake too much and feel they overslowed the corner. So they compensate by accelerating at a point in the track they shouldn't be. For more details, read the info at the bottom.


If so that begs the question of I would you be able to put more power down with a gleson style unit as it is always torque biasing and would allow for a twice the contact patch?
That's not accurate. When you apply power to a Detroit locker it applies full power to both rear wheels. The cool part was it completely disengaged in the roll through zone where you want ed it to ... providing you don't have springs that are too stiff for your tires.

Sorry for all the questions I just want to get it right the first time.
No worries. I want to help. There are just some misconceptions I want to clear up about how Lockers work, what you need the diff to do on track & driving techniques in a corner.



I want to clarify some critical things about cornering on track or an autocross course. Break the corner into three sections (Entry, Middle & Exit) & break the driving into five actions. You can see where the actions “should be” in the diagram below. The actions are, in the proper order:
1. Braking
2. Turn in
3. Roll through zone
4. Throttle roll on
5. Steering unwind

98588

The smoother you are, the more grip the car has. Grip is safe speed. Don’t initiate two driving actions simultaneously … steering, braking or throttle. They can & do overlap. Just don’t start them at the same instant. This upsets the tires.

Do this on corner entry …
• Start throttle roll off … then start to apply the brakes.
• The throttle roll off & braking actions cross or overlap. Just give the throttle roll off a head start.
• Then, when you’re at the right point, start steering turn in

Do this in the roll through zone ... often called mid-corner ... but if done correctly starts before mid corner & ends at or just past mid corner:
• Roll smoothly off the brake pedal.
• Keep your foot off the brake & the gas & let the car roll (coast) for a bit.
• If the car needs any additional steering input to achieve your line, now is the time.
• Then, when you’re at the right point ... usually at, or just past, mid corner ... start rolling the throttle on progressively.

Do this for corner exit …
• Start throttle roll on … then start to unwind the steering.
• You’re doing these at the same time, just give the throttle a slight head start.

--------------------------------------------------------------

The key points I want to make are:
• After the initial turn-in ... all the way to the point where you need to start throttle roll on ... a Detroit Locker (with the correct springs) will disengage and let the rear tires operate independently ... allowing optimum rear tire grip without causing a push condition.
• When you start throttle roll on (or unwind the steering enough) the Detroit Locker will re-engage and drive both both tires.
• A Detroit Locker (again ... with the correct springs) will do this more consistently than any worm drive or clutch disc design differential.
• Oil temperature will not affect it like clutch style diffs. Wear will not affect it like worm gear diffs.
• And that is basically why they are the most popular choice of top race teams.

[LT1Nova]

Ron,

Would changing the springs in a Detroit soft locker have helped with the bit of "wander" my car had on light throttle application when going straight?

[Ron Sutton]

Ron,

Would changing the springs in a Detroit soft locker have helped with the bit of "wander" my car had on light throttle application when going straight?

Hi Jon,
I doubt it, as a locker is either engaged or not. The softer springs just allow the locker to dis-engage easier on corner entry, so there is no push (understeer) on corner entry or middle due to the differential.

I suspect your "wander" is not differential related.

Best wishes.

[WallaceMFG]

I have a locker in my Torino, it only wants to go straight when you give it power. Even going around a curved freeway overpass at 70, if you stand on the gas it tries to go straight off the road. I'd look into a different diff for autocrossing. Lockers make it really easy to do burnouts and donuts though! :twothumbs

[Ron Sutton]

I have a locker in my Torino, it only wants to go straight when you give it power. Even going around a curved freeway overpass at 70, if you stand on the gas it tries to go straight off the road. I'd look into a different diff for autocrossing. Lockers make it really easy to do burnouts and donuts though! :twothumbs

I politely disagree. Lockers are the best differential for competition events like autocross & road course track days ... as long as they have the correct spring in them for the application. They are super consistent & don't change how much they engage as they heat up or wear. We have Detroit Lockers with 40# springs in a cars that have won a wide variety of autocross events including Optima/USCA events.

If a car pushes on exit under throttle, that is a suspension tuning issue, not a differential issue. Of course it can be masked with a diff that slips the inside axle. But that is not the path to the fastest laps times. Being able to roll the throttle on hard & accelerate with the grip of both rear tires is fastest. It just requires the suspension be dialed in to achieve that.

:cheers: