Rearend Question

[4coil]

When switching over from a 9" rear to a quick change, does the car act differently? If so please give particulars about what you have experienced. This is on a 3-link set-up with pullbar and solid mounted lower arms. Thank you in advance for any replies................

[7uptruckracer]

No really the quickchange can unless you really get the low drag stuff kill more HP. The Pinion static height is different between the two so you have to compensate with your static pinion mount on the Jbar. other then that if all your shocks and bars arm mounted in the comparable locations there isn't really a difference

[JustAddDirt]

9" drives off the LR
QC drives off the RR
have to add a smidge more wedge to compensate
Pinion is about 2" lower on QC. generally you have to move back of motor down a bit to correct driveshaft angle.

[7uptruckracer]

This I have to hear. A spool Is a spool and locker is a locker they don't know what they are in....someone fell asleep in physics class......

[JustAddDirt]

It has to do with the direction of force (downward pressure) applied to tire when the pinion gear tries to climb the ring gear. Torque
On a 9" rear, or any conventional style axle, there is more pressure applied to the LR wheel on acceleration.
Which is why on an open rear end, you punch the throttle to accelerate in a straight line, the RR wheel spins, even though motor torque tries to twist chassis and plant RR, it still unloads the RR tire.
that is why a lot of drag racers add their battery to the right rear corner of their vehicle.

On a qc, the pinion is on the back side of the axle, and on the opposite side of ring gear, so the torque applied when pinion tries to climb the ring gear more pressure is applied to the RR wheel.

It has nothing to do with lockers, or spools.
It has to do with torque, and the directional forces in which items react when power, or rotation is applied.
That is why you have to add a bit of wedge to compensate, typically I add about 25lbs on a 4 link car.
Just my opinion.

[bittight]

Mark Bush talks a little about it and I believe Steve smith does to, it's no opinion, guess u wasnt asleep in physics lol.

[Mosidebite]

Some people...thanks to those who provide real and understandable responses to questions.

[JetSpeed22]

It has to do with the direction of force (downward pressure) applied to tire when the pinion gear tries to climb the ring gear. Torque
On a 9" rear, or any conventional style axle, there is more pressure applied to the LR wheel on acceleration.
Which is why on an open rear end, you punch the throttle to accelerate in a straight line, the RR wheel spins, even though motor torque tries to twist chassis and plant RR, it still unloads the RR tire.
that is why a lot of drag racers add their battery to the right rear corner of their vehicle.

On a qc, the pinion is on the back side of the axle, and on the opposite side of ring gear, so the torque applied when pinion tries to climb the ring gear more pressure is applied to the RR wheel.

It has nothing to do with lockers, or spools.
It has to do with torque, and the directional forces in which items react when power, or rotation is applied.
That is why you have to add a bit of wedge to compensate, typically I add about 25lbs on a 4 link car.
Just my opinion.

Thank you Dr. Sheldon Cooper for your physics lesson. Your theories on mechanical quantum physics & string theory is enlightening.

Knock Knock Penny! Knock Knock Penny! Knock Knock Penny!

[MEB4U]

And I just thought all he could do is drive!!!!!

[7uptruckracer]

This is the first I've heard of this and if you run a spool or locker you can't bust one tire loose without the other so what's the true difference? We are loading the cars through bar angles and springs to control dynamic weight transfer and thrust angles and this pertains to neither so for all PRACTICAL purposes if he mounts all his bars at the same toe angles and static angles and distance away from axle centerline he should be fine. I've never talked to a manufacturer on a modified where its commons to see both rear ends and see them list or ask which one your running so they can dial you in. Mark has never even mentioned this stuff to me, in the ever changing traction world of dirt keep it simple.

[7uptruckracer]

I'm pretty sure your not meaning to say the whole balance of force is different LR to RR MAYBE slightly toward one way more then the other which that might be true it's not really even worth mentioning unless he's going to be drag racing especially when you're also suggesting he move his motor down which most you can't just "tilt" the motor back with central block mounts and midplates you can really only raise and lower which would be a significant change I've played with before trying to get my shaft height right and that also is not a compromise to make with that weight drop it in see what you feel and go from there

[JetSpeed22]

9" drives off the LR
QC drives off the RR
have to add a smidge more wedge to compensate
Pinion is about 2" lower on QC. generally you have to move back of motor down a bit to correct driveshaft angle.


I'm pretty sure your not meaning to say the whole balance of force is different LR to RR MAYBE slightly toward one way more then the other which that might be true it's not really even worth mentioning unless he's going to be drag racing especially when you're also suggesting he move his motor down which most you can't just "tilt" the motor back with central block mounts and midplates you can really only raise and lower which would be a significant change I've played with before trying to get my shaft height right and that also is not a compromise to make with that weight drop it in see what you feel and go from there

I think if you go back and ready what JustAddDirt said, you would see that he said you generally have to move "the back of Motor down a bit" From where Im from that's the same thing as tilting. Didn't see anywhere in his post where he suggested to move the whole motor down.

Looks like someone fell asleep during reading time....

[7uptruckracer]

Yes and I said the motors with midplates you can't just tilt the motor didnt I? By this theory it should also unload the RR on decel too correct so adding bite would just be a compromise

[JustAddDirt]

Yes, you can adjust height at mid-plate, if your mid-plate has multiple holes for height. My chassis builder has 2 holes in the mid-plate just for the type of rearend used.
top hole QC
bottom hole 9"
And yes before you say it, it does twist the front motor mounts just a tick. But car does not know it, nor does motor.

I guess 7uptruckracer, we can just agree to disagree here. I am not here to get into a pissing contest, just trying to help a guy out with his question.

[Leeracing40]

Anyone have a link to support the rotational forces acting upon the rear end? You would still have the rotational force on the thru shaft in a quickchange, which would be the same as the pinion acting on a 9". I would think if you vectored all the rotational forces from one to the other there would be much of a difference. You still have the drive line in, and the tires to the ground.

[7uptruckracer]

Well we can agree his biggest change will be the pinion height so the Jbar will be different. That's going to be the most critical. I assume people want no binds in engine and midplate mounting that stuff cracks enough at the midplate mounts as it is.

[Fraley Racing Ent.]

It has to do with the direction of force (downward pressure) applied to tire when the pinion gear tries to climb the ring gear. TorqueOn a 9" rear, or any conventional style axle, there is more pressure applied to the LR wheel on acceleration.Which is why on an open rear end, you punch the throttle to accelerate in a straight line, the RR wheel spins, even though motor torque tries to twist chassis and plant RR, it still unloads the RR tire.that is why a lot of drag racers add their battery to the right rear corner of their vehicle.On a qc, the pinion is on the back side of the axle, and on the opposite side of ring gear, so the torque applied when pinion tries to climb the ring gear more pressure is applied to the RR wheel.It has nothing to do with lockers, or spools.It has to do with torque, and the directional forces in which items react when power, or rotation is applied.That is why you have to add a bit of wedge to compensate, typically I add about 25lbs on a 4 link car.Just my opinion.thank you for stating this.... I am glad some can agree with me on this.... I have had customers with modified's including my own modified have issues with changing to a quickchange.... my own personal car after changing to a quick change has a ton more right rear drive and it mad the car hike up the entire rear instead of just the left rear. we had to change a lot to make the car drivable.

[Wheelman33]

I have a car built by a "big nut" and the set up sheet says 20-30# more LR with a quick change.

[JustAddDirt]

leeracing40.
driveshaft and thru-shaft do not matter, it is were the pinion contacts the ring gear, and the torque applied at that point, which makes the rotation forces that effects wheel weight.

7uptruckracer
sounds like you might need more ridged mounting of engine. If you are cracking and breaking stuff in the motor mount area might be other problems. Sounds like chassis builder needs to use something other than muffler tube, or thin wall elecktra-weld tubing...say DOM ,or moly.
I have never had any problems with anything binding, cracking or flexing anything including the powercoat in the motor mount area.

[7uptruckracer]

We get cracks in the ears that you attach your midplate to every now and then. We run Chrome Moly Tig chassis. Most manufacturers will not heat treat your chassis unless you ask and we have never bought them brand spankin new always a year or two old. I guess you don't find Rocket Chassis to be of good quality muffler tubing. Super Lates can twist up a good chassis.

[JustAddDirt]

yes late models can do that as much as the RF hits the track.
Rocket welds a flat tab on there don't they?
I think a tab with ears on it would be better in that application.
Rockets are moly, but are not tig welded, they are mig welded, just with correct wire.
(unless he has changed his welding processes) or something special was ordered.

[xxxmod]

Any difference you feel would probably be because the 9 inch and the quick change
use different length axles.

[7uptruckracer]

I'm sure that has some bearing, I know the QC and 9" Pinions are oriented differently as far as how it makes contact and left to right and front to back wise. I know the QC can absorb more torque and HP because your running it thought that intermediate shaft. I'd just count it all as a shove mount it all at the same points redo your Jbar height and see what your bottom feels and adjust from there, dirt is never the same any time its out anyways

[4coil]

Thanks folks for the valuable info..........................A lot of goodstuff here!

[el paso mod 19]

If a 6.0 gear was perfect for 9", what ratio do I run in QC? I've been told they're not the same.

[JustAddDirt]

I would start with a 6.03

[not clamped up]

I would start with a 6.03
JustAddDirt gives some of the best advice I see on here,I just wanna add to me alot of people have ended up with the 411 Ring and pinion in there quick change.If so you need to add 40 points to the gear you ran in the 9 inch.

[el paso mod 19]

Thanks to both of you.

[1Blacksheep]

9" drives off the LR
QC drives off the RR
have to add a smidge more wedge to compensate
Pinion is about 2" lower on QC. generally you have to move back of motor down a bit to correct driveshaft angle.

Agree completely . The balance we try to tune into a car has been a little harder to hit the sweet spot with the QC for this reason. There is more than one reason this JAD Cat wins a lot of races.