nautiluscont

As the title implys, I took the stang racing friday night. This is the first race I have had this year after putting the detroit locker in.(raced all last season with a best pass of a 12.71 n/a) I made 5 time trial passes at about 13.03 with a density altitude of over 2700' which would equate to a 12.61 at sea level. My first round pass, I red lit due to an autostart tree and not being stage deep enough. Anyways, the car hooked up great on the launch but I quickly discovered that something broke as well. I ended up breaking three teeth off of my 4.30 gear ring gear, which is the 3rd 4.30 gear I put in this car. I just put that gear in a week ago too.

The current setup I have in the car appears to be to aggressive for the gear. I have the 4.30 gear set at a tight backlash, about 8 degrees, ET street slicks, BMR adj lower arms w/ relocation brackets, high preformance Ram clutch, billet flywheel, and the Detroit Locker, while launching the car at 5500 rpms.

After further investigation and speculation.....
I believe what is happening is that naturally a Detroit Locker has quite a bit of backlash to the unit itself. This is normal based for its operation. Now couple that with a clutch that isnt slipping, and sticky tires; all creating the most traction possible. When the car is launched, the power is transfered through the driveline into the locker, that in a sense spools up to lock, than bam.... slams the gear (instead of ramping up slowly like a spooled rear end would - keep in mind this all happens instantiously), creating a hell of a force and stress on the gear. This could also be explained by why three sequential teeth broke (each decreasing in size) which would be about the amount of teeth in contact with the pinion at any time.

In summary....
I think im going to reevaluate using a Detroit Locker and go with a less shock application such as a ECTED locker or spool. I hope this helps any other guys looking to use a similar setup.

Mustang7302

Any thoughs of cryo or heat treating the fourth set of 4.30's?

nautiluscont

I have not heard of this before but if it works its worth a try. I did drive the car prior to racing about 100 miles to break in the gear. I really think the locker is causing the shock. This is the first gear set the actually broke. The first gear set was the stock one, the second was a 4.30 gear which always had a slight whine to it which progressively got worse. The third was a 4.30 which the pinion threads ended up stripping when I replaced the pinion flange for the alum. driveshaft (never had a pinion strip before), and the fourth is the recent one that broke at the track.

Maybe I should look at buying stock in FRPP gears. I will say though that I can change a gear setup, with the correct pinion depth a backlash in about 3-4 hours by myself and that is including removing the rear end from the car. [:@] I have only done it 5 times now.

cekim

Don't suppose you have enough miles on it to see the wear pattern?

That is the ulltimate check on the install....

CrazyAl

Cryo treating can improve wear resistance. It has no effect on shock loading.


You might look into race-oriented gears. They don't harden the teeth as much, so that they are less brittle. This enables them to better handle the shock loading at launch on a drag car. One example that I know of is the Reider Racing "Pro Gear" series; I'm sure there are others. Keep in mind that these gears do have a lower wear life than normal, so don't expect to get 100,000 miles out of a set...

StartMeUp

Do you have any concerns that if you strengthen this weak link you will begin to break more costly parts?

nautiluscont

Actually the wear pattern looks to be right on target, well centered on the ring gear.

nautiluscont

Yes, but for the most part the driveline has been pretty well beefed up with all of the mods. My guess would probally be the axles.

cekim

Wow, I am a little scared to see you having this issue at those times with that power - your theory sounds as reasonable as any...

Thanks for the heads up...

GTSLOW

There will always be more breakage the higher numerically you go, Just look at a 3.55 vs your 4.30. Look at the gear teeth/splines