Acceptable differential play questions

[6667fan]

I’m doing some upgrades to the third member in Fairlane. Swapping some Ford 31 spline axle shafts for Moser units and replacing pinion yoke with a yoke that takes 1350 u-joints. With the wheels off I can move the existing pinion yoke 1/2” before the “clunk”occurs.  Not a scientific way to assess backlash I know. Is that much play normal? This car is destined for abuse at the track.
Thanks.

[GerryP]

About right.  The play is not only backlash between the ring and pinion, but in the pinions(spider gears) too.

[Rory428]

Do you have a Detroit Locker? They have considerable built in backlash.

[6667fan]

I should have noted that it is a Detroit Truetrac.

Thanks guys.

[Henrysnephew]

TruTracs definitely have "slop" built into them.  I installed one in my brother-in-law's car - he was so convinced I had messed up the installation he later paid big $ to have it r&r'd and "checked" only to be told after the work that everything was fine - it's a characteristic of them.  I do like them though - they're tough and reliable.  Randy M 

[My427stang]

Did you replace the yoke on the car, or pull the pinion housing to do it?

If the latter, sometimes it can be hard to feel the pinion bearing preload.  Other than that though, a yoke change should not change backlash.  With the axles out though, it's a pretty easy job to pull the center section out completely and see what it has at the ring gear

[6667fan]

Ross, the (formerly) worrisome play was with the current yoke. The new one has not been installed yet. I’ve been holding off the axles and yoke installation awaiting the valuable feedback I have received here.
Thanks all!