[Fot] Urgent! TR4 Detroit Locker problem, locks wheels going backwards

Mon Sep 11 10:20:16 MDT 2017

I researched these a few years ago because I began rebuilding a Morgan race car that has a Detroit Locker.  I puzzled over the behavior of the differential until I removed the rear cover and realized what I had.  These are better described as a Detroit “unlocker” since they are always locked until the one wheel is trying to turn faster than the other — it sounds odd, but as far as I can tell, the inside wheel takes all the drive while the outside wheel is along for the ride.  If the inside one begins to slip, it seems the diff locks again so drive goes to the outside wheel again.  I imagine the trick is to set it up so that it doesn’t lock/unlock constantly while cornering.  

They are great for drag racing and apparently were designed that way to allow easier turn-off at the end of the 1/4 mile run.  I know of another person in the Pacific Northwest who races a Morgan with a Detroit Locker and has no complaints about it.  Yours behaves like mine except for not being able to back up.

But to your situation — one clue is that you just put the transmission back in the car, which suggests that even if the gearbox did not undergo disassembly it was at probably disturbed.  Might it be possible that the gearbox is selecting reverse and another gear at the same time?  I suppose the only way to check this is to d/c the driveshaft, select reverse and see what happens when you let out the clutch.  No need to have the engine running — if you select reverse with the clutch disengaged you would normally be able to overcome the drag of the gears to rotate the driveshaft.

Duncan

> On Sep 11, 2017, at 10:02 AM, timmmurphh--- via Fot <fot at autox.team.net> wrote:
> 
> We have a race this weekend at Elkhart Lake.  Just put engine/trans back in car.  Test drove on road.  In trying to backup, both rear wheels are locked solid.  Trying to reverse just stalls engine.
>  
> Last time the car was on the road was in May at Gingerman.  No problems.  Since then been sitting up in the air on the lift getting “air time” while new block being machined.
>  
> Very puzzling how sitting up in the air would cause diff problem.  Car now has more “air time” on the lift than track time!
>  
> Have taken cover off diff, everything looks okay.  No pieces of metal.  Gear oil pretty black, has been in there about 10 years.
>  
> Both ring and pinion look okay.
>  
> Put fresh Reline gear oil in and buttoned up.
>  
> Tried again on lift.
>  
> Turning drive shaft (trans in neutral), can turn both forward and backward.  Both wheels turn.
>  
> Try in driveway, same result, cannot backup, trying just stalls engine.
>  
> We could get the car back on the lift by driving forward and turning around in the cul-de-sac by the house.  Did donuts in the cul-de-sac to see how diff reacted.  Left two nice black marks in the donut.  Accelerated forward and the diff was unlocked because there is just one long black streak.  I’ll have to ask Ryan how it sounded and acted.  He was driving to do that.
>  
> When car back on lift, same thing, both rear wheels locked up when trying to turn backwards last night.
>  
> We can make diff lock and unlock by holding one wheel and turning the other wheel forward.  Not sure about specifics, wasn’t taking notes.
>  
> So far, we can make it work, sometimes on the lift, by turning the driveshaft.  But once on the ground we cannot make if work under power.  We could push the car backwards out of the shop but once we drove forward and tried to back up the wheels were again locked.
>  
> Any insight or suggestions will be much appreciated.  Is this a typical failure mode for a Detroit Locker?  Any suggestions for further examination and testing?  The last time we drove the car back into the shop to put up on the lift we heard a pretty loud “clicking” noise from the diff.  Never noticed this before but wasn’t necessarily listening for it before either.
>  
> Very interesting, I just tried turning the wheels with car on lift and can turn both wheels, individually, both forward and backward, no problem.  It is now not locked up in the backwards direction.  When turning one side the other side also turns in the same direction.  It’s acting like the diff is locked up in both directions and the wheels turn in both directions.  Last night, the last time we tried turning the wheels backwards it was locked up.  Maybe it only works up in the air!!!!
>  
> Very puzzling!!  I am not at all familiar with how the Detroit Locker works.  It was the one thing on the car we never had to worry about.  I guess I’ll learn something now😊
>  
> Tim and Ryan Murphy
> Murphy’s Law Racing  (very appropriate today!)
> 1961 TR4 #317 BRG
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