56 plymouth OD trans slipping

I have a 53 Studebaker Starliner with a mild 315 dodge hemi tri-power and 56 Plymouth 3 speed manual with Borg-Warner R-10 overdrive. The problem is that the engine runs away at about 3500 rpm. I'm trying to decide if it is the clutch slipping or if it is something in the overdrive.

I looked at the clutch adjustment and it is good. No rear main or front tranny oil leaks at all and there's plenty of pedal after engagement. The car will easily spin the tires in low and chirp them pretty good when hitting second. The engine runs away regardless of whether the OD lever is in or out and no matter if it is energized or not. It just doesn't seem like the clutch is the problem. I can't make it slip any other way and it holds tight on hard shifts.

I'm a little slow on how the over-running (O-R) clutch in the back of the OD works so I'm fishing for solutions. Is it possible that the OR clutch is not able to hold the power at higher RPM's and allows it to slip uncontrollably? Even if this is the case, does the OR clutch even come into play when the dash lever is puller out (OD disengaged)? Will the design even let it slip under any circumstances? the overdrive seems to work exactly the way it should. I pull 2000 rpm at 75 mph (according to my GPS.)

I have only had the car for a couple of months and really don't know much about the car's history. Any OD experts out there who can tell me whether a slip is even possible from a bad OD unit? The problem is repeatable each and every time I run the R's up from 1-2 and 2-3.

Thanks!

Dave

Gotta be the clutch, there's nothing in the trans that will slip in Direct with the lockout engaged. Check to be sure the engine isn't rocking on the mounts and taking up the play in the clutch linkage. Those old Hemi's have some tremendous torque, they need a really good clutch. It's common for a clutch to slip only in high gear.

Actually, the only gear I can't get it to slip in is high. And it doesn't slip on the shift. It slips when it hits about 3500 R's before the shifts. It doesn't even have to be accelerating at WOT, I can run up to 3500 mildly then it just slips away. It won't pull more than 3500 or so before the engine rev's and tach just buries. It's very strange. Intuition says it has to be the clutch but as soon as I shift it, the clutch grabs firmly and it chirps the tires. There is zero slip under a hard shift. It seems to be related to R's more than load.

Okay,if it slips with the OD in freewheel mode but not when the freewheeling feature is locked out, it's the overrunning clutch. If it slips locked out, it has to be the clutch. The lockout stops the O/R clutch from doing anything. A slipping O/R clutch usually screeches like the hounds of Hell.

That's what I was hoping to hear. I needed to know if it was mechanically possible for the OD to slip. sounds like it can't so I'll focus my attention to the clutch. Thanks for the input.