When I tighten up the lugs on the back wheels the hubs lockup. It appears that the rims of the drums are making contact with the backing plates. Any ideas?

Herb

 

Which studs are you using with which wheels?

Aren't there two different length studs for these cars?

 

Lug bolts right? Are they original, original wheel(s)? Are brake drum/backing plate original? Are backing plates bent? Brake shoes replaced,compare with old,same width? Do you have retainer screws for drum installed & can you turn drums both sides with out wheels installed? I know,20 questions...

 

Original wheels, drums, and lug bolts. When the brakes and wheels are removed the hubs spin fine. I installed just the drums (no shoes or other brake parts) and bolted on the wheels and the drums seem to be dragging on the backing plates. Could the hubs be in too far?

Herb

 

Putting just drums on with retainer screws should be able to duplicate the problem without wheels being in the way-installing wheels won't change drum installed depth. Is there any rust in the machined area of the drums that seat on axle to prevent drum from seating squarely on axle ? Has rear differential been out of car sitting on ground with weight on backing plates possibly bending/distorting them ? Have axles been out of housing(to replace bearings?) and maybe got distorted somehow when bearings pressed off/on?

 

its really only possible if the spacer didn't get on the axle, but you have the backing plate on there, so this seems unlikely.

as you recall, its axle, backing plate, bearing spacer, bearing and then retaining collar.

axles are the same on both sides, so it can't be that.

there are a couple of different drums, did those get replaced?

 

Try putting just drums on with retainer screws to duplicate problem. With wheels out of the
way may be easier to see what is going on. Wheels installed will not change installed brake drum axle
relationship. Has differential been out of car,on ground,with weight on backing plates possibly bending them? Have axles been out of housing(to replace bearings?). Possible backing plates got distorted during pressing off/on axle bearings. Pretty certain there's a spacer that goes under bearing when put on axle with a collar on the other side of bearing,was that reinstalled if bearings were replaced?
Other than distorted backing plates,a missing spacer is only thing i can think of that would
change axle depth dimension causing a serious interference fit with drum & backing plate.

 

The missing spacer sounds like the most likely problem I'll pull them off and check. Thanks.

 

Make sure you have the right drums. The SA drums have a slot machined around the edges that fits over the
backing plates to kind of seal up the assembly. If you got new drums they may be FB ones which don't
have this slot and so they will not fit on the SA backing plate.

Take a look at rockauto, 81-85 have a different part number from 79-80.

 

This; fell for this issue myself one, the other way around - years back I got a replacement rear axle which had the wrong backing plates for my year drums. Drove me crazy until I finally noticed the difference.

Pretty sure I posted pictures about this oh, 7 years or so ago... heh.

UPDATE: Searched - -yep:

https://www.rx7club.com/1st-generati...brakes-787270/

 

The problem was missing spacers. Got a new set from Mazda, new bearings from autozone and paid the same machine shop 40 bucks to remove and install correctly this time. Thanks for the help. Herb