Trying to wrap-up a rear-end rebuild. Went by the book for the most part. All parts looked good, and measured within spec. New inner seals, new pinion bearing (Fun Projects) to eliminate a bit of drive shaft end play. Also new fiber washers (sanded to correct fit), and new brass thrust washers and all new thrust pins. U-joint looked good as well. When pre-assembled, the ring gear turned by thumb, with a little drag as the book stated. Ring/pinion clearance a little more than spec at 0.015".
Question: After final assembly, with the radius rods installed and adjusted to the same length on each side (measured from u-joint pin cover screw to the front edge of the backing plate), when turning the shaft at the u-joint, no binding or grinding, but there is some noticeable "rebound". In other words, when I turn it by hand, it springs back a little when I release it from my grip. Is this normal, or is this an indication that something isn't right somewhere? Glen's book says it should turn by wrench. I'm turning it by hand, but get the same "rebound" effect using a wrench. Thanks for any help.
hmmm.. this is a question for the experts but i will propose something. have you installed the outerbearings? these rear ends do funny things when not fully reassembled. Also, i was under the impression that it should be to tight to turn by hand (at first.) and needs to be wore in before tolerant enough to turn by hand.... If nothing else, i got your thread back to the top of the list
are the inner seals felt or modern? could the felt be acting as a spring?
Only thing I can think of is the neoprene seals causing a slight rebound. I like that you set the ring and clearance at .015" and you can turn the ujoint by hand.
Nathan - Yes, all bearings are in. The only parts not on yet are brake shoes and drums. The inner seals are the neoprene ones, and the outer ones are the felt ones.
Richard - Yes, I was thinking the same thing; that the neoprene on the axle shafts is causing the slight spring-back in the rotation. Otherwise, all seems good. Just want to be sure before I move forward, as I'd rather not go any further and find out later that it all needs to come apart again! Thanks.
If there is noticeable slack in a back and forth movement of the driveshaft, it is too loose, but if when turning it, there is roughness, that is you can feel tooth by tooth the ring and pinion as they turn, then it is too tight. If you are using used gears, you need a little slack, because the gears have worn to fit and if you tighten them, they will have high spots which cause the above problem. A shim between the drive shaft spool such as a thin gasket, will usually correct this.
Norm - No slack when rotating, and no roughness. Just a little rebound, like it's springing back a bit. All the gears (ring/pinion, spider, axle) looked very good when I had it apart.
Dave -- As Norm says, the ring/pinion engagement may be a little too tight. I'm not a proponent of setting that relationship using a feeler gauge; as with many other adjustments on a Model T, I do it by feel. If you can feel each tooth engage as you turn the driveshaft, it's too tight.
You might try adding another gasket or two between the rear end and the spool, just to see whether that makes any difference in your situation. It's easy to do, and it will tell you whether that's what's going on with yours.
I'll try adding a gasket between the axle housing and the spool, as suggested, and see what difference that makes. I measured the ring/pinion clearance with a dial indicator. I could feel it also. Thanks, I'll let you know what I find.
Must be the seals causing the rebound. Got the radius rods and the driveshaft off; still have the rebound when turning the ring gear by hand. No binding or grinding, just a bit springy when turning. Went together fine. Only noticed this after the seals were installed.
Any further thoughts? Thanks.
It sounds as if you've eliminated everything but the seals. I can't imagine what else it could be. Did you put some oil on the seals when you installed them?
Yes, but not a ton. I suppose I could remove the outer felt seals and roller bearings, and see what's what...
Or, I could add some gear oil to the diffy and swish around a bit to get some into the inner seal area...
Your second idea gets my vote.
Yeah, but oh the clean-up if I have to take it apart again!
Ok, it's the neoprene seals. Took one outer felt seal off and pulled the bearing. When turning the ring gear, I watched as the seal boot gripped on the axle shaft, causing the springy rebound effect. I think with some lube, all will be fine. Plus, I can keep my ring/pinion clearance at 0.015" with no spool gasket. I think I will use a little gasket sealer to make sure it doesn't leak though.
For anyone who reads this, be aware that if your new neoprene inner seals are a little dry, you can get rebound when turning your u-joint! Thanks for all the input.