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Knocking in rear axle

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C

Cutlass

Jedi Warrior
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Well, the BJ8 is about done, but..... On a short drive Friday, a knocking began from the rear axle area. I checked wheel and hub tightness, as well as drive shaft and universal joints, and exhaust. With the car on jack stands and no wheels, and in gear with engine running, the knocking is evident, and related to speed. The wheels will turn through maybe 5-10 degrees of rotation before the driveshaft begins to turn. I'm thinking that something is awry in the differential, possibly a broken tooth on the pinion gear. I can pull it out and get it to a pro, but before I do that, I just wondered if there might be another diagnostic approach before major surgery. Thanks.
 
Had a similar occurance last year, and as I went thru the checklist one of the splined hubs was loose ...solved the problem.

I have never had a rear end on the 20 or so Healeys I have owned so I am inclined to think it might be a simpler issue..Keep looking and good luck.

Pete
 
Might check the driveshaft as it passes through the tunnel. You may be just hitting the Emergency brake mechanism. Worth a check before removing rear diff.
 
While you have it on jack stands you might pull the brake drums and run it again to rule out a brake component issue - JUST DON'T PRESS THE BRAKE PEDAL TO STOP THE REAR AXLES FROM TURNING WHILE YOU HAVE THE DRUMS OFF!!!
 
Thanks. What about that slop between the axle and the driveshaft? I would think that there might be a little slop, but 5-10 degrees?
 
MY slop on my hundred is very similar......Originally thought that was the issue!

Pete
 
The "slop" is called gear lash. There is a certain amount of play inherent/required in the hypoid and spider gears. It's taken up when the differential is under torque. There is a spec, but you have to remove the pumpkin and test it on the bench (along with bearing preload). The shop manual has excellent instructions in "proper" English. 5-10deg at the road wheels sounds about right.

BTW, the knock could possibly be due to a loose shock (although you usually notice that on the road and it's not necessarily proportional to speed--just something else to check).
 
Thanks, Bob. The noise is present with the wheels off and the car on jack stands. I'll just have to start slowly taking things apart till I find the culprit. Jim
 
Hello Cutlass,

Did you by any chance replace the pinion seal in the differential and not torque the nut on the flange properly?. These differentials are usually quite reliable.

The movement at the wheel you are talking about seems about right.

Best regards,

bundyrum.
 
Thanks, bundyrum. There are some things I just won't do, and work on differentials is one of them. I had the seal replaced, along with one or two bearings, by one who does such things for a living. I'll probably get the time this weekend to sort out the source of the problem.
 
I used to get a knocking from my BJ8 at the rear, particularly going over bumps and holes in the awful Sydney roads.

After a long search it was found to be the bolts holding the shock absorbers to the chassis - they simply needed tightening as they'd come a bit loose.

Not sure if this is th same as your problem but every bit of info helps....!
 
RobWarren said:
I used to get a knocking from my BJ8 at the rear, particularly going over bumps and holes in the awful Sydney roads.

After a long search it was found to be the bolts holding the shock absorbers to the chassis - they simply needed tightening as they'd come a bit loose.

Not sure if this is th same as your problem but every bit of info helps....!
Click to expand...
I found the bolt with the same "knocking sound" problem and an added problem...the hole had been enlarged due to letting the "knocking" sound go too long. Rounded out the hole and welded a large washer in the mount with the correct size bolt hole, and it took car of it.
Patrick
 
Well, it's the Great Pumpkin, Charlie Brown. Two teeth on the pinion gear broke off in chunks. I believe that the damage was old, because of the discoloration on part of the fracture sites, with no discoloration on the fresh part of the fracture.

I've never had to replace either a ring or pinion gear before. Certainly I won't be doing the work, but do these gears have to be replaced as a matched pair? My guess is that the answer is yes. Any other advice before I take the Pumpkin to the Great Pumpkin Doctor?
 
Cutlass, FYI. Ed K. has a matched ring and pinon set for sale in the BCF classified. I sold Ed my differential serveral months ago. They came off my 1960 BT7 and are in perfect shape. I replaced them with 3.54 gearing. If you're looking for a good set, give him a call.
 
Hi Rob,

That's right. The set I have on the classifieds came out of the assembly I purchased From Rob and is now installed in my Healey with the 3.56 Lempert gear set instead of the factory set.
The ring and pinion set for sale on the classifieds has no visible wear. That is they way it should be after 100,000 miles when you keep the differential full of oil all the time.

... Cutlass, Notice the price is right !

Ed
 
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