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Hi all, need some thoughts on this. Just recently finished a ground up resto, have noticed when i put the foot down after backing off and vice versa I can hear a definate click/clunk in the rear end area. Have new uni joints, new wheels, new axles EN36 steel, diff was overhauled (did they get the preload/backlash right?), trans and o/d overhauled any thoughts on the noise? Wheels on ground in neutral i can move the driveshaft about 1/2-3/4 inch in rotation
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Diff Backlash
- Thread starter zblu
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ZBLU,
"Wheels on ground in neutral I can move the driveshaft about 1/2-3/4 inch in rotation "
This is a whole lot of backlash. Factory specs for the BN2 call for .006" to .012" movement of the ring gear with the pinion held firm. I would guess that this translates to about .016" to .032" movement at the outer diameter of the driveshaft. The BN1 specs are even less at .005" to .008" at the ring gear. If you run it very long in this condition, it may be impossible to get it correctly reset. As Keoke says, make sure that the pinion flange is not loose. It's nut must be torqued very tight.
D
"Wheels on ground in neutral I can move the driveshaft about 1/2-3/4 inch in rotation "
This is a whole lot of backlash. Factory specs for the BN2 call for .006" to .012" movement of the ring gear with the pinion held firm. I would guess that this translates to about .016" to .032" movement at the outer diameter of the driveshaft. The BN1 specs are even less at .005" to .008" at the ring gear. If you run it very long in this condition, it may be impossible to get it correctly reset. As Keoke says, make sure that the pinion flange is not loose. It's nut must be torqued very tight.
D
ZBLU
Back lash should be 0.010" at the ring gear. This is to allow a lube film between the gears as they slide. I'd also check the flange nut on the drive flange of the transmission, and both 'U' [universal] joints of the drive shaft for play, they are also part of that same equasion, before I'd start tearing the pumpkin out of the rear axle. Remember Dr. E. Demming - root cause of the problem is 95% of the solution.
Regards, Bob
Back lash should be 0.010" at the ring gear. This is to allow a lube film between the gears as they slide. I'd also check the flange nut on the drive flange of the transmission, and both 'U' [universal] joints of the drive shaft for play, they are also part of that same equasion, before I'd start tearing the pumpkin out of the rear axle. Remember Dr. E. Demming - root cause of the problem is 95% of the solution.
Regards, Bob
Keoke
Great Pumpkin
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Zblu/Bob, To check for excessive backlash does not require one to tear the pumpkin out of the rear suspension. Just drop the driveshaft and check the pinion's rotational play by rotating the pinion flange by hand.If the play is found to be excessive you are a leg up on tearing the pumpkin out of the rear axel.---Fwiw---Cheers- Keoke
thanks all, its a very early BN1, new uni joints, if its in neutral then the tranny flange shouldnt come into the equation,and the noise is coming from the rear end, put my head under today (as best you can!)can see drops of diff oil, seems to be from front oil seal behind the nut in question!
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On the spiral bevel BN1 axle, this axle is not like the later & more familiar hypoid designs:
The ring to pinion backlash is set by shims which set the side to side location of the carrier/ring gear assembly. The pinion depth in the housing is fixed & pinion bearing preload is set by shims. The pumpkin MUST be removed to properly set up the gear mesh adjusting shims. On the later hypoid type axles (late BN1 & up) these same pinion shims are used to set a specific depth of the pinion in the housing.
On rare occasions where things have been operating normally & suddenly get out of whack, the pinion preload setting shims have been known to break up & allow the pinion to go out of depth adjustment. This is the only instance where the assembly might be corrected for excessive backlash without removing the pumpkin. I certainly doubt if this is your problem, considering that it was just worked on.
Most likely - someone just set it up wrong the last time it was worked on. Either pinion preload or ring gear lateral position. I would return it to the mechanic & insist that it be reassembled correctly & with the PROPER .005" to .008" backlash between ring & pinion. Obviously, ring gear runout must be checked for a maximum of .002" with this small backlash. The correct shims for this axle are not so readily available, but a good shop should be able to come up with something. Don't accept any attempts to "fix" it without removing the pumpkin from the axle housing, or the story that it will get better with a few miles on it. It won't. As I said before, if you run it very long in this condition, it will be permanently screwed up.
The front pinion seal is a separate problem. Sometimes the seal wears a slight groove in the pinion flange & the new seal needs to be set at a slightly different depth so that it can seat on a "fresh" pinion flange surface. Oil can get out between the flange inner splines & the shaft splines. It is a good idea to apply sealer to the splines when assembling.
If I "have" to leave the car with a shop that is not familiar with the car, I leave the factory shop manual with them. Many shops do not have the needed information available for the particular car & have to guess at or assume things. If you don't have the manual, get one. The reprint of the Austin-Healey factory service manual, BN1 with BN2 supplement is very good. British Car Specialists in Stockton, CA has it along with a pretty good selection of parts.
Sorry you are having this problem.
D
The ring to pinion backlash is set by shims which set the side to side location of the carrier/ring gear assembly. The pinion depth in the housing is fixed & pinion bearing preload is set by shims. The pumpkin MUST be removed to properly set up the gear mesh adjusting shims. On the later hypoid type axles (late BN1 & up) these same pinion shims are used to set a specific depth of the pinion in the housing.
On rare occasions where things have been operating normally & suddenly get out of whack, the pinion preload setting shims have been known to break up & allow the pinion to go out of depth adjustment. This is the only instance where the assembly might be corrected for excessive backlash without removing the pumpkin. I certainly doubt if this is your problem, considering that it was just worked on.
Most likely - someone just set it up wrong the last time it was worked on. Either pinion preload or ring gear lateral position. I would return it to the mechanic & insist that it be reassembled correctly & with the PROPER .005" to .008" backlash between ring & pinion. Obviously, ring gear runout must be checked for a maximum of .002" with this small backlash. The correct shims for this axle are not so readily available, but a good shop should be able to come up with something. Don't accept any attempts to "fix" it without removing the pumpkin from the axle housing, or the story that it will get better with a few miles on it. It won't. As I said before, if you run it very long in this condition, it will be permanently screwed up.
The front pinion seal is a separate problem. Sometimes the seal wears a slight groove in the pinion flange & the new seal needs to be set at a slightly different depth so that it can seat on a "fresh" pinion flange surface. Oil can get out between the flange inner splines & the shaft splines. It is a good idea to apply sealer to the splines when assembling.
If I "have" to leave the car with a shop that is not familiar with the car, I leave the factory shop manual with them. Many shops do not have the needed information available for the particular car & have to guess at or assume things. If you don't have the manual, get one. The reprint of the Austin-Healey factory service manual, BN1 with BN2 supplement is very good. British Car Specialists in Stockton, CA has it along with a pretty good selection of parts.
Sorry you are having this problem.
D
Good reading this, I have a very early BN1 and have started to get a whine from the diff under load and want to strip the diff out to adjust the backlash .can Dave post any pictures of the shim details please ? Any more comments would be very welcome on this job . The diff is the 3.67 , option which is an original , I bought it at Beaulieu Autojumble years ago brand new still in the waxed paper / plywood box !
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I'm sad to say Dave passed away a number of years ago. It is always nice to see his posts pop up from time to time. He was a wonderful guy with a wealth of knowledge. We are lucky to have his spirit keeping on in this manner. Perhaps someone else ( Randy Forbes are you out there?) has what you need.
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Dave was the best and I had the opportunity to communicate with him directly as we both had NICAL hardtops for our 100's. He was a great source of info and helped so many of us.