[amolpol]

Originally Posted by slalom

Got a bit carried away , on a serous note ,what If this has happened on your Kerala or Mumbai drive at speeds on the highway ?

From your TBHP reports and the blog its evident that you don't abuse your thar , that's the main reason why I jumped the Gun .

Anyway All's well that ends well

No problem mate, the story had to be told some day!

Well, that's the exact thought that crossed my mind as well. The last trip to Mumbai happened in July first week and we drove 900kms non-stop from Pune to Bangalore on the way back with speeds ranging from 80-110kph. The jeep showed no signs of trouble all through the trip. But had something like this happened on the highway, I'd probably not be here to write this comment.

The jeep has been standing in the parking ever since that trip because it was still dirty with all the mud from the OTR and my family just refused to use it until I had gotten it serviced. I had just taken it out one day in between I think but that would have been hardly a 10-15km run. So essentially, this was a disaster waiting to happen but thankfully it chose a better day where there wasn't any significant damage except to the vehicle ofcourse.

In the end, its a machine and things can go wrong sometimes, hopefully I'll have it back in time for the Goa Great Escape

['72 Bullet]

Originally Posted by amolpol

No problem mate, the story had to be told some day!

Well, that's the exact thought that crossed my mind as well. The last trip to Mumbai happened in July first week and we drove 900kms non-stop from Pune to Bangalore on the way back with speeds ranging from 80-110kph. The jeep showed no signs of trouble all through the trip. But had something like this happened on the highway, I'd probably not be here to write this comment.

The jeep has been standing in the parking ever since that trip because it was still dirty with all the mud from the OTR and my family just refused to use it until I had gotten it serviced. I had just taken it out one day in between I think but that would have been hardly a 10-15km run. So essentially, this was a disaster waiting to happen but thankfully it chose a better day where there wasn't any significant damage except to the vehicle ofcourse.

In the end, its a machine and things can go wrong sometimes, hopefully I'll have it back in time for the Goa Great Escape

Glad it didn't happen at high-speed.

[DHABHAR.BEHRAM]

Originally Posted by Rajachu

awaiting to hear from BD!!!!!

Dear Amolpol - please post photograph taken from wheel outer face showing the 4WD free wheeling hub to enable me to pinpoint the failure mode and its root cause. This must never happen, it is unpardonable. The tire size that you have mentioned is 245, please confirm that it is 245/75R16, if so, it is design proven on Scorpio Getaway (double / single cab).

Best regards,

Behram Dhabhar

[Rajith]

Originally Posted by DHABHAR.BEHRAM

Dear Amolpol - The tire size that you have mentioned is 245, please confirm that it is 245/75R16, if so, it is design proven on Scorpio Getaway (double / single cab).

Best regards,

Behram Dhabhar

See the Maxiss MT 764 specs.

[amolpol]

Originally Posted by DHABHAR.BEHRAM

Dear Amolpol - please post photograph taken from wheel outer face showing the 4WD free wheeling hub to enable me to pinpoint the failure mode and its root cause. This must never happen, it is unpardonable. The tire size that you have mentioned is 245, please confirm that it is 245/75R16, if so, it is design proven on Scorpio Getaway (double / single cab).

Best regards,

Behram Dhabhar

BD Sir, unfortunately I dont have a picture taken from the outer face of the wheel. You're right about the tyre size, it is 245/75/R16. Pretty much the same tyre that is being used in all of the Mahindra Adventure Thars. I'm not sure if a component like this one should fail in the 9000kms that I have done so far. Also considering that I haven't hit anything at high speeds apart from the little offroading that was done at organized events only where there are marshals guiding you all the way.

As of now I am told that the drive shaft, hub assembly, knuckle joint and brake pads/discs are damaged and will need replacement. The parts have been ordered and detailed pictures have been sent to the Mahindra technical team for investigation. No word yet on the warranty as of now, but the Mahindra representative was pretty confident that I won't have any issues on that front atleast. I will wait till the final confirmation happens before I express the state of my mind.

Originally Posted by Rajith

See the Maxiss MT 764 specs.

Thanks Rajith, the size is the same though I have the MT 762 which is a version earlier than this.

PS> Just found a picture sent to me by a very near and dear friend who was the first one to reach the breakdown spot for help. This was when the tow van finally arrived and the jeep was being pulled up from the front.

[AVR]

Originally Posted by amolpol

As of now I am told that the drive shaft, hub assembly, knuckle joint and brake pads/discs are damaged and will need replacement.

Do you have negative off-set alloys? I believe that also adds to the problem.

[amolpol]

Originally Posted by AVR

Do you have negative off-set alloys? I believe that also adds to the problem.

Yes, I do believe these alloys have a negative offset. But they're not totally out of whack since this design is a popular SUV design as well. Moreover, I wouldn't really want to think that a jeep component would be designed to fail at the slightest variation from the stock values. If that's the case and Mahindra makes me believe it as well, the jeep may very well be on sale shortly.

To me, this looks like an isolated incident but it still needs to be investigated and changes made to production based on what they find. It's risking a bit too much for too little.

[AVR]

Originally Posted by amolpol

Yes, I do believe these alloys have a negative offset. But they're not totally out of whack since this design is a popular SUV design as well. Moreover, I wouldn't really want to think that a jeep component would be designed to fail at the slightest variation from the stock values. If that's the case and Mahindra makes me believe it as well, the jeep may very well be on sale shortly.

To me, this looks like an isolated incident but it still needs to be investigated and changes made to production based on what they find. It's risking a bit too much for too little.

Quite possible its isolated but generally if tire up-sizing increases failure probability by X% and negative offsets by Y% then a combination of both is going to be additive and then you might have possibly missed slowing down for a few potholes. It all adds up when you look back at it..doesn't it??
Looking forward to hearing the MASS side of the diagnosis.

Hopefully you'll have this sorted in warranty and all is good.

Cheers,
Adi

[DHABHAR.BEHRAM]

Originally Posted by amolpol

I am told that the drive shaft, hub assembly, knuckle joint and brake pads/discs are damaged and will need replacement.

Dear Amolpol - the dis-assembly sequence is as follows: Remove the free wheeling hub by removing the 6 nos allen head screws & circlip. The "wheel end" of the front drive shaft will be visible. Remove the big locknut holding the wheel bearings in place by first dis-engaging the lock washer lug. Then remove the second big nut. There is a special tool to perform this operation.

As your second photograph shows, the issue has resulted due to loosening of the two big nuts holding the wheel bearings. Damage as indicated to above components is consequential, as parts have touched each other after the nuts loosened enough to cause tire tilt.

Now the real question: Why did the nuts loosen? Did the operator get any indication or was it sudden? What type of noises did he hear? How did the issue progress? What is the state of the wheel bearing grease? What was the pre-load on the bearings as assembled on the assembly line / field?

For information: as wheel offset goes from positive to zero to negative, the eccentricity on the wheel bearings increases and thus its load bearing factor of safety theoretically reduces. Offset also changes the scrub value, which in turn increases the eccentricity on the suspension bushes / ball joints, reducing their design life. You can check on CAD to see the effect. Now you know why I tell you to stick to specifications! . All this is very elementary.

Best regards,

Behram Dhabhar

[amolpol]

Originally Posted by AVR

Quite possible its isolated but generally if tire up-sizing increases failure probability by X% and negative offsets by Y% then a combination of both is going to be additive and then you might have possibly missed slowing down for a few potholes. It all adds up when you look back at it..doesn't it??
Looking forward to hearing the MASS side of the diagnosis.

Hopefully you'll have this sorted in warranty and all is good.

Cheers,
Adi

Well the theory should hold good if the variation was beyond the stock specifications by a significant margin. BD sir has already clarified that the 275/75/R16 size is design tested so that leaves out only the offset which IMHO cannot cause a catastrophe in 9000kms of about 50kms or so would be off-road while the rest of it was on proper tar roads in the city and highways.

Any jeep owner can tell you how not to forget a pothole on the road coz more than the jeep, the occupants are subject to a safety hazard. If this were my Safari, I would have said that I don't remember slowing down for potholes anytime in the 70k I've done on it, I've done 60-80kph speeds on gravel and mud tracks in Ladakh for that matter. The 2.5tonne beast hasn't complained even once till now. But with the Thar, there is hardly a chance that I've hit a big pothole or a speedbreaker without slowing down since the jeep just cant soak in any of that.

Anyways, I'm going to wait for next week when the ASC comes back and tells me about the future course of action. I'm anyways going to be in Kabini for a week so won't be needing the jeep immediately. Have told those guys to make sure everything is checked properly and to take their time instead of hurrying up on the repair work.

[amolpol]

Originally Posted by DHABHAR.BEHRAM

As your second photograph shows, the issue has resulted due to loosening of the two big nuts holding the wheel bearings. Damage as indicated to above components is consequential, as parts have touched each other after the nuts loosened enough to cause tire tilt.

Now the real question: Why did the nuts loosen? Did the operator get any indication or was it sudden? What type of noises did he hear? How did the issue progress? What is the state of the wheel bearing grease? What was the pre-load on the bearings as assembled on the assembly line / field?

I had all the brakes cleaned up at the ASC right before my trip to Mumbai since there was some mud in them from the Kottayam MGE. I was told not to worry by the Mahindra guys when I wanted them to open the brakes and clean up before I returned back to Bangalore, but they said it would be okay. I did get a underbody wash done promptly before I started for Bangalore on the next day. Once I reached home, the jeep was given to the ASC for a thorough check on the brakes and the coolant leakage issue which were both done.

Now, would that involve changing any of the things that you have mentioned above?

Also, as I said, there was no problem whatsoever during my Mumbai trip where I attended the Lonavala MGE. It was only that fateful day that I realized that the steering wheel was feeling kinda funny and then this happened, all of this under 5kms since the ASC is just 6-7kms from my place.

[commander]

Originally Posted by DHABHAR.BEHRAM

For information: as wheel offset goes from positive to zero to negative, the eccentricity on the wheel bearings increases and thus its load bearing factor of safety theoretically reduces. Offset also changes the scrub value, which in turn increases the eccentricity on the suspension bushes / ball joints, reducing their design life. You can check on CAD to see the effect. Now you know why I tell you to stick to specifications! . All this is very elementary.

Best regards,

Behram Dhabhar

Would a minor offset in the rims be one of the reasons for failure in this case when we have already heard cases of cv joint failures in the Thar? Will the resulting load of the offset rims be sufficient enough to overcome the factor of safety of the designed component. It would be interesting to get the actual data related to this. I do have a 2008 bolero (2WD)which has done 145000 kms with the HR offset rims but never had unusual wear and tear of the bearings to date.

Curiosly Mahindra Rally Xuv500 have used negative offset discs for events which I fail to understand given the consequences related to it.!!!

Dear amolpol,
IMHO I doubt that could be considered as one of the causes but lets leave it to the gurus to decide. I do hope that all goes down well with your jeep. Cheers

[DHABHAR.BEHRAM]

Originally Posted by amolpol

I had all the brakes cleaned up at the ASC right before my trip to Mumbai since there was some mud in them from the Kottayam MGE. I was told not to worry by the Mahindra guys when I wanted them to open the brakes and clean up before I returned back to Bangalore, but they said it would be okay. I did get a underbody wash done promptly before I started for Bangalore on the next day. Once I reached home, the jeep was given to the ASC for a thorough check on the brakes and the coolant leakage issue which were both done.

Now, would that involve changing any of the things that you have mentioned above?

Also, as I said, there was no problem whatsoever during my Mumbai trip where I attended the Lonavala MGE. It was only that fateful day that I realized that the steering wheel was feeling kinda funny and then this happened, all of this under 5kms since the ASC is just 6-7kms from my place.

Dear Amolpol - can you find out exactly what I am writing here: Did they do something called "hub greasing" / "wheel bearing greasing"? They have a nasty habit of doing things and not reporting / doing things not required to be done / not doing things and reporting, all three are possible all the time, so it is all very confusing. I wish you all the best in your endeavor to find out (poor you). Please reply in "yes or no" only. Inferences from either answers will be very clear. Even if the answer comes out as "maybe", I will guide you, don't worry!

This is called DOE (Design of Experiments), a statistical tool used to conduct root cause analysis. I will exactly control your vehicle, sitting 850 kms away from you. . Again (I can't help it, as usual), if this was 521, I would have completed the whole DOE and finished it off long time back. 521 was not a vehicle, it was my moving laboratory! Enjoy! .

Best regards,

Behram Dhabhar

[Timson]

Originally Posted by DHABHAR.BEHRAM

Dear Amolpol - can you find out exactly what I am writing here: Did they do something called "hub greasing" / "wheel bearing greasing"? They have a nasty habit of doing things and not reporting / doing things not required to be done / not doing things and reporting, all three are possible all the time, so it is all very confusing. I wish you all the best in your endeavor to find out (poor you). Please reply in "yes or no" only. Inferences from either answers will be very clear. Even if the answer comes out as "maybe", I will guide you, don't worry!

This is called DOE (Design of Experiments), a statistical tool used to conduct root cause analysis. I will exactly control your vehicle, sitting 850 kms away from you. . Again (I can't help it, as usual), if this was 521, I would have completed the whole DOE and finished it off long time back. 521 was not a vehicle, it was my moving laboratory! Enjoy! .

Best regards,

Behram Dhabhar

Dear DB Sir,

In my decade and half experience in maintenance of jeep/other double taper roller bearing hub setup have i faced this scenario of locknuts loosening. It would be enlightening to know the actual method of setting the pre-load.

The method i follow is once the hub is installed by tightening the innner locknut to max troque and then loosing it by 1/6th round. Check for any free play then place the lock washer tighten the outer lock nut to max torque and fold the locking washer tab, A set of TIMKEN (made in England) 501349 has lasted more than 200k kilometers.

As you rightly said it must be due to the handy work of the ASC staff.

Regards,

Chengappa.

[DHABHAR.BEHRAM]

Dear Chengappa - as you very well know, taper roller bearings work in pairs, they need extremely close positioning tolerance to be maintained (I cannot provide actual value for obvious reason). If assembled properly and lubricated as per schedule, 2,00,000 kms is achievable as the load bearing factor of safety is very high. The process of 1/6 turn that you mention is completely subjective / operator dependent and is long since discarded. This was used in designs without intermediate spacer. Nowadays, selective shimming is used to meet the design axial dimension with an intermediate non-collapsible spacer. I have observed and caught extremely minor differences in handling behavior, just by changing this dimension. Everything is mentioned in the drawing and specification sheet.

As far as your last paragraph is concerned, god help poor customers! There is no shortage of grease monkeys, monkeying around with their prized possessions! .

Best regards,

Behram Dhabhar