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Old 14th December 2012, 16:24   #16
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Default Re: Using 4L for Engine Braking/Torque with FWH Disengaged

OK, in such situations something will break. However, the prop shaft in our jeeps is a weaker link than the axle and it gets twisted most of the times.
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Old 14th December 2012, 16:33   #17
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Default Re: Using 4L for Engine Braking/Torque with FWH Disengaged

Quote:
Originally Posted by star_aqua View Post
You can refer the below post for understanding how the interlock works.

http://www.team-bhp.com/forum/4x4-ve...ml#post1141430 (4x4 gearbox crisis)
Dear Mr Star Aqua,
Thanks for link, but problem discussed here is different. Whether you use T-18 or KMT-18, you need to be in 4wd. here Tini and Dhanush is using FWH to fool this system.
And my limited experience says Prop shaft would be stressed along with rear diff. Can you please explain what components might be affected and why?

Shubhendra
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Old 14th December 2012, 16:36   #18
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Lightbulb Re: Using 4L for Engine Braking/Torque with FWH Disengaged

Some thoughts...

Let us assume that the torque available at each axle is X kgm.

The forces acting on the axles, due to load (weight/friction/contact with ground) are called stresses...these stresses ultimately cause material to break. Let us assume it is Y units acting on each axle, for the following conditions :
  • when in low-gear of the tcase
  • when the vehicle is with all four wheels in contact with the ground
  • FWH in lock position.
Now, considering the scenario when the FWH are in unlock/open position, the torque to the rear axle remains the same X kgm, BUT the stresses acting on the rear axle (as a result of the X kgm going to the front axle going waste due to open FWH) will be 2*Y units. If this additional stress is going to exceed the material-strength limits of the axle shaft, the axle will break.


Hope my understanding is right.


http://en.wikipedia.org/wiki/Strength_of_materials

.

Last edited by Blue Thunder : 14th December 2012 at 16:52.
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Old 14th December 2012, 17:34   #19
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Default Re: Using 4L for Engine Braking/Torque with FWH Disengaged

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Originally Posted by dhanushs View Post
Going by this logic, even if FWH is locked, if, any one of the front wheels are spinning freely.. Meaning, when front diff is open, the rear axle can break if load is high and both rear wheels have traction?
The T18 has a torque bias of only 50-50 right? So its either a 50-50 split, or 0-100. Now if 2L is engaged, this multiplied (by low ratio) torque at rear is sufficient to break something. In 4L, whether FWH is open or not, rear axle gets just 50% of the multiplied torque, which it is designed for.

Quote:
Well, things get even messier if you got a rear locker and one front wheel is spinning and one rear wheel has no traction. So, all the effective torque has to be borne by one rear axle, and it should break like a matchstick. Right?
Good point Dhanush. Here too, the rear gets 50% of total torque. But with the diff locked and one wheel in the air, the other gets 100% of that 50%
If the axle is going to break with just this torque, none of you guys would be claiming the advantages of difflocks no?

This is just my analysis of it. I could be proved grossly wrong.

Cheers,
Rahul
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Old 14th December 2012, 19:01   #20
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Default Re: Using 4L for Engine Braking/Torque with FWH Disengaged

Tini,

Thanks for starting this topic, it is turning out to be a huge learners paradise, for myself and many others, I am glued here, post to post.

Behram Sir's expertise and experience is being counter weighed by, on field experience and logical explanations.

Awaiting the final conclusion here, as long as it takes.
Regards,
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Old 14th December 2012, 20:36   #21
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Default Re: Using 4L for Engine Braking/Torque with FWH Disengaged

I think Blue Thunder has summed it up perfectly!

There are a multitude of factors that are at work. The ground resistance, gross weight of the vehicle, etc.

As they say, a chain is as strong as it's weakest link, the weakest link in the jeep would let go first.

In my experience, the weakest are the FWHs (local ones) (though not applicable in this case), next would be the prop shaft, gears in the differential and then the axle.

But we are talking about offroading situations where tremendous load is on the axle and if the axle can take that load, shouldn't it hypothetically take the downhill load?

NOTE: I'm not denying the fact that BD is right and the axle can break, i'm just thinking out loud.
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Old 15th December 2012, 10:13   #22
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Default Re: Using 4L for Engine Braking/Torque with FWH Disengaged

Quote:
Originally Posted by fazalaliadil View Post
Tini,

Behram Sir's expertise and experience is being counter weighed by, on field experience and logical explanations.

You don't get hired as a test engineer, B.D.'s current position, without a lot of field experience in your resume. He gave one example right here in this thread.

You guys may remember a member named "Red" something from maybe 3-4 years ago? He had a juiced up SWB jeep that had 2 transfer cases in series. I am now wondering about the torque stress that thing generated.

At any rate, the risk of busting something, maybe far from help, does not make me want to run right out and try 2wd in low. Too much risk for too little gain IMHO.

Last edited by DirtyDan : 15th December 2012 at 10:16.
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Old 18th December 2012, 09:53   #23
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Default Re: Using 4L for Engine Braking/Torque with FWH Disengaged

Dear all - it was February 1981. I was a trainee in M&M Kandivli plant. The vehicle was MRG7962, a 1971 model blue CJ3BLHD. It was an R&D prototype. As an R&D trial to verify the theory, I fitted a production transfer case with the interlock mechanism removed completely during manufacturing on the assembly line and engaged low range without engaging 4WD. This took quite a bit of effort, some rails had to be modified if I remember correctly. The LH axle shaft broke like a matchstick (expected as it is longer) within 100m of drive from the R&D workshop. It broke from the inner end of the keyway which holds the brake drum in place. Please don't attempt it, the wheel will come out as it is a semi-floating axle shaft. On MRG7962, it came out and damaged the brake assembly completely. This trial was done on the test track so it was expected and therefore adequate safety precautions were taken.

Best regards,

Behram Dhabhar
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Old 18th December 2012, 11:03   #24
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Default Re: Using 4L for Engine Braking/Torque with FWH Disengaged

Quote:
Originally Posted by DHABHAR.BEHRAM View Post
The LH axle shaft broke like a matchstick (expected as it is longer) within 100m of drive from the R&D workshop. It broke from the inner end of the keyway which holds the brake drum in place.
Sir,

Point noted.

Now let us hypothetically look at the reverse situation, where the rear drive shaft is broken and due to this we are engaging in 4X4 mode for moving the Jeep using and powering only the front differentials.

Will the same law of physics apply to the front shaft as in the (mentioned) rear shaft and end up in a break down?

If not, why and what is a safe distance of travel before one can reach a repair place?
Regards,
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Old 18th December 2012, 15:03   #25
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Default Re: Using 4L for Engine Braking/Torque with FWH Disengaged

Quote:
Originally Posted by fazalaliadil View Post
Point noted. Now let us hypothetically look at the reverse situation, where the rear drive shaft is broken and due to this we are engaging in 4X4 mode for moving the Jeep using and powering only the front differentials. Will the same law of physics apply to the front shaft as in the (mentioned) rear shaft and end up in a break down? If not, why and what is a safe distance of travel before one can reach a repair place?
Regards,
Dear Fazal - you have asked a very relevant question. In 1981, I was conducting acceleration test on a fully loaded (1.6 tons) FC straight chassis 4*4 first prototype vehicle with XDP4.90 engine, 3 speed transmission and 4.88:1 axle ratio (47/8, made in toolroom). The location was Eastern Express Highway, outside Godrej factory. The rear axle shaft broke (fully floating). It happens quite regularly in acceleration test, nothing alarming. I calmly removed the outer side of the broken end, removed the other axle shaft, took a long bar from a passing truck driver and removed the broken inner piece, put the sheet metal cups back without the axle shafts inside to prevent dust from going in, calmly put the vehicle in 4*4 high and drove with 1.6 tons of stones inside the vehicle from Vikhroli to Kandivli, without applying jerky acceleration inputs. I reached Kandivli. As long as you don't exceed the factor of safety, you can operate the vehicle to reach the nearest repair place. Obviously, this is possible only with fully floating axle assembly.

Best regards,

Behram Dhabhar
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Old 18th December 2012, 16:00   #26
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Default Re: Using 4L for Engine Braking/Torque with FWH Disengaged

Quote:
Originally Posted by DHABHAR.BEHRAM View Post
...In 1981, I was conducting acceleration test on a fully loaded (1.6 tons) FC ...The rear axle shaft broke (fully floating). It happens quite regularly in acceleration test, nothing alarming. I calmly removed...
Chances of the front axle snapping were also possible, especially if it was in 4L?
Sir, no offence to you or MM, but if it was a regular (and expected) occurrence, couldn't they have just sent along tools and two spare axles amidst that 1.6 tonnes of stone instead of putting you through a circus?
Or maybe they expected you to report failure of all axles after you walked back to Kandivli?

Only kidding!

Cheers,
Rahul
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Old 18th December 2012, 16:59   #27
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Default Axle Strength

Hi Guys,

My little experience with M&M Rear FF Axles.

1) The Older 2piece FFR Axles are prone to breaking. I have damaged one set in 2WD lo Ratio.

2) The New Generation 1piece/Flanged FFRA is much more studier and can be driven in 2WD Lo. I would STRONGLY ADVISE AGAINST this practice.

Regards,

Arka
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Old 19th December 2012, 09:50   #28
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Default Re: Using 4L for Engine Braking/Torque with FWH Disengaged

Quote:
Originally Posted by voodoochild View Post
Sir, no offence to you or MM, but if it was a regular (and expected) occurrence, couldn't they have just sent along tools and two spare axles amidst that 1.6 tonnes of stone instead of putting you through a circus? Rahul
Dear Rahul - you can't just carry axles all over the place during testing. You wouldn't believe all the "things that have happened" to our test vehicles when we test them to the limits and beyond! That's why I always say that I have the best job in the world. When we test, we really go! Please don't attempt it, ever! .

Just a couple of months back, I broke an axle during acceleration test, no sweat at all. By the way, please look up "Acceleration Test Procedure" as you guys are experts at googling things. It will be an eye opener for everybody. I cannot describe it on an open forum for obvious reasons.

Dear Arka - hello after a very long time, it is indeed nice to read your comment. Flanged FFRA has dowel location, the previous axle did not have it. To introduce flanged FFRA was one of the major decisions on the Bolero platform. Changing from 139.7mm pcd to 160mm pcd got us the space to do it. That's NGCS!

Best regards,

Behram Dhabhar

Last edited by DHABHAR.BEHRAM : 19th December 2012 at 09:53. Reason: add info
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Old 19th December 2012, 12:44   #29
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Default Re: Using 4L for Engine Braking/Torque with FWH Disengaged

can I ask to all here ?

but how much max torque a standard 540 or 550 axle can handle in a straight line position ? ( xdp 4.90 & xd 3p engined respectively & whatever the GB ,TC , CP ratio is ).

Sudarshan .
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Old 19th December 2012, 20:53   #30
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Default Re: Using 4L for Engine Braking/Torque with FWH Disengaged

My (2 bits) take:
As long as the driver is sensible, keeps in mind his current limitations, and has a feel for the vehicle, 2L operation is not a problem.

Why (my thoughts only):
The maximum torque an axle shaft has to endure is that placed on it by the traction of the wheel (and in case it is accelerating, the (moment of) inertia of the wheel). Any more torque, and the wheel will loose traction and start spinning.
Add to this the fact that we normally use our jeeps as 4 wheeled motorcycles (ie hardly carrying any load), and that by itself the Jeep rear axle has hardly any weight on it (we normally do not cart around 1.6t payload), the maximum traction will be modest.
Plus we normally use low range not to send humungous torque to the wheels, but to send reasonable torque at very low road speeds, in the interests of better vehicle control and not to burn the clutches.

Regards
Sutripta
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