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Old 18th May 2006, 09:17   #1
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Default Gypsy 4WD help wanted

Hello

I have a slight problem with my 4WD. I had given my car for some work in a garage. when it came back the car was in 4L mode. Theses mechs have a habit of messing things up even on prior instructions not to touch the transfer case.

The transfer gears smoothly engage in 4H and 4L which are in one straight line. The problem is that the gear wont shift from 4H to 2H. It does go after it has been worked with for 15 mins but thats not a guarentee. Most of the mechanics have no idea how the system works and hence i fear consulting them.

What could be the problem. Hs anyone of previous gypsy owners encountered similar.

Mine is wide track 1995 gypsy ( No need to manual lock hubs)

The problem is only while changing from 4H to 2H. the gear just wont engage.

Please help
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Old 18th May 2006, 10:40   #2
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Quote:
Originally Posted by lodhra
Hello

I have a slight problem with my 4WD. I had given my car for some work in a garage. when it came back the car was in 4L mode. Theses mechs have a habit of messing things up even on prior instructions not to touch the transfer case.

The transfer gears smoothly engage in 4H and 4L which are in one straight line. The problem is that the gear wont shift from 4H to 2H. It does go after it has been worked with for 15 mins but thats not a guarentee. Most of the mechanics have no idea how the system works and hence i fear consulting them.

What could be the problem. Hs anyone of previous gypsy owners encountered similar.

Mine is wide track 1995 gypsy ( No need to manual lock hubs)

The problem is only while changing from 4H to 2H. the gear just wont engage.

Please help
Quick question:
With the vehicle stationary, can you move the lever from 2H to 4H and back to 2H, smoothly?
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Old 18th May 2006, 12:56   #3
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Hi, There,

Yes this problem with the 4H to 2H is sometimes there in my 97 Gypsy King too. What u could try is to shift from 4H to 2H while crawling..Its works..though you are not suppossed to do it. Try & post your feedback.
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Old 18th May 2006, 17:42   #4
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i did not want to get stuck in a situation in far away place and ruin my tyres. Opened the transfer case and the box. Now ther is a peculiar problem. If anyone has seen the gypsy gear shifts its 4L- N-4H in onse straight line. From 4H to 2H you have to shift the gear left and up. Now when the problem occured the gear goes left and down which turns the car in neutral mode. After working its now engaging smoothly.
I think that there are 2 small rods one for 4L and 4 H and one for 2H inside the transfer case. Must check after dismantling the hubs and the rod must of 2H must be slipping down. Now evrything is fine.
I was going to dismantle the hubs but feared doing that since gypsy spares are not available that easy
Headers your info gave me some relief but i never tried in running position ( if thats what u mean by crawling)
Ram the answer is No. Now that i have worked out i will see oif that helps

Thank you guys
Would like to know more about this stuff as practically nothing is there on the web
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Old 18th May 2006, 18:44   #5
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Default The classic 4x4 transmission wind-up phenomenon

With the Gypsy stationary in 2wd mode, if you can move the lever from 2H to 4H and back to 2H, smoothly, you don't have a linkage problem.

Difficulty in switching from 4H to 2H, is most likely due to
the classic transmission wind-up phenomenon.

Geometry
When a 4x4 is traveling in a straight line all four wheels rotate at the same speed.

When it attempts to go around a corner, each of the four wheels has a different turn-radius. So it spins at different rpm. See my diagram below:


Each axle differential allows its wheels to rotate at different speeds from each other. The crown gear and planetary cage in the differential typically rotates at the average rpm of its two road wheels.

As you can see from my diagram, the front wheels travel more than the rear wheels.
This causes a difference in speeds between the front differential crown gear and the rear differential crown gear. Therefore, a difference in speeds between the rear propeller shaft and the front propeller shaft.

When you are in 4wd mode, if you try to steer the vehicle, one of the four tires must lose traction and spin or slip momentarily to defuse the torque-buildup. This is easy when driving on soft clay, sand or snow.

However, it is close to impossible on non-slip terrain such as a dry tarmac/concrete road or rock surface.
This puts the driveline under heavy torsional stress ("transmission windup" (sometimes also called "axle windup"), preventing smooth shifting from 4H to 2H.

High stress is placed on the drive shafts and transmission, eventually causing one of two things to happen:
  1. One of the wheels slips or spins to relieve the stress or
  2. The drive-shaft/transmission breaks.
This is why part time 4x4s should never select 4wd mode on paved surfaces.

This torsional stress can wreak havoc on the "U" joints, pinions, crowns and gears. Then the component that is most brittle will shatter and relieve the stress.

Caveat:
Don't use 4wd mode on dry firm hard surfaced roads, unless you have really bald tires.

If you've driven on a dry hard surfaced road in 4wd mode, you've stressed your driveline in a way it was never designed to be. Now when you need to switch back from 4H to 2H, do this:

Put the vehicle in reverse gear and back up a very short distance (maybe a few feet). While doing this turn the steering wheel left or right. Reversing a short distance with the steering wheel turned, it will reverse the torsional stress and free the transfer case to shift from 4H to 2H.

Now try shifting from 4H to 2H.
It should be easy. Let me know if this worked! 

Caution: Don't overdo this, otherwise excess reverse torsional stress, will again twist your driveline.

Center Differential
Simple 4x4s which lack a third "center" differential, are only meant to go four-wheeling on soft muddy, snowy or sandy terrain where tire-slip is possible.

This applies to the Maruti Gypsy, as well as the Mahindras, the Jonga, the Carrier (Nissan D4W73), the Shaktiman, the new Tata 407-4x4, ...

Expensive full-time 4x4s and all wheel drives have technology to handle this transmission windup.

Interestingly, the center diff was pioneered in the Dutch, 1902 Spyker 4WD, along with the world’s first 6-cyl. engine and brakes on all four wheels!

The old 1981 Audi Quattro all-wheel-drives had a center differential. The newer ones have an electro-hydraulic center Haldex limited slip coupler.

The Range Rover is a fulltime 4x4. It is always in 4WD and cannot select 2WD at all.

Most Indian 4x4s are part-time 4WD. They can switch between 2WD and 4WD.

A Mitsubishi Pajero can be both a fulltime 4WD and a part-time 4WD.
It can select 2WD, fulltime 4WD and locked 4WD.
The Pajero has a center differential. This allows 4WD to be used on normal roads (fulltime 4WD) and can be locked for offroad use (part-time 4WD).

Even a Center Differential must be lockable
However on soft wet clay, sand or snow, a vehicle with a central differential will let one wheel spin and the vehicle will get stuck!

This is why the central differential must also have a lock-out mechanism that defeats the center differential action and simulates a part-time 4x4 drive in 4WD mode. All open center differentials usually also have a mechanism to lock them. Typically an air-locker, viscous coupling, TorSen (Torque sensing) or other limited slip device.

Hope I was able to explain the transmission wind-up issue clearly here.
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Old 19th May 2006, 14:51   #6
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Mr Ram

You are nothing less than god for me. That explanation i was searching for so long and cpould not get it. I will try your description. When i read your article i immediately called my mech and told him not to mess withe the hubs. I think ur explanation is right. Cause when i jack up the car it easily moves from 4h to 2h but on road it doesnt. Your tarm,ac/ soft roadexplanation is of immense help
Thank you friend
I owe you a drink. Thanks once again will reply soon
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Old 19th May 2006, 15:05   #7
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Mr Ram

One thing i forgot to mention is that when i drive in 2 w and them stop. Neutral my gear then shift to 4H it engages smoothly. After that again if i try to go to 2H it gets stuck and does not fall. When i opened the gear box the bushing was gone, ball was not there and gear oil was min. I serviced that part and rengaged the gear. My mech was about to open the hubs and see if there was a linkage problems. Now on yor advice i have told him not to lose the hubs. Do u think following your instructions along with the service which i have done will solve the problem
My only fear is that if i takje my car out of bombay and if some person just moves the lever to 4H and does not pop to 2H i am dead. Do u recomend openong the hubs and checking the interior mech of the gearbox.
You know there arent any skill gypsy mech around and i dont wanna lose my 4wd as i often visit the forests for medicinal plants. what do u suggest
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Old 19th May 2006, 16:10   #8
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Quote:
Originally Posted by lodhra
When i opened the gear box the bushing was gone, ball was not there and gear oil was min. I serviced that part and rengaged the gear. My mech was about to open the hubs and see if there was a linkage problems. Now on yor advice i have told him not to loosen the hubs. Do u think following your instructions along with the service which i have done will solve the problem
If some driveline components are already damaged,it is wise to replace them.


Quote:
Originally Posted by lodhra
My only fear is that if i take my car out of bombay and if some person just moves the lever to 4H and does not pop to 2H...
If some person moves the lever to 4H and it does not pop back to 2H, just move the vehicle in the opposite direction a few feet with a slight steering action (left or right does not matter). This will reverse the torsional stress and free the transfer case to shift from 4H to back to 2H, easily.

It's just a procedure that will work everytime.
This behavior is typical of all part-time-4wd type vehicles, regardless of showroom-new or well-used.
Nothing to worry about.

And, in wet कीचड़, or on slippery roads, this problem will never show up!

Warm regards
Ram
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Old 19th May 2006, 16:22   #9
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Hey Ram,

That was a detailed explanation clearly explaining the different 4WD systems. I have a similar problem on my Gypsy which occasionally does not come out of 4H mode while on sand / river beds etc..

Reversing a little helps a lot in enabling a smooth transfer to 2H.

Thanks again for your detailed input
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