Reverse recoveries and Reversing through obstacles

[Bongani]

This is a spawn from this thread.
http://www.4x4community.co.za/forum/...?t=7301&page=6


When doing a reverse recovery or driving a obstacle that requires power and torque in reverse the pinion is likely to climb out of the crown-wheel.

If you look at this image you will notice that the teeth of the pinion is slanted.


When driving forward the pinion teeth will bite into the crown wheel and pull tight. When reversing or snatching in reverse the pinion will try to climb out of the slots. If it manage to succeed it will strip the crown-wheel teeth and it will be the end of the diff.




If possible, avoid reversing in obstacles that puts load on the front diff. The front diff is typically not as strong as the rear (very evident on SFA vehicles where the diffs can clearly be seen and where it is easy to compare the size of diffs)

Off course, in some vehicles you will find that the crown wheel in the diff have straight teeth (IIRC the SFA hilux has) so forward and reverse should be the same but it is actually not, because when reversing the load of the vehicle is shifted to the front diff that was not design for that type of abuse where as the over sized rear diff can take the weight, thus load.

That is why I am saying that to reverse up an obstacle looks cool but do so with caution as it has much more likely to brake your vehicle, especially in a snatch recovery scenario.

Comments?

[SimonB]

Bongani

Cool! Thanks for that advise! Something to bear in mind, but I probably would not contemplate reversing through obstacles simply because you can't see them clearly (even with a co-pilot)!

[Trevor_Mathews]

Hey Morne,

Very informative indeed, thanks ! ...I was talking to a Mahindra (single cab 4x4) and he said that his truck only operates in 4x4 'mode' while driving fwd...otherwise 'normal mode' when reversing...I found/find this VERY strange indeed...maybe something to do with this 'issue' ? WIERD !

Trev

[Bongani]

Here is a pic of what happens when the pinion climbs out of the slots on the crownwheel. Apparently the person was reversing up a dune (not confirmed) in a 105 GX Cruiser.


.

[Barto]

For those that might wonder.....the second pic shows an EZ-locker just installed in a 4.5 GX 80.......it wasn't a good idea as it only lasted 2 months and 3 trails.......another reason why I hate auto lockers!!!

[Stefan]

Thanks for this Bongani, very informative!

[SimonB]

Hey Morne,

Very informative indeed, thanks ! ...I was talking to a Mahindra (single cab 4x4) and he said that his truck only operates in 4x4 'mode' while driving fwd...otherwise 'normal mode' when reversing...I found/find this VERY strange indeed...maybe something to do with this 'issue' ? WIERD !

Trev

Trev

I'm not sure if that's entirely true. I have a mate with a Scorpio and I believe his works in 4x4, but to disengage it you have to go into 2WD and then into reverse....

[David Maritz]

Not only the crownwheel and pinion that is going the reverse gear in the gearbox as well, as that gear is very small and get damaged quickly with a lot of strain.

[Cecil]

Hi Bongani, Please dont show this to Engel.
"Groot B@llas drif at outrekpad"

[maniec]

For those that might wonder.....the second pic shows an EZ-locker just installed in a 4.5 GX 80.......it wasn't a good idea as it only lasted 2 months and 3 trails.......another reason why I hate auto lockers!!!

Might the fact that they break be linked to the engine size?
I have had an easy locker in my rear diff for approx. 10 trials - 8 months (not scenic), and I am very happy with it. I wouldn't say that I abuse the vehicle, rather that I rather go over than around, and still the wear on the diff and locker has been negligible.

Add to that that my vehicle only churns out 65 kW8), compared to 100+ kW of the vehicles mentioned above.

[SimonB]

Hi Bongani, Please dont show this to Engel.
"Groot B@llas drif at outrekpad"

Even better - I have video of this

http://uk.youtube.com/watch?v=O2Yzx3D3rG0

[Barto]

Manie, yes the problem was probably the power. After it stripped, I upgraded to a full Detroit and only paid in the difference in cost, since it was replaced under warranty. My 265/75R16 tyres was apparently borderline for the warranty replacement. I should have gone for an Aussie locker in the first place, but I only heard of them and their excellent warranty after I bought the EZ-Locker. The Aussie locker has no limit on tyre size or engine power.....or at least, that's what the owner of Aussie-locker told me on e-mail in 2004.

[Engel]

he he........the breaking is usually under huge strain like recovering. Your 4.5l and other big v8 like breaking cos of power. You can break anything under strain if you are windgat genoeg and dont understand mechanics.

......ps never hand a clutch or drive terrain problems on my vehicles when driven to 500000kms.

[Andre.Nortje]

Engel post bietjie 'n foto van daai dual suspension MTB van jou toe? Ry jy gereeld? Waarvoor gebruik jy hom?

[Scrat]

Ye I was told by my dad years ago that Propshafts also tend to snap seen as they are stressed all their lives to go forward and any serious strain in reverse tends to weaken them Problems they used to have in Angola in the War, he was Spanner head then.

Thanks for the info, always good to understand why it is a problem and not just believe what you hear.

[BigRed]

Ye I was told by my dad years ago that Propshafts also tend to snap seen as they are stressed all their lives to go forward and any serious strain in reverse tends to weaken them Problems they used to have in Angola in the War, he was Spanner head then.

Nope...... we drive some serious equipment with cardan shafts much larger than that in big trucks. They do come in for overhaul where mostly only the needle bearings get replaced. We have never had any question nor come back on difference in direction to date..

Further that diff pic that Bongani posted looks like a sudden burst of power, not reversing up a dune. (Maybe he hit a rock,,,,,) But if you look at the teeth before the first one, thay are clean and still look good. If this would have happended over time, one would see a general increase in wear throughout the crown, which I dont see here. M2CW though...

[Barto]

And a few more cents worth
Kai, that cruiser diff did strip from reversing on a dune, but as you say, probably not from gentle acceleration. It has happened on cruisers with very low mileage as well, and caused huge warranty claim fights, so it's not always related to wear. Cruiser axles are borderline strong enough for their application and a bit too much (sudden) acceleration does that in reverse.

[BigRed]

OK, Bliksem I didn't know that Zantus.

thinking about it, he must have done some serious bouncing then.

[Engel]

vehicles does not bounce on sand.....er dunes....usually

ek sien DATSUNS is nie KROOZERS nie, breek nie so maklik nie. [wag om weer geban te word]

[Henris]

vehicles does not bounce on sand.....er dunes....usually

ek sien DATSUNS is nie KROOZERS nie, breek nie so maklik nie. [wag om weer geban te word]

You know how to stir don't you.?

You were the one that said that Datsuns have sh1t front suspentions. 3000cc Datsun engines don't last much more than 150,000km. So who is badmouthing who here?