4WD Downhill Braking/Towing

Submitted: Friday, Feb 25, 2011 at 18:40
ThreadID: 84603 Views:7211 Replies:18 FollowUps:16
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G'day All

Your opinions please.

I frequently drive down Clyde and Brown Mountains towing the Jayco Outback - both are relatively steep downhill descents - and use both third and second gears to manage speed and braking.

It has been suggested to me by an experienced mechanical engineer that engaging high range 4WD is a better way of managing the downhill progress. Further, his suggestion is that gearbox torque can be dispersed simply by running the near side wheels in the rough on the side of the road for a short distance.

I had previously been under the impression that running 4WD (Hilux TD) on bitumen is a no-no.

waddayareckon?

Cheers
John
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Reply By: Harry and Ann (WA) - Friday, Feb 25, 2011 at 19:11

Friday, Feb 25, 2011 at 19:11
JOHN, I WOOD BE GETING A SECOND OPINION. Harry.
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Reply By: aussiedingo. (River Rina) - Friday, Feb 25, 2011 at 19:28

Friday, Feb 25, 2011 at 19:28
G'day jg, your engineer is correct, if one wheel is running on a non sealed road at the same time - tension (wind up) will be released & you will still have the benifit of 4wd traction as all caravans/trailers of all types always want to go straight ahead as you turn, particularly tandem axles, in wet conditions you need to start turning marginally earlier to start the process to change the inertia, the heavier - the sooner, hope that helps, hoo roo,
"the only thing constant in my life is change"




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Follow Up By: Member - John G- Friday, Feb 25, 2011 at 20:16

Friday, Feb 25, 2011 at 20:16
Thanks dingo
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Reply By: Member - Tanka (NSW) - Friday, Feb 25, 2011 at 19:30

Friday, Feb 25, 2011 at 19:30
John,
I would suggest that if you are making this descent regularly with no problems, then why would you change you approach. Increasing driveline friction and resistance with the engagement of 4wd could possibly help slow you, but then to have to unload the driveline by driving half the car in the rough, kind of defeats the safety purpose in my opinion. I tow very rarely, but when I do one of the things I watch out for is avoiding putting half the tow vehicle in the soft verge.

Cheers Tanka.
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Follow Up By: Member - John G- Friday, Feb 25, 2011 at 20:15

Friday, Feb 25, 2011 at 20:15
G'day Tanka

I agree with you. But I raise the issue because I had never thought that engaging 4WD was an option for such situations, and we are never too old to learn or to improve.

Cheers
John
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Reply By: Mike DiD - Friday, Feb 25, 2011 at 19:35

Friday, Feb 25, 2011 at 19:35
I assume these roads have sharp/hairpin bends.

Then it would be foolish to use 4WD on a sealed road windy, unless your vehicle has on-road 4WD.
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Reply By: landseka - Friday, Feb 25, 2011 at 19:42

Friday, Feb 25, 2011 at 19:42
I would give anyone a VERY wide berth if they suggested putting one side in the dirt whilst towing a caravan down Brown OR Clyde. Coming down a steep hill with one side of the car having good traction and the other having NO traction is a sure fire way to suddenly start going UP the mountain...(or over the edge).
AnswerID: 446554

Follow Up By: landseka - Friday, Feb 25, 2011 at 19:43

Friday, Feb 25, 2011 at 19:43
I meant to add that he may be an experienced mechanical engineer, but not a very experienced driver I think.
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Follow Up By: Member - John G- Friday, Feb 25, 2011 at 20:11

Friday, Feb 25, 2011 at 20:11
G'day landseka

In his defence, his 'CV' progresses from motor mechanic, to driving heavy vehicles including road trains, to servicing and modifying heavy automotive vehicles, to qualifying in engineering the hard way (part time) and so on.

He did refer to the impact on steering, and the reference to dispersing torque included doing it safely once the descent was completed.

As another response has suggested, the hairpins on both Clyde and Brown Mountains would be difficult in 4WD.


Cheers
John
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Reply By: Axle - Friday, Feb 25, 2011 at 20:34

Friday, Feb 25, 2011 at 20:34
G/Day John, Yes it is a option, but not on sealed roads, Gravel by all means, what your engineer says will release diff wind up, but" Holy Moly" dangerous stuff with something in tow!!, And those fragile hilux diffs won't take any extra abuse.


Cheers Axle
AnswerID: 446557

Reply By: petengail - Friday, Feb 25, 2011 at 20:37

Friday, Feb 25, 2011 at 20:37
When you go by can you wave to pooh bear, at the corner if he is still there?
AnswerID: 446558

Follow Up By: Member - John G- Saturday, Feb 26, 2011 at 06:28

Saturday, Feb 26, 2011 at 06:28
G'day Pete and Gail

He's still there, but I usually have both hands on the wheel on that bend.

Cheers
John
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Reply By: Member - Joe n Mel n kids (FNQ - Friday, Feb 25, 2011 at 21:06

Friday, Feb 25, 2011 at 21:06
Extremely dangerous.........
With a downhill run and anything being towed behind it would be foolish to run any wheels off the sealed road, in or out of 4wd, when you drop one side in the "rough" it tends to yank it over as it "rides" the ridge, the van behind will also "jump" down into the ridge, that will start the van swaying and trying to stop it when half on and half off, downhill and braking would be extremely hard, it will all go really pear shaped within a few seconds and being in 4wd will do squat to help you get out of that .......... you WILL without a doubt lose control and get really messed up...
On gravel YES, on any sealed road NEVER do it.......
I would ask him again as it is done going UPHILL but never downhill, maybe got his wired crossed eh......
Cheers
Joe
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Follow Up By: Member - John G- Saturday, Feb 26, 2011 at 06:34

Saturday, Feb 26, 2011 at 06:34
Thanks Joe

His reference was certainly to downhill, but what we didn't really discuss was the distance involved in remaining in 4WD. I certainly wouldn't contemplate dropping wheels off the side of the road while going downhill, or at any sort of speed.

Cheers
John
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Reply By: Robin Miller - Friday, Feb 25, 2011 at 21:35

Friday, Feb 25, 2011 at 21:35
No way John

Your mechanical enigneers statement about dispersing torque etc I can agree with , but there is more to the story, and like others above, putting a wheel in the dirt needs careful consideration, not something down routinely.

(We are assuming yours is live axles part time)

Things need to be very even before you attempt anything like that often going downhill, weight is thrown forward compressing the front tyres and making windup very likely in that type of car (worse with corners as per Mike above).

Wind up across axles is more likely to cause the car to actually break traction on wet surfaces and promote a slide.

I have actually seen a Navara come to a full dead stop within 50meters of driving onto bitumen cause of unequal tyre diameters - bit of an eye-opener actually.

If you need more downhill braking without modifying your car drop your tyre pressures 20% and drive a bit slower. This extends your brakes capability.
Robin Miller

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Follow Up By: Member - John G- Saturday, Feb 26, 2011 at 06:50

Saturday, Feb 26, 2011 at 06:50
Thanks Robin

He did refer to tyre diameters but more in relation to turning.

I can manage the descents comfortably using third and second gears and will continue to do so. The fols behind just have to be patient, altho' there are plenty of passing opportunities on Clyde Mountain.

I raised the issue because my limited experience (and mechanical savvy) led me to believe that torque buildup was sufficient reason never to engage 4WD on bitumen. I only break that rule for a few metres when reversing the camper up a steep pitch at the start of our driveway.

Cheers
John
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Follow Up By: Member - John G- Saturday, Feb 26, 2011 at 09:38

Saturday, Feb 26, 2011 at 09:38
A typo there Robin - read 'folks' not 'fols' and certainly not 'fools'.

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Reply By: Rangiephil - Friday, Feb 25, 2011 at 22:06

Friday, Feb 25, 2011 at 22:06
Of course if you bought a vehicle with constant 4WD like a Pajero, Triton, Prado, Land Rover the issue would not arise.
Regards Philip A
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Follow Up By: Member - John G- Saturday, Feb 26, 2011 at 06:39

Saturday, Feb 26, 2011 at 06:39
Good onya Phil

As a retiree the budget is not going to make it, but your point is well made and maybe it's something all folks who tow vans should consider when they are making their purchases.

I was new to 4WDriving seven years ago and I am occasionally overwhelmed by how much there is to learn, but also amazed at how capable the vehicles are.

Cheers
John
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Reply By: Madfisher - Saturday, Feb 26, 2011 at 08:15

Saturday, Feb 26, 2011 at 08:15
I often run the aircon as well even if not needed going downhill, it does make a difference,
Cheers Pete
AnswerID: 446580

Follow Up By: Member - John G- Saturday, Feb 26, 2011 at 09:59

Saturday, Feb 26, 2011 at 09:59
Thanks

I suppose if I open the door and drag my foot, then that'll help as well.

Cheers
John
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Follow Up By: Madfisher - Saturday, Feb 26, 2011 at 11:41

Saturday, Feb 26, 2011 at 11:41
NAH get a boat anchor and attach it to the back of the van lol, or put a log through the back wheels.
Good to have a since of humour a.
Cheers Pete
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Reply By: vk1dx - Saturday, Feb 26, 2011 at 08:24

Saturday, Feb 26, 2011 at 08:24
No way.

I only read down to about half way and it appeared that the majority agreed with my thoughts. Stick to what you are doing and don't use 4wd in your car.

4WD is not recommended on hard bitumen. Maybe an AWD car that is designed to do it, but not your car. The AWD as, I believe, has a slippery centre diff that will take the wind up out of the system and also not try to make it go straight ahead on sharp corners. Yours does not. I would worry about the sharp bends with it in 4wd and wanting to go straight ahead on a wet or icy road. Not for quids would I do it.

I would NEVER put one wheel in the dirt/rough. Both or none.

Phil
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Reply By: Steve - Saturday, Feb 26, 2011 at 09:00

Saturday, Feb 26, 2011 at 09:00
John

with all due respect, I think between the pair if you, you may have your wires crossed.

I have a Defender and select low range, without the diff lock on, when negotiating similar hiils when towing. Don't know if you are able to do that with your vehicle but it would make far more sense.
AnswerID: 446587

Follow Up By: Member - John G- Saturday, Feb 26, 2011 at 09:55

Saturday, Feb 26, 2011 at 09:55
G'day Steve

My original post could not reflect the full detail of our discussion. Our wires weren't crossed, but my wire remained cautious about his advice and hence the reason for my post.

Regrettably, the Hilux does not have the sophistication of your Defender.

Cheers
John
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Follow Up By: Steve - Saturday, Feb 26, 2011 at 10:27

Saturday, Feb 26, 2011 at 10:27
sorry if you were offended by my trying to clear things up

Anyway, the Japs will get around to it one day - they usually catch on eventually.
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Follow Up By: Member - John G- Saturday, Feb 26, 2011 at 11:30

Saturday, Feb 26, 2011 at 11:30
No offence taken Steve. Nine times out of 10 my mechanical mentor's knowledge and experience makes good sense and his advice works, this time, I reckoned on seeking wider counsel like your own. But . . .I can't afford a Defender.

Cheers
John
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Reply By: whisky_mac - Saturday, Feb 26, 2011 at 09:24

Saturday, Feb 26, 2011 at 09:24
John, I would not be dropping the left wheels into the dirt. I once did the right thing going up hill towing a horse trailer with two horses by moving to the left to let cars following pass. As I came back onto the road the edge of the bitumen ripped the inside tyre wall apart. If you have ever had to change wheels on a float on a hill it is not nice. You have to first unload the horses, have somebody with horses brains mind them and then jack and change the tyre.

I was recently down Clyde Mountain towing a Tvan with my automatic Range Rover and had no problems. The Tvan has electric brakes and I was able to adjust from the cabin if needed but did not need.

Jim
AnswerID: 446591

Reply By: ob - Saturday, Feb 26, 2011 at 12:31

Saturday, Feb 26, 2011 at 12:31
John, got to agree with previous posters when they say don't do it and given good reasons. The other factor to consider is your going down hill two LH wheels in the gravel and two RH wheels on bitumen and an emergengy braking event happens. Now you have two wheels on one side with good traction and two on the other with very little.

ob
AnswerID: 446608

Reply By: Dave(NSW) - Saturday, Feb 26, 2011 at 18:02

Saturday, Feb 26, 2011 at 18:02
John G,
just stay in the low gears your useing, Maybe you could find out about fitting an Exhaust brake to the vehicle to help hold you back on steep decents. Ive driven down both those mountains many times with a Semi you just have to take your time and don't worry about the cars building up behind you as there is plenty of places for them to pass.
Cheers Dave..
GU RULES!!

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Follow Up By: Member - John G- Sunday, Feb 27, 2011 at 08:59

Sunday, Feb 27, 2011 at 08:59
Thanks Dave
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Reply By: Member - Tour Boy ( Bundy QLD) - Saturday, Feb 26, 2011 at 18:08

Saturday, Feb 26, 2011 at 18:08
John, I agree with the others, as the hilux has an lsd in the rear it will try to push you in a straight line around corners in 4wd on the blacktop.

I realize you have an SR5 with the hubs permanently locked and the ADD 4wd activation. Maybe you could get an auto sparky to fit an override switch to stop the front diff from connecting and use low range 2wd say 3rd or 4th gear. The torque and gearing would be better. This way it would be like using low with the hubs unlocked in most part time 4wd's.

I wouldn't fit free wheeling hubs to yours because if you went to 4wd with the hubs unlocked and the vehicle moving, the transfer case which is spinning the rear driveshaft and not the front will try to mesh them both together with some very nasty grinding. Yours need the front hubs locked to work as designed.
Cheers,
Dave
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2015 Fortuner
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Follow Up By: Member - John G- Sunday, Feb 27, 2011 at 09:05

Sunday, Feb 27, 2011 at 09:05
Thanks Dave

I think I'll just stick with the system as is, and use the gears for braking. All the responses have added to my learning experience, and it's good to have such a site.

Cheers
John G
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Reply By: G.T. - Monday, Feb 28, 2011 at 15:58

Monday, Feb 28, 2011 at 15:58
John G-- Dave (N.S.W.) is on the money. An exhaust brake is the way to go. Regards G.T.
AnswerID: 446882

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