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declutching front hubs?


skapunkninja

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my MB has a turn switch on the front hubs, so i can select 'lock' or 'unlock'. I've looked in the shop manual, and they are listed in the accessories section as 'declutching front hubs'.

 

What do they do? and how should they be used?

 

The switch turns easily, but nothing seems to happen.

 

I'll probably switch them out for standard hubs at some point, but just interested to know a bit more about them

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They simply disconnect the drive shafts from the hubs so that in rear wheel drive and with hubs disengeged (unlocked), the wheels do not turn the drive shaft, differential or propshaft from transfer box. Significantly less drag.

 

To use 4 wheel drive, you need to turn them to locked position. If you forget, it will not do any harm but the front wheels will not be driven.

 

VERY IMPORTANT - always make sure they are both locked IN or both locked OUT!!!

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In a series land-rover with free wheeling hubs you had to periodically engage them.

 

when "de-clutched" the front propshaft is stationary.

 

Normally the front prop shaft turns very slowly in relation to its drive in the transfer gearbox (due to variations in tyre size.) there is only a simple plain bronze bush to allow the prop to turn at a different speed to the driving shaft.

 

When delcutched the relative speed of rotation between driving shaft and propshaft is many many times greater, and the oil soon gets forced out the bearing which runs dry and either seizes or wears rapidly.

 

One day a week a I used to run with hubs engaged to ensure parts rotated and oil was thrown about near the bearing to keep it lubricated.

 

I am un-familiar with MB but may have a similar design and a similar need to regularly engage the free wheeling hubs so that the wheels drive the propshaft and ensure continued lubrication of this bearing.

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Another reason to periodically engage front hubs on Land Rovers is to lubricate the top swivel bearing. Don't know if it's the same arrangement on the Jeep but suspect as Land Rover copied it probably is. The top swivel bearing is actually a railco bush similar material to bakelite but absorbs oil, it eventually dries out. The bush relies on splash feed lubrication from the moving UJ in the oil filled swivel housing joint. Run with the hubs out and this joint doesn't rotate or feed oil to the top bearing.

I had front free wheel hubs on my Land Rover and never ran with them disengaged. I should've refitted standard drive flanges really.

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Another reason to periodically engage front hubs on Land Rovers is to lubricate the top swivel bearing. Don't know if it's the same arrangement on the Jeep but suspect as Land Rover copied it probably is. The top swivel bearing is actually a railco bush similar material to bakelite but absorbs oil, it eventually dries out. The bush relies on splash feed lubrication from the moving UJ in the oil filled swivel housing joint. Run with the hubs out and this joint doesn't rotate or feed oil to the top bearing.

I had front free wheel hubs on my Land Rover and never ran with them disengaged. I should've refitted standard drive flanges really.

If only Landrover had copied Jeep re front swivels, the Jeep has taper roller bearings top and bottom, very rarely give any trouble, easily shimmed up for the pre load, the swivels are filled with grease, unlike the archaic Landrover railco bush arrangement that wear out and sieze up

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I'm not really sure how land rovers got into this (did the US employ a Land Rover vehicle called MB?)

 

The biggest gain is in reduced rolling resistance and easier turning... Drag is typically an aerodynamic force caused by an object moving through the air.

 

With the front wheels not being affected by the drive shaft (because the hub is not longer meshing with the splined axle) it will not have to rotate it, nor will it have to overcome the force needed to fully articulate the bendix joint during turns. There are still some losses because the axles will pivot, but the largest loss is in the rotation and pivoting.

 

The original poster also mentioned a part number for the lock out hubs... um.. from what book? The WWII jeep did not have lock out hubs, nor did any M series jeep to my knowledge. Most likely the are from civilian jeep CJs or aftermarket.

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I'm not really sure how land rovers got into this (did the US employ a Land Rover vehicle called MB?)

 

The biggest gain is in reduced rolling resistance and easier turning... Drag is typically an aerodynamic force caused by an object moving through the air.

 

With the front wheels not being affected by the drive shaft (because the hub is not longer meshing with the splined axle) it will not have to rotate it, nor will it have to overcome the force needed to fully articulate the bendix joint during turns. There are still some losses because the axles will pivot, but the largest loss is in the rotation and pivoting.

 

The original poster also mentioned a part number for the lock out hubs... um.. from what book? The WWII jeep did not have lock out hubs, nor did any M series jeep to my knowledge. Most likely the are from civilian jeep CJs or aftermarket.

 

Land-Rovers got into this because they use similar design features and the same caution is needed with both vehicles when keeping hubs dis-engaged for long periods. The first one (or three) ( depending on the source you read) Land-Rover(s) were built on a jeep chassis. The Wilkes brothers copied a lot of design features, including the wheelbase, when they built the series ones.

 

Speaking of stupid ideas, free-wheeling hubs are one of them. There really isn't any point in them. If you are talking about from a reducing drag point of view, how much drag is there really? B*gger all if your vehicle is well serviced. :cool2:

 

Fuel economy figures I have seen for free-wheeling hubs are about 3%.

 

Servicing does not come into this, and well serviced or brutally ignored the economy is about the same.

 

You are saving the fuel on not building up angular momentum and then having to convert it back into wasted heat again each time you accelerate and brake.

 

It takes energy to accelerate the half shafts and diff, prop shaft etc from rest to its maximum rotation speed, and it uses extra braking force to slow these down again, causing more brake wear, etc.

 

Free wheeling hubs improve acceleration, improve braking distance, save wear and tear on brakes, improve fuel economy

 

However well serviced a vehicle is, this pointless waste of energy happens on each and every acceleration/ braking cycle as angular momentum is built up and destroyed, if rotating masses have to be accelerated from rest and then stopped again for no good reason.

 

Once accelerated, and driving at constant speed it takes little energy to keep front wheel drive parts rotating. The significant waste comes from creating and destroying angular momentum.

 

You will get a significant improvement in economy in start/ stop town/ city driving, and far less improvement when making longer Motorway/ dual carriageway trips.

Edited by antarmike
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As a note of caution, you can certainly cause damage to a Land-Rover by engaging four wheel drive with the hubs locked out, in certain circumstances . In a Landy you don't have to be in Low Ratio to get four wheel drive, and in High ratio this selection is OK, front hubs free or not.

 

However if you select four wheel drive by going into Low Ratio, you increase the torque driving into the back axle, and you over-stress it. The extra torque low ratio gives is intended to be split equally between two drive axles , not all pushed through just one diff.

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Having had Hilux 4x4 pickups as my main transport for 7 years I'm so glad they were both fitted with freewheel hubs! The difference in performance was very noticeable.

 

Were those automatic free wheel hubs as most of the Japanese motors seemed to have at the time? Took the hassle out of engaging and disengaging manually.

 

I think from the economy figures Mike gives it's hardly worth bothering with freewheel hubs. I never noticed any performance or economy difference myself, but perhaps that's due to the more than ample power of a 2 1/4 petrol land rover. :D

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Were those automatic free wheel hubs as most of the Japanese motors seemed to have at the time? Took the hassle out of engaging and disengaging manually.

 

I think from the economy figures Mike gives it's hardly worth bothering with freewheel hubs. I never noticed any performance or economy difference myself, but perhaps that's due to the more than ample power of a 2 1/4 petrol land rover. :D

for every £97.00 you spend on fuel can you give me £3.00? You might not miss £3 out of every £100 but I could do with the money!

 

3% figure comes from mid 1970's sales literature, and since savings are greatest in stop/ start driving, less so in cruising at constant speed, increasing congestions in our town and cities means that nowadays the savings are likely to be greater than this.

Edited by antarmike
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Were those automatic free wheel hubs as most of the Japanese motors seemed to have at the time? Took the hassle out of engaging and disengaging manually.

 

I think from the economy figures Mike gives it's hardly worth bothering with freewheel hubs. I never noticed any performance or economy difference myself, but perhaps that's due to the more than ample power of a 2 1/4 petrol land rover. :D

 

No. Manual ones. And never mind any improved economy, the reduction in transmission noise alone was enough!!!

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As to lubrication, Land Rover now do a 'One Shot Grease'. I've used it on standard hubs. Has anyone used it on freewheel?

 

 

Tony,

 

It is not the type of lubricant used in Land Rover swivels that causes the drying up of top Railko bushes, it is the fact that if freewheeling hubs are used and operated in disengaged mode, then the lubricant, whatever it might be, is not being distributed around the housing, and thus to top bush, as the shaft is not turning.

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Tony the one shot grease was introduced for the later vehicles fitted with bearings top and bottom but having said that I know of people who have successfully used it for years in Ralko bushed vehicles with no problems.This doesn't surprise me as we used to frequently use 140 grade oil in front hubs when customers didn't want to spend on repairs. The 140 grade oil has a similar consistency to the one shot grease. The joint spinning in the grease warms it up and thins it which means that it does splash feed, if you do use the grease you need to warm the sachet in hot water which makes it much easier to fill the hub and obviously it's necessary to jack the vehicle up and turn the wheels to full lock to get the grease into the spherical part of the hub.

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Thanks for the advice Degsey. The Sries 2 LWB is finally coming together and the question was which to refill hubs with.

 

 

No problem Tony, if the chrome and the seals are new or in good nick I'd go with the original oil, if not then use the grease.

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