LJ78 transfer case swap

[Polyarkos]

Have a friend running a 1KZ-TE LJ78 with 35's and an auto. With the standard 4.88 gears it runs poorly (compared to 31's). Instead of swaping the gears he wants to know if you can swap the transfer case from a 70/75 series to bring the revs up (i.e. is it a straight swap, dimensions etc...)?

Thanks in advance

 

[ForealBoreal]

it would bring the revs up for sure. Why not switch the gears?

 

[Radd Cruisers]

I do not think the ratios differ, really.

If they both have a split case, they will be the same ratio.

~John

 

[Radd Cruisers]

it would bring the revs up for sure. Why not switch the gears?

Please explain...

~John

 

[ForealBoreal]

Please explain...

~John

wouldn't gears overall be an easier swap? 33s with 4.56 gearing.
Trans case swap seems like there could be some headache involved.
I think gearing would be easier than the trans swap, but if it wasn't enough go for the trans swap.

 

[Radd Cruisers]

wouldn't gears overall be an easier swap? 33s with 4.56 gearing.
Trans case swap seems like there could be some headache involved.
I think gearing would be easier than the trans swap, but if it wasn't enough go for the trans swap.

You meant diff gears, the discussion was transfer gears.

The KZJ has 4.88s in it most likely (and as stated), so he would need to have 5.29s or better.

The real problem is the small engine, tall gearing in the auto, and the higher rolling resistance of the 35s.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Mark's gears with the underdrive would give about 8%.

Going to 5.29s would give about 8%.

I'd go for the 'case gears and get the better low range option. Cost won't be that much different - one relatively easy T'case gearset swap (4 - 6 hours) vs. two diff gear setup and swaps - about 14 - 16 hours. Cost will be less for the diff gears, but the labour is very much in favour of the T'case gears.

~John

 

[SimonInAustralia]

The real problem is the small engine, tall gearing in the auto, and the higher rolling resistance of the 35s.

I'd say it is more the change in overall gearing that the larger than standard 35's create, rather than the higher rolling resistance.

Mark's gears with the underdrive would give about 8%.

I am interested in Marks overdrive-high/underdrive-low transfer gearset, along with 37/38's, to counteract the 5.99 diff ratio I will soon have under my troopy, but am a little concerned about the reports of these gears being noisy.

Anyone had experience driving with Marks transfer gears, and is the higher noise an issue?

 

[Polyarkos]

I agree with 5.29's or the Marks option.

However its the cost that he is trying to avoid (New Zealand has a poor exchange rate with AU and US).
Marks kit = $2000+nzd +fitting
R&P = $1500nzd + fitting (brand new)
70/75 gear box/transfer case = $300+nzd

All the above can be done with secondhand gear, hence wanting to try the transfer case option.

 

[Radd Cruisers]

I agree with 5.29's or the Marks option.

However its the cost that he is trying to avoid (New Zealand has a poor exchange rate with AU and US).
Marks kit = $2000+nzd +fitting
R&P = $1500nzd + fitting (brand new)
70/75 gear box/transfer case = $300+nzd

All the above can be done with secondhand gear, hence wanting to try the transfer case option.

What are the gear ratios in the transmission / transfer cases combo? There will some advantage in going with the manual transmission, as the overall gearing will be lower. Then there's the cost of the conversion.

~John

 

[Radd Cruisers]

I'd say it is more the change in overall gearing that the larger than standard 35's create, rather than the higher rolling resistance.
[...]
Anyone had experience driving with Marks transfer gears, and is the higher noise an issue?

35s have quite a bit more rolling resistance than the stock tires. A larger engine, and it's less of an issue. With a smaller engine, it can make a very large difference.

The Mark's gears have a distinct whine to them.

I am running the 1:1 / 3.05:1 gear set and the noise is quite tolerable in my BJ74. In low range, they are certainly noisier than in high range - much like the old three speed transmission and J30 transfer case when they were getting tired.

In a truck with better sound insulation, such as an HZJ7* then the noise would certainly be less notiveable.

If you want a very nice usable low range and can tolerate a slight whine, then don't hesitate to put them in. They really change the behavior of the truck in so many good ways when off-road.

~John

 

[SimonInAustralia]

35s have quite a bit more rolling resistance than the stock tires. A larger engine, and it's less of an issue. With a smaller engine, it can make a very large difference.

The only way to compare the effect of the different rolling resistance of the two tyre sizes on the same model truck is to modify the gearing (transmission/transfer/diff/etc.) on a truck with 35's to have exactly the same overall gearing ratio (including tyre size in the overall gearing ratio) as a truck with standard size tyres, and the two trucks should have identical performance before the larger tyres are fitted.

Unless you have done this, you are not comparing the rolling resistance of the two tyre sizes, but are probably comparing more the overall gear ratio difference between the two.

With your experience, it is quite possible that you have done this sort of direct comparison, with matching overall gear ratios, but until that is confirmed, I just can't agree that the difference felt by the driver is going to be the rolling resistance of the tyres and not the difference in overall gearing between the two trucks.

 

[crushers]

4.90 gears in the diffs of the LJ78
4.30 gears in the diffs of the KZJ78 (according to the specs in the book)

both have the same ratio in the t/case so no advantage there.

i would say, confirm the gear ratio in the diffs. if the gear ratio is actually 4.30 then buy the center units from a dead LJ78 and install. call it a day.

if they are 4.88 as John stated then either swap the engine to a larger one, swap the tranny to a manual or go to smaller tires...

i don't like the Marks gears, too noisy for a D/D.

 

[cambelt]

Same here , ive fitted a few sets of marks gears and all are noisyer
than the stock ones .
Dave

 

[Radd Cruisers]

The only way to compare the effect of the different rolling resistance of the two tyre sizes on the same model truck is to modify the gearing (transmission/transfer/diff/etc.) on a truck with 35's to have exactly the same overall gearing ratio (including tyre size in the overall gearing ratio) as a truck with standard size tyres, and the two trucks should have identical performance before the larger tyres are fitted.

Unless you have done this, you are not comparing the rolling resistance of the two tyre sizes, but are probably comparing more the overall gear ratio difference between the two.

With your experience, it is quite possible that you have done this sort of direct comparison, with matching overall gear ratios, but until that is confirmed, I just can't agree that the difference felt by the driver is going to be the rolling resistance of the tyres and not the difference in overall gearing between the two trucks.

Been down this road many times before: the width of the tires, tire construction, brand of tire, tread type, and the pressure that they are run at will all dramatically affect the rolling resistance.

Given the exact same tire manufacturer, tread, and approximately the same tire pressure, the difference between something like a 33x9.50 and a 33x12.50 can easily make a 5 to 10% difference in fuel economy and a noticeable drop in performance.

If you're comparing bias tires to radial, then that percent change can climb greatly as bias tires have significantly more rolling resistance.

For most use, I prefer a relatively tall skinny tire (255 85R16) - better fuel economy and performance.

When I need flotation I move to a wider tire like a 12.50 or more (33 or 35x12.50 R15).

Width can and does make a big difference in a given diameter, and is especially noticeable when a smaller engine is doing the work.


~John

 

[crushers]

think about it this way,
a tall skiny tire 33X9.5X15 with have a foot print of roughly 4"X6"
a fat tire 33X12.5X15 with leave a foot print of 4" X 9" which is an increase of rolling resitance at 50%.

this increase will affect braking, starting, turning as well as just driving down the road. fat tires are more expensive to buy as well as more expensive to use (usually).

this being said my d/d has 35X12.5X15 on 12" rims which gives these particular tire design a full 11" of foot print width. as you can see, i like the looks and the ride of the fat tires and am not concerned about the actual fuel mileage.

also a taller tire affects the final ratio aspect which can affect the fuel economy.

agree / disagree?

 

[SimonInAustralia]

I agree, but disagree that the increase in tyre width does nearly as much to the performance as the change in overall ratio by changes in tyre size.

If you look back at what I first said in this thread...

The real problem is the small engine, tall gearing in the auto, and the higher rolling resistance of the 35s.

I'd say it is more the change in overall gearing that the larger than standard 35's create, rather than the higher rolling resistance.

...I still think the issue is not really the greater rolling resistance of the 35's over standard, but more the change in gearing due to the change in tyre size from whatever the standard tyre size is (29"?) to the 35's.

 

[crushers]

agree, an extreme increase of tire size will affect the fuel mileage, power, braking etc more than width change of tire
but
going 50% fatter also affects the fuel mileage.
so
he is experiencing a double whammy here, 6" taller in tire PLUS at least 50% increase in width = s***ty fuel mileage and performance.
he will have to change the diff gears to compansate for the changes... or live with the way the truck performs after all diff gear swaps are not cheap, marks gears are not cheap so he could buy a lot of fuel instead... depending on how long he plans on keeping the truck.

 

[SimonInAustralia]

I wish there was a way to find out how noisy Marks transfer gears are, some of you say it isn't too bad, some say it's too much for a DD.

Really need to hear them myself.

 

[Radd Cruisers]

I wish there was a way to find out how noisy Marks transfer gears are, some of you say it isn't too bad, some say it's too much for a DD.

Really need to hear them myself.

I think it's more about whether you are sensitive to that particular frequency or not. I don't mind it, but for some people it drives them nuts...

Also the oil you use and the level of sound insulation will play a big role in whether you can live with it or not.

Try one of the Aussie forums, I would bet there's someone in your area who has a set installed.

~John