differential off (1 Viewer)

[chrisdecker]

I purchased a 91 FJ80 about a year ago. The differential that engaged the front wheels was taken off (I have it) and the CDL light on with the switch removed. I would like to know how exactly this effects economy, transmission wear, etc.
And if I reattach the front differential will the full-time 4WD engage or do I need the CDL switch to trigger it
thanks for any help

 

[StucknKS]

By differential are you referring to the drive shaft? If the drive shaft was removed this will help reduce wear and tear on the front end and possibly result in a small increase in MPG. If the drive shaft was removed the CDL should be engaged. Sounds as though the PO engaged the CDL and then removed the switch. You will need to reinstall the switch to disengage the CDL if you reinstall the drive shaft or you will be in 4 HI instead of AWD.

 

[chrisdecker]

driveshaft, that's it! thanks mate
I'm in the process of acquiring the CDL switch, I wonder if anyone has recorded more MPG with the driveshaft off.

 

[powermad]

I wonder if anyone has recorded more MPG with the driveshaft off.

Several have posted that they did not see an increase.

A hazard switch also works if you don't have the CDL switch.

 

[BILT4ME]

You will not see an increase in MPG just by removing the driveshaft and locking the CDL. This is because you are still passively rotating the internals of the front axle (axles, carrier, pinion) because the front hubs are splined to the axles. As the wheels rotate, they also rotate the front axle shafts.

The only time you will see a POSSIBLE increase is if you also install manually locking front hubs in order to disengage the rotating assembly. Even then, it will only be a minor % of increase since the friction in the rotating assembly is low.

 

[jonheld]

If the drive shaft was removed this will help reduce wear and tear on the front end and possibly result in a small increase in MPG.

No and no. Everything is still rotating, just not being driven by the transfer case.

 

[CJF]

No and no. Everything is still rotating, just not being driven by the transfer case.

I disagree with the first no. Surely having no load on the front end reduces wear, even if everything is still rotating.

 

[Kohle]

I disagree with the first no. Surely having no load on the front end reduces wear, even if everything is still rotating.

I would agree that wear would be reduced somewhat.

 

[Timpanogos Slim]

Haven't the few people who have done part time conversions reported maybe 1mpg increase on the freeway at best?

 

[StucknKS]

Haven't the few people who have done part time conversions reported maybe 1mpg increase on the freeway at best?

That is what I have seen as the average (at best) on here. But it is still a small increase as I stated previously. In my case my 80 gets about 11mpg on the highway. If I increased it to 12mpg, that would be a 9% increase in mpg.

I am not a mathematician so I might be off a little.

Either way I still think it would reduce the wear and tear if by just a little.

 

[Gray Rider]

Just for reference:
10,000 miles at 14 mpg = 714 gal at 3.50/gal = $2,500.00
10,000 miles at 15 mpg = 667 gal at 3.50/gal = $2,335.00
$165.00 savings per 10,000 miles

 

[StucknKS]

Just for reference:
10,000 miles at 14 mpg = 714 gal at 3.50/gal = $2,500.00
10,000 miles at 15 mpg = 667 gal at 3.50/gal = $2,335.00
$165.00 savings per 10,000 miles

Exactly. And if you go off of my numbers, 11mpg and 12mpg, I would save $260 for every 10,000 miles. Even though it is a small increase in savings, to me it is still not worth it.

 

[Pin_Head]

The difference is more like 1%.

There are a lot of other less costly ways of getting a 2wd truck. Sell your Cruiser. You could get a Corolla beater and save a bundle.

 

[StucknKS]

OP, regardless of whether or not you increase mpg or save wear and tear, you said that the CDL light was removed? Or was the switch and the light removed?

Never mind. Just re read it and I believe you are saying the CDL light is on and the switch is removed.

Get a switch. Put the drive shaft in and don't worry about the mpg or wear and tear.

BTW - I hate auto correct. 3 edits to get the words right.

 

[chrisdecker]

alright, thanks for all the input guys. as soon as I get a switch the driveshaft will be right back on, after I check fluids and such. any pointers on that process?

 

[StucknKS]

There are several good threads in the faq on doing a baseline on your rig. That is where I started. You might look into your front axle to try and determine if you need to service it (FAQ has some good info on the subject).