front diff operation

[ddgts68]

Can someone explain/ point me to a video on how the front diff works on 99 xlt 5'4l 4wd? I did a search only find how to change fluid. I have the Haynes/ Chilton ( I don't remember which) manual and It explains how my f150 works (vacuum modulator on front diff) but it's not setup that way on exp!!

 

[toomanytoys]

Yes it is. It uses a push/pull vac operated solenoid to engage/disengage the front drive. Unless of course yours is awd. Then the front drive would be always engaged

 

[5starChad]

Yes it is. It uses a push/pull vac operated solenoid to engage/disengage the front drive. Unless of course yours is awd. Then the front drive would be always engaged

This is correct. The solenoids are on the passenger side firewall above the ECU.

 

[ddgts68]

I do not have the solenoids or any sort of vacuum operated push/ pull device. I do on my 97 f150. That's my question I don't have any of that. The switch in truck says A4wd/4hi/4lo. does that mean there is some sort of limited slip in the front diff?

 

[ogre20012001]

Your frond diff is always engaged.
It doesn’t have the disconnect like your f-150 has.


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[ddgts68]

Wouldn't there have to be some sort of slip or brake in the diff to be able to turn with out binding and such/

 

[and0r]

i seriously doubt the front diff would always be engaged, that doesn't sound right

 

[toomanytoys]

In a awd system the drive is split around 35/65 front rear. More drive is applied to the front wheels through the transfer case when rear wheel slip occurs. The front diff is always active hence no vacuum solenoid to engage or disengage

 

[5starChad]

Yea if you don't have the 2wd option on your switch it's always engaged. I didn't notice you had a 99. I believe only 97-98 had that.

 

[ddgts68]

Thanks, I was going to change fluid and don't know if I will need to add a modifier also.

 

[ddgts68]

Didn't now we had owners manual. Have control trac system. It does not say to add anything other 75/90 oil. Also does not say to add modifier to rear either!

 

[1955moose]

Friction additive is for rear differential. Most Expeditions use a limited slip rear differential that requires it, along with the proper weight and type. I believe short of finding it on the internet, the additive is dealer only purchase.

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[ddgts68]

Yea I put it in the rear diff, owners manual doesn't say to put in the rear diff either. Previous owner removed front driveshaft because of a front abs sensor going bad. Since I believe I fixed the shudder problem,(believe it had something to do with drive shaft) was going to reinstall front drive shaft after changing fluid.

 

[Plati]

http://www.strutmasters.com/v/vspfiles/SMPages/PDFTSB/LincolnNav97-02PDF/TSB05-23-3.pdf

 

[ddgts68]

Put shaft in today, had it on jacks and front diff would engage about 10 mph. Made all kinds of noise engaging and disengaging probably because it was in air ( no load). Has a slight vibration on deceleration and steering feels heavier but seems to be working. Now I need to find some dirt!

 

[1955moose]

Check your door sticker, if you have the limited slip then yes to the additive. If not then I'm assuming not. Anyone else want to comment on that.

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[ddgts68]

Didn't see anything about it on door sticker.

 

[1955moose]

Look at the tag on the rear differential, it will say 3L73 or whatever gear ratio it is. Being yours is a Awd setup, its very doubtful that it's not limited slip. If the tag doesn't have a L in-between the gear ratio, its standard, and not limited slip. Hope that helps.

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[ddgts68]

Yea I got the rear done and added the modifier. Was trying to figure out the front since I see no obvious sign of a break in the front axle. Didn't know if it had some sort of limited slip in it?