My mother has a 1999 Crown Victoria with 125,000 miles on it. Sometimes when it goes into overdrive it will "shudder". The guy at Ford told me to change the fluid to synthetic and add a 4 oz. bottle of limtied slip friction modifier. He told me that it will let the clutches grab harder. Would this be something good to put in my Lightning? I have the Mercron/Dexron 3 fluid in it now and I am not sure if its synthetic or not. Should I change it to the new synthetic Mercron 5 like I put in the Crown vic, or stay with the 3? Thanks!

 

Ummm, friction modifiers are for rear ends. DO NOT put it in your transmission. :santa:

 

Mercon 5 is NOT made for our transmissions - do NOT use that - they are two different transmissions.
As usual, most ford techs who do not work on Lightnings do not know what the hell they are talking about!

 

Well, he did not say put it in my Lightning. So I should just stay with the regular Motorcraft Mercron Dexron 3?

 

for the tranny, YES: use Dexron III / MERCON (not the Mercon V)
for the differential, YES: use the friction additive (to be 100% sure, you must check the tag in your diff cover and write the numbers down.

Then call your local FORD service shop: pretend to ask the price for diff fluid change and have the numbers from the tag ready. They need this to check what weight your diff needs and if an additive is needed or not). Got this from a Ford Tech neighbor.

 

Guess I'm the only one that doesn't use friction modifier; what have I figured out that others havn't

 

let me shed some insight. I just had my axle seal replaced. I would not go by the diff cover label. In the svt book, it says to use 80w-90 (trying to remember off top of my head) and the diff cover says to use 75w-140. Keep in mind that the L rear end housing is also used on reg f-150s. Going by the SVT Supp book, use the 80w-90 and 4oz of additive. For the trannies, never use anything other than mercon 3.

 

Unless your ROB02.

 

SVTinVA
Thanks for the info

 

Thanks for the helpfull post a-hole! Nothing like helping out your Lightning brothers!

 

You guys might want to review this website before adding addatives

http://www.bobistheoilguy.com/

 

The additive is used to make the clutches SLIP, not grab. Not using it will make your launches (in a straight line) better, but it will not corner as well.

Ya pays ya money and ya takes ya choices.

 

if our rears do call for the additive, make sure to use the Ford recommended brand vs some off the shelf stuff. i found out with my F-body to only use GM's limited slip additive. i changed my gear oil in that car using off the shelf limited slip stuff I found at Advance Auto or Autozone and it immediately started acting up on tight turns and back up, etc... drained it and put in GM's limited slip and problem immediately solved. not sure what the difference is in the fluids, or if that knowledge carries over to these ford rears, but just wanted to note this to avoid any similar headaches for anyone else.

 

the additive is put in to keep the clutches form chattering in turns.The clutch pack will hold ALOT better if you leave the additive out.clutch wear is up to how you drive.But if you want both wheels driving longer[bias] in turns and different friction amounts between the wheel[ie icey surface on one wheel and wet on the other] without the additive it will lock harder.Stan

 

Nice to see some things have changed; last time I said something in a post about the addative everybody jumped all over me for saying to leave it out.

Only side effect I've had is yes mine will tried to "pop" or "chatter" in a parking lot tight turn. But, it will lock and leave 2 black marks anywhere I want

Not bad for 600+ passes on the stock rear diff