Has anyone here used a Fel-Pro gasket on the rear diff.? The dealer told to just use RTV Silicone it would be fine. But a Fel-Pro gasket would be better, wouldn`t it??? And how much silicone would I need to use with it?
Lariat#1

 

Just use some RTV blue or black. Clean both mating surfaces with brake cleaner or acetone to remove all oil. Apply a 1/4" bead all the way around and mount back together. Wait about and hour or so for the RTV to cure and then add your diff oil.(don't forget the LS additive if applicable). Did this on my '91 aerostar when I first got it and went 100K before trading it in with no leaks or problems.

 

Yep the silicone is fine in fact that is what ford uses and recomends . Follow directions and you will be fine. As for gear oil I highly recomend Redline 75w90 Great stuff and it does not require Friction Modifier if you have a LS.

Richard D.

https://www.f150online.com/galleries....cfm?gnum=2479

 

I'd reccommend not going with that and using 75W140 which is what is the reccommended oil wieght for the rear diff. It also says it right on the diff too. Only problem with it is that since its full synthetic its around $14 a quart, but its what was specified from the factory.

 

I disagree Redline even recomends that you use the 75w90 not the 75w140NS You do not need the 75w140 NS all it takes is the Redline 75w90 in fact all the diffrential shops around here that i have talked to about it all use and recomned the 75w90. Go to redlines site yourself and read up on it. Maybe if you are going to go with some other brand you might want to think about the 75w140 but as far as the Redline products all you need is the 75w90. If You really want to stick witha 75w140 you may want to look into Royal Purples gear oil. But as far as he Redline goes 75w90 is fine.

Richard D.

 

I used Royal Purple 75W-140 along with the Ford friction modifier since it's L/S. I agree and would only use what is recommended unless your warranty is over. If something happen to the rear-end and you had the wrong weight in there, I would be willing to bet that Ford would say "sorry, no dice"

At the time I paid around $8 for the 75W-140 full synthetic.

I too only used RTV like Axel described, 1/4" bead all the way around. It works great and that is what Ford does from the factory. When I asked my dealer about a gasket they told me to just use RTV since that is how Ford puts them togeather.

 

also when you go to put the bolts back in put a little sealer on the threads to prevent any past thread leaks since some of the lower bolts are exposed to the back side of the flandge

 

Just to pass this on when i had a problem with my diffrential Shuddering when going around corners the LS was not releasing properly after changeing fluid to a Stalube Synthetic 75w140 with Ford Friction modifeir so I called Redline and they recommended the 75w90. They do not make a 75w140 however they do have a 80w140 which they said was not needed.I will however call them again Monday and see what they tell me this time but when i first went with the 75w90 it was on Redline's recomendation.I am jst passing on what i have been told by many Rear End shops and Redline.

Richard D.

 

When I did my diff I found a gasket at NAPA so I used that AND RTV when I switched over to Royal Purple which I also got at NAPA.

I also did my Mustang GT at the same time and wasn't able to find a gasket so I just went with the RTV.

I figure the gasket doesn't hurt, heh

 

Rear differential gasket (8.8) FelPro part # RDS55341 You can get it at Autozone for $5.49 plus tax.I use it plus just a slight touch of red RTV to make it tacky.I have had several Fords with 8.8 differentials and "always" used a gasket!

 

Hey 01,

You and I have the same year truck, any reason why you have changed the rearend oil already. I'm just curious.

 

I had a rear axle seal leaking on the pass. side about a year ago. I really wanted to put a different cover on it , a chrome one. So I got one from Ebay real cheap. Then I got all the stuff I needed to make the switch, new lube 3 x $ 15.00 a Qt. & fri. modifier $6.00 a 4 oz. bottle !!.
When I drained the rear diff. I was 2 pints low!!! So I`m glad now that did this. I used a gasket & brushed sealer to put on the chrome cover. Really L@@KS nice now , plus no silicone all over the place. SS bolts to bolt it up with. I hope this answers any questions.
Lariat#1

 

Well, yes this damn site...

I even did the manual transmission. You people are EVIL... LOL

I did it for just routine maintenance. I had no problems with it. I plan on doing the rear-end and manual transmission every 30,000 miles. Hey it's cheap insurance and you people are EVIL and addicting...

 

WOW what brand of Differential oil did you use that cost 15.00 a quart? I bought 5 quarts of Redline 75w140 today for 8.87 a quart and it does not require the Friction Modifier as it is already in the gear oil, I will be installing my Mag-Hytec diff. Cover tomorrow if it arrives early enough. Justa word about the Chrome Cover keep an eye on your fluid I have heard that Chrome covers tend to really heat up and not disapate the heat well. I do not know for sure this is just something people have past on to me over the years. I also change my Diff,Transfer case and transmission fluids every 30,000 miles

Richard D.

 

Just putting my 2 cents in. When you apply the sealer, make a bead completly Around each bolt hole. Could be overkill, but that's my nature. Good peace of mind.