Need some help here guys. I currently have a 9.75" open rear end now. I am thinking about swapping to 4.10 gears though. I was thinking about going to a junk yard and getting a complete 8.8 limited slip axle....this way i wouldn't have to buy the LS diff and i would also my stock axle in case something went wrong. My question is: Will the 8.8 bolt right up to the truck with no exchanges? I am worried that i will have to buy a new drive shaft for one thing. Will I? Another reason i am thinking about getting an 8.8 axle for the swap is that I can get cheaper prices on parts and a cheaper price on the install. Does anyone have any insight on this? Are there any differences with drive shaft, U bolts, or anything else between a truck with a 9.75 instead of an 8.8??

justin hart

 

Look it is your truck and you can do what you want but why on earth would you want to go to an inferior axle to supposedly save a few bucks? The money you are going to spend on buying a 8.8 and having it installed I would bet will end up costing you more than just buying the gears you want and having them insatlled in the 9.75. Your truck came with the 9.75 becasue it is better able to handle the HP and Torque of the 5.4 engine. Stick with what you have and spend the m oney buying a LS for it or just forget about it. But like i said it is your truck but this is something I myself would not even think of.

Richard D.

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

 

Richard D..... i appreciate your concern and you do have a valid point. I just feel with my schedule, money, and warrenty issue that i "might" be better off buy a whole other axle and just swaping the two out. I'm not saying that that is what i am going to do. Its just a thought for now. BUT i do have a question for you: I see you have an aftermarket throttle body on your truck. Could you tell any difference in performance with the install??


I am just curious as to what other things would also have to be replaced if i changed from a 9.75 to an 8.8? Any help or input is appreciated.

justin

 

Well you're going to have to find an 8.8 with disk brakes not drums. Otherwise all the spring perchs will be in the right place as well as shock mounts so you don't have to move them. The driveshaft flanges should be the same between the 2 axles so yes it should be basically a direct bolt in. But I'd go along with Richard D, there is a reason that Ford put a 9.75 behind the 5.4L. Some of the early F150s had an 8.8 behind a 5.4L and they couldn't hold up to them. I'd rethink your axle idea, either gear the axle you have or find another 9.75, I mean its not like its hard to find and not like its tons more money than an 8.8 with the same setup.

 

Justin,

I did the opposite. I went from an 8.8 LS to a 9.75 LS. Did you price out the 8.8? They are not cheap. For $600.00 I picked up a brand new, was sitting in a warehouse since 2000, 9.75 LS w/3.55 gears. I destroyed 3. 8.8s before I wised up and switched. Regardless if you choose to go to an 8.8 you will have to get a longer drive shaft. The distance from the pinion flange to the slipe yoke is different. The 9.75 is a bigger diff so it uses a shorter driveshaft.

Regards

Jean Marc Chartier

 

i definitely didn't want to change drive shafts so there goes that idea. I may look more into buying another 9.75 that already has the LS but more than likely i will do the swap with the rear end I have now. Thanks for the help though.

justin

 

Justin,

Yes i do have a larger TB and the improvement in throttle response is a minor improvement over stock it is nothing that is extremely noticeable I beleive when I finally upgrade toa FIPK of some sort it will perform better however. But my priorities on upgrade mods has not been for a FIPK there are other things I wanted to upgrade first. That will. however probably be my next upgrade and I will either go with a AEM or the AIRFORCE ONE not sure exactly I have heard that the AEM and AF1 give the best peformance out of the ones that are available.JMC I thyink you have used a couple of them what do you think about the FIPK's?

Richard D.

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

 

Richard,

IMHO they are all the same just different paint I made my own. http://www3.sympatico.ca/jmc.chartier/air1.html

I have a question for you. Did you match the TB to the elbow? If you did not you have a 75mm TB feeding into a 70mm hole. That leaves a 2.5mm ring around the TB flange that is flat and will cause some seroius terbulance going into the elbow.

JMC

 

You don't have to get a new driveshaft, you can have yours shortened. A good driveshaft shop would charge around $100 for this.

 

svt,

If you go from a 9.75 to an 8.8 you will need a longer drive shaft. I went the opposite so I had about 1¼ inch taken off.

JMC