CL fam I need your help with a problem I’ve encountered with my Cusco Differential a few months after installation. So I just bought back my very first ISF (2008 SFP) I sold to a buddy years ago. Back in August or so, my friend installed a Cusco differential and a CF driveshaft. The Cusco diff was purchased from another member that bought it brand new from RR Racing.

Of course, the disk chatter was present but not loud at all but everything else was fine. Fast forward a few months, around November time frame, the car started to make a loud grinding/binding type of sound while turning left or right at low speeds. Along with the grinding/binding, we noticed the rear wheels felt like they were hopping as if the rims were flat. The only thing I could relate the feeling to was if a car that’s been sitting for a really long time as if the tires have a flat spot. During the time of the installation obviously we filled the diff with Cusco fluids and rebuilt the axels while they were out.

So, things I’ve done to try to troubleshoot the problem. Remind you, I not very mechanically inclined lol (no, I didn’t install the diff, we had it professionally installed by a well known import car mechanic).

Drained the diff and filled with Cusco along with friction prevention fluid that Rafi recommended.

Inspected and rebalanced wheels and tires.

Inspected and verified axles are operating as normal.

Inspected and verified rear hubs are operating as normal.

Can anyone provide info or opinions of what could be causing the rear wheels to hop. I know that the Cusco diff is tunable, however it was fine for a few months and all of sudden we have problems. Shoot it may not be a diff problem for all I know lol.

Any help would be greatly appreciated.

 

Could be diff bushings or rear suspension arm bushings. Or even bushings/bearings in the rear knuckles.

 

I recall reading the Cusco needs fluid changes more often. How many miles has the diff been in?

 

Thank you, I will definitely take a look at those bushings. I wonder how hard it would be to replace them? Hopefully there’s some DIY’s or previous write ups to help guide me.

 

From my understanding, the previous owner put 3k miles, maybe less.

From the time it was shipped to us and installed, we put maybe 2k miles. Within the 2k miles, the fluid was changed twice.

 

The by the book usually recommends a press system to slide them out..

Mine got whacked out with a bearing sized perfectly..!!



Old / aged 2008 diff mounts..



Removed / cut out



Install


Installed new RC F - units L & R


Installed new RC F - units L & R

Joe Z

 

Mine came out with an air chisel. Took seconds to complete.

 

Thank everyone for all the info.

Im taking the car to a shop that professionally rebuilds differentials and driveshafts. I’ll have them flush and fill the diff and check out the bushings. As soon as I get confirmation the bushings are the problem, I’ll place an order with figs (hopefully they have the bushings in stock).

meanwhile, I’ll take a torque wrench to all the suspension components in the rear and check torque specs.

 

That's a normal characteristic of a RACE LSD.

Bushings will change nothing, my entire chassis is from FIGs.

You're hearing the LSD doing what's it's designed to do- lock the rear wheels. This is why you add friction modifier - to allow a small percentage of slip.

You can try restacking the clutches for less lockup.
I'll attach a picture of my restacked Cusco RS to 60% lockup. I've yet to swap it back into the car to confirm it helps, but in theory it should help significantly.

Note the plates order.

 

Thankfully the OS Giken TCD for the IS F is nothing like this. Install, run. No chatter, just both wheels working. Change the oil every 20k miles.