'18 3.73 PP Diff whine

[HourlyB]

Just by the noise. They will look fine if taken out and inspected.

This is most likely what happened, assuming they were quiet before the pinion swap.

Damn.

I'll have to see if I can swing it so they repair it, but I don't have much in the way of evidence that it wasn't like this before. Only that the pinion swap might've ruined the ring/pinion alignment and the person who sold it reported no noise.

Not looking great.

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[andrewtac]

Shop said wear pattern was pretty far off, don't remember which direction. Hopefully have an update by tomorrow if the noise is gone.

 

[HourlyB]

So something else I've been noticing is that the noise gets a lot louder when the car is going downhill and the throttle is lifting off. Don't know if that means anything, just something I noticed.

 

[andrewtac]

New gear, still whines. Sorry hoped to have a solution for you.

 

[K4fxd]

New gear, still whines. Sorry hoped to have a solution for you.

Are you working on the OP's car?

 

[andrewtac]

Are you working on the OP's car?

Nope, similar issue (have a different thread). Had new gear, bearings, etc installed. Figured it would give OP something to work with if it fixed it for me.

 

[K4fxd]

What ratio are you running? What brand of gears?

 

[HourlyB]

New second whining noise. Similar ""tone"", in fact it seems to resonate with the original one. While the original one goes away when shifted out of gear, this one stays.

To me, that seems like it might be the bearings. Which are new.

 

[HourlyB]

New gear, still whines. Sorry hoped to have a solution for you.

Honestly with how this swap has gone, I fully expect something like that to be the case.

 

[HourlyB]

So, got a new set of gears, but I've been wondering a couple things;

The first is what is the most amount of damage could I be doing driving on this diff? Would I be risking ruining the bearings that got put in? Because there is definitely still vibration in the driveline, I can feel it.

The second is how to fix this throttle, it's gotten unsafe at this point. I have a OBD FORScan tool so I can change the gear ratio value (change 0726-12-01 to 0175) and then do a KAM reset until I get a actual tune. Is that pretty much all I can do?

 

[krishelnino]

@HourlyB, @andrewtac I was trying to swap to a 3.73 Torsen diff on my 2018 GT last weekend and the whole process has been a nightmare.

Story:
I got a used 3.73 PP Torsen diff out of a 2019 GT last year from a reputed take off car parts store for $700. The diff looked good, just like new. After I got it, it was just sitting for more than a year and never got around to installing it mainly because I was lazy lol. I finally decided to do the swap last Saturday

Day 1: I took my old 3.55 diff out and compared it to the PP diff I got, I noticed a lot of play in the pinion flange. I wasn't sure if it was normal and with hesitation, I put in the new one and filled with BG 75w90 fluid. Immediately after I started driving around the block, the driveshaft was making lot of noise. I realized something was wrong with the diff so just parked the car and decided not to drive to risk further damage. This was after 8 hours of work between me and my friend in his garage. I noticed the diff was leaking from the pinion flange after parking the car

Day 2: I found another 3.73 Torsen diff in local Mustang group who said it was out of a Bullitt with about 1k miles. I did a 3 hour round trip in the morning to get the diff. So in the afternoon, I again start pulling everything apart, mounted it and realize the driveshaft wasn't bolting on to this one. I did some research and still couldn't understand why the driveshaft wasn't lining up to the flange. When picking up the guy said the diff was stock and he didn't do anything to it. So I asked the guy I bought it from, and to my surprise, he then tells me that he swapped the pinion flange to a 15-17. I was so pissed at this point, because he never told me until I asked him. He then proceeds to tell me pinion flange swap isn't a big deal, advises to use impact to remove the nut and pry the flanges off, and then use impact again to send it home. I know this isn't the right way to do it, so with huge disappointment put the old 3.55 diff back in again. This is my DD and can't afford downtime. I just couldn't believe my cursed luck.

Now, since both the differentials that I got are literally useless, I'm thinking to take one of the differentials to a shop to rebuild the whole thing and also have them install 4.09 gears at the same time I'm ordering these parts

M-4209-88409A
M-4210-B3
M-4413-B

I hope 3rd time is the charm lol and will let you know how it goes this time.

 

[shogun32]

@HourlyB, @andrewtac I was trying to swap to a 3.73 Torsen diff on my 2018 GT last weekend and the whole process has been a nightmare.

ouch. at least now you can take the 1st 3.73 apart learn how to build a 4.09 setup. The gears are 'cheap' though require a rebuild/shim kit.

 

[krishelnino]

ouch. at least now you can take the 1st 3.73 apart learn how to build a 4.09 setup. The gears are 'cheap' though require a rebuild/shim kit.

Yeah I don't have the knowledge to do this, so just letting a shop do the gear and pinion install

 

[WildHorse]

To me, that seems like it might be the bearings. Which are new.

The coast side preload is out of spec. I installed a set of FORD PERFORMANCE 3.73 into my 8.8. I paid particular attention to the coast side. No noises for 3500 miles now. Tell whoever installed them to get it right.

 

[HourlyB]

The coast side preload is out of spec. I installed a set of FORD PERFORMANCE 3.73 into my 8.8. I paid particular attention to the coast side. No noises for 3500bearings miles now. Tell whoever installed them to get it right.

I'll get that checked/make sure that it is in spec, but I've already bought a new set of gears, bearings and a install kit.
At this point it's pretty close to a total replacement.

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