How critical is setting the preload really

[unspankable]

Hello I just had my Ford dealership install a wave trac differential and even though I provided them with every single shim size available, the mechanic assigned to my car just decide to throw it in there so it's currently installed with a stock shim in.
I would never have Ford install this part normally but it was in for warranty work on the third gear synchro so while the bell housing was out of the vehicle I figured it would be a good time to do it.
How critical is this actually because I read differing opinions.
Has anyone installed a wave trac without correct preload and if so how's it going.
For the ones that have done it correctly I'm seeing that usually a .03 is required which means my current preload would be .02 too tight.

 

[scooter123]

I would suggest a call to Wavetrac. Because they will know exactly how critical this is and how much damage can result if it's not installed properly. Personally my hunch is that you'll probably burn it out in under 10K miles but that is just a guess. If you hear any new whining noises from the transmission that is a sign it's already been damaged. Folks who write installation instructions because they are in the mood to write some unimportant fiction, they do it to insure the customer has the means to get the job done correctly.

 

[foodtruck]

Wow, your Ford dealership agreed to install an aftermarket diff? I actually wanted mine to install it because I figured they would go through all the preload measuring steps properly but they wouldn't touch the diff with a ten foot pole for warranty reasons I guess. How did you find out they just threw it in, did the tech tell you?

Did they also replace the bearings? FWIW, the shop that did my diff kept the bearings and they reused the same shim as well (although I got Quaife, not Wavetrac). I've also seen a few discussions which reasoned that the diff itself is likely machined to true spec and the shim is really there to compensate for case manufacturing tolerances, so if you kept the same case and bearings, there's a good chance that you'll be okay.

 

[unspankable]

Wow, your Ford dealership agreed to install an aftermarket diff? I actually wanted mine to install it because I figured they would go through all the preload measuring steps properly but they wouldn't touch the diff with a ten foot pole for warranty reasons I guess. How did you find out they just threw it in, did the tech tell you?

Did they also replace the bearings? FWIW, the shop that did my diff kept the bearings and they reused the same shim as well (although my diff is Quaife, not Wavetrac). I've also seen a few discussions which reasoned that the diff itself is likely machined to true spec and the shim is really there to compensate for case manufacturing tolerances, so if you kept the same case and bearings, there's a good chance that you'll be okay.

Yeah I provided the differential, the bearings, seals, ring gear bolts, all the various shim sizes and the ford performance install instructions, which unfortunately don't mention anything about preload but I figured they would know what they were doing. Fml
I'm reading that most of the quaife & mfactory diffs end up requiring the stock shim once float is calculated. Unfortunately it looks like the wave trac needs a smaller shim than stock so mine is probably .02mm too tight.
The transaxle is already in and they said it would cost 5 hours to pull out and redo and that I should have told them that they need to shim it.

 

[foodtruck]

Not sure where this info is from but https://www.fiestastforum.com/threads/differential-pre-load-shim-size-up-or-down.24876/#post-419591

Most have said the 0.05mm-0.06mm difference wouldn't have a noticeable impact, and I would probably be fine either way.

If the transmission is already in, might as well try driving it around and see how it feels. If there's something grossly off I think you'll feel it, at worst you might need to open it up and get new bearings, at which point you can insure the correct shim is in, it would be the same 5 hours.

 

[unspankable]

Appreciate the input man. Just keep my fingers crossed.
I called wavetrac and they said "we don't do the installations, we just manufacture the differential, and as the manufacturer of the differential we're supposed to tell you to take it out and do it properly because you could do a lot more damage if you don't. - If you don't want to do the extra work to pull the whole thing and do it over confirm that with somebody with a lot of ib6 specific knowledge and then go from there.

Not sure where this info is from but https://www.fiestastforum.com/threads/differential-pre-load-shim-size-up-or-down.24876/#post-419591


If the transmission is already in, might as well try driving it around and see how it feels. If there's something grossly off I think you'll feel it, at worst you might need to open it up and get new bearings, at which point you can insure the correct shim is in, it would be the same 5 hours.

 

[foodtruck]

Hm, so before taking the whole thing out again, if they haven't put the half axles back in, wouldn't they still be able to at least check the preload by pushing into the diff from one side, zeroing the gauge, and then pushing into it from the other side? I figure they just need to take the seals out?

 

[unspankable]

Fyi to anyone needing this. They pulled the transmission and checked preload. Stock shim was correct in this instance.