3.73 switch to 3.55 noise

[cfriedman67]

Earlier this summer I had my gears switched from 3.73 to 3.55 in my roadster with a coyote gen3 and TKO 500 transmission. When I ever I take my foot of the gas pedal the engine/transmission or axle makes a whining sound. Once you touch the gas pedal in the slightest way it goes away. I assume it is the load being taken off the transmission or axle? Do I need to add another shim or is it some other problem. As far as I can tell the car shifts perfectly besides the whine. Also, the car makes the same noise if in neutral when coasting to a stop.

Thanks
Craig

[Railroad]

It is the axle gears. What did your tooth pattern look like? Most of the time you can get by with the same shims if using Ford brand gears.
The coast side pattern is off. You can check your pinion preload without taking anything apart. Make sure you do not have any play front to rear in the pinion.
A pry bar on the pinion flange or yoke will confirm it for you.
good luck,

[narly1]

Obvious question maybe, but I like to eliminate the simple things first.

Did you remember to replace the diff oil and add friction modifier?

Earl

[cfriedman67]

Yes, replaced the diff oil and added friction modifier.

[cfriedman67]

to be honest a friend who is a retired mechanic did most if not all the work. When he showed it to me it looked good. I'm pretty sure we used new shims and not necessarily ford.

[rich grsc]

Obvious question maybe, but I like to eliminate the simple things first.

Did you remember to replace the diff oil and add friction modifier?

Earl
Friction modifier is for the clutch packs in the limited slip differential, nothing to do with gear whine. Back lash is just off a bit

[edwardb]

Regular Trac-Lok or Torsen? I've the 3.73 Torsen in our Gen 3 Coupe and it does make a little noise compared to the Trac-Lok's we've had before. The Mustang guys say the same thing. Keep in mind that diff is is just past your RH elbow. Doesn't take much for it to be noticeable.

[tonywy]

In this case I don't think the ratio has anything to do with it. I would want to see what specs were used to set your gears up. If Ford Gears were used 99% of the time you would just use the old shims. There is a rule of thumb, if you hear noise on acceleration it's the rear pinion bearing, if you hear noise on deceleration it's the front bearing (small bearing). I would verify the pinion preload. All these specs are on the Ford Motorsport website.

[cfriedman67]

The car transmission/axle was dead silent before I made the switch. It is a Trac Lok.

[cfriedman67]

They were Ford performance gears that I purchased. I bought I new shim kit and used those as well.

[Railroad]

There is usually a shim under the pinion bearing. If you had to install the bearing on the shaft, which is the case on new gears, you have to make sure and get the shim off the old pinion shaft.
If you are running syn lube, regular gear oil might quieten it. If you do not have a bottom drain plug, it might be a lot of work.

[Jacob McCrea]

I'd remove the differential cover and check the pattern, the backlash, and (using the same dial indicator) whether there's side to side movement in the carrier, and post photos here. Also, there is a Ford factory instruction manual floating around on the internet that describes the setup process very well.

For what it's worth: You may have the backlash appearing to be "right," but need to shim both sides of the ring gear carrier a little tighter to get slight preload on those bearings - otherwise the carrier can move laterally and screw up a backlash setting that looks to be in spec sitting still, but is wrong under acceleration or deceleration. If there's any side to side movement in the ring gear carrier, that play needs to be removed.

By the way, is this a solid axle or IRS, and if IRS, is it an aluminum or iron case? I ask because the old aluminum 8.8 IRS diffs were said to need a case spreader to put preload on the carrier bearings. Hope this helps.

[cfriedman67]

Hi Jacob,

It's an 8.8 solid axle. All the comments and suggestions help. Just more knowledge to get it corrected.