70 whine in rearend only when coasting

[Bob H.]

I think my rear was rebuilt during restoration. It has a bad whine only when coasting. Thought it was the trans (4 speed) but pretty sure it is the rear. No noise under acceleration and if I put the clutch in and coast, all is dead silent too. Any ideas? Thanks

[Gary R.]

Re: 70 whine in rearend only when coasting

Bob, a lot depends on the rebuild. Do you have any information from the build, pictures of the pattern, notes on the lash? Were the original gears reused or new gears installed? A bad pinion bearing or gear setup could be the cause of the whine but if new gears were used then it usually is setup or the gears.

Since most gears are 2 cut vs 5 cut today many have a gear whine about 50 mph letting off the gas. The last USA made gears were from US Gear, now gone about 3-4 years. They started printing a notice in their assembly sheets that a certain degree of noise is to be expected. That started when they changed the process.

Today, there are no more USA made gears. You can select from Chinese or Italian. Many places just rebox them and put their names on the box. One place is selling what I would consider "2nds" and make note of the fact they don't meet the inspection QC standards of the company they were made for.

No oil or additive is going to change a gear whine. If they are new gears and setup wrong and you have driven it for some time, chances are they are not going to change if you were to take it apart and wanted to reshim it.

Brings to mind one of the last sets of USA made Richmond gears I set up about 10 years ago for a local kid. I had a textbook perfect pattern, lash perfect, hand rotation and mesh were good. Yet as soon as he installed the diff it was howling and not in the 50-mph range, but all ranges and loud. I checked it and everything was as I set it up. I removed the Richmond gears and installed new Tom's (US Gear) and set it up the same way and had no noise.

Lastly, it also depends on who did the work. I have repaired the work of probably every vendor you can think of over the years. While I am not naming names many would be surprised if I did and have the pictures to back it up. I would be concerned if you used some shops or individuals from some of the Southern states.

[Bob H.]

Re: 70 whine in rearend only when coasting

Thank you Gary. It was done almost 10 years ago with 3k miles since. Hopefully some US parts. I have no idea who did the build or even for sure it was done. Likely though since every other bolt was touched. I will follow up once I decide to mess with it. Thanks again. I may just put the top down and turn up the radio!

[Gary R.]

Re: 70 whine in rearend only when coasting

well that is certainly an option. I doubt it will lock up. If you do decide at some point to take it out of the car let me know and I can give you some tips on what to check

[Mark E.]

Re: 70 whine in rearend only when coasting

Gary,

You said changing oil and additives won't help. Given Bob's description of the problem are you confident there's virtually no chance this will help?

You're the expert, not me, but I'm asking because changing the oil is quick and low-cost, so may be worth a try if there's even small chance that changing 10 year old oil will reduce noise a bit.

Bob,

You said you're "pretty sure" it's not the transmission or something else. I would make sure what's causing the noise before tearing into it.

[Gary R.]

Re: 70 whine in rearend only when coasting

Hi Mark
If the issues is indeed a gear setup or machining issue, then oil will not change that. It doesn't sound like a posi chatter issue where an oil and additive change will make a difference. Given there is only 3k miles on the diff I don't expect that will make a diff.

If new gears were used, then heat cycling is required.

From Bob's description it sounds like set up or gears. However, Bob, if you want to change the oil give it a shot.

I installed a set of 336's in my '72 17 years ago and had the same issue. I called Lucas to see what they had or could recommend. The guy told me to try the gear oil supplement and it would quiet it down. It didn't make a difference and after 800 miles I pulled the diff and replaced the gears.

[David M.]

Re: 70 whine in rearend only when coasting

Run a magnet into the fill and dredge the bottom and see how much metal you come out with.
Deceleration whine is either gear lash or pinion bearings. Grab the pinion yoke and see if it has up/down play.