Gear whine and vibration

[Pedigry]

Hey guys,

Just got done with a 20 hour round trip run to Tail of the Dragon and back. Great trip. Lost a fuel pump in Georgia, was fortunate enough to be close to Summit so I was able to get one and swap it out road side, other than that, great trip.

I noticed the car developing a pretty good whine in the rear end on deceleration. I just swapped to a newer Ridetech 4 link and have read that they are pretty notorious for transferring sound into the car with the new ends on the heim joints. Interesting enough, it's only on decel and coasting. As soon as i load the rear end with either a hill or power, the whine goes away. I am wondering if it's the back side of the ring gear that's worn and not just the 4 link transferring noise.

I also have a vibration in the rear at the same time, on slight decel or nuetral throttle. Not 100% sure they are connected but they happen at the same time. I spoke with Currie this morning and they said it could be either too much end gap in the ring and pinion or potentially the axle bearings are shot. I am going to get home tonight and check end play on the axles and make sure I have the correct retainer plate on the axles. Currently the pinion angle matches the engine at 3.5 degrees (up/down).

Any help is appreciated. What do you think?

[dontlifttoshift]

You need to figure out the working angles on the U joints.

Make sure the pinion nut is tight.

[streetk14]

I just put one of these 4 links in my car, and I don’t think there’s any way around hearing some gear noise with it. Unfortunately, I did a new third member at the same time, so I wasn’t able to do a direct comparison from my DSE leaf spring setup.

The first new third member from Quick Performance was really loud at steady freeway speeds, and also had a decel whine at lower speeds. They built me another one and tested it prior to shipping it to me, and I’m pretty happy with it. There’s still some slight whine in certain speed ranges, but I’m accepting that as a combination of the aftermarket gears on the market today, along with the R-joints amplifying everything.

My car is smooth with no vibration though. Like Donny said, make sure your working angles are good. You want them less than 3 degrees ideally, and less than a degree apart.

[Z06vet]

Ideally you'd like to have the engine/trans at 3 degrees or less. Raise the trans tailshaft as high as possible using shims under the mount. If your driveshaft is sloping upwards towards the rear pinion, you need to lower the pinion angle so that the driveshaft is at least .5 down to the pinion at ride height. I've built over 20 f bodies- and the lowered 4 link cars always end up with the rear pinion close to zero degrees- give or take .5 deg. If the driveshaft is sloping up towards the rear pinion, it creates nasty working angles. Load the Tremec app on your phone, and test all your angles- engine/trans, driveshaft, pinion- into the app. One the gear whine, that likely is from the quality of today's aftermarket gearsets. Gearfx has been by far the best at quiet setups. Their new 8.8 ford gear option for the 9" carrier has got to be the go to for quiet operation, using a ford motorsports gearset.

[dontlifttoshift]

I somehow missed that product release, thanks for bringing it up. https://www.holley.com/blog/post/rear-end_game_changer_new_8_8-inch_dropout_case/

[dhutton]

Yes that looks great.

https://www.detroitspeed.com/products/rear_axle/assembled_center_sections/

[Hotwire]

Stupid question... have you checked the rear fluid level?

[Pedigry]

Hey guys,

Thanks for the replys. The engine is 3.5 degrees down, the rear end is 3.5 degrees up. The driveshaft slopes down, not up. I will get the working angle this weekend. I can't raise the transmission anymore because i have a gear vendors strapped to the back of it and it's already 1/4" away from the tunnel so it's limiting my angle. I'll check the oil for sure. The guy at Currie suggested I run 85/140 in it. I think it's got 90 synthetic, as per the previous owner. Currie suggested NON synthetic CE 9015 (85/140) so I'm going to swap that out this weekend and see if it makes a difference.

Interesting that you had a loud third member and then sent it back, they replaced it and now it's better. That tells me that the back lash is affecting the whine. That, or the contact patch wasn't very good on the first one.

As far as the pinion nut goes. Doesn't that go up against a crush washer? If so, I can't just hit it with a impact wrench, at least that was my understanding, I could be wrong.

My third member was set up from Currie with 3.75 gears. They do everything in house including the back lash and contact patch engineering. So I'm assuming that it is correct but the truth is, I bought this car used. I have no idea what type of abuse or how many hard miles are on the rear end so it may just be worn out. After reading a little on rear end noise, I have found that if the noise is under excelleration, the front of the ring gear is potentially worn, if it's on decel, the back, which makes sense.

I'll start with swapping out the rear end oil this weekend, see if that makes a difference. If not, then potentially I could get a rebuild kit for it and swap out the ring and pinion and see if that makes a difference. If not, then I guess I am stuck with the whine.

The guy at Currie did say that he gets calls about the cradle/4 link install and the noise they create. On framed cars, the body is isolated from the noise, but on unibody cars like mine, especially after the cradle gets boldted/welded into the rear seat area, it acts like a big amplifier and runs the sound directly into the car. It makes complete sense. But I would like to eliminate it if possible. I will also get the working angle of the driveshaft and get back with you. I have been told only relational angles between the engine and third member are important, but people go back and forth on working angle importance so I will check it. I know i get a pretty good vibration at low load cruise and slight decel, but full decel or accell is smooth as silk. I basically have learned to drive through it but it's a pain in the neck.

[streetk14]

Yeah, the backlash seemed excessive on my first third member. Gear pattern definitely wasn’t great. The second one was quieter, but not silent. The gear pattern on the 2nd one also wasn’t ideal, but it looked to be variation in the gear itself. Meaning there has to be a compromise in how it’s set up, unfortunately. That’s the aftermarket gear problem that’s been seeming to affect the 9” builds these days.

Wish I’d known about the 8.8 solution from DSE, but I still don’t think they’re available. I’m happy enough with my noise level now that I probably won’t mess with it.

[Pedigry]

Andy,

I have read there are a number of companies that are making "quieter" 9" ring gear sets. "stealth" was one of them, I'll have to look for the rest. I'm not expecting silent, especially with the ridetech cage mounted to the body. That and the hiem joints, even though they have a poly bushing set, are going to transfer more harmonics than the old larger rubber press-in bushings. But if there is an improvement to be had, I would like to get it done. Especially if I either have excessive backlash or wear on the ring gear. Guess I'm going to have to pull it and get a pattern on it. There is always something to do on these cars...

[streetk14]

The Stealth gears are no longer in production. I guess US Gear got bought out, and the new owners dropped that from the line. I know QP has some stashed away, but I don’t know if they’ll sell them. They offered me a 3.89 set for $500 if I wanted it, but I think this was only because I bought my third member from them and was concerned with noise.

QP has a test rig with a bunch of decibel meters they use to test third members in situations like mine. They assured me my replacement would be quiet. I feel like it could maybe be better, but I’m pretty satisfied. I don’t think I’d hear mine at all with a stock rear suspension. I know Gear FX has a dyno where they test them too. I’d imagine Currie has one as well, but I’m not sure if they’ll be willing to test yours in the name of customer service. I have to hand it to QP; they really did go above and beyond for me.

[Pedigry]

Andy,

When I called Currie, they offerred to put it on the dyno for me, I believe they quoted me $350 to do it. They would also check backlash and wear pattern. If it was out of spec, they would fix it for me but they didn't say how much. I'm sure it won't be cheap. I would also have to buy a third member shipping case and ship it to them and then back to me. They only offer fixes for their own product, outside of that, they only sell complete third members.

I'll go to quick performance page and take a look at what they have. I don't know if they have a rebuild kit or not. I have watched some videos, I would be comfortable rebuilding mine. I have to change the fluid, it has 80/90 synthetic and Currie suggests 85/140 non synthetic. I'm going to swap it out this weekend. I will pull it, do a pattern test and check backlash to see where it's at. If it's in spec and good, I'll change the oil and maybe just live with the noise. It's not terrible, just louder than I think it should be.

For those that have rebuilt rear ends. Did you change the diff as well or just the ring and pinion and reuse the diff? I have a trutrack in it, I am assuming I can reuse it. They say it's not a "rebuildable" unit but I have seen videos of guys doing it. I think Eaton just wants you to buy a new one and swap it. But I don't want to buy one if I don't have to. It works great so there is no issue. I just didn't know if it was normal to swap the diff at the same time as changing the ring and pinion.

I also may order a set of axle bearings just because. Currie said they can be the culprit of rear end vibration. Figured it was an easy thing to swap out if I have the rear end out anyway.

[streetk14]

I’d like to think they’d fix it for free if they built it and it’s out of spec, but I don’t have any recent experience with Currie. They only built my housing and axles. I’d probably want someone very experienced setting up my gears. Not saying you won’t be able to handle it, but do you really want to be learning on the job in this situation?

[Pedigry]

I’d like to think they’d fix it for free if they built it and it’s out of spec, but I don’t have any recent experience with Currie. They only built my housing and axles. I’d probably want someone very experienced setting up my gears. Not saying you won’t be able to handle it, but do you really want to be learning on the job in this situation?

lol, your right. Though that seems like the story of my life. I continue to quote Jeremy Clarkson on these types of things, "How hard can it be"? The truth is, I am pretty mechanically inclined, have build motorcycles from the frame up, restored cars, built boats, etc. So I am not too concerned. Youtube has some really in-depth videos on rear end setup. Backlash and pattern are the two major components. Before I took it apart, I really just wanted to check backlash and pattern. Both of those things can be checked without taking anything apart. I can pull the third member, check the pattern with paint and check the backlash with the caliper. If both are in spec, then I would just put it back in the car. At that point, maybe look into the "quieter" gear setups that are available.

I didn't have a chance to change the oil, but I got the 85/140 non synthetic in from Summit that Currie suggested so that may cure it the noise issue. There is a big difference between 80/90 and 85/140. I would think that the 140 would help quiet the gear noise down by the sheer thickness of the oil, we will see. I will try and get it swapped out in the next couple days and give an update. Thanks for all your input. It's always hard to know how much noise other people are dealing with and whether it's "normal" or "acceptable" or not. I just don't have anything to compare it to.

And you might be right about Currie, I will give them a call back to see if they would fix it for free if it were out of spec. If that was the case, the shipping and dyno charge would be worth it.

[streetk14]

I do pretty much everything myself, including ECU tuning and wheel alignments, but setting up gears is something I leave to someone else. That and exhaust fabrication, as welding stainless steel takes some me skills I don’t have.

It’s worth checking the pattern and backlash yourself for sure. I don’t think the oil will make a difference as far as the noise is concerned, but you can give it a shot.

[Pedigry]

Update: So I swapped the diff oil last night, it did seem to make a noticable difference. 85/140 is THICK. It pours out like syrup. It makes sense that it might quite the gears down since it's creating more cushion than a 80/90. I will get some more miles on it and see how it goes. But for now, the whine on decel is much less than it was.

BTW, when i pulled the old oil out, it was full in the rear end, so the whine wasn't from low oil.

[Pedigry]

Update: So the whine is still there. I thought it was gone but alas, it's there. I am wondering if it's the tires, I switched recently to a set of rear Toyo Proxis R888R's and some have said they are loud. Others have said they don't hear them. I only hear the whine on decel from around 80 to 65. I am not sure how to decifer whether the noise is coming from the tires or the rear end, it's a bit of a tough one. Any ideas are appriciated.

The vibration I am chasing is still there as well. Only on really slight decel. I changed the oil in the rear end, didn't make a difference. I also checked the endplay on the axles to see if the end plates were the wrong ones, no dice. End play is zero on the axles. I checked the pinion angle, which the shop that installed the 4 link said they would set at 3.5 degrees up (apposing angle to my engine and trans) and it was at 6.7 degrees up. WTF. So I was sure that was it. I dropped the angle to 3.5 up to match the engine/trans 3.5 down. No change. lol. For those that are interested. The engine is 3.5 down, the driveshaft is 1.9 down, the diff is 3.5 up. So working angles are 1.5, which is pretty good.

Next thing is to pull the driveshaft, make sure the pinion nut is torqued to spec and check the endplay on the driveshaft UV joints. I might switch them out. They have the spicer greasables in it and I want to change to non-greasables as they are a better UV (if your curious why, there is a ton of good youtube vids on it).

Any other suggestions on either the whine or the vibration, I am all ears. The wheels and tires are all new and have just been balanced. I guess I could get it done again but the vibration was there with the old set of tires as well.

thanks.

[dhutton]

Pretty sure the whine is typical 9” whine. They are noisy, especially with aftermarket gears. Guys have been complaining about it for as long as I have been on this forum.

[Pedigry]

Pretty sure the whine is typical 9” whine. They are noisy, especially with aftermarket gears. Guys have been complaining about it for as long as I have been on this forum.

Thanks, your probably right. I have seen that as well. It doesn't bother me, as long as it's not a sign of another issue. I'll stop worrying about the whine and concentrate on the slight vibration.

[416velle]

Personally I wouldn't worry too much about the whine, like some have said its "normal" to an extent.

If your vibration is happening on decel ONLY and you're 5000% sure everything else is "in spec", then theres no point in checking the same stuff you've checked 5 times, the culprit is something you're glossing over.
Something you should look at is the transmission yoke. Get under the car while its on the ground at ride height, grab the yoke, and wiggle it at all angles. If it wiggles basically at all, that's your source of no-load vibration.
H*ll, the "grab and wiggle" test can be utilized on all your driveline parts to see where you have a possible source of vibration.
Anywho, if the yoke wiggles unnecessarily (you have to determine what's unnecessary, necessary movement is basically enough to spin and THAT"S IT)

-Your transmission yoke bushing could be worn (ask me how I know)
-you could have an out-of-balance driveline that wore out the bushing, though this is unlikely given the vibration ceases under load)
-the yoke might not have enough spline engagement (ask me how I know), do some measurements or simply slather grease on the output shaft to see what kind of engagement you have.
-your actual transmission output shaft might have weeble-wobble (ask me how I know), wiggle the shaft with the driveshaft removed to find out.

Your angles are 3.5/3.5, I personally would try to get those as low as possible (I'm running 1degree/1 degree on my chevelle) and reassess the situation.
But I think you'll find a weeble wobble at the yoke.

[Pedigry]

Thanks for the response. I did actually do the wiggle test last time I was down there and there wasn't any noticable movement, everything felt secure. But I did notice the joints are greasable 1350's. So I ordered a set of non-greasable, I wanted to upgrade them anyway. That will give me an opportunity to pull the driveshaft, give it a good once over, look for any damage and swap the joints out. Then I can set the endplay and know they are in spec.

It will also give me the opportunity to look at the transmission/spline engagement. I'll measure it and see how it looks. I only have about 2 inches of spline sticking out so I think I have at least 3 in the transmission, but I will measure it and then post my findings.

I wish I could get the trans angle number down, but I am running a gear vendors overdrive and it's about a 1/4 inch of the tunnel as it is. I am maxed there until I swap the C6 for a T56 and massage the tunnel a bit. My working angles are decent though. Right at 1.5 degrees. But your right. I have read that most builders try to keep their engine as flat as possible and try and keep the angle number below 3 degrees. Who knows, that might be it right there.

I wish my rear end housing had a rear cover that I could take off, I would run some paint on the gears and check the pattern and lash but I don't. To check that, I have to pull the whole 3rd member.

Here is a pic of the spline engagement at the transmission:
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