Regardless of the semantics, it does not drop to idle as in the trans being in neutral.
Need help shopping for new gears
- Thread starter LCL-Dead
- Start date
Yup, the math about total revolutions is just more fun. I always find it very impressive how an oil barrier can support the amount of pressure that the power stroke pushes down with (if my wording makes any sense). When it comes to the bottom end of an engine, I've usually found that everything is working properly until suddenly it isn't, things don't really wear over time.
The only reason to not re-gear is simply expense. 10's of thousands of customers that are satisfied with the improvement is all the proof anyone needs. That and the fact that their vehicles can now do what they want them to do.
Higher revving engines built correctly last. The famed 22RE Toyota used in their pick up had a 27" tall tire and 4.10's stock and would go seemingly forever. Show me a Model A engine with 400k miles on it.
Engineers build a vehicle for a specific set of parameters. TJ owners violate those parameters with regularity so the original parameters become a moot point to a large extent.
You aren't the first to try and "re-invent the wheel" so to speak. But in the end, there are those that do the job, know how to do the job, and are doing the job correctly. Believe me when I say if there was some super involved mathematical way to come up with proper gearing, my old boss would have done it. Randy was obsessed with math and too smart for his own good at times. This is what we used, pretty simple: mph x final drive x gearing x 336 / tire diameter. Pick your desired rpm, then pick your gearing.
To be clear and not send folks down a rabbit hole of no return, your rig had other issues that contributed to the overall impression of the harmonic.
Pinion angle in front was off, way off.
Slip spline was worn badly allowing lateral movement in the front driveshaft at the pinion.
Control arm jam nuts were loose, all of them.
Two rearmost seat belt mounting bolts were screwed hard into the back side of the outboard shock mounts.
Exhaust was hard mounted to frame.
Once those issues were resolved, the harmonic diminished to almost non existent at 65 and below. Once above 65 it builds a bit but is fairly acceptable even though annoying but quiet enough to have a conversation in the rig.
I did forget that the nuts that hold the transmission mount to the trans adapter were laying on top of the skid plate. We also fixed several other things but none of note that would have contributed to the perception of the harmonic.
My single all time favorite example of engine RPM is from a Top Fuel Dragster.
At 8000 RPM, from the time it leaves the starting gate until it crosses the finish line 1000 feet later, the engine has turned over a total of about 500 times.
It took me a minute the first time I read that and then I did the math.
8000 RPM is 133.3 revs per second.
The typical time to go 1000 feet is 4 seconds. 4 x 133.3= 533.2 revolutions.
The other most terrible thing imaginable is miles between rebuild or refresh of the engine in those things.
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You're a better man than I.
I forced myself to do that for 6 months before I re-geared. No matter how I tried to make it a habit, it was a constant irritation to me to be forced to use a "work around" for normal driving. It might have been different had I used an "off" button on the gearshift like @pagrey does rather than the factory switch on the dash, but shifting out of OD was too inconvenient for me.
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You probably have a remote control for the in dash head unit.
Something that makes me giggle every time I see one in the cupholder. Seriously, you have to pick it up, find the buttons, point it at the head unit 18" away, and then try to read the tiny little buttons while piloting your vehicle.
When you put your hand on the shifter to take it out of park, the button is less than 6.875" away from your index finger.
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I turn my stereo on and turn it up and my harmonics mysteriously deminish.
Wow, all things I never had any idea of. I guess I've learned my lesson on who I will not use for a shop future projects.
Those vibrations weren't present until I had it re-geared from 4.10 to 5.38. At that time it still had the Savvy short arms on it and Rancho shocks. Admittedly, I didn't get a chance to take it up past 65 mph after the mid-arm install.
I suspect some of that quiet may come from the two layers of Noico sound deadening material that I put in there. @psrivats said that the Noico in his definitely quieted the harmonic vibration down some.
I remember taking mine up to 90 mph after the re-gear and it was so piercing loud (the harmonic vibration) that it was driving me insane. Of course most of us don't drive our rigs that fast, so I suppose it's not as much of an issue.
The bolts screwed into the back of the outboard mounts were causing a lot of the interior noise. Turns the tub into a giant speaker.
That's something I never would have found, I'm glad you did.
I thought mine was bad, but the harmonic vibration @psrivats has in his is probably 3 times worse than mine, happens at 45 mph and above, and his barely has anything done to it other than the 2" lift and 4.88 gears.
It's amazing how some of these things do it, while others don't.
Additionally, the tires were rebalanced. The difference in felt vibes was noticeable on the 15 minute return drive from the shop. They were rebalanced twice actually since at least 2 tires lost their balance and were bugging me after leaving CA (I'm not going to comment here on the reason why they lost balance).
So would you say the harmonic vibration is "livable" now, or is it still so annoying that you feel like you're going to keep trying to track it down?
Dave has been trying to track down @psrivats' vibration for months now. Apparently he went as far as replacing the torque convertor in the transmission which didn't do anything, now he's going to be replacing all the bearings in the transfer case.
Dave said it's the worst he's seen in all his time working on TJs. Here's been fiddling with it a lot and he wants to replace the TC bearings and the torque converter in the 42RLE. I hope something comes with those two items. I'm actually meeting him this weekend.
@mrblaine have you ever tried high rpm rated bearings in the transfer case to curb these harmonic vibrations? I remember someone mentioned it in @Mr. Bills' thread a while ago.
Oh, I guess I misunderstood! I thought you had told me he already did and it didn't do anything. I'm not sure where I got that from.
Well, in that case, there's still hope!