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What could cause this? Should have bought new I know, I may have to order a new set. I bought a set of 3.42 factory gears for an 8.5" off Ebay. The gears looked practically new. When I installed them both the carrier flange and ring gear mating surfaces looked clean. But when I checked the backlash there were two spots that had a closer fit, you know what I mean. Why I didn't check the run out of the carrier flange and ring gear is beyond me. I just set up the back lash at the tightest spot. Now when I drive the car you can feel a very slight harmonic about 60MPH.
I can't believe that there would be specs of dirt or something in just two spots on the mating surfaces, if it requires pulling everything apart again I will. You would think that if there was dirt or some foreign objects between the mating surfaces that the gear mesh would be off in a linear circumference patten not just in two little spots.
I'm just wondering if anyone has set up gears and had that problem, how to deal with it and so forth. Is it possible if I wasn't totally antiseptic in my assembly that a couple teeth here and there could have more run out than all the rest? Seems almost impossible.
I would wonder if its ring gear run out or possibly deflected teeth on the ring gear.
I have seen a few aftermarket gear sets that had did have a bit of run out in them, but GM gears are usually pretty good.
Most of the run out that I see is in the carrier itself.
I have seen several carriers that where the carrier brgs press on the part that the brg fits on gets "bent" and its very hard to salvage that properly. On the axles that use the small carrier brg but the big axle spline that area of the carrier seems very weak to me.
If the carrier has run out in the flange its fairly easy to true it, but in my opinion its very important to measure the run out in the housing using good brgs and mark the carrier.
Its also important when you machine that flange that you are sure the system you use to mount the carrier is accurate (90 degrees to the flange). I have had a lot of trouble in the past with carrier that were not machined accurately on the inside of the brg mount and the champher itself was not concentric as well.
I finally converted a disc brake lath that used an arbor that went through the rotor to support it on both sides to be able to chuck the carrier on the brg mounts, it works pretty well.
This is probably not much help to you and its probably some thing simple.
Personally the first thing I would is mark the ring gear and carrier in the tight spots (pinion too) . I would the take the ring off and check the carrier run out in the housing. If its ok I would mount the ring gear a 180 degrees from where it was and check it again.
Sorry to ramble, and I hope you get it fixed, and its simple.
All good points. Never ran into this before. I'm gonna take it back out today and have a look see at the mating surfaces, then check the run out and not take it for granted this time. Ohhh we all learn from our mistakes. I know it's not the pinion because it's the same spot every time on the ring. If it were the pinion the tight spots would wind up more frequent and in different spots. It just puzzles me that it's only like three or four teeth in one spot and and two or three in an another.
If I can't find anything I think you've given me a good idea with turning the ring 180 and see what happens. I've read that some rings CAN have a couple teeth higher than rest but you wouldn't think that with used factory gears.
Maybe one of the carrier bearing bosses IS bent, pretty much I believe the carrier would be junk at that point. Not like you can machine it true and still have the bearing race a press fit.
I think gears have to be one of the worst jobs us Hot Rodders can do. I'd take it somewhere but no one around here is competent enough to get it done right. Or can do it at all.
I'll keep my progress updated here, if nothing else it can be a lesson in what NOT to do when setting up your gears. LOL
So far I've found nothing except my pinion may have not been pre loaded enough. Would this cause a rhythmic vibration if the ring gear did have a tooth here and there that were higher? I did turn the ring 180 anyway, it's still there but not as bad. Funny thing is the vibration doesn't jive with the gear ratio. Meaning at 60 MPH the vibration comes and goes about every 5 seconds. The vibration lasts about 2 seconds. If I were feeling those high spots on the ring or what I think are high spots the vibration should be constant, frequent and follow the gear ratio. Do you know what I mean?
Im not sure about the vibration, harmonic. noises stuff and ratio . It could be but im not sure.
I do quite a bit of differential service and sometimes its hard to tell were its even coming from, but then again im getting old.
I used to do a lot of warranty type differential service on Dana drive axles for some local Jeep dealers, on new Jeeps (and used for that matter) and sometimes it was hard to pinpoint some noises.
I have Techtronics dual trace digital storage type oscilloscope that I coupled with two transducers that I could attach to the drive axles. transfer case, etc and I could store the vibration level and frequency. It was very educational as to how some noise will travel.
As far as the pinion preload goes in my opinion it will deffinatly have the possibility of causing a vibration if its loose.
I have seen rear pinion brgs that would cause a similar problem with varying backlash as well. They would have one or two bad spots (I want to say "brinelled" but im not sure thats the right word) on the race and a bad roller as well, and when they came together just right there would be an interference. I have seen this caused on new brgs by the races being "dented" by hitting them with a steel punch in a bad way, so to speak.
Remember these are just my ramblings, so please read with caution.
I think I'm gonna let it be for now. It's not bad enough to warrant taking it back apart right now. I'm gonna get started installing the ZZ383, I just wanted everything in the drive train to be spot on before I went onto something else. Maybe taking my mind off of it for a while then coming back to it something will hit me. If nothing else I'll just order up a Currie or something. I may break the stock posi if I spray that motor. Maybe I'll get lucky, send an axle into the stands and me into the guardrail ending all my misery.
You know nothing goes as we plan, I just put a shift kit and TCI Breakaway in the TH350. That went superbly, barks first to second and sometimes when REALLY into the throttle 2nd to 3rd. I'm having much fun incinerating the junk tires that came on the car. This is still with the bone stock 305! What's the ZZ383 gonna do? However the cheap crappy pan gasket is making a mess on my garage floor. DOES IT EVER END???
I'd have to say I'm glad I went with 3.42 gears. Anything lower would be a pain on the highway and I really don't think the new motor is going to care what is back there. It could be 2.56 gears and I believe tires will be bought on a regular basis.
I hope it works out for you. It sounds like the 383 will a lot of fun.
I also understand the gear ratio thing. Im about spoiled in my old age. When I was young we would cruise around in cars with 5.57 or so, My 67 Nova still has 4.88 and I have 4.10s un the rest of my stuff, but I built a 92 Camaro for my youngest daughter and I to kinda play with and I put a 4.10 in the 7.5 untill I can fab a 12 bolt for it and when we drive it on the high way I keep tying to up shift it. Its 400 turbo and 3 speeds is all its got.
I think my corvette with a 700 only turns about 1300-1500 at high way speeds, My Nova about 3500.
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