Hi all, My car has been running slow the last few times I ran it and on the last pass I made it shook something terrible. So I decided to put it up on stands and give it a good going over. I pulled the rear cover off and had a ring gear with half a tooth missing staring at me. I know it is not the cause of the shake or slowing it down but what would cause this? I am thinking it is because the pinion depth was off a little and put pressure on the outside end of the tooth. The gears were always quiet on the road so it couldn't have been to far off and when I marked the gears and checked the pattern when I put this rear together a couple years ago it was good. They are old GM 4:10 gears. I have another set of gears here so it will be a cheap fix. Could it be that now the car 60fts so much better that things are moving around under the torque and the pattern move to the edge of the gear? The rear has stock caps and stock tin cover. It seems to me that I read many years ago in hot rod or one of those mags about setting up the gears for slicks and high torque engine different than just a street car, I assume to let the pattern move to the center of the gear? Or is that a bunch of BS? Would running less backlash help? To bad they don't have 4:10 pro gears, I think the lowest is 4:33? I would think that a TA cover would help the problem also. Sorry for the long post, :3gears: Tom
12 bolt problems well that is took bad sorry to here of your problems. How old were the gears you installed? What was the backlash when they were installed ? What is the 60 ft and how is the car launched (trans brake?) more backlash on a race typre application is usually worse (drag race) . I set drag race to .004 backlash. there is not much heat up time for the gears to expand in a 1/4 mile. for street about .007 .006 GM spec is .005-.008 so anywhere between there is cool. You really should get it in there to be safe. They have specs for a reason. As for the gear tooth it really could be anything. a burnout gone bad with a vilant stop could have done it ... never do hard revesre typ burn outs that is bad news on gears. reverse to drive to quick with out vechile fully stopped. locking up the rear with brake mayhave done it. or it was just plan and simple weak tooth and it was its time. lol if you get them out send a picture of the ring and pinion so I can look maybe I can determine something. Good luck with the next. Jim mitschke454@earthlink.net
Hi, The gears are very old GM gears. My 60s are high 1.4 to low 1.5 leaving with pedals not much above idle. The car has never gone from reverse to forward. I don't remember the backlash but I think it was on he high side of GM specs. I blew up the posi gears a couple years ago, maybe it messed up the gears then. I am glad I found it before it went boom again. Tom
Hi again, It came to me today that the last weekend racing it did something odd, I can't say it "Rattled" the tires, not fast enough for that, but it did kinda like skip the tires a couple times on one run which really got my attention, I can kinda see how a real shake will knock your teeth lose, anyway maybe then is when the gear broke. The other gears I have are also used, would a magniflux tell me if they are cracked? I have done magnfluxing on heads and blocks so I understand how it works but never tried it on gears or stuff like that. Tom
tire shake The tire shake will definetly torture the gears. quick loading and unloading will smack the gear teeth together and could have caused the tooth decapitation... :beer But that is really not your fault it will sometimes happen on high horsepower vehicles and a super sticky launch . Remember that is why I put that backlash tighter for that very reason of the slap that takes place on the launch with trans brakes and such. The gear does have a life and maybe this was its last breath. o No: good luck on the next set. Jim
Hi, just a little correction to something I said, I got a new Jegs book today and they do list a 4:10 12 bolt pro gear. I thought they went from 4:33 and up. Tom
Hi, Just wondering how fast some of you are going with street/strip GS [full weight] and a 12bolt with a posi unit? What is the point were ring and pinion breakage become a problem? The gears must be pretty strong because I know a couple racers with very fast cars that run the 9" ford rear with the 12 bolt gears. I understand they take less power than 9" gears? Tom
Hi again, could about a 3rd of a tooth missing from the ring gear cause it to shake at the finish line like a out of balance tire? Tom
tire shake very possible. They all need to be there for proper performance. Who intsalled? Go back to them and see what they think on the install. what could have caused the tooth to snap. BacklasH for over worn gears? install incorrect? defective gear..etc. But YES it could cause a shake hum, just about anything. Jim
Tom, Stock factory gears are too brittle. If you go to a Richmond gear you shouldnt break gears anymore, they are softer than stock. I wouldnt run a pro gear unless you absolutley have to. Jeff
Hi, Which has stronger teeth, 3.90 or 4.10 12bolt gears? 4.10s are great for drag racing but not much fun on the street with 27" tall tires. So if the 3.90s are stronger maybe I should go with them, or maybe I would even consider 3.73s. I have a 4 series and a 3 series case I can use. I supose less gear would put more strain on the trans and converter though. Tom
Tom, I run 3.73s in my car in the avitar with 30''slicks. I think it would be a little quicker with 4.10s. If you drive on the street I would go with 3.73s. I think they are all pretty close in strength. Jeff
stronger gear? The only thing that makes one stronger than another is the material used to make the gear. The only reason one would wear out quicker than the other (if properly installed) is the number of teeth.more teeth more life less teeth less life. less teeth and small ring will build more heat and turn that many more revs per same mile as the ring gear that is larger diameter and more teeth per pinion and ring. That is why freeway gears like 2.56 last forever. count the teeth there are tons of them. more teeth less heat and wear. There are just some things you give up for performace...unless you use a overdrive tranny. or gear venders unit. Good luck on your next install. Hope some info has helped. Jim
Hi, yes you all have helped me on this stuff, When I was asking about strength I was wondering if a smaller pinion with bigger teeth would be stronger than a different ratio with more pinion teeth but smaller or other way around, I hope you understand what I mean. Kinda like 12 bolt spider gears, the 17x10s are stronger than the 18x10s because the 10 tooth gears have bigger teeth. Tom
strength Yes in this case bigger is better and more teeth is better. But remember as with anything , there comes a point of over doing it. You should pick the proper (needed) equipment for the job if possible. Over kill is bad too. It will always take more horsepower to move a larger heavier object and or gears in this case. Like a 400TH trans takes more horses to move than a 350TH so you have to choose the right stuff for your needs. I only race with a 8.5 4.10 and a 350TH sbc 350. 11.60's in a monza. Will the trade off be good for you (more power or more reliablity??). In this case: What will the gears be mostly used for drag racing or street? How fast is fast enough 3.73 or 4.10??? . In this case reliablity is really all on you, the install makes the biggest deal. Just take that extra day to go back and check the pattern one more day with fresh eyes...Don't rush it . I would keep your backlash on the smaller end of the tolerence specs Keep the gears from slapping on launch with a trans brake or four speed car banging through the gears. I put my car that never goes to the street at .004 I would say .005-.006 is good for yours if you are street driving and racing. Again good luck. Jim
72GSX good 60 ft Your 60 foot time is really good. What traction devices are you using to keep the tires planted?
Tom, I have a perfect set of Richmond 3.73's, only slightly used I want to sell for 12 bolts. If you are going to drive the car on the street AT ALL, DO NOT use the pro gear. They will not last.
Pro Gears That is correct...they are much softer metal type to take the shock of transbrakes and high stall hole shots. Like tires ...some are softer for more grip but do not last as long . If you are not interested in the gears. I might be depending on the price. Jim mitschke454@earthlink.net Thanks, Jim
