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Hi, as you all know the results from the change over from the chevy 12 bolt 3.31 to the 1970 olds 12 bolt 3.91 netted the car 3 tenths slower, all that info is on this site how that came to be, so i put want ads for 3.42 gear set on c/l classic Oldsmobile etc etc, i have found these 1970 olds GM 3.42 gear set on C/L, 12A41 GM NH 048 The pinion bearing seems ok i should really replace it any ideas or possible numbers on a new one ?? Has a little war wound on the end of the last 2 threads iam pretty sure i can fix that, my question is i found these 3.42 gear se
t on oldsparts.com if you go to there site punch in SKU# 18-010
Ring & Pinion Gear Set – 12 BOLT – 3.42 – SPECIAL ORDER
if for some reason i can not fix the end of the threads will this bolt up to my 588 carrier thanks to all for responding, john....
Last edited by john mann; Dec 29, 2019 at 07:19 AM.
Reason: adding picture..
you can use your 588 carrier only with a gm 3:42 gear set, the aftermarket set are made to use with the 671 carrier
Attached is the chart for gear original gear usage, not after market. the threads on the gear in my axle were worse than that and are working fine.
That site says it’s a special order part, which sounds like it’s an aftermarket gear set. That would mean it is made for use on a 3.08-3.23 series carrier and NOT for your factory 588 carrier.
Thanks Ken,and Nick, seems like every time i see something that looks right it isn't right, i wish they would really let you know what they are selling, very frustrating, thanks to you guys on classic Oldsmobile iam getting a PHD on differentials which is ok with me, the reason why iam asking is the gentlemen that i bought this gear set from said it came out of a 1970 olds 442 that should have the 588 carrier in it for the 3.42 gear set that i bought from him, he said he went with the Richmond 3.90 that he got from summit part #49-0050-1 i looked on the bottom of the ad and it says 3.23 to 2.93 i don't know how the 3.90 from summit could work for him with the 588 carrier ?? john.............
Last edited by john mann; Dec 29, 2019 at 09:50 AM.
Flip it over on the teeth measure the height of the ring gear to the machined surface from a true flat surface. Post the measurement to the closest 1 /16" I will measure a aftermarket gear from our shelf and will see.
IF yours is .180 ish shorter you will be good to install on the 588 carrier if we are the same with in a ..010 your not going to be able to use it on the 588 with pout machining the gear down at least .150
Why were the aftermarket gears made to fit the 3.08 and 3.23 carrier? Weren't most cars optioned with the 2.56 and 2.78 gears? Just curious on why Richmond selected that carrier.
Ken, the only numbers on the ring gear are in the picture, i know its hard to see i have one more pic i will post they read 12A41 GM NH 048 Thanks john.
Why were the aftermarket gears made to fit the 3.08 and 3.23 carrier? Weren't most cars optioned with the 2.56 and 2.78 gears? Just curious on why Richmond selected that carrier.
Probably two reasons. First, the standard ratios on 442s with AT in the 67-70 range were 3.08 and 3.23. People with performance cars were probably more likely to want to change ratios. Second, the 2-series carriers require an even thicker ring gear than do the 3-series carriers to use 4-series ratios. This extra ring gear thickness likely caused additional problems with things like heat treating.
Nick, are those GM gears ?? what does that tell us compared to my dimension OF 1.350 are we in the game or mine after market ?? Nick thanks for taking the time to checking those gear sets for me john !!
John both are genuine GM gear sets. If I understand correctly the gear set would need to be thicker than what I have to be an aftermarket set, so with that said I believe they should work with your carrier. Monzaz and others should be able to tell you for sure.
Nick, that was my thought also but right when i think things are ok there not, so ill hold on tight for now, thanks for chiming in hopefully we will be ok, John !!
Yes those look like GM gears and not Richmond new production. Richmond O type gears have the Richmond symbol stamped on them that I have seen. If he went 3.90 he could have milled his ring so it would work on the 588 posi.
WOW !! great info !! that tells me the bolt circle then on the ring gear is the same the difference is the thickness my thoughts,, thanks Magna86 !! waiting for the ace Jim to see what he has for dimensions !, thanks for your response, john...
I get 1.432 on that measurement on the 3.42 gears we stock which i believe only Richmond ...which is really Motive gear and axle.
so 1.350 (what you measured) is what you get that is about ..082
I would say it is a 3 series carrier...BUT it will be close. If it were me I would try it with a 588 and see what you get.
You also could try it with a 3 series... and see how far it has to be moved in the saddles for correct engagement.
The advantage you have is the side gears are one piece in the posi units unlike the old Auburn BOP cone 2 piece side gear system that will not tolerate the offset.
Meaning you can have one side axle having less or more spline engagement in the carrier. As long as the axles do not hit the cross shaft it can work... YOU DO NOT want this too far shifted as it will cause minimal spline engagement which means lees contact on one side which means it will be weaker on that side.
For most street stuff it will not make a hill a beans difference...BUT drag racing and hard spirited driving is will .
Hope you understand what i am talking about...If not you can call and I can discuss it person to person to help. Jim
Jim, yes i do get what you are trying to tell me, i need some knowledge on this carrier stuff, is the 588 and 672 4 series carrier and is the 671 and 673 3 series carrier ?? i do have a some pictures of the differential these gears came out of iam sure it wont help but i will post them anyway, thanks for all your info Jim, i have a 1967-68 12 bolt 31 spline right now at JMJ transmission in st cloud for a refresh i dont think he has assembled it yet, i was thinking of bringing the 3.42 to them and have him put them in and pull out the 3.91 that are in there just a thought iam by no means a differential rebuild guy that don't mean i cant learn it !! thanks again Jim John....
Last edited by john mann; Dec 31, 2019 at 06:49 PM.
Hey I noticed you have you exhaust aimed at your rear differential...MIGHT NOT be a good idea...Your throwing more heat onto the differential and it has to deal with enough friction heat already... Try to aim it a different way...To the ground is always best. JIm
