My friend has a 79 Trans Am 8.5 rear with 2.41 gears. Will a "GM10-342" gearset fit? His carrier is a 410400N Also what pinion bearing spacer would be best for starters? Thanks for any help on this. Gary B.
The S spring 8.5 posi carrier you have is the common high ratio 28 spline unit, used with 2.41 & 2.56 factory gearing. To get to lower ratio (2.73-5.57) gearing, you will need either another posi, or a Mr Gasket or Summit 8.5 ring gear spacer kit ALONG with 10 hardened lock washers from a Mr Gasket small block chevy head bolt wasker kit ($7-8 a pkg). Will also need some red loctite for the new ring gear bolts. Don't buy the hardened washers & the bottom 2-3 threads of the new ring gear bolts will often strip... not good. Note there are limitations to ring gear spacer useage. If car is getting close to a 1.90 or better 60 foot time, you'd be better off with the correct ratio 8.5 posi carrier. On the pinion shim, hard to tell you with the Richmond gears as I won't use 'em. Usually with US Gear or US Gear/Strange 8.5 gears I'll start with an .035 pinion shim. Original GM 8.5 gears usually will have between an .038 & an .041, but aftermarket 8.5 gears seldom ever set up with that thick of a pinion shim. :3gears: Roger
Motive gear set The GM10-342 is made by Motive, if that makes any difference. The ring gear is also much thicker than the 2.41 ring gear. The guy at O'Rileys Auto Parts said it would work, but you know how that goes!
Gary, Hello, the ring gear of the 2.41 is very thin as the pinion is so big. As gear ratio's get lower (higher numerically), the ring gear gets thicker & the pinion smaller, thus the 3.42 ring gear looking so thick compared to a 2.41 ring gear. You'll still need a low ratio carrier, or get there by propperly installing an 8.5 ring gear spacer. Realize O'Reillys can get the Motive gears out of the Tulsa warehouse pretty fast, but after setting up a few sets of Motives from O'Reillys, I'm back to US Gear-Strange gears, they're worth the extra day or two wait. :3gears: Roger
A magnifying glass revealed the carrier is a 410409N. The 9 indicates it is for 2.41 & 2.53 only unless a spacer is used, if i'm right at this point. So if washers are not to be used, the bolt head goes against the ring gear and red Loctite holds it, correct?
The washers need to be obtained & used, as the bolts supplied in the 8.5 ring gear spacer kits are slightly too long & will bottom out in most 8.5 ring gears. Years ago, to try & solve this problem when using the 8.5 ring gear spacers, I used HD split lock washers from a local bolt supply. Bought a whole box of them. Problem was, the split lock washers are designed for rh thread bolts & when torqued in lh thread application, will spread out. The Mr Gasket SBC head bolt washers are small outside diameter, correct ID, & work perfectly. A pkg is like $7-8, & will contain 34 or so washers. I usually order a pkg every other order from Summit or Jegs. Have no use for the remaining washers, can always sell them off to others doing 8.5 spacer installs. Good luck on your gear set-up. :3gears: Roger
