I have a 68GS 400 4 speed that originally came with 3:42’s. I installed 4:30’s in the original rear years ago but had to to shim the carrier to obtain the correct backlash. Never had a problem with it but feel the gear should have had a spacer. From what I have read, there is not a lot of support for these rears. Was hoping to find a spacer with the correct length bolts.
the problem is the ring gear spacer thickness. You likely only need to move it over .125 to .140 thous. soooo if the rear is working ...?? You might wantr to just leave it alone...donot open a can of worms. YES, it is not correct...but buick carrier only moves 1/8" each series carrier which is not as much as chevy 1/4" spacers. A 8.5 spacer might work...but them you will be again the other way spaced too far...lol. like I said ...maybe do not open this can. Jim JD race
The 3:42 posi unit is a different series than the 3:64,so yes,the 3:42 unit would require a spacer with the 4:30 gears to keep the carrier centered and correct inside the housing. By shoving the carrier all the way to one side,you are decreasing engagement to one of the axle shafts and also increase the chance of damaging the posi unit,due to how those cone units are designed to work. Here is an example of one of these Buick rears that was originally a 3:23 and someone attempted to install 3:91’s. Basically,everything was trashed,due to improper installation. They just shoved it all the way to the right and hoped for the best. They didn’t hope enough.
I'm sure a steel plate of proper thickness can be had then have the center hole and bolt pattern water jetted or plasma cut on a table......it not like the holes need to be exact to the .001 if they are a little big by the time it's sandwiched in it won't go anywhere. It only needs to be the thickness you have it spaced out and clearly the bolts you have are working. Should be very reasonable to get done. There are 4 ppl near me that have cutting table or
However you do it,it needs to be perfectly flat,same thickness everywhere. In the past,I took the 908A spacers and had them milled,but that proved to be a challenge because I couldn’t find anyone with a magnetic table. I sent them out to a place in Illinois. Yes,cutting them out of the proper thickness to begin with would be great. I tried that locally,but a lot of talk and no doing,or they wanted to do 1,000 of them. I might have a place now. I will be looking into that shortly.
Thanks for everyone’s input. I would imagine that the 3.64 + carriers would be hard to find. Brian, I would be interested in a spacer if you decide to have them done.
Also the next problem with moving the carrier over that far is the engagement of the POSI unit side gear to cone engagement... If the axle can not engage BOTH the cone and side gear 1/2" thick pieces you will just tear up a posi unit lickity split... Jim
That was the result of the picture above. The carrier was over all the way it could go to the right,and still wasn’t enough,but it also pulled away from the driver’s side axle shaft,which left only the cone engaged and not the side gear,which tore it up.
Shoutout to Jim and Brian. V8Buick is lucky to have two experts in the field that would normally have every right to be fierce competitors, and instead go out of their way to jump in and help everyone here while never stepping on each others' toes. Hat is off to you both, and I make a point to read threads that might otherwise be uninteresting to me, knowing I'll probably learn something worthwhile from each of you. Devon
I’ve noticed that also, being were an older group of guys, we’ve reached the point in our lives, or Carreers that sharing info or parts is no big deal. I like that!
Brian, where can I find a 908A spacer? I have access to a magnetic milling machine. As far as removing material, do I need to measure the difference between the 3:42 and 4:30 ring gear thickness?
You could buy a flat ground sheet from Mcmaster Carr or another supplier. https://www.mcmaster.com/products/f...-air-hardening-a2-tool-steel-sheets-and-bars/ Then have the shape and holes cut with a water jet or laser. If you're on a really low budget, then saw cut the shape and drill clearance holes yourself.
