I have a 70 Stage 1 GSX Non-A/C 4 speed car. The information from Wayne Roberts says it has a 3:42 rear end gear but I was under the impression that the 4 speed Stage 1 Non-Air cars had the 3:64 in them. How can I tell with certainty which rear end gear I have? I was looking through the assembly manual and it indicates that all rear ends would have numbers stamped on the passenger side bottom of the axle housing. I've looked and mine does not have any numbers there. There are some numbers on the center portion of the rear. Thanks for the help!
all I do is jack it up, mark the tire, rotate it around once, and if the drive shaft goes over 3 1/2 its 3.64, less than 3 1/2 its 3.42.
My soluion is to pull the rear cover, drain the grease, & look for any trash in the grease. More times than not, differentials suffer forever, w/o having the gear lube changed. While the cover is off, count the teeth on the pinion & the ring gear. Simple division will get you the gear ratio. Over the years, I've often pulled the cover on similiar rare posi rears just in the nick of time. Broken pin bolts, metal filings in the lube, a lightly tracked posi case & a loose pinion... all are problems that can be caught early through regular maintainance. Got Posi? :3gears: Roger
Roger, I am planning to drop the cover and change the lube as my next maintenance task. How can I learn more about "what" to look for when I have it open? I can remove the cover and take a look, but I don't have any knowledge about the things I'll be seeing. Are there any threads with photos or a book I can get that would be a good resource? Thanks!
There is a code stamped on the tube, drivers side bottom about 6" from the pumpkin. Sometimes hard to see/find, but it's there. Even the WI rust belt cars I was able to find them. Wire brush and a fashlight. Rich
If is is a non AC car I would expect a 3.64. If it is an AC car expect a 3.42. When you take on the cover off look at the the numbers stamped on the face of the ring gear. A 3.42 will be stamped "41-12". A 3.64 will be stamped "40-11".
Rob, See the articles on the site about the 8.5" posi units. I have a pic of the GM ring gear with GM part number and ratio stamped on it. Also, see the rear disc brake conversion article....it shows the rear axle code stamped on the pass tube. I have always found the codes....may require a wire wheel and some degreaser if your rear axle tube is dirty. You may also have to look in the general area......the guys stamping the tubes were not too particular to stamp the code in the same area every time.
The tire rotation solution works pretty good but with 342 and 364 being kinda close--I would rotate the tire 10x and get either 34 rotations or 36 too be sure. Pete
I bought a new cover gasket and some gear oil today to "finally" change the rear end fluid. I asked for the GM posi additive and was offered a product called "Trans X" as the posi additive. I also bought 80-90 Valvoline gear oil. Is this "Trans X" additive a good product to use? I want make sure I am filling the rear end with a good quality gear oil and posi additive. Thanks!
I would use nothing but GM Posi additive. You csan get it from any GM dealer. The parts store stuff is shaky. GM stuff proven real deal.
If it's a posi, that method will work. If it's open, you will need to jack up only one side, then rotate the tire twice (or 20 for more accuracy).
For what it is worth, the original " Limited Edition 70 Buick GSX Advertising Brochure" Says: 4 speed manual transmission - 3.42 axle ratio with positive traction differential. Obviously it could have been changed but thats what the sales brochure says they are supposed to come with.
That brochure is only correct for AC cars. All 70 stage one cars without AC came standard with a 3.64 ratio regardless of whether they were auto or manual trans equipped. So the factor than was outcome determinative was the AC option.
The brochure was referring to the standard 350 hp 455. The 3.42 was standard A/C or not. If you optioned for the Stage 1, then the 3.64 came into play without the A/C.
on the 1968-1970 GS rears the stamping seems to always be facing the ground if that helps to find the numbers stamped into the axle tube. Jim
oH and to help with what you are looking at. Look at the ring and pinion teeth they should be shiney and have a smooth surface on both sides with a even pattern across the face of each side of the gear. Posi : if you can see inside the unit (which most auburn factory Buick 8.2 ones are not easy to see through little 1" x 1" window. ) Look for again nice flat surfaces no indented teeth or pitting on the surfaces. For single pinion pin posi units look for that pin oblonging the carrier case...that is not good. Finally the oil will be your biggest indicator of trouble in the rear diff. if you fine chunks of metal or other debris...see if you can determine where it came from? missing teeth when spinning the ring gear and or pinion. listen for bearing noise or grit? Leaks indicate seals are bad or old. You should not be able to wiggle the carrier or pinion yoke up and down or in and out , If yes you have trouble brewing fast. Just some things to look for. Jim
