68-69 Small block diff. INPUT yoke vs. posi ratio code

[Wayne M.]

Codes for small block differentials are AL (for 3.08 posi) and AM (for 3.36 posi), irrespective of whether they are installed in a manual trans car or automatic (Turbo Hydro 350).

And yet, the input yoke is of the larger design for automatic trans, but the standard '65-70(?) size for manual.

Now, AFAIK, these differentials (along with trailing arms, half shafts, strut rods and brackets) were delivered to St. Louis as an "assembly", from Warren MI, where the proper pinion gear torque/lash was set-up.

Am I correct to assume that the input yokes were NOT R&R'ed at St.Louis according to the trans that the car was scheduled to have ? If so, why was there not a unique code stamp for manual versus automatic for these two posi ratios ? And how did they segregate the AL /AM coded rear ends to avoid St. Louis screw-ups ?

[Edward J.]

Re: 68-69 Small block diff. INPUT yoke vs. posi ratio code

Wayne, I am not sure but I believe that the option code dictates(M40), if the axle had either has the heavy duty shafts or the std. duty ones, just as if you got C60 you got the smaller radiator or the H/DUTY radiator.I think the day of the build, the parts for each car were picked according to the build sheets.

[Joe L.]

Re: 68-69 Small block diff. INPUT yoke vs. posi ratio code

Codes for small block differentials are AL (for 3.08 posi) and AM (for 3.36 posi), irrespective of whether they are installed in a manual trans car or automatic (Turbo Hydro 350).

And yet, the input yoke is of the larger design for automatic trans, but the standard '65-70(?) size for manual.

Now, AFAIK, these differentials (along with trailing arms, half shafts, strut rods and brackets) were delivered to St. Louis as an "assembly", from Warren MI, where the proper pinion gear torque/lash was set-up.

Am I correct to assume that the input yokes were NOT R&R'ed at St.Louis according to the trans that the car was scheduled to have ? If so, why was there not a unique code stamp for manual versus automatic for these two posi ratios ? And how did they segregate the AL /AM coded rear ends to avoid St. Louis screw-ups ?

Wayne-----


First of all, there were no THM-350 transmissions used for any 68-69 Corvette. For 1968 through 1975, the THM-400 was the exclusive automatic transmission used for all Corvettes that were equipped with an automatic transmission.

As far as rear carriers go, 1968-70 with manual transmission used a different pinion yoke than those with THM-400. However, I am quite sure that there was no "swapping out" of pinion flanges performed at St. Louis. I think the application of the codes found in some references have been mis-identified or there were codes used that are not shown in references. I think that code "AV" was used for small blocks as well as big blocks with THM-400 and 3.08:1 ratio (all small blocks with THM-400 had 3.08:1 ratio). If so, such small blocks would have also used the HD, cap-type axles.

[John H.]

Re: 68-69 Small block diff. INPUT yoke vs. posi ratio code

Now, AFAIK, these differentials (along with trailing arms, half shafts, strut rods and brackets) were delivered to St. Louis as an "assembly", from Warren MI, where the proper pinion gear torque/lash was set-up.

Wayne -

The diff arrived at St. Louis all by itself - all the other items you mentioned were added in the rear suspension subassembly area in the basement. St. Louis never touched the pinion flange; the codes have been mis-interpreted, as Joe noted.

[Jim T.]

Re: 68-69 Small block diff. INPUT yoke vs. posi ratio code

Codes for small block differentials are AL (for 3.08 posi) and AM (for 3.36 posi), irrespective of whether they are installed in a manual trans car or automatic (Turbo Hydro 350).

And yet, the input yoke is of the larger design for automatic trans, but the standard '65-70(?) size for manual.

Now, AFAIK, these differentials (along with trailing arms, half shafts, strut rods and brackets) were delivered to St. Louis as an "assembly", from Warren MI, where the proper pinion gear torque/lash was set-up.

Am I correct to assume that the input yokes were NOT R&R'ed at St.Louis according to the trans that the car was scheduled to have ? If so, why was there not a unique code stamp for manual versus automatic for these two posi ratios ? And how did they segregate the AL /AM coded rear ends to avoid St. Louis screw-ups ?

Wayne my smallblock 70 350/300 original documented information on the rear end and what is printed in the warranty booklet's metal plate is CAV0702W and it is a 3:08 ratio. Have straps/bolts to retain u-joints at the sides of the unit. All 70 and newer Corvettes had posi-traction rear ends as standard equipment.