Just as a helpful FYI I wanted to make a short thread showing the differences I have found when I needed to replace the "Transmission Control Case" of my 87 Turbo II. Otherwise known as the shifter housing, tail end top case or whatever you want to call it, I'll be using the terminology of the parts diagram.

Schematically shown, it's the aluminum casing on top of the extension housing (or tailshaft housing if you prefer) that has all the little shifter bushings and springs in it.

I wanted to replace the shifter return spring to get rid of the sloppy gear stick in my S4 Turbo, however I ran into issues doing so. I will not go into full detail into how to remove it, but I will say the shifter needs to be in the position pictured. Any other position has the potential to ruin the control case, ask me how I know.

Anyway, the differences.

• S4 NA and Turbo share the same casting and have a [1] cast into the bottom.
• S5 NA (I'll assume turbo as well) uses a similar casting, but has a part number cast into it M508 2.
  • I say similar because some features of the casting were smaller, as shown in the interior. of the housing. Once again, I believe weight and cost savings the S5 is known for.
• S5 NA uses a longer control lever 343mm vs 326mm.
• S5 uses a larger diameter control lever end, similar to how the NA miata is done.
• S4 uses an angled reverse lock out pin
• S5 uses a necked cylindrical pin, I assume for cost savings.

Beyond that, if you find yourself in need of one, S4 and S5 casings appear to be interchangeable except for the differences noted.




The only position to remove the control lever end roll pin. if pointing downwards you will damage the casing, ask me how I know!

S4 control case on left, S5 on right.

S4 control case on left, S5 on right. S4 only has a "[1]" cast into it while S5 has "M508 2" cast into it.

S5 control case, notice the bumps are smaller than the S4.

S4 control case, notice the bumps are larger than the S5.

S4 Turbo control lever 326mm in length

S5 NA control lever 343mm in length

S4 reverse lockout pin on left, S5 on right.

S4 control lever end on bottom, S5 on top. The S5 uses a larger bore to use a plastic bushing like NA miatas use.

 

Very interesting. Is the rod (17-461) diameter the same for S4 vs S5?

 

Yes, it's 14mm diameter (14.00 +0/-0.04)

 

Ok, thanks. That good to know because in the past there have been multiple posts asking if S5 shift changer (17-461A) will swap out with the S4 changer.

 

I love finding these threads, so detailed and focused. Engineering mind for sure.

I am looking everywhere, do you think an S4 shift lever assembly would fit into an S5 casing?

I am restoring the car and want to keep the part original as it is in immaculate condition.

Thank you.

 

As long as they are the same model, e.g., S4 NA and S5 NA I think they should be ok.