I hear from this attached source below that 3-4 clutch clearance is better when less than 0.060. I知 using BorgWarner grey frictions that were included in my transtar kit. I mentioned in a related post that one of my old 3-4 frictions had the splined teeth completely gone. I知 wondering if this was caused by the large clearance over time. I知 getting 0.070 with my existing backing plate which is what the atsg manual says.
4L60E/4L60 Rebuild Procedures 68
Step 23: Measure the clearance between the backing plate and the top friction plate. The factory clearance specification is 0.035"-0.083" (0.90mm-2.10mm), but it's a good idea to keep the clearance under 0.060" for a good, clean 2-3 shift. Clearance can be adjusted by either mixing thick and thin steels or by changing the selective backing plate to a plate of the proper thickness. The backing plates are available in three sizes:
0.154"-0.161" (3.90mm-4.10mm) 0.187"-0.196" (4.76mm-4.99mm) 0.224"-0.231" (5.68mm-5.88mm)

 

I知 having a hard time attaching this section of the manual. It is called the ATRA manual of 4L60/4L60E by Cliff McCormick

 

Your post makes perfect sense. I bet you can find thicker steels quicker and cheaper. But one move thicker on the backing plate would take care of you nicely.

 

Typical practice when setting/adjusting anything within a range of a-to-b is to hit the middle of the range; 0.060" is in the middle of 0.035" and 0.083". Okay, it's really 0.059" but close enough.

I'm running an 8 friction 3-4 clutch (B-W Hi-Energy) and the specified clearance was 0.020" - 0.035". As-received, the clearance ending up being 0.031" so I just ran it like that.


I vaguely remember reading on another forum (unfortunately it no longer exists but it was a wealth of reliable information) where one theory to the question of, "why do the 3-4 clutches fry themselves" was: frequent 2-3 shifts = heat; fluid is what cools the clutches; more clearance = more fluid flow when released = relatively more cooling; less clearance = less fluid flow when released = relatively less cooling. IIRC, the theory was in regards to autocross or road racing. Not exactly the kind of thing you'd be doing on the street but something that stuck with me.

As far as loosing the friction teeth, this is normal when the clutches start to slip and you continue to drive it.

 

I went back and assembled my old 3-4 clutches and forward clutches below are the numbers. I got 200k and my forwards look new. It’s kind of hard to tell the 3-4’s because they are dark


1) 3-4 clutches ( 0.092)
2) forward clutches (0.040)