4L60E Servo questions

[zhaarnak02]

I found something interesting when I started to disassemble the 93 4l60E core that I plan to rebuild for my truck. Here are a few casting numbers: Transmission ID: 3KKD1544 (1993 K-series, 5.7 V-8), Valve Body Identification Number: 8678393, Pump Identification Number: 8682132 (Non-PWM), Torque Converter Number: 2017467482 (06/12/23, GM33CW).

The 1st thing I noticed was the fact that it has been gone through before, the newer converter gave that away. Endplay (rough measurement via MK 1 hand/Eye testing apparatus) seems to be “close”. Seller had mentioned that 3rd gear had “gone away”. I performed a stomach pump and found burned fluid and evidence of lining material in the pan, but no hard shrapnel. I then popped the servo in order to remove the o-rings, then reinstall and check band clearance. In the process of doing this, I came across something interesting. I immediately noticed slots that had been cut in the steel cover and wondered if I was holding a corvette (.74 ratio) servo. Being my first time in a 4L60, and lacking information on servo casting numbers, and noticing what was to me, a horrific amount of slop between the servo 2nd piston and housing bore (absolutely NO drag felt from the sealing ring to bore interface) I did some measuring with my dial calipers. I found the following: while the second gear housing (casting # 8642115) I.D measures at 1.792, (which leads me to think “corvette” servo, the 2nd gear piston (casting # 8642093 AC) measures at 1.755 O.D, and incidentally, also fails the “fingernail method” of surface roughness calculation of the oem machined surface.

My questions are as follows:

1. Do these casting numbers correspond with Corvette servo numbers? (the dimension of the 2nd gear housing supports this).
2. Is this amount of slop between the 2nd piston and housing acceptable? To me, this amount of clearance (.037”) seems to be just begging for leakage.
3. The casting number on the 4th piston appears to be 8642482 and I need to know if than number denotes a stock 4th gear piston, which is what I desire.

Last question, I am looking for a part number for the seal kit for a corvette servo as I am getting ready to do another transmission oil and filter change on the old girl (109,000 miles) and I am planning on installing this servo along with checking and making any band adjustments, installing the Sonnax 4L60E-LB1 boost valve, checking the separator plate for any damage, and other easily addressed items while the pan is off. It will be interesting to see what the band clearance is now. The servo pin on the “vette” servo is a 2-groove.

Any information is greatly appreciated! I hope you all had a great Christmas, LOTS of leftovers, and have a great New Years!

 

[AdmiralYoda]

paging @clinebarger, our resident transmission guru/expert!

 

[zhaarnak02]

CODE BLUE! I salute him. I sincerely enjoy absorbing the knowledge he documents here for us. I have a tad bit of experience with various brands and models of earlier 3-speed transmissions, but no experience with any 4-speed auto. His way of building these newer transmissions "Jives" with the way I would build the earlier ones. I.E. not getting in by the bright "shiny" gimmicks (solutions in search of a problem). Poor guy, I wonder if he ever gets a vacation from...........US

 

[clinebarger]

The last 3 digits of "093" denotes it is a Corvette Servo, I can just about guarantee the servo is worn out as GM hasn't made them is 20 years. Sonnax & TransGo sell aftermarket ones that work well.....Some lesser aftermarket servos aren't worth the aluminum they're machined from!

All GM 4th servos are the same.

Sonnax 77787-02K servo pin is what I use in all 4L60 builds.

The slots cut in the servo cushion spring retainer is a TransGo SK shift kit modification....Keeps fluid from building up behind the retainer causing rough 1-2 shifts, Also helps with 3-2 downshift clunk.

 

[zhaarnak02]

The last 3 digits of "093" denotes it is a Corvette Servo, I can just about guarantee the servo is worn out as GM hasn't made them is 20 years. Sonnax & TransGo sell aftermarket ones that work well.....Some lesser aftermarket servos aren't worth the aluminum they're machined from!

All GM 4th servos are the same.

Sonnax 77787-02K servo pin is what I use in all 4L60 builds.

The slots cut in the servo cushion spring retainer is a TransGo SK shift kit modification....Keeps fluid from building up behind the retainer causing rough 1-2 shifts, Also helps with 3-2 downshift clunk.

And there he is, riding hard to the sound of the guns.......... Thank you Sir! (Your steed wouldnt be named "Silver" would it?)

It had not crossed my mind that the original Corvette servo had been discontinued years ago. I was jumping with joy when I suspected the servo in the "core" transmission might indeed be a vette servo I needed, but am a tad bummed that it is badly worn. Oh well, a new quality vette servo is not that expensive. I have indeed noticed the flood of cheap imported servos that have flooded ebay and other places, and gone NOPE!! heck, is everybody with a smelter and scrap aluminum casting these things?

I will pick up a new Transgo servo. Hopefully I will be able to reuse the 4th piston and cover as wear here does not appear too advanced. I can still feel drag from the old piston seal in the cover bore. If not, I will purchase a Superior K034.

Yep, as soon as I saw the slots ground in the steel cover I started to wonder just what other work/mods have been done to this transmission. I am looking forward to finding out. I am hoping for a totally (and competently) remanufactured pump that is in fantastic shape, Sonnax Smartshell, and whatever else "Lady Luck" will throw my way. Of course, now that I think about it, what "modifications" might they have done to the valve body, and other areas..........CRAP!

 

[zhaarnak02]

I would prefer to retain the stock OEM 4th gear servo because I never subject my girl to a heavy tow situation. If I had to tow anything, it would not be while she was in overdrive. That would be, in my mind, abuse, pure and simple. I am also not one that desires to impress myself (or bystanders) with tire chirping shift points. Treating equipment with care can definitely lower maintenance costs.

If I am unable to source a new, stock OEM 4th gear servo piston and cover, I am am going to be concerned that if the upgraded (oversized) servo is going to be hitting 4th gear harder than it would like. If I have to do this, my thought is that I will most likely leave the separator plates 4th gear servo apply orifice at the stock/oem diameter. True, it will not affect how much force is being applied by the oversized servo when it applies, but it will hopefully slow the apply rate so it does not hit as hard.

And lastly, the aftermarket 4th gear servo pistons and covers I find are a tad expensive for me due to severe budgetary issues. (this is why I hope that there are some nice/new/usable hard parts lurking inside this recently built transmission)

I am thinking of taking photos and detailing just what I find during the tear down. It may be a while yet as I do not have a warm place to work. When I am able to start, I could post them here if anyone would be interested.

 

[BrianPaul69]

The last 3 digits of "093" denotes it is a Corvette Servo, I can just about guarantee the servo is worn out as GM hasn't made them is 20 years. Sonnax & TransGo sell aftermarket ones that work well.....Some lesser aftermarket servos aren't worth the aluminum they're machined from!

All GM 4th servos are the same.

Sonnax 77787-02K servo pin is what I use in all 4L60 builds.

The slots cut in the servo cushion spring retainer is a TransGo SK shift kit modification....Keeps fluid from building up behind the retainer causing rough 1-2 shifts, Also helps with 3-2 downshift clunk.

Hello, I'm also dealing with 2 different aftermarket Corvette servos from unknown sources. One has TAIWAN casted right on it which I should have caught sooner and the other set just have some number that doesn't match anything. My question was sort of asked already but not addressed. I am wondering what the clearance should be between the servo piston and the housing?

I measured the both servo dimensions with my dial calipers and found almost the same numbers as zhaarnak02 who started the post. The servo piston O.D. where the small D ring goes measures at 1.758" and the servo housing bore measures approximately 1.795" I.D. leaving a clearance between the two parts at about 0.037" which seems VERY excessive. The D seals on the servo I removed ( the TAIWAN unit ) were looking funny like there was a small 90 degree twist when installed it. What I would ultimately like to know is the correct clearance between the OEM servo piston to the housing as this one cocks sideways quite a bit. Thank you in advance.

 

[clinebarger]

I don't have a new Vette servo to measure, Not that I've had a need to.

First off....D-Rings are trash for this application! OE style scarf cut PTFE seals work very well.
I install the small seal & test fit the 2 servo halves together, They should fit snugly.
Then do the same with the larger seal in the servo bore in the case.

I've never had issues with the TransGo 7-2P.

 

[zhaarnak02]

I personally agree with Cline. This is my first dive into this transmission family, and I am still doing research. I do NOT apologize when I say that when coming across all the servo "D-Ring" "hoopla" my "Gut Feeling" was to immediately file the D-Rings in the "solution in search of a problem" category. It has been MY experience, from my earliest forays into transmission rebuilding when I was a brash young lad, that a significant percentage of the parts offered by various transmission parts suppliers fall squarely into that exact category, and a great number of these supposed "solutions" can and will cause problems. It can take a significant amount of research in wading through the sheer number of "Solutions" that are available to a beginning transmission rebuilder, and until their knowledge base expands, they can (and WILL) be at the mercy of the parts suppliers. That is why people like Cline, those individuals that freely give of the knowledge that took years to acquire and learned in the "school of hard knocks" are such a treasure to the people just getting started in this field. My SINCERE thanks to ALL of YOU!