Sonnax Servo Modifying question

ON the Sonnax Servo is it -.014 you take out of the grv dia on the larger of the 2 diameters?

Thanks Tore

From what I've heard/seen, this is only a problem with the Superior R servo. The Sonnax part fits in the bore nicely to me usually.

the groove in the large piston that fits in the case needs to be cut , but check it in the case first -the spring should pop the piston out on its own
Frank

Never yet had Sonnax one fit the case nice , to get them to move nice they need the large groove machined

Tore , I trim a little at a time till it fits nice and returns easy on the return spring. They seem to vary a bit , I find some only take about .010" to get a nice fit . I'm always worried about taking too much so creep up on it .

The tranny had the Sonnax spring in it and we had to walk it out of the bore to get the piston out.

Thanks Tore

I always use the factory spring as Frank Recommends . 135 or .143"
Have no idea how some even fit . The last one I did wouldn't even go in the case .

Were you having issues Tore ???

Yes I could feel there was flair.


Tore

So what does the groove diameter need to measure when done?

MIne was -.012 of what I originally started with.


Tore

I've done to -.014" as Frank advises although last one I checked the fit with .010" removed and was good so left it there

I've done 2 and had to take the 0.014" out both times.

And just to throw a curve  ball .. I fitted one today , was a nice fit , no machining needed .  I'D of large o'ring groove measured 3.255

Have to edit this , I originally tried the piston is with assembly lube , worked ok. Today went to assemble with trans oil and was sticky. Back to the minus .014" and nice again.

Thanks Gregaust. It has always been confusing to me if someone was saying to remove .014" of material in the cut for a diameter reduction of .028" or remove .007" material for a reduction in diameter of .014". Thank you for measuring the diameter of a groove on one that fit good.

Jon

.007" cut = .014" reduction
Frank

I have edited my previous post . What I found when I trial fitted I used trans assembly lube and piston returned ok
With trans oil obviously not as slippery , had to cut the -.014" .

Note I have edited previous posts .
Originally tried piston with blue trans assembly lube , obviously slipperier than trans oil. Nasty little trick I'm glad I found

I ended up having to cut the .014" . Started at 3.255", final measurement 3.241"

If this is a common known problem with their unit why don't they cut the extra .014 so the buyer doesn't have too?

DILLIGASDAVE wrote:If this is a common known problem with their unit why don't they cut the extra .014 so the buyer doesn't have too?

I guess it's not consistent from housing to housing on needing to have it cut. That being said, I've had to do it on the 2 that I've built.

When buying a replacement/upgraded servo for my C6, I purposely went with a Superior Super Servo due to all the feedback pertaining to the extra machining that had to be done to the Sonnax servo for it to work correctly. The only change that was made was using the original "P" servo spring instead of either of the springs sent with the Superior servo(as advised and/or recommended by Frank Merkl. Mr. Merkl, thank you once again for the great advice).

I've looked at the superior one , and fit was good ? I'm guessing it has the lighter springs like supplied with the Sonnax?
Does anyone ever use those ? I got quite a collection

Gregaust wrote:I've looked at the superior one , and fit was good ?  I'm guessing it has the lighter springs like supplied with the Sonnax?
Does anyone ever use those ? I got  quite a collection  

Gregaust,
Yes, the fit was good (although I'm NOT a transmission tech) with just a slight drag when manually pushing or pulling the servo piston in/out of bore. Never have had a flare or "bind-up" on 2-3 shift, whether at part throttle or at WOT. The servo was used in a '75 case.

Nice , thanks for the feedback, might look to that one in future.

Gregaust wrote:Nice , thanks for the feedback, might look to that one in future.

You are more than welcome, you have replied to a few of my C6 inquiries(between here and Network 54), always with great info and tech tips. Many thanks for the previous help.