c6 shifting hard into high gear

what are some of the causes for a c6 to shift hard into high? trans brake valve body, sonnax servo ,
it shifts good firm/ crisp into second but just driving around on the street it shifts hard and violent into high. it seems good going down the track at full throttle.

possible band dragging? loosen adj 1/4 turn?
it does not flair going into high at all according to the data log.

thanks, wayne

Has it always done this, or has  it started after a major change in parts in the transmission or other drive line changes?

Any changes to band servo piston or spring or apply lever? Edit: I see it is a Sonnax piston, I was trying to find out about the spring and supply lever combination and when everything went together timeline sequence of events deal.

I am just trying to get more of a baseline/timeline of events, not saying any of these are the cause.

I don't have a time I have not driven it on the street until recently. so i don't use high in the pits. the most recent changes were brake, servo and light spring.
it has a JPT apply lever .
thanks, wayne

wayney wrote:I don't have a time I have not driven it on the street until recently. so i don't use high in the pits. the most recent changes were brake, servo and light spring.
it has a JPT apply lever .
thanks, wayne

Is it a Frank Merkel valve body? If so I would contact him first before you change anything.

If you follow any ones well meaning suggestions it may compound problems for and easy solution and he will have the best advice to proceed forward from the start on his own setup.

Was the Sonnax servo machined? Not seen one yet that doesn't require it . And then with the light spring , could possibly be a tie up on the shift, I.E ,
Band not releasing before Top clutch applies

From the Sonnax instructions. Although their light spring is way lighter than a factory spring

For maximum servo apply, start with lightest
spring. If the 2-3 shift has excessive overlap,
switch to the return spring with larger wire diameter.

Some spring Weights for a comparison

Sonnax Light 20LB @ 1.84"
Sonnax Heavy  30LB @ 1.84"
Factory C6 0.135" wire  40LB@ 1.84"
Factory C6 0.146" Wire  60 LB@ 1.84"
Franks Double spring setup 60LB @ 1.84"

My c6 has one of franks trans brake valve bodies it shifts hard into third .I think it is supposed to do this .At the track it isn't a problem to me .But on the street it could become annoying .You might send your valve body back to the builder but really I think it is made to do so for clutch life .

Some more details would be good , valvebody type , clutch setups etc ..

the valve body is a broader . can't remember what I set the clutch pack clearance to . I looked at the data from the last pass and the the rpm nosed on the 2-3 gear change . dropped about 100rpm before the change.

I am thinking I am going to loosen the band adjustment and drive it and see if it makes any difference. or I might do it at the track and watch the data depending on time. does that sound like a solid plan?

wayne

wayney wrote:the valve body is a broader . can't remember what I set the clutch pack clearance to . I looked at the data from the last pass and the the rpm nosed on the 2-3 gear change . dropped about 100rpm before the change.

I am thinking I am going to loosen the band adjustment and drive it and see if it makes any difference. or I might do it at the track and watch the data depending on time. does that sound like a solid plan?

wayne

From the limited data we have in this thread here and what others have reported with these parts before is what I am leaning to.

1. If you try the band adjustment, check the shift at part throttle and see if it helps. It's never good to check thing's at full throttle or at the race track if it can be avoided.

2. Check the servo piston to your bore. There are a few threads around on that subject. It is widely known to be a problem and may be sticking.

3. Good luck with that Valvebody.

supervel45 wrote:
2. Check the servo piston to your bore. There are a few threads around on that subject. It is widely known to be a problem and may be sticking.

3. Good luck with that Valvebody.

I mentioned that earlier and asked if the servo was machined . With that light spring if it wasn't machined I'd near guarantee the servo is very slow if not sticking on the return. Especially since it is showing an RPM drop. That may indicate a bind??? on teh shift

To be honest I doubt the band adjustment will do anything. I'd be trying either the heavier Sonnax spring or a .0135" factory spring

Supervel, Have you had issues with that particular valvebody?

No I have not but, another member here I spoke with it about awhile back, who's opinion I respect on C6's threw in the towel on his and went to one of Franks and achieved what he wanted. It was also not due to lack of trying and contact with the manufacturer. Yes I do know you mentioned the servo piston mod. I was responding more to the OP's question on trying a band adjustment at WOT at a race track more them doing it under part throttle to find if a part throttle complaint gets better. I doubt it will help either.

Thanks for the input guys.

What should the piston to bore ( case ) clearance be ? The piston fit the bore smoothly by feel without the spring when I put it in there .

Time permitting I will try the band adjustment and drive it . I don't think I would have time to pull the servo but maybe . worst case what it burns the band ?

thanks, wayne

wayney wrote:Thanks for the input guys.

What should the piston to bore ( case ) clearance be ? The piston fit the bore smoothly by feel without the spring when I put it in there .

Time permitting I will try the band adjustment and drive it .  I don't think I would have time to pull the servo but maybe . worst case what it burns the band ?

thanks, wayne

The only way I can see the band burning is if it was way out of adjustment on the loose side, and a 1/4 turn more out causes it to not fully engage and it slips. That should be noticiable on your shift at WOT when you data log it again.

There is a difference to me in a hard shift discription and a violent one. A violent on to me is when it feels like the glass is about to break out the car on the shift. Is yours that bad?

what it feels like is excessive backlash in the rear gear . only during light throttle normal street driving . The gear has .009 backlash.

the band should not be way out of adjustment. I set it when I put the brake in . probably 9 or 10 passes.

wayne

Your backlash is not real loose in my opinion but U-Joints add a little to the driveline slack also and if you have solid motor mounts them there's that to consider in the combination of it all. It's about the hardest part of building a C6 to get a good WOT 2-3 shift that I would put up with a hard part throttle shift if it is not too brutal and nothing is sticking or malfunctioning.  Geargaust has the dope on the Sonnax mods I am sure so you can check yours or mod it if it need be. On the full manual valve bodies you have to remember that the governor and accumulators are not usually in play like an automatic valve body and they cushion some of the harsh shift feel at part throttle.

I would check that Sonnax against Geargausts spec's though since so many others have had problems with them if you truly feel that the trans has a problem.

it is supposed to shift hard into 3rd


you dont want it to shift easy

supervel45 wrote:Your backlash is not real loose in my opinion but U-Joints add a little to the driveline slack also and if you have solid motor mounts them there's that to consider in the combination of it all. It's about the hardest part of building a C6 to get a good WOT 2-3 shift that I would put up with a hard part throttle shift if it is not too brutal and nothing is sticking or malfunctioning.  Geargaust has the dope on the Sonnax mods I am sure so you can check yours or mod it if it need be. On the full manual valve bodies you have to remember that the governor and accumulators are not usually in play like an automatic valve body and they cushion some of the harsh shift feel at part throttle.

I would check that Sonnax against Geargausts spec's though since so many others have had problems with them if you truly feel that the trans has a problem.

thanks very much. U-joints and all are good . I will drive it around on the street some more and see how bad it is. I haven't driven it much at all light throttle .

wayne

On the Sonnax servo , I have followed Franks advice , the groove is cut .007" deeper , ( .014" from the total diameter ). Final piston diameter 3.241", originally 3.254" . I usually cut a little at a time and try it . I've not found one yet that has been the correct size

Be sure to test with trans oil. Assembly lube gives a false feel

Wayney if your valve body isn't using the modulator you really cant expect it to shift easy .With the solenoid replacing that modulator and a reverse pattern valve body hard shifts are the norm.C6s need a hard shift on the 2-3 so the clutches will last .As others have said band adjustments servo this and servo that isn't going to change the 2-3 much I don't think .I like mine to shift hard I know my clutches are going to last .You might call Jay to see if he can do something to your valve body .Somehow though I think you need to give it a chance I don't know your car but most likely you aren't going to the mall in it .Good luck and check back in with us .Doug

Gregaust wrote:On the Sonnax servo , I have followed Franks advice , the groove is cut .007" deeper , ( .014" from the total diameter ). Final piston diameter 3.241", originally 3.254" . I usually cut a little at a time and try it . I've not found one yet that has been the correct size

Be sure to test with trans oil. Assembly lube gives a false feel

THANKS,
wayne

manofmerc wrote:Wayney if your valve body isn't using the modulator you really cant expect it to shift easy .With the solenoid replacing that modulator and a reverse pattern valve body hard shifts are the norm.C6s need a hard shift on the 2-3 so the clutches will last .As others have said band adjustments servo this and servo that isn't going to change the 2-3 much I don't think .I like mine to shift hard I know my clutches are going to last .You might call Jay to see if he can do something to your valve body .Somehow though I think you need to give it a chance I don't know your car but most likely you aren't going to the mall in it .Good luck and check back in with us .Doug

I am going to drive it some more, It just caught me off guard that it was soo much harder than the 1-2 shift .

I'd be verifying the servo first before going much further . Unmachined and that light spring could sure be the issue. If it is a tie up on the shift it will lead to early band and clutch wear

As I quoted earlier right from the Sonnax instructions. Excess overlap can be felt as a hard shift. The servo is easily removed from the outside. Can also verify then that it is free and can easily return on its own
From memory that valvebody relies on the spring only to return the piston. There is no pressure to help push it off. Jay I think supplies a heavy return spring

For maximum servo apply, start with lightest
spring. If the 2-3 shift has excessive overlap,
switch to the return spring with larger wire diameter.

Backing off the band adjustment is only going to help the wedges fall out. Don't do it.

Gregaust wrote:I'd be verifying the servo first before going much further . Unmachined and that light spring could sure be the issue. If it is a tie up on the shift it will lead to early band and clutch wear

As I quoted earlier right from the Sonnax instructions. Excess overlap can be felt as a hard shift. The servo is easily removed from the outside. Can also verify then that it is free and can easily return on its own
From memory that valvebody relies on the spring only to return the piston. There is no pressure to help push it off. Jay I think supplies a heavy return spring

For maximum servo apply, start with lightest
spring. If the 2-3 shift has excessive overlap,
switch to the return spring with larger wire diameter.

pulled the servo last night. piston did not come out with spring pressure. took to work, machined to 3.242 put back in with factory spring .13? wire. i will find out friday how it does.

wayne