Burned direct (third) clutchs on my c6

This is my street car.Fe power 427 with 428 crankshaft 3800 lbs.It has 3.50 gears a 10" ATI convertor .At one time I had a nice hard 2-3 shift this is manual or automatic .Over a period of time my 2-3 shift has gotten softer and softer .Couple of months back I changed the fluid (type f) lot of clutch dust in the pan .I built and installed a nice 950 out of spare parts and some new parts I bought just for a spare carb. Well after the carb swap that old 427 liked it so much it fried my c6 ! I did a pressure test before I pulled it .140 psi in park reverse 200 1-2-3 all 135 .This is with a tci automatic valve body.This am I got the transmission out again lots of clutch dust in the pan and in the fluid .Well it is like I suspected my clutchs and steels in the high gear pack are gone .This is a clutch drum I bought from Broader with the holes drilled in it and it holds five clutchs .The only thing is the steels aren't as bad as some I have seen these aren't really blue in color more of a black color not blued at all .On the other hand the clutchs have hardy any lining left on them and one is stuck to a steel plate .These were red altos .I am afraid I am to blame I found some of my notes on the and I believe I set my clearances in the 0.30s .Even with the worn clutchs you would have a firm 2-3 shift if you reved it up to 5000+ .Just driving around it was a soft 2-3 shift .The forward clutchs look great as well as the band .Reverse low look good too. I did an air test on the direct drum and there is no air leaking from the piston .I believe I went by the manual on the springs for the clutch piston .Finally this is my question do you all think my tight clutch clearances caused this ? Or do you think I would benefit from a better valve body ? Is there something I need to look at in the valve body this is an old style clicker valve body with the detents in the valve body itself so coming up with a replacement is harder than a newer one .All the hard parts look good inside also .I knew this transmission wasn't going to last much longer the added power killed it .It was slipping in drive and locked up in low .I will check back in a couple of days thanks Doug

I would keep the valve body, and put more clearance in the drum, and new seals, and try it.

Today I was able too look at my v.b. no sticking valves or other obvious issues .Really wondering if there is another pressure relief valve spring I could try .This one is a blue color .I have another valve body similar to this one .It has a green spring and it is at least 3/8-1/2 shorter than my blue spring .Everything else looks good .I had some thin steels and a new set of clutchs coming up with .050 for clearance should be a problem .Somehow I believe I need a little more pressure though

http://www.tciauto.com/tc/trans-line-pressure TCI specs at 2,000 RPM.

Loosening the clearance may work .  How hard do you turn it in first gear ? Those frictions would be dragging backwards in first gear could be what caused the heat . If the 2-3 upshift felt good that's a positive . If there was a tie up on the shift you'd think the band may show wear also



The pressure may be better a little higher . Did you do the pressure test with the vacuum disconnected ?  Less vacuum must = more pressure.

The band looks good I spoke with TCI and Broader they think my pressures are ok .No I didn't check the pressures with the vacuum line disconnected .My modulator is probably 2 1/2 turns in .So maybe try 1 more ? Looking over my notes my 460 drag car with a trans go shift kit has 150 psi in park .But it is a forward pattern manual valve body .In reality this car had a good firm shift in 1-2 and 2-3 maybe the cause of my clutches failure was my tight clearances .I will probably be going to the big city (Atlanta) to get my parts tomorrow .Thanks for all the comments and suggestions. Doug

https://www.429-460.com/t22747-c6-cluctch-clearance?highlight=5+clutch+drum+clearance+c6modulator+setting I always used to go by .010" per clutch, but there's this.

On your modulator you might want to check the pin lenght and the modulator valve clearance specs., while you have the trans apart.

Supervel the pin is the one that come with the transmission .I pulled this c6 from a 68 galaxie YEARS ago it should be the factory pin .With the screw in modulator you don't have to many to pick from .I believe mine has a white stripe .I can easily measure the pin length and possibly find another in my parts stash.What is it do I need a longer pin ? In my previous post the screw is turned in 2 - 2 1/2 turns whenever I get it installed and running I will give it another 1 1/2 turns .I believe my engine just has to much torque .With the 428 crank that my old 427 is a street beast .I had direct clutch problems in another c6 with a 460 that I fixed with a different valve body .But they weren't as bad as this one .I just don't want to do this again in 4-5 years .This transmission was built in 2008.I am getting to old to be pulling transmissions .Thanks for your and every ones help Doug

Doug you may have the correct pin, especially if it is original to the transmission. I went and found my old C-6 book and shift kit instructions, to find the specs. for you, that  "they" have. This was a SK6-7 shift kit from Gil Unger, so it may not apply to your deal at all, and you should ask your other sources for more input. The measured vacuum modulator is to be set at 10 3/8 lbs spring pressure on a scale, and fine tuned in the car. They list 1 5/8" lenght for 1973 and latter pin length. They show in their digram .030"-.050" clearance on the modulator on valve at the back of the center port to the rear of the trans with the valve pushed to the back " towards the modulator to remove free play ". In step four of the check they say and I quote word for word this, " 4. If less than .010, use a longer pin. If more than .030, shorten pin. " The instructions and the diagram seem to be in some conflict, but that's what they say and picture. It looks like they want .030" clearance to the rear on the center port of the valve and the case. The kit recommends a purple stripe modulator for 1973 and latter non EGR applications also. I would not make to many changes at once to your transmission, if you know the clutches did not have enough clearance before and it was shifting good before it went south.

Supervel you have been a great help to me and I really appreciate it! I picked up my new clutches and with a set of thin steels I am at .057 clearance to the snap ring .I also looked at my old steels I had three thin and two thick steels .With the two thick steels I was in the .030s on clearances probably .037 maybe a little more or less .I believe this is my problem at least I hope so .Whenever I built this c6 I went by the book and probably thought stock clearances would work on a street car .Doesn't seem so now .On my drag car I am at .050 plus .I will look in to the modulator pin but I believe it is alright .I got sticker shock yesterday at the trans. parts store .My red direct clutches were $76.00 for five .Luckily I had the steels .I will probably get this together in a couple of days and installed next week .It might be a couple of weeks before I can fire my comet up though .I have a new set of FPA headers coming so it might take a while .Thanks again for your and every ones help .Doug

Your welcome. I was thinking about the modulator pin lenght, and the instructions. I would double check it as it will affect your part throttle 2-3 shift, like you describe being weak and "cut loose" also. You have the screw in modulator so you don't have a lot of choice there. Could you follow my description on checking the modulator valve without a diagram, if not let me know?

Those instructions are a bit vague for me .when I installed my modulator whenever it was about go all the way in I could feel the resistance of the pin.I do plan to work on more adjustments whenever I get the comet back on the road .I have another Question about my return springs that I about to post so it doesn't get lost in this one .Thanks for your time and help .I really appreciate it .Doug

Well my comet is off the jack stands I am glad too!My transmission is shifting fine no leaks either .I did have to adj. my shifter cable and I gave the modulator an additional turn in but I have a nice 1-2 and 2-3 shift,The reason this has taken so long was my waiting for headers .Well that is another story they didnt work out as intended and I installed my old reliable hedmans .Hopefully my direct clutches will last longer somehow I believe they will .I haven't really kicked it to hard just yet but being an old gear head it wont be to long .I big thanks to all of you that responded to my call for help I have learned a lot from this and hopefully others will come to benefit from this post .Finding real info on old c6 transmissions is hard .The best I know of is right here Thanks and I will be back latter Doug .