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c6 3rd gear weak?? How to build it better???

5K views 22 replies 7 participants last post by  59megawagon 
#1 ·
Hello All: I am tuning on my 9.4 L twin 76mm turboed motor again and am wondering if anyone here has a fix for a weak 3rd gear in a C6? My motor makes 800 ft. LBS. of torque at 2300 RPM and I rip out 3rd gear all the time on the street. Yes my 59 ford ranchwagon 5500 lbs and has huge sticky rear tires so I do know that hurts it more. I run a 3.20 rear gear with a 32" tall tire. I am just wondering if there is any real fix for these trannys or should I just give up on it and build a th400 or a glide???

Thanks for any info.

Tom.
 

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#3 ·
Hello: I think high gear only has 3 plates and mine has a thinner steel end plate so I am able to add a 4th friction plate. as for line pressure I dont know? My trans is a 74 lincoln with a long tail shaft. But I think I have a truck valve body with a full manual shift.
 
#6 ·
Everyone talks Hp Hp Hp.... all the time but what I am talking about is low RPM torque???? 800 ft lbs of torque at 2300 rpm. I cruise down the road at about 2500 rpm in 3rd gear and floor it and it will rip 3rd gear right out. The transmission pump pressures I would think would be low and would have a harder time holding the torque?? Correct?? I dont care about horsepower... My car makes massive grunt and weights over 2 tons... Will this c6 ever hold up or should I just go to a Glide???

Thanks for any reply.
 
#7 ·
Put at stock powerglide or a stock th400 in it like your doing with a stock C6 it will be the same result!!you Need line pressure! a stocker VB with 50@ 2300 psi line pressure isn't going to cut it! you need a VB without modulated pressure ie ; 150 psi @ 750 rpm - 210psi@ 1500rpm and a stock pump it capable of making
Frank
 
#10 ·
Hello Frank: Thank you for all your input on this thread. You talk about unmodulated line pressure? Are you talking about just not using a vacuum line to the modulator or are you talking about a change in the valve body for a set line pressure??

Thanks for your comments..
 
#8 ·
Before you knock the C6 you need to address what was listed above . Franks info is all there ib the links . 4 frictions won't cut it . You need at least the 5 and a good brand clutch . But even the best components won't live without the line pressures listed above

C6 is more than capable but you at least need to know exactly what's inside the trans for it to have a chance of living
 
#17 ·
Or package up your VB and send it to Frank and he will make it happen.

D
 
#16 · (Edited)
as far as I know I have a truck VB with a Transgo manual valve body kit installed.

I also have a low first gear from a Aod and a 2.5 in. kevlar band. Oh and a "R" servo in the case.

Tom.

Frank: Have you seen this problem before? It is major wear on the forward planet. This is from less than 500 street miles. It is like a 1/16 in. groove in the steel planet.
 

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#19 ·
I thought with the weight of my car a lower first gear would be better.

P.S. I also use a 2500 stall converter.


This trans has been built by 3 different shops over the last 10 years. I have been led by the nose and told what I should do by all of them and this is what I have.... I am not a transmission builder at all but I have taken mine apart and put it back together and it still worked... I know there are guys out there like yourself that know everything there is to know about these but there are none like you in my town.
 
#21 ·
I was running this trans with no vacuum line to it and I guess that runs full line pressure all the time??? after the first failure the tranny guy said the planet was being eroded from running full line pressure all the time on the street???? Again I have no idea???? I run a vacuum line now to the trans....

Tom.
 
#22 ·
Not exactly . Running the Transgo kits with no vacuum does raise line pressure , BUT from testing i have done the line pressure tends to be erratic and a bit out of control .. It does clearly state in the Transgo instructions that vacuum must be hooked up..

With the vacuum connected it could be ok BUT again you'd need to be checking it with a vacuum gauge to ensure the pressure did rise fast enough to cope with the torque load you are throwing at the trans ..
The best way IMO is as Frank said , a manual valvebody with a good constant line pressure . You will find with this type V.B the pressures should be very stable , unlike leaving the vacuum off what you currently have .

As you've probably seen here Franks valvebodies are the best available for a C6 if you can get one .

Then build the trans up as per his specs and i think your issues will go away . All Franks setup and clearances are listed in the sticky post .. They are good tested + proven specs that work with his valvebody .

I don't know that i agree that excess line pressure eroding the planets , not heard or seen that before . After the trans is built a pressure gauge is your friend , needs to be checked then you know it is right and has a chance of living .
 
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