Technical C6 shifting early and soft

I've got a c6 in my f100 with a 460. I bought the truck from a buddy that never finished it. He installed a B&M shift kit in the trans that was supposed to be good. It sat for 5-6 years before I got it. Now the problem.
It shifts into second almost as soon add the truck moves and you can barely tell it's shifting. It goes into third early also and flares a little when shifting. If I manual shift it, it shifts pretty good but still flares a little in 3rd but not as much as auto shifting. I put dex/merc fluid in it before I realised it was supposed to take type F. Would this make that much difference? It seems to me that it doesn't have line pressure? I pulled the pan last night and pulled the valve body apart and everything is in line with the B&M instruction sheet. I also adjusted the band a few weeks ago. Its spot on. I also changed the modulator and adjusting it makes no change. I'm lost. Anything i can check or look at while i still have the valve body and pan off?
Thanks in advance for any help!

 

I would air pressure check it while the valve body is off. I have seen on several occasions where someone has a trans that starts shifting like that and they think a shift kit will fix it. Most cases the clutches are toast causing the flair up or the lip seals are hard as a rock and that can happen from sitting for several years.

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How do I air check it? The trans has been completely dry until I put fluid in it a couple of months ago.

 

You need a transmission manual that shows the ports to check. You should be able to find one at the library or online.

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I air checked the trans. The low reverse clutch apply tested just fine. It had a thud, and held pressure. The forward clutch apply had no thud and all air escaped just as fast as it was going in. The reverse/high clutch would thud slightly but I would say 75% of air escaped by very quick. And the servo never moved. So what does this mean?

 

Time for a rebuild..........

Ray

 

That's what I was thinking but just wanted to make sure that's what it seemed to someone else also.

 

The seals are probably rock hard. A bandaid temporary fix that has worked for me in the past is to pour a little bit of brake fluid in the transmission, about 2 shot gl***es full. It causes the seals to soften and swell. It is not a permanent repair. I did several customers cars before who did not have enough money to rebuild their ******'s . It got them by until they could save up for the rebuild.

 

Well guys, I pulled the trans out and sure enough there were a few lip seals that were hard as plastic. I just totally rebuilt it. Everything checked out great and tolerances were great going back together. No hiccups or left over pieces so all is well...or not. IT STILL DOES EXACTLY THE SAME THING! What could be causing it? Would a bad servo cause this? I'm so frustrated with it.

 

Just a thought, you do have the vacuum modulator hooked up to manifold vacuum and not ported vacuum right?
Bill

 

Yes it's on full manifold vacuum. And adjusting the modulator has zero affect. I've tried a couple of different modulators also.

 

The servo operates the band for second gear. If the servo piston lip is hard like the lip seals were..
Would cause a slow or no shift to second. I would hook a pressure gauge up to it and check line pressure and governor pressure. Look at the chart in the shop manual and it will tell you what those pressures should be in which gear and speed.

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Put air to it again.

 

The seals in the servo are new also. I did a total rebuild. Everything looked great except for a couple of lip seals and the forward clutch pack was smoked. The others looked brand new. It doesn't seem to slip while in gear. It just goes into 2nd very early and almost unnoticeable and it has a fast flare up when it goes into 3rd. It also will not down shift at all when slowing down. You have to come to a complete stop for it to go into 1st unless you manually down shift. It will downshift at WOT so the kick down is operating correctly. I can't figure this one out.

 

your TV pressure is low.
Is the modulator pin installed? If it is, most replacement modulators are adjustable, screw it in clockwise to increase pressure.

 

Double check that you actually have good vacuum at modulator.....
and that the modulator pin is the right length.....

LW

 

Could your kickdown rod be out of adjustment? Disconnect it all together and go for a drive and see what it does

 

The modulator pin is installed and it has great vacuum at the modulator. I disconnected the vacuum from the modulator and plugged it. I wanted to verify that it would not shift. It would only shift if I manually shifted front 1st to 2nd. But it had a great feel, firm and positive. Would not shift into 3rd at all. Then I bottomed out the modulator adjustment and backed out 1 turn and put the back on it. Now it seems a little better shift timing but still very soft 2nd and flare going into 3rd. What the heck is going on with this thing?
I also have the kick down unhooked

 

The modulator pin seems to be one of the shorter ones. If I made a longer one at the Max length of 1.677, would that make a big difference? Is it normal to have the modulator all the way in and a long pin? I had some out of adjustment before and they didn't flare up when shifting like this.

 

I would check the governor.
Make sure the seal rings do not have to much side clearance. You don't want more than .005.

 

I put new sealing rings on the governor but how would I check side clearance? It was doing the exact same thing before and after the complete rebuild. Could it be something with the valve body?

 

Just use a filler gauge from the side of the ring the grove it sets in.

 

I just made a pin that is apprx 1.677 and is maybe a little better shift timing and feels ok going into second but not firm like it should be with a shift kit. It still flares fast right before shifting into 3rd. If I manually shift it from 2nd to 3rd it seems to not flare but still is too soft and lazy. Could it be a torque converter? I didn't change it, only drained it with the drain plug. It seems like a hard part failure or crack causing no line pressure since it happened before and after the rebuild?

 

If that governor support is worn and has to much side clearance on the seal rings it can cause shifting problems.
Personally I wouldn't use a B&M shift kit I would use a trans go shift kit.

 

Flare shifting into 3rd gear is a combo of several things. Primarily the 2nd gear band is dropping out before the direct clutch is applied.

The direct clutch clearance is too large perhaps. The band adjustment is too loose. The feed hole for the 2-3 shift is too small. Pressure is too low

2nd gear shift feel is a combo of the servo size and the apply arm "letter" on it. the letter denotes the leverage angle design of the lever. An "A" Lever would be for a 6 cyl application. I would use a D or E letter apply arm on a 460 eng application. An "L" servo cover works well with either of those apply arm letters mentioned.

Early shifts; Wrong governor for the gear ratio used. If a longer pin and screwing in the modulator adjustment screw does not help shift timing. Change the governor. The governor maybe sticking or the valves not moving at all

Vacuum feed to the governor.. Is this a direct manifold feed? Vacuum must drop at the modulator so the trans knows the engine load has increased. If vacuum is not dropping , that will cause early shifts.

Only thing I use B&M shift calibration kits for is to hold the trash can down. Personal opinion: after a few decades in the transmission biz

 

The vacuum going to the modulator is tee'd into the direct manifold vacuum going to the advance on the distributor. Do I need to move it to its own source? Mine has a 'N' on the servo cover. I adjusted the band to 120 inch lbs and backed off 1.5 turns. Is this correct? Would it hurt to turn it in a 1/4 turn or so and try it?

 

Curious to what this ends up being. We have one that's doing something similar but only after we hooked up the kickdown rod. Havnt had time to pull it off and see if it fixes it but if it does I can ***ume the rod is out of adjustment.

If it doesn't then I'm throwing darts just as you are.

 

It is best to have the vacuum hooked to a port by itself.

 

I am going to ***ume the trans has a push in modulator?
There are some really ****py modulators out there. I think I would try another modulator.
The one it should have has a purple strip. Reliable brands to use, are Pioneer #747013 or BWD #VM130.
If its a screw in modulator, I would put in a white stripe, I don't have the part number offhand.

The brand of shift kit probably is not the cause if installed properly. I have been building transmissions for 38 years and have used B&M many times without issues. Everybody has their own preferences.

The use of Dexron III instead of Type F is also not a problem.

Is the intermediate servo piston a black molded rubber type piston or an aluminum one with two O-rings?
If it is the molded rubber one, it can get hard as a rock and not seal.

Bill

 

The "N" servo is the smaller one. I generally use 80 inch pounds and 1 1/4 turns out. Likely you may not see a change if the band is readjusted slightly tighter. If too tight, the band will drag on the drum. Burn the band & drum.

I would check the modulator for colored stripes as mentioned.