I've got about 20K miles on my rebuilt C6. It is in a 79F150, with a fresh 400. For awhile I have noticed getting an occasional slip on the 2 to 3 shift, where the RPM's will quick up for a 1/4 second or so. The other day it did something new. I was towing my heavy boat up a long, windy, fairly steep grade that went on for several miles. As I got near the top, the tranny downshifted from 3rd to 2nd, and it just revved instead of engaging. It did this twice. Afterwards it acted as it always had and I made it home with no further problems. Tranny temp seemed fine, and my fluid level is good. Is this likely something as simple as a band adjustment, or a precursor to a failure?

 

do you have factory kick down linkage? if not this can cause a rev on the 2-3 upshift. the band could also be a problem. to adjust it loosen the lock nut (15/16 i believe) then tighten the square head bolt to about 12 ftlbs, after that loosen it 1.5 turns and tighten the lock nut. let us know what you find.

 

Check the band adjustment first. Tighten it to 110 INCH lbs and then back it off 3/4 of a turn and see if that helps. If not, then I would check the servo on the side of the trans to make sure its not sticking.

 

I will check the band adjustment. Yes I do have the kickdown linkage, it seems to operate as it should. What is the function of the servo? Thanks for the info!

 

The servo is what applies the pressure to the 2nd gear band. If it was sticking for whatever reason, it would not apply enough pressure to the band and then you would have a slipping 2nd gear

 

Ahh, I see. Now I'm eyeing those heavier duty servos with several springs to adjust your shifting. It's always gotta be something, not that I don't already have enough things to spend money on with this truck!
I'll check out the band setting next weekend. Is there a way to test the servo to see if it is sticking?

 

BeeBoy, did you in the past since the rebuild change you filter? If you did you may have blown the gasket that is between the lower valve body and seperator plate. On one pressure port the gasket is about 1/8" wide by 1" long between ports and can blow out, not uncommon. With the gasket failure the trans has a slow death. Better to lap the seperator, lower and upper valve body and install without the gasket. One less problem to worry about with the C-6. By the time you detect slip, alot of heat is generated, your in the damage zone. Carl .......o&o>........

 

I have changed the filter and fluid since the rebuild. I had the 2 to 3 shift slip before that. What is the correlation between changing the filter, and blowing a gasket in the valve body? I never opened up the valve body.

 

beeboy, when you unload the torque on the gasket during a filter change there is a chance later on the gasket will blow out. some trans shops add adhesive compound to the gasket in this "known to blow" area. It's after you do a filter change and pat yourself on the back for a good job done that things start to go bad. Like wanting to do good and you make things worse.
With a 1 to 2 lazy or slow shift engagement you may need the band reset. 2 to 3 where the most torque is thru the clutch pack, your screwed. When you have internal bleeding in the trans (seals, gaskets or clearances) this results in less applied pressure to the clutches. The trans shop who rebuilt it will tell you you worked on it and your screwed, warranty? If the clutch pack isn't smoked you may want to check the gasket against the seperator plate. By the time you have symptoms pulling heavy loads, damage is done. Carl.
......o&o>.....

 

So if it is a gasket issue, this may be a good time to put in a Transgo kit. If it is the clutch pack..rebuild time. Sounds like I may need to take it in to get checked.

 

beeboy, if it's still slipping your goose may be cooked. Pull the shifter body off yourself and check the gasket. As far as shift kits go i'm running without one and have a full kill 2nd, around town it annoys me. I have the forged band, extra clutches, pressure fed sprag, high leverage arm and heavy governor At full throttle the shifts are still firm and this is all done with normal oil pressure.
Up shifts at 12 & 18 mph or 4,400 full throttle up shifts. The trans stays in 3 rd at 15 mph around town with light throttle, none of the up, down, up, down shifting that some trans do. Less wear. Report on what you find in the trans.
Carl.....o&o>.........

 

It only did twice on the hill, then acted fine after that. Drove several hours home without any further shifting issues. I'll try to pull the shifter body off this weekend and have a look.
I called a few tranny shops today to see their opinions..and everyone has a different one! From a fried intermediate band to a worn actuator.

 

Many people are thinking that 2nd is slipping, band adjustment, piston seal leaking, stuck piston. you stated 2 to 3 slipping, that means 3rd is slipping not 2nd, correct? Just like in a manual trans, a weak clutch will slip in high gear. With it not slipping all the time you may not have destroyed the clutch pack for 3 rd or high. Go inside the shifter body. Carl....o&o>..........

 

Well, it sometimes doesn't shift crisp on the 2 to 3 shift, the RPM's kick up for a split second until 3rd grabs. That isn't my major concern. Biggest concern is that 3 to 2 downshift where 2nd never engaged.

 

beeboy, i ran your symptions across my trans friend, he is a 66 year old X top fuel drag racer that designed the "Lenco" transmission". A custom trans one man shop that repaired "B & M CRAP" for a time but did custom transmissions for over 40 years. His P U is a 67 Dodge 440 with a 4-barrel progressive linkage propane, hand made, back to story. Without burnt oil, foaming and over temp conditions you may be able to save what you have. If you ever got hot or replaced the filter, the gasket may be blown after between the seperator plate and shifter body. Ford shifter bodies will stick and not shift with any dirt vs GM that can handle dirt particles and still shift. Remove the shifter body, check for gasket failure and freedom of valve function, clean the shifter body. Lap the seperator plate, shifter body and assemble without a gasket. If everything is lapped flat any leakage will be harmless. If you screw up and miss any spring or check ball, your screwed, be careful. The oil filter in the trans will only filter out the big lumps, add a remote filter in line with the cooler line. This can be mounted on the inside of the right frame rail. I have photos some where on my installation. Add a flat magnet in the oil pan as well as in the remote filter. Install the shifter body without the paper gasket under the seperator plate. If the trans filter gasket (between the filter and shifter body) is metal, use it. If it's a paper gasket it will crush down in time and you will loose bolt torque. This will help with blowing the gasket between the seperator plate and shifter body. If you use a gasket it can cause the problems you have. Do the above and report back with results. Good wrenching, Carl.....o&o>...........