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Discussion Starter · #1 ·
OK, so I got this problem with the trans slipping. This might seem long, but I want to give as much details as i can.... :whiteflag

Background; mud bogging it, my fist time for years, started to sink a little much, dead stop... and "rocked" back and forth and out... one of the "rocks" I went from 1st to R at like 3/4 throttle...(I know, I know... :banghead been a while since I played in mud, I'm out of practice and pannicked a bit.) :doh0715:

The trans was a little slugish before this, but no slip realy, and shifted OK, just shifted lighter than I am used to in the other truck... Figure it was tired/worn good before I rev shifted it. Ie not all my fault... ;)

Adjusted the band, no help. Changed the fluid, no chunks or anything beyond normal clutch wear particles... no antifreeze in the fluid, fluid not burnt, wasn't low on fluid either.

The slipping got twice as bad or more after changing the fluid... before it was a slight slip starting(in drive) in 1st, slight slip as i went into 2nd, 3rd fine. Shifted fine.

After the change it was chatter type slip(In drive) in first(feels like a regular clutch does when its going out so I know at least that pack need re-built) and a slip all the way up through second till it went into third. Still shifted fine.

Sometimes when you start out cold, it feels like it needs to pump up pressure or something... put it in reverse and it grabs fine, but in drive you can floor it for a minute or so, let off and it will catch fine... sometimes it will start cold in D fine, but do that and not catch In R... Won't do it again after a mile or so. Since one gear is fine but not the other, I assume the torque converter is OK, if it was that, it wouldn't go in either one.

You can barely feel it go into gear,both by hand, and real light shifts while in "D"rive.


Since I know the feel of the chatter in 1st from other clutches is the friction plates worn, I got a rebuild kit(deleuxe sucker with all friction and steel plates, kevlar band, millions of seals and gaskets :shocked, etc.) when the band ajustment and oil change didn't help it...

I'm putting that off until I finish the garage(running out of summer, need to do that instead of work on the truck) and I will rebuild it this winter.


I've been driving it off and on, about every other day for 3 weeks, 4 or 5 miles a day playing around on a back road or the highway since the oil change. sometimes its almost perfect and sometimes its real bad... its not gettng any worse.. it just won't stay any better.

If I put it down in 1st, and punch it, really lay into it, and shift up as I hit the end of acceleration in each gear,to 2nd, then D(feel it go into 3rd); For a while after, in drive or otherwise it goes back to almost no slippage, and shifts harder(feels normal) for a while.(few miles; 2 or 3)


OK; I think I am getting somewhere;
When you drive it in "D"rive, and say you get going fast enough to go into third, then stop, but leave it in drive, engine running; when you start out again its sopossed to start in first again right?

it doesn't.

Sometimes it stays in third, some times it starts again in second.
To get it back into 1st, I have to pop it into neutral, then back into "D"rive.

So, its not shifting down right... Questions;
Could that cause the slip all the way through 2nds power range?

I have a vacuum modulator here to change, if that doesn't fix the shifting then the valve body is shot, right?

I've tried to give as much detail about what its doing/has done as I can, without repeating myself or rambling on in the process... :whiteflag

G.
 

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my 79 hangs in a high gear when i stop sometimes... its ether the vac modulator or the governor (im no tranny guy but this is in the tail) mine is messed up some how.
 

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Sounds like you might have more then one issue with your tranny. The chatter could be your clutch plates or a worn drum and the plates are slipping in the drum. As for the no go in first after you start it up, sounds like you have a bad seal that is allow the fluid to drain when it sits. Once you start the truck, this pumps the fluid back up and once prssure has built up, away you go. Either way, sounds like you may be looking at rebuild in the near future.
 

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Discussion Starter · #5 ·
OK, the vacuum modulator fixed the shifting... :chili::chili: it shifts down like its soposed to, and up with a better feel. Yo can feel it pull/engage good when you put it in gear too. Less throttle needed to get up to 55 too... more power getting to the ground.

What gets me, is that the 1st gear chatter went away. Gone. I was sure it was the clutch pack, but aparently it was the vac. mod. Maybe not shifting fully/engaging fully as it should and made it chatter as it went in/out/into gear?

She was a quart low on fluid too... not sure where that went, she was full the last I checked, a day or two after the fluid change. its dry on the bottom, and the Vmodulator wasn't obviously leaking in to the vacuum line(its got good vacuum too BTW) but a slow leak there and it would just pull it all into the engine...not like a fast leak the that would run fluid from the line when its taken off

When I drove it from cold start again later after changing that, it didn't need to do the "pump up" bit...but then again it didn't do that consistantly before. Will see how it is today when I go get it(ran out of gas at a buddies place... found a fuel pump leak)

It still slips some, I think in 1st, if you punch it and it kicks down it 1/2 slips/pulls for a couple seconds, making a gratting/slipping sound(started that sound yesterday afternoon before I changed the modulator) then goes fine...

Maybe since it shifts and catches harder now, the 1st gear chatter then catch became a full slip then catch?

I dunno.... :shrug All I know is that the Vac Mod change put me back to 95% of what it was before I messed up that day... Hell, its better than the trans in my 71(another C6) has been for 20 years... I'm happy.

Gonna get a buddy that knows a lot about trans to ride along tonight and see what he thinks about the sound.

I realy need to do some more reading on how these things work, I had no idea that Modulator could effect so many things...

G.

G.
 

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My C4 is having a similar problem at startup, if I punch it, it kind of slips around and finally catches gear. Also takes a while to drop into reverse. Doesn't always happen, just sometimes. I may have to change out the modulator.
 

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Discussion Starter · #7 ·
Yeah, change it out... only one bolt holding it in.. nothing to loose, except time, since a rebuild should include changing it anyway.

I've been driving it for a couple days, the rest of the slip went away... so did the hesitation it had from before I messed it up. better than it was when i got it. Sweet. It even worked great under load in 2 feet of mud last night(until I got stuck...). And this time when i rocked it to get it out(didn;t work though) I made damned sure the wheel stopped spinning and I wasn't at like half throttle(like the last time) before i shifted down to reverse or visa versa... I am painfully aware of a bad shift now... won't do it again for a loooong time.

Since I got the kit, I'll still rebuild it this winter.

G.
 

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Anyone know what the deal is with the different colored stripes are on the Modulator?

I see there is an option for a black, green, or purple, all are called out for '78-96 Bronco according to my parts guide.:beer
 

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Discussion Starter · #9 ·
I'm guessing here, so don't take my word for it, but I'd bet different ones for harder or softer shifting..... The one I got didn't have any stripes, but was adjustable, I was told for shifting sooner/harder or softer...


G.
 

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How are you checking the fluid? I found through the years with my auto trannies the best way is to pick a time of day thats not too hot or cold, fire it up (cold) and drive around the block at a normal speed. Up to 45 cruise stop turn around up to 45. Drive for a total for say 2-3 miles with a couple start stops then check the level. This gives you a good final top off oil level check and your initial slipping may go away.
 
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