C4 skips 2nd sometimes

[74bronc]

My C4 skips 2nd gear sometimes, but only under really light throttle. If the throttle is in normal acceleration or hard acceleration, it shifts great, but every once in awhile, it will shift from 1st to 3rd. Ideas? this tranny has about 2500 miles on a rebuild. It doesn't run hot, the fluid is full and looks good, modulator is good and hooked up correctly, nothing else is affected yadda yadda yadda. Anyone have this happen?

 

[thesnake]

My 73 did that just before it fried. I have not had it checked yet, so I'm not sure if the bands had slipped or what.<br><br>snake

 

[66horse]

I would ask whoever rebuilt it.

 

[Newt]

I agree with 66horse. With only 2500 miles I'd be talking to the rebuilder. What kind of guarantee did he give?

 

[74bronc]

[quote author=66horse link=board=5;threadid=12090;start=0#89408 date=1039315809]<br>I would ask whoever rebuilt it. <br>[/quote]<br><br>LOL!! That would be me!!!! I worked in a tranny shop at the time and my boss was a Ford dealer mechanic most of his life and knows the C-4 back and forth, and he helped me rebuild it. I have rebuilt quite a few GM products but this was my first C4. I am wondering if the bands just need to be adjusted a tad. Doesn't really bother me, I just don't want to jack up the tranny.

 

[Explore74]

The c-4 is probably the most simple rebuild of all because of the lathe cut drum seals instead of the @*$#? GM balloon type drum seals that always seem to get nicked. it sounds like you have a problem with the intermediate band. there is an adjustment on the side of the transmission, it's been too long since i have messed with it, but I know you loosen the lock nut, tighten the center bolt down snug, then back it off a specified amount(maybe someone in here can help me out). What has happened is either the band was defective, and the lining came off, the band looked okay at the rebuild, and wasn't replaced and now the lining has come off, or it was misadjusted to begin with. If you do try to adjust it, look at the bolt first, and if there arent 6 or 8 threads showing, that means it was probably adjusted right and the lining has probably come off. Don't try to tighten the band at this point, because you will burn up the drum it controls, and this is actually a pretty stout part in the ole c-4.

 

[Explore74]

oh yeah, if it is only occasionally, then you need to check the pressure accumulators(servos). You may have one with some lint (red rags are the mortal enemy of automatics) on the side of the piston.

 

[66horse]

[quote author=74bronc link=board=5;threadid=12090;start=0#89445 date=1039321145]<br>[quote author=66horse link=board=5;threadid=12090;start=0#89408 date=1039315809]<br>I would ask whoever rebuilt it. <br>[/quote]<br><br>LOL!! That would be me!!!! I worked in a tranny shop at the time and my boss was a Ford dealer mechanic most of his life and knows the C-4 back and forth, and he helped me rebuild it. I have rebuilt quite a few GM products but this was my first C4. I am wondering if the bands just need to be adjusted a tad. Doesn't really bother me, I just don't want to jack up the tranny.<br>[/quote]<br><br>Thats what I thought and the reason for the .<br><br>

 

[Broncobowsher]

My guess is valve body. Did you do any type of shift kit?<br><br>I am guessing that you may have a tired spring in the valve body. At light throttle you get the 2-3 shift before the 1-2. It has been too long since I studied hydrolic schamatics to see if the 2-3 has to wait until the 1-2 signal, or if it will override it?<br><br>Does when it shift normally does it shift 2-3 right after the 1-2? Light throttle, normal shifts?<br><br>Trade the valve body in on a reman unit before redoing the whole tranny. Most of the odd tranny problems I have seen are valvebody related. Hard parts usually have a real serious problems.

 

[74bronc]

[quote author=Broncobowsher link=board=5;threadid=12090;start=0#89826 date=1039463251]<br>My guess is valve body. Did you do any type of shift kit?<br><br>I am guessing that you may have a tired spring in the valve body. At light throttle you get the 2-3 shift before the 1-2. It has been too long since I studied hydrolic schamatics to see if the 2-3 has to wait until the 1-2 signal, or if it will override it?<br><br>Does when it shift normally does it shift 2-3 right after the 1-2? Light throttle, normal shifts?<br><br>Trade the valve body in on a reman unit before redoing the whole tranny. Most of the odd tranny problems I have seen are valvebody related. Hard parts usually have a real serious problems.<br>[/quote]<br><br>Yeah, if I accelerate normally, like off the line, it winds up, shifts 1-2 exactly how it should and then shifts 2-3 exactly how it should. If I start out with really light throttle, it will sometimes shift to 2nd and sometimes it will shift straight to third. It is most noticeable when I am turing in a green turn arrow lane and start out in light throttle. It did it this morning. After it does this, if I jump on the throttle a little bit, it will shift back down into 2nd and then to third, just like it should.<br><br>A little history on the tranny. I rebuilt it with the help of a Ford mechanic. Put it back in and got it running, but didn't have 3rd or reverse. Thinking it might be valve body related, I got a used valve body and threw it in there. That didn't fix the problem, so I pulled the tranny back out and found they had given me the wrong sealing washers that go around the front pump hub and fit into the forward/reverse clutch assembly. Put some new rings on, and it has worked great ever since, except for this skipping second. I still have the original bronco valve body but I have hesitated to put it back in because I put a B&M street/strip shift kit in it and I should have gone with the street, not the strip version!!! It is a little bit too hard of a shift for me. Feels like it is beating up the rest of the drivetrain when it shifts. maybe i will throw it back in the tranny and see what happens. I am also going to adjust the bands again to see if theat helps. I seriously doubt that the bands or drums are jacked up since the tranny works perfectly most of the time. Doesn't slip at all.<br><br>By the way, does anyone know the correct band adjusting procedure? I don't have a book that tells me.<br><br>Thank for the ideas.

 

[Explore74]

upon further description, i think we are making this all too complicated. 2 questions.<br>#1 Is the cam original, or is it of longer duration?<br>#2 Is the vacuum modulator of original type, or adjustable?<br><br>with a longer duration camshaft, you may not be pulling enough vacuum to initiate a proper shift under mod. acceleration, and the centrifugal weights are the only thing dumping pressure from the accumulator. If you have an adjustable regulator, pull the vacuum line off the regulator and adjust it a turn at a time untill you get in the ballpark, then fine tune it. If you don't have an adjustable regulator....get one.

 

[74bronc]

[quote author=Explore74 link=board=5;threadid=12090;start=0#89920 date=1039475341]<br>upon further description, i think we are making this all too complicated. 2 questions.<br>#1 Is the cam original, or is it of longer duration?<br>#2 Is the vacuum modulator of original type, or adjustable?<br><br>with a longer duration camshaft, you may not be pulling enough vacuum to initiate a proper shift under mod. acceleration, and the centrifugal weights are the only thing dumping pressure from the accumulator. If you have an adjustable regulator, pull the vacuum line off the regulator and adjust it a turn at a time untill you get in the ballpark, then fine tune it. If you don't have an adjustable regulator....get one.<br>[/quote]<br><br>The cam is a Crane Blazer 260/272, which is fairly mild in this motor. The engine develops plenty of manifold vacumm and runs very smoothly at idle. The modulator IS an aftermarket adjustable unit and I have played with the adjustment a little in the past. I haven't for awhile now.<br><br>Some more info. After thinking about this for awhile, I realized that it started doing it more noticeably after i fixed a small vac. leak in the line that goes down to the modulator. Before I plugged that leak up, I had a fairly hard 1-2 shift, especially when it was cold and it would rarely skip 2nd, really only when it was cold. After I fixed that vac. leak last week was when I noticed it would skip 2nd most of the time under light throttle, alot more than before. Maybe we are getting somewhere with the adjustable modulator. Maybe I should adjust it in a little more and see what happens. thanks for the ideas.

 

[Hnrys69]

Yeah sounds like vacum or modulator. I hooked mine up wrong (the vacum line) and it shifted all over the place missing gears and such. I would recheck that vacum line then maybe replace the modulator and see if that helps.

 

[74bronc]

I think the adjustment on the modulator is just a little light. I will try to adjust it this week and see what happens. I guess all I can do is experiment with it. The modulator is only about 18 months old and 2500 miles, so I doubt it is bad. Possible though.

 

[Explore74]

aawesome! hope you get that bad boy back on track!