C4 is a major bog

[bbyrnes1]

Hey guys,
I can't help but notice that the C4 is totally dogging down what power my 240 actually has. The engine revs free as a bird while in park, but I put it in drive and hit the gas, tires don't spin and it sounds like everything that's in the engine wants to come out.

I've read that C4s and C6s are known to suck power, but even when I let off the gas to coast I have a lot of drag from the tranny that tries to slow me down.

Is this just the nature of the beast, or is there something in the guts of this thing that could be providing more resistance than normal?

Thanks guys,
Brandon

[Donnie]

While it is true that a gear pump takes 4 or 5 HP away from your engine.....I would suspect something else ...Throw it into neutral at 50 mph & see if it is still "dragging"......Does it shift OK up thru the gears? Are you noticing ANY other symptoms ? Do you have engine braking in Manual low?..Burned fluid? A converter sprag slipping will give you a slow driveaway & a seized sprag will feel hike you are hitting a wall at 40 / 50 mph. But will be strong when pulling out.........Engine tired? Brake dragging? A converter sprag not holding will feel like your engine is working hard, but you are hardly moving...........wait for other opinions............Donnie.............may be the converter???????????

[bbyrnes1]

It does shift kinda hard through the gears, but nothing crazy. That's probably just the modulator.
My theory is the converter. When I'm stopped the truck just wants to go-baby-go, but when I floor it seems like there's just seems to be a lot of load.

Engine is rev happy in park and neutral, brakes are all in adjustment, diff fluid and trans fluid is new.

[Whateverman]

you can rev the p1$$ out of nearly any motor in neutral (even ones that barely run) i really doubt the transmission is the real bad guy here... how many miles are on your 240? i'm betting its getting a little tired.

[jzjames]

Yeah, I think C4's are one of the best trannies.

[Donnie]

Stop by your local trans shop & ask if a tech can drive the truck.. CONVERTER problem's are easy to diagnose while the truck is driveable, or the converter is cut open & all part's are on the bench...A converter on the bench is a bit more difficult to diagnose by the untrained eye..Donnie

[bbyrnes1]

OK back to the modulator,

Is there supposed to be just a rubber vacuum hose running to the vacuum modulator, or is there supposed to be a hard line with vacuum hose on either end? A pic if anyone has one would be awesome. BTW it's mated to a 240.

Thanks,
Brandon

[Whateverman]

hard line

[Donnie]

Before going too deep, have you pulled the shift lever into manual low to make sure that you are not getting 2nd gear starts??....Donnie

[bbyrnes1]

It's shifting through all the gears. I reckon the biggest issus I'm having is it downshifts smooth as glass, you don't even notice it. It upshifts where the RPMs should be, but the upshifts are definitely noticeable, and they really thud into gear at higher RPM.

Given the accurate RPMs of the shifts, I'm not sure it's the vacuum modulator. I did notice that one time I put it in drive after parking uphill, and it really didn't like shifting into gear under a load (no I didn't use the e-brake). And since then it seems to be acting even weirder. It'll clunk when I'm slowly coming to a stop at a traffic light when everything disengages.

I don't know if it's necessary to rebuild this thing, since all I'm really noticing noteworthy is hard upshifts, but they happen at the right RPMs. And maybe I'm asking too much of this transmission? Should it glide through the gears like butter or do these things inherently jarr you a little bit when upshifting?

Thanks,
Brandon

[Donnie]

Hi, did you just get this truck? Has this problem with the firm upshifts just started, suddenly? If you just got the truck, perhaps the PO installed shift program? When you say that "the downshift's are smooth" are you talking KICKDOWN, as in 3rd to 2nd?
Or COASTDOWN like when you are doing 50mph & are approaching a stop sign....coastdown shifts should be smooth as it shifts to lo to prepare for a driveaway...full throttle kickdown 3/2 shift should be firm
WHAT HAVE YOU DECIDED THAT MAY BE CAUSING THE LAZY STARTS......that you first mentioned at the beginning of this thread?...donnie

[bbyrnes1]

No I didn't just get it. It's never upshifted very smoothly. And it's a later C4 transmission. So the history of it is unknown. I'd seriously doubt someone put a shift kit in this truck; when I got it it was nursed along with zipties, jacked wiring, and shade-tree fixed parts.

The downshifts from a coast are perfect, the kickdown downshifts are as expected, a little lag then it engages. It's only hard upshifts that are my problem. It's not a firm upshift, more like a thud and a lurch as it goes into gear. After a little more attention being paid to the lazy starts, like you guys said it's probably just a tired engine, so I'm not concerned with that.

What parts or adjustments do I need to pay attention to?

Thanks again,
Brandon

[Donnie]

Brandon, is it the 1/2 shift or the 2/3 shift that is bothering you , or both?....The only adjustment that you can make is the second gear band.
If you have an inch pound's torque wrench, loosen the lock nut & tighten the adj screw ( that's the one on the drivers side) to 120 inch pounds & back it off 1 & 1/2 turns. Hold the screw there & lock it down. If you lack a torque wrench, loosen the lock nut & tighten the screw snug with one hand using a short 5/16 wrench, no gorilla pull here, just snug....kinda hard to explain "snug" on a keyboard, but I think you get it. Back off same 1 & 1/2 turns..Hold the adj screw & lock it down.
That's it for the band...........the only other adj that you have is the downshift rod...it is adjustable at the carb end...you want the rod fully stroked at WOT..a 5/16 screw is here to adj..........also make sure that the RETURN spring for the downshift rod is not broken or dis-connected and that the rod is not rubbing on ANYTHING........heater hose, vacuum hose to brake booster, etc.........good luck..donnie

[bbyrnes1]

It's 1-2 shifts and 2-3 shifts. I'm actually starting to think it might be either the modulator or the raggedy hose that connects it to the intake manifold.

hard line

Is the hard line supposed to connect directly to the intake manifold, and then have a short rubber piece that goes into the modulator?

Also, I found that gas was getting to the modulator. Is this normal and how can I fix it?

Thanks again,
Brandon

[Donnie]

YES, gas will destroy your modulator. Replace it & loop the line to the modulator up to the firewall, higher than the fuel bowl before heading down to the trans.
Ford corrected this problem in later years by installing a plastic connector with 3 or 4 ports up high on the firewall & running lines from it.
If the carb sneezes it will allow fuel into the mod line & destroy the diaphram , usually this will makes shifts late and firm, carb backfires(sneezes) can also take out the economizer valve in the carb, mostly with Holly carb's though, less with Autolote's / Motorcraft
Repair the line & replace the modulator & see what happens..........let us know........donnie