transmission slipping, please give advise!

Ok I put this c4 in the car last summer with new fliud and filter and never had any drivability plroblems until last week. now it takes forever to shift gears. it will shift out of gear and then the rpms will go up and then it will finally shift into the next gear. I really dont need this right now, I'm very tight on money. I added a full bottle of lucas stop slip, didnt help at all. I checked the vacuume line at the modulater and it isnt leaking fluid. I need this trannyto last until fall, then I will do the manual swap. it seems the only way to drive her now is like an old lady. and I am NOT an old lady! please tell me theres something I can do besides a rebuild.

I checked the fliud, it looks and smells brand new

 

mine was doing EXACTLY the same thing. the cure was a new vacuum modulator and vacuum line to it. they are adjustable but the best way to tell if your vac-mod is bad...pull the hose off it. if you get a bunch of tranny fluid coming out, change the modulator and hose. good luck

 

I agree with Scott. It could also potentially be a problem in the valve body also, though I'd lean toward the modulator. Either way, it is a mechanical problem and even though Lucas makes a superior product, their oil treatment really works, a "snake oil" fix only will compound the problem in time.

 

got a new modulater and put new vacuume hose on it, but no fix. I also adjusted the band. I did the procedure right and turned it out 1.5 turns. that didnt help either. what can I do guys?

 

I hate transmission fluid, but it's possible that your filter or should I say screen might be clogged. It's a gamble but if all else dosen't work change the filter and fluid.

Is this car a daily or have you been on it hard lately, the reason I ask is I've seen bits of clutch disc in the filter before and clogged it up right after racing. The tranny was ready to go the tranny heaven at that point or to the rebuild shop.

Good luck I've got my fingers cross for you!

Terry Gates
AKA Bossmav

 

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There are 2 bands to adjust on the c-4 if I recall correctly. I rebuilt a c-4 a few years back. I was very very careful when I did my band adjustments, I marked everything and did everything exactly how the books said to do it. I think you have to tighten it a certain amount and then loosen it a certain amount to adjust the bands properly. So if you have tranny fluid, the bands are adjusted properly, and the modulator valve is good and adjusted correctly, then your clutch disks are probably worn out which would require a rebuild. One other thing: if you pull the vaccum line off the modulator valve, there should be an adjustment screw on the modulator valve where you can adjust when the transmission shifts. I'm not even close to sure about this, but I think if you turn the screw counterclockwise with a small standard screwdriver that the tranny will shift sooner. Either way, you need to check all three things, and if everything is ok, your tranny needs a rebuild. There is a big difference between a shifting problem and a slipping problem though, I couldn't really tell which was the case with your car. If the car shifts out of gear under acceleration and then shifts back to the SAME gear a few seconds later, that's not something a modulator valve adjustment can fix. If that's the case, you check fluid and adjust the bands and if that doesn't work you have to rebuild the tranny. You can buy a rebuild kit for about 100 bucks at a good tranny shop, and you probably want another torque converter too which is another 100. Overall, not that bad when you think about it.

 

trans prob.

Sounds to me like rather than taking forever to get from one gear to the other, it's slipping all the way through 2nd on its way to 3rd.
Make sure you adjust both bands according to procedure:

Start with the intermediate band, as that is likely to be the trouble if it is a band problem. All the intermediate band does is apply second gear. That's it's whole life.
It's the square screw just in front of the selector linkage on the drivers side.
make sure you clean all the crap off the screw first, then tighten it to 10 ft lbs. Now back it off exactly 1 3/4 turns, hold it right where it is, and tighten the lock nut.
While you're at it, the low-reverse band is on the passenger side of the trans by where the vacuum modulator is.
Clean this one too and tighten it to 10 ft lbs as well. This needs to be backed out 3 full turns, then lock it down and test drive.
The other thing you may want to check is for good movement of the intermediate servo. It's the one on the passenger side.
There is a gasket there you'll want to replace if you decide to pull it apart to inspect.
It's spring loaded so it's kind of a pain to get back together, but if you use a pry bar against the floorpan it's no problem.
Pull the piston out of the hole and have a look at the Oring type seals.
other than that, there is a good possibility that something has gummed up one of the many passages running through the valve body and the trans case itself.
I have a diagram that tell what is what, if none of the above stuff works, I'll see about finding a scanner and getting you a copy of the pic.
Hope you win,

 

Have you access to a 10 feet of hydralic hose and a guage that goes up to 300 psi

If you do there is a port on the tranny that you can hook up to and watch the pressure of the main pressure curcuit during gear changes If it falls right off and comes back ever so slowly you probably have a leaking seal in the clutch pack or band actuator. . If the pressure is going goes down a little and comes right back up you can rule out the forward clutch seal or all of the seals but have a slipping clutch pack and or band actuator .

 

you guys have no idea how much I apreciate your help. courier11sec, Yes I tightened 10 foot pounds and backed it out 1.5 to 1.75. I havent adjusted the one on the passenger side. what would that do? Its not a problem of getting into gear. when it finally gets into gear it feels like a normal quick shift, it just takes a very long time between gears. it is only noticable under hard or moderate throttle, if I accelerate slowly than it seems normal. I am entering a car show next weekend, and I'd hate not to be able to street race anyone I dont know anything about rebiulding an automatic, and I dont have the money to pay a shop to do it. I'm sure I could do it with some help but Truthfully I'm scared of these auto trannys. Would a can of transtune do anything? I just am mad at myself for puting a couple thousand dollars in my motor and then puting a used hundred dollar tranny behind it. I should have gone all the way. ps. the new modulater I bought has an adjustment screw. which way do I turn it and what exactly does the adjustment do?

 

Modulator

I don't think adjusting the modulator will help you out.
All it does is allow you to raise and lower your shift points a bit.
Lightning has a good point. The port is on the drivers side right in front of the adjustment screw for the intermediate band.
The adjustment screw on the passenger side is for the low/reverse band. I just mentioned it in case you wanted to service both while you were there.

As a Last Ditch effort, if you are planning on replacing the trans anyway and have already tried everything else, an old trick
is to add about half a pint of dot 3 brake fluid in with your trans fluid. While this is absolutely NOT the right way to fix it, it has been known to squeak a bit more life out of a worn out old C4 or two.

 

Ive never heard that. does it actually help? does it act like a detergent for cleaning out valves or something?

 

Thats a OLD timer's trick and yes it does work to help a fading trans give a little more life. Sounds like it time for a rebuild.
Now I'm not saying that courier11sec is an old timer he just knows the tricks


Terry Gates
AKA Bossmav

 

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Brake fluid is pretty corrosive. Maybe it eats up a little of the clutch disks and makes them grab a little better. Who knows, but it's a decent idea. But BEFORE you do that, try adjusting the modulator valve. If the car only has a shifting problem, that is very fixable. But if the car is really slipping out of gear when you're driving, then you're most likely going to need to rebuild it. Best piece of advice i can give you is trial and error. Turn the modulator valve 2-4 full turns counter clockwise and take it out for a spin, see what happens. If it's shifting later/worse, start turning it clockwise, until you get the shifting points that you want. I know how you feel because my car wasn't shifting automatically from first to second when I finished my transmission rebuild. I was really pissed and then I decided to adjsut the modulator valve, and guess what, everything worked perfectly after that. Be sure that you're trying to fix the right problem here. If you add that brake fluid to a good tranny it's most likely going to eat your clutch disks away and ruin the whole thing (assuming that the clutch packs aren't already ruined). And even if you do have to rebuild it, it's not expensive. If you do it yourself you can do it all for about $200, which is thousands less than a shop would charge you. And when you're done you will have a brand new transmission.

 

I hear brake fluid softens the rubber seals and o-rings, making them seal better, so operation is improved. I've never heard that it was hard on clutch packs.

Also, rebuilding a C4 doesn't cost "thousands" at a shop, it's more like $750.

I would bring it into a good independent shop and have them do a pressure check through all the ranges. You could probably get a pressure check and any external adjustments necessary for under $200.

There is really only one way to really tell what's going on in your tranny and that's through reading pressures.

And quit dumping crap-in-a-can in there! If that crap actually worked, there would be no tranny shops. You're wasting your money.

 

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I guess it depends on whether or not you pull the tranny yourself. If you have a shop pull it for you and rebuild it, I don't think the bill would be under 2k.