C4 transmission seems to don't convert the power to the wheels


Apr 27, 2019
Hello everybody,

After a rebuild/restore of the engine it is not given the impact which i hoped for. Because i had to brake the engine in i found out that when i am standing still for a while eg. traffic light then the car really accelerate from a standing still. After the shift 1/2 and or 2/3 and you press the pedal to the floor it goes not with a really- expected- acceleration. I purchased the Hayness manual for the Ford Tranny's and following the troubleshoot it seems that the oilpump could be the rootcause. Has/can anybody confirm this idea. So far i am -yet - not able the measure the pressure, but if this can point out i will do some efford the measure it.( manometer no problem but the right coupling and hose ) Something i must do to point out the problem??
I haven't yet inspected the filter but i guess even its dirty it won't clear this major problem.Something i must do???
If it is the oilpump given not enough pressure is it then possible to repair only this item with the C4 still under the car or is a overhaul the only answer?
Also some expected problem inside the torque-converter because when you drive a bit backwards, brake, shift to Drive manytimes then the engine stalls. Hayness points here to the one-wayclutch inside the torqueconverter.
Question, does an overhaul of the converter give you more power towards the system.
Reparing/overhaul a C4 costs a few bucks, say about 800-1000 euros including the converter and sometimes it looks that overhaulingshops tells you not the real story so they can sell you a new one instead of some repair. Aside of this i can tell that the tranny shift quit well no delayed or slipping shifts . The oil is a bit brown and after a ride and i checked a few times the dipstick there are always black deposits on it.
So the main question remains, complete overhaul or is an repair possible and worth it.( This car is getting making me broke). Is this the right expression, i doubt . Sorry.
Again greetings from Huissen, the Netherlands Jos T.
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A C4 can be rebuilt at the house. Suggest all TCI kit and parts. A C4 does not have a lockup torque converter. The last couple years were upgraded to C5's and did have a lock up converter and a small extra valvebody to run it. For performance use stay with the C4 version. A C5 can be easily set up as a C4 if needed. A C4 has to be full on fluid, have the bands adjusted and is best with the kickdown linkage in place. If not using the kickdown, make sure the lever on the trans is in the normal not kicked down position.
Hello Rcdgl and mr General Karthief, Thank you so far for the reactions.
An overhaul is about 1000 dollars wich is a lot concerned the value of the car. Say rougly between 2000 and 3000 worth if im happy (PS what is a foxbody 1979 worrth in the USA?).. Maybe dum question but what is a TCI kit? As mentioned i do have the hayness manual. Also i did a quote for an overhaul only on the torqueconerter. Expect a message this week.Maybe i should in mind hat an automatic has always slip say up to 20% and deal with the what sluggish performance. Also it is very difficult to get a good reading on the dipstick. ANY TIPS or Techniques???
Question: if i drain the tranny And the converter how much oil i have to put in ,aprox? I have a new gasket and modulator waiting for exchange. I checked and retorques the bands as good as possible( i do have a torque wrench but had to improve a bit on the socket to adjust the bands). When you drive the car on full trottle the shifts a firm not really slipping. Can the tranny be too full with oil and causes some bad things ??? O yeah i also did install an oilcooler cocncerned an upgrade of some 40Hp. Was/is this an good idea or is just the oil to cool for a good performance??.Thank you in advance
Hello, Based on your inputs i start with an overhaul of the converter.I own two converters i hope i get a refund or the overhaul cheaper if if i leave one there.According to Hayness-manual i shall trie to feel with a pair of pliers if one-way clutch is okay.Thanks sofar
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Hello everybody, i did another quote for an overhaul of the converter.This company will do it for 190 euro´s. yesterday i brought me spare one for an overhaul. Also ordered four bolts and bearings to do a driveshaft overhaul. Aproxx 250 euro for all is the quote of this company. They expect friday or monday he work will be done.Then its my job the exchange the converter and later the driveshaft in my own workshop.
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Stators aren't typically high failure rate items, HOWEVER, sprags can be.

The sprag sits inside of the stator and it is splined to the stator support (the larger spline you see when the converter is removed from the transmission).

The stator redirects fluid that is thrown from the "pump" portion of the torque converter at low speeds. In doing this, torque is multiplied. That means at low speeds, particularly during take-off, the sprag is holding the stator still, giving torque multiplication, which gives you that "feel" of lots of torque/power right off idle. When the sprag fails, the stator is no longer held, so it freewheels, much the same as what happens at low load and more engine speed, such as "cruise". And...there is very little torque multplication (if any, depending on the converter's design). But then when you punch the gas while you're cruising to accelerate past a slow car in the fast lane, the fluid flowing through the converter will help slow/stop the stator, redirecting fluid, giving you more torque multiplication for the pass.

So if the stator fails (or more often, the sprag), your take-off performance generally sucks. Steady cruise is not affected much at all UNTIL you give it some gas to pass or whatever, then it just feels like there is no torque, very similar to a manual transmission in high gear, you throttle up but it doesn't really do much unless you downshift.

finally, most of the time if the sprag or stator (or, well anything else inside the converter) fails, it will fill the entire transmission, the cooler, lines, quick couplers, basically anything that the fluid touches, with metal particles. Remove the transmission oil pan and then check for metal. If there is any, you're going to want to disassemble and clean the entire transmission. Failure to remove all of the metal (by flushing the cooler, lines, etc) WILL result in repeat failures of components.
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Thank you a lott Mr Junkyardwarrior. The man of the overhaulshop noticed already something strange on the converter while testing with a pair pliers (just as in the haynesmanual). he said that onewayclutch or?sprag fails a little already.
I have a geasket for the pan already so the plan was already to remove the oilpain. I wont to have look at the oilfilter etc. I will pay attention to metalparts etc. If so i will make another plan for the nearby future. Has to do with the costs.
PS what are the costs of an overhaul in the USA by the way.
Hi everybody, Last week the overhauled torqueconverter arrived . Because the car has no MTO at this time i took the engine out with the help from a hoist from a friend. I took the oilpan off the trannny and there were no metal parts in there, only a few particles wich were non/magnetic.(brakebeltparts??)
I collected about 7,5 liter of ATF thats 7,8 qts out of tranny and converter. Has anybody an idea how much ATF stays inside the trans??. Otherwise i ran with too less ATF inside. Following the books it should be between 9.5 till 10 qts!!?? I always find it hard to see what the level was on the dipstick. Yes i followed the procedures- oil warm, shifting through all gears and back and then check the dipstick. Anybody some tips how to check better
Now its time to get the engine back in place. Last time i managed to do it on my own. Friday night it failed during two hours on my own. Tonight another shot and asked my friend to help on monday. Expectations are high on the new converter. Although no MTO i planned to do a roadtest end of the week. A fine is a part of the deal/risk.
Thanks in advance.


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The 7.5 Llr was in with the torque-converter included.So still missing a few pints.
You can't drain the torque converter completely, even after repeatedly dumping fluid from it and getting it to the point nothing drips out, it will still have a quart or two in it. There will still be fluid trapped in the valvebody and elsewhere in the transmission as well.
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