What causes the engine to surge when the transmission shifts to third gear? It doesn't happen all the time;are there some seals that are wearing out or is it something more expensive? It's a '79 C-4 out of a Merc. Thanks.
Sounds like a valve body gasket. Could just be old fluid or need of filter change, but sounds like a valve body gasket.
I assume you say that the transmission slips when it shifts to third. The lip seals may be wearing out. Does it only do it when its cold or also when its hot? Pretty much the transmission needs to be rebuilt if the seals are bad. Have you chaged the oil in it? How did the oil look did it have any metal on the bottom of the pan?
check and see if it surges (slips) in Reverse too. If so your reverse high clutch seals or discs are shot. If not it may be a slow apply of the clutch when in Dr, meaning valve body area.
This is called flashing (over rev) between 2-hi. This is a common happening with the C-4 and there are several things you can do and one is to modify the servo. If you google this flashing problem you can find a world of information on making simple corrections. This is of course if you have a good C-4 to begin with.
its called a 2-3 flair.... theres a valve and spring under the filter, if someone has changed the filter they could have dropped that valve out of its seat. This will cause a 2-3 flair.
Does this happen under hard acceleration? Does it shift on time or a bit early? It could be that your modulator pin is too short. DAVE
Short modulator pin???? First time I have heard this, how many lengths are there? My C4 shifts fine manually, but too early in drive. It was fine after rebuild but has not shifted good in drive for awhile. Doubt it has anything to do with pin, just did not know different lengths existed. Joe
Thanks for the responses. New filter,new oil,no metal in pan,happens only when hot,and only in 2-3 gear shift. Reverse is fine,modulator valve pin is the original,modulator valve replaced as the original was leaking fluid into the manifold. Well if I pull the tranny for a valve body gasket change ,I might as well get the rest of the transmission seen to as well. It will last out this season I guess. Appreciate the tech info.
Okay, Some of these responses are accurate, but the most obvious cause for this problem has not been posted yet. How long has it been since you have done a band adjustment? I build exclusively c4 trannys mild to wild (daily driver all the way to my own c4 trans brake valve bodies) and this is the most common cause of c4 problems along with improper fluid level. 120 inch pounds and back off the adjuster 2 turns on both the low / rev and intermediate band adjusters.
There are different lenght modulator pins for the later c4 but you can convert to an adjustable modulator instead of changing pin lenghts and it makes the job of tuning shift points much easier. For a non EGR engine, use a "yellow stripe" adjustable modulator. For firmer and later shifts turn the screw clockwise. NEVER turn the adjuster in more than 5 turns.
thats called a 'ford shift'. fmx trannies do it worse, but c4s do it to. run an auxilary cooler and a deeper pan and you can tame it some.
Snake9t9;I think you might have nailed it.....band adjustment ! I dont recall doing that particular job,probably CRAFT disease .I'll do an adjustment tomorrow. The fluid level is right on the mark. Thanks.
After you check that the linkage is adj. correctly,fluid is up and looks ok, pull the vac. line off your modulator and see if any trans oil comes out,if so replace with an adjustable green band mod. They do make packs of different length pins for modulator pressure, it's the best way to get proper pressure but you can get the adj. mod and will work ok.(when your playing with the screw on your mod.your distorting the diaphram in the mod)Each full turn in is 3-5 lbs. of pressure.The band adj. for your C-4 is 10 ft.lbs on both ,the front one (for second gear) back off 1 and 3/4 turns and the rear is 3 full turns. I think your prob. is maybe in the intermediate servo (opposite side from the front band adjuster) or in the High/Rev. clutch.Will it happen more cold then hot? Theres some sharp guys on here and I know we'll get it figured out.
57 shaker;The modulator valve is new and is the adjustable variety.The overspeeding happens only when the transmission is hot. I'll be out in the shop tomorrow and will adjust the bands and do another linkage check. I'll let you know the results tomorrow. Thanks for the help.
I really can't see adjusting the intermediate band helping your situation. When you adjust the manual linkage adjust it in the drive position not 2nd,1st,park,only in drive.If your not sure how to do this start car,pull lever from park ( with foot brake on) to rev.,to neutral and slowly pull lever down just to engage drive ( not against the detent but just to where you feel it go into gear, turn car off leave handle where it is and get to the adjustment nut on the linkage under car and loosen the nut free, now go up top and pull lever down against the drive detent and hang a 5-7 lb weight on the handle or someone to lay their arm on it while you go under car and tighten nut and your linkage is adjusted.You should have already made sure that your mounts are in good shape especially the trans mount. It sounds like a long drawn out process to adj. linkage but you can do it pretty fast.Let us know what you find.
Thanks for getting the band adjustment correct! That is exactly what I was thinking too for band adjustment. However there are two things that come to my mind first: 1) He says it flairs on 2-3 shift, not while in 2nd, so the band adjustment may not be the problem. 2) What I am thinking is that one of two things or both may be happening. The band release port is applying too soon, but I am thinking this is almost impossible. Would possibly happen if the valve body heats up and causes a leak to the release port. The reverse high clutch is not applying fast enough for 2-3 due to sticking 2-3 shift valve when transmission is hot. I am leaning toward this area. I would go over the valve body really carefully and hopefully you will find the issue.
Hey D2 Willys When you speak I listen cause I respect your transmission knowledge. I like you have built a lot of C-4s. I Don't pretend to know everything but what I do know I like to share. It could very well be in the valve body.It's hard to diag. with so little to go on. I've been stuck doing all these new Ford trannies and to get a chance to do an old C-4 would be fun. I just think it's really cool to discuss these trans problems without trying to make someone look bad,I don't judge anyone,we're all just trying to help. I think with a little input from all us people we can help, what one guy forgot another might remember etc.it could be fun thinking together
57 shaker, thanks for the compliments. C4's are fun little guys to rebuild, easier than some carburetors IMO. Yep we are here not to criticize, only to give our help to others and have fun. You are out in my old stomping grounds in AZ. Lived there for 12 years before blasting off to OZ in 06. Need any transmission info, just PM me.
Mine used to do that too. The factory manual talked about an adjustment screw up inside where the vacumn line goes. When I pulled it off the screw just fell out. Screwed it back in till it shifted like it should and has been ok for over a year.
Alrighty then;adjusted linkage,adjusted bands according to spec,fluid OK.I took the car out for a long drive,got everthing up to temp........not a hint of a problem;it shifted just fine in traffic and on the road. I'm not going to pimp around with the tranny until the rodding season is over,but when I pull the car apart for paint this winter ,I'll get the transmission redone properly. Thank you all for your feedback.
shifts, you took me wrong. I was not questioning your knowledge, just showing my ignorance on pin lengths. Joe
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