Hi from across the pond, and many thanks for this great video, which I've only just found! You've sorted my '71 Mach 1 transmission problems, where shifting became erratic and, at the same time the 351C starting running really rough. Turns out the modulator vacuum pipe had 'self - destructed' and hence the problems. All sorted now, thanks to you👍. I've subscribed and looking forward to running through your other videos. Thanks again
@@Mistermopar greetings, thank you, much appreciated, I’m glad you enjoyed the video and that it was helpful to you. Nice car too by the way and great engine, I love the cleveland family engine’s they’re my favorite. I’m actually gonna be swapping in a 351c into my 76 ford truck. Thanks for subscribing and thanks for watching.
@@FastFords289I’ve got a c4 in my 65 Stang and it doesn’t shift to 3rd first and 2nd seem ok I changed the modulator and I’m wondering if I should put the original back in if I can find it 😂 but what direction should I turn it to try and get 3rd gear if I keep the aftermarket in Thank you
@@user-xn9it8df3s have you tried adjusting the modulator valve, try backing off the screw some, see if it’ll shift then, perhaps it’s just holding it in 2nd too long. Hope this helps, good luck, let me know if it works. Thanks for watching.
@@FastFords289 👍 I’ll try that I’m hoping that’s the problem I’m worried if it’s possible that someone put a 2spd valve body in it if that’s possible I’ll keep my fingers crossed
@@user-xn9it8df3s I just thought about something, I had completely forgotten about. If it’s the original transmission or original style for your 65 then it has what they call the cruise o matic. Your shifter should have P,R,N,drive, then a green dot, L. Those transmissions are the exact same as the traditional C4 except the valve body. Those cruise o matics start off in second gear and shift to third when in drive and shift from 1st,2nd,3rd in green dot. They stopped that in 1967, in 67 they made it how we know them today with P,R,N,D,2,1. I think this may be your problem, if your shifter doesn’t have the green dot then someone probably changed the shifter some time in the past without changing the valve body. So if this is the case then just put your shifter in 2 and it’ll shift all three gears. Hope this helps, if you have any other questions feel free to ask.
Your garage looks a lot like mine haha, stuff EVERYWHERE. I get it man, I have 20 projects going all at once too. Good video by the way, straight forward and easy to understand.
Lol, that’s what separates the real mechanic’s from the posers lol 😂. Seriously though, yeah I been cleaning it up here and there which eventually I’d like to build me a garage to my liking on some land at some point, but I hear ya man. Thanks for the comment and thank you for watching, glad it was helpful to you.
did this on my '77 tbird after i rebuilt the 351w to make 425hp. Put a 2500 stall Hughes converter in and needed to firm up the shifts so make sure i dont smoke the bands now that the engine make 3 times the power
Very nice, cool car too! You don’t see those old T Birds anymore. You can also tighten the band some as well so it doesn’t have to travel as far to fully engage either, that’ll give you a nice firm shift. I did this in my 76 ford truck, made a world of difference. The factory setting is large and they did this for a smoother shift for the average person but they slide into gear like that so righting the band some takes that slag out of it. Thanks for sharing and thanks for watching.
New subscriber here. Thanks for creating & sharing this vid. I just had the transmission rebuilt on my daughter's 66 mustang 6 cylinder. The transmission seems to be working fine but shifts from first to second before I can get some decent rms and catch speed. If I turn the screw in the modulator to the right will this allow for a longer period before the shift? Trying to pick up speed after it shifted into second is rather slow in doing so. Also, being that its a straight 6 with the one barrel doesn't help with acceleration. Any tips/advice/pointers would be greatly appreciated!
That’s great! Welcome, and Thank you for being a supporter. You’re welcome, glad to help. Yes turning the modulator in, or to the right will hold each gear longer, which will delay shifts longer. Yeah those little 6 cylinder’s for cars aren’t very powerful at all, I don’t believe you have any Perth vacuum because that would generally cause later harder shifts. With that being a rebuilt transmission, it probably just needs tuning on the modulator, so I’d turn it in 1/4-1/2 turn at first and drive it and see what changes. As you turn it in it should get later on shifts so just keep turning it in a 1/4 turn at a time until you get desired shift points. It can be tedious but the end result will be worth it. Good luck and I hope this helps. If you have any other questions feel free to ask. Also very nice car, thanks for watching.
I bet you’re getting a whitish smoke out the tailpipe huh? When these go bad they will leak internally and the vacuum will pull the fluid into the engine and burn transmission fluid resulting in a white smoke and low transmission fluid with no visible signs of leakage. Hope this helps, good luck. Thanks for watching.
Okay, we are new to Fords. My granddaughter just got a66 mustang with 302 and a C4. Seller said it had been sitting a long time and would not shift until 65mph. We cannot get it to shift to 3rd at all. Tranny shop wants to rebuild$$$$. I do not think there is a vac line
Nice, welcome to the wonderful world of classic fords, and nice car too by the way. Sounds to me like it’s not getting vacuum, if there is no vacuum line then that would definitely cause it not to shift. There is supposed to be a vacuum line coming out of the back of the intake behind the carburetor and down the passenger side of the transmission on a C4 and plugged into the modulator valve. So if there is no vacuum line then I’d install one and see what you get then. I doubt it’ll need a rebuild, usually they only need a rebuild if they start slipping. Hope this helps. Try that first if you need any more help just ask and I’ll do my best to help in any way that I can. Good luck and thanks for watching.
@@richardgolightly4258 no problem man, that’s what I’m here for, I’m glad to help when I can and I love seeing the comments, so thanks for commenting. Yeah I’d check to see if it leaks, which if it’s original then it would t hurt to replace it anyway, after 50 years rubber tends to get dry rotted and crack. Even if it looks solid a lot of times they get little cracks which can leak as well. Good luck.
@@moparmadman1134 well that’s a new one on me, usually they shift or they don’t, but perhaps the diaphragm is getting hard and it shifts once it warms up, idk. I’d say for no more than they cost, yeah replace it and see what happens. If it still does it then I’d say it may be a valve body issue, perhaps a piston in the valve body is sticking slightly after sitting for a while and after it warms up it gets loose and starts working again. Hope this helps, good luck. Thanks for watching.
Yes absolutely it can, it can delay the shift by a lot and if you get on it alittle and let off the gas then generally it’ll shift then and it’ll shift hard because it’s shifting based of fluid pressure only. Also the motor will probably run a little rough if the line pops off because it’ll have a vacuum leak. Hope this helps. Thanks for watching.
Going to try this out. Have a 69 f100 with c6, at 35-45 mph just cruising, when you let off the gas fully it automatically kicks down to 2nd and then any input back in the throttle goes straight back to 3rd. Ever seen this?
Nice truck, no that’s weird, I’ve seen them where they delay on shifting and you let off the gas and they shift into 2nd or 3rd but not like you’re describing. I’d try looking for any kind of vacuum leak because vacuum leaks can cause problems with the shifting pattern. Also check your kick down rod and make sure it’s not partially activated under throttle or activating too soon or just any weird things going on. Make sure it can work freely and that it’s only activated when throttle is 3/4 to fully open. Then you can try adjusting the modulator valve as well if everything else looks good but it may be a faulty modulator valve. Hope this helps, good luck. Thanks for watching.
@@FastFords289 thanks! I know it's got something to do with vacuum. No kick down linkage hooked up. And runs perfectly going through the gears from a stop up to running speeds and from running speed to a stop. it's just the lower speed curvy back road speeds I'm having the issue.
@@dwaynehunnicutt3052 no problem! Yeah I’d definitely check for vacuum and make there’s no cracks in the line or a like that. If everything looks good I’d replace the modulator valve and see if that fixes it. They don’t cost much last time I priced one. Good luck Thanks for watching.
Yeah, so some of the factory original modulators didn’t have a screw and no way to adjust it. I guess they were trying to keep people from messing with stuff, but however you can go to an auto parts store and buy a new one and it’ll be adjustable. Hope this helps and thanks for watching.
Thank you for the video. I have the FMX and it goes and drives in reverse just fine and has a hard stumble in all forward gears. Has a new modulator on it. Does it need to be adjusted upon installation?
You’re welcome, yes, sometimes they do. I would also recommend checking and making sure the fluid level is correct and also make sure you have no vacuum leaks, hope this helps. Thanks for watching.
Back of intake behind the carburetor, you can also connect it to the carburetor itself on the ported vacuum port if you have an aftermarket carburetor, but it hooks into the vacuum tree at the back of the intake. Hope this helps. Thanks for watching.
No that means the modulator valve is bad and fluid is leaking past and the vacuum will suck it into the engine. So just get a new one and you’ll be good to go. Hope this helps, thanks for watching.
Possibly, could also be a vacuum issue, does it downshift earlier than it should, like say you’re coming to a stop sign and it downshifts kinda hard before you get to a complete stop? If so then you could have a vacuum issue cause that could also cause it to delay in upshifting. Hope this helps. Thanks for watching.
Valuable info currently resolving no 3rd gear on my c6 replaced modulator (the factory one wasn’t adjustable) vacuum seems strong but not sure if lack of 3rd can be solved by adjusting modulator screw I guess I need to apply patience
@@TomSkyNet usually if it’s a vacuum problem Then it’ll shift once you let off the gas at a higher than average RPM. It won’t have a ton of suction but you should feel it, sounds to me that vacuum isn’t the problem. Does it shift normal from 1st to 2nd or is it delayed as well?
@@nunya6379 ok, so it sounds like it could be a possible vacuum leak, I’d check the hose running down to the modulator valve and make sure it’s not cracked or something. You can spray it with carburetor cleaner and if the engine idle changes then you know you have a vacuum leak. Usually the modulator valve won’t cause hesitation in one gear if the other if shifting at normal speed. If you check or replace the vacuum hose and it still does it then I’d try backing off the modulator screw maybe 1/4-1/2 turn to see what it does then. Hope their helps and if you have any other questions feel free to ask. Thanks for watching.
So I have a FMX, it was rebuilt a couple years ago, and it has a drawn out shift. It doesn’t shift hard at all. Would this make it shift a little harder/quicker?
Yes it could be a possibility, another thing is what color stripe is on the modulator valve, they came with different colors depending on what engine/ type of vehicle application you had, I can’t remember which colors are which now off the top of my head but I know that either the black or green stripe was the more aggressive one and the yellow was the pretty standard one you found on most vehicles. I would try adjusting it down some to see if it changes, but remember to do it a 1/4 of a turn at a time until you get to your desired shift point. Hope this helps, if you have any other questions don’t hesitate to ask. Thanks for watching.
