Vacuum Modulator Installation GM TH350/TH400 Transmission | FIXES SHIFT PROBLEMS!
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- Опубліковано 6 лют 2025
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The vacuum modulator on my CUCV M1009 gave out. This is also applicable to any 73-87 chevy truck, squarebody, or anything else that uses the TH400, TH350 and more. If you are experiences problems with shift points, this could be your cure. This one is adjustable which allows the user to change the shift points to what one prefers. This is the best way to go!
I just replaced my vacuum modulator. Some people may not be aware that there is a modulator reaction lever inside the transmission body that actually inserts inside the new vacuum modulator. Kind of threw me off since nobody else on UA-cam had talked about this piece of metal or lever. Luckily I had a schematic showing the lever.
One of the most well done tutorials I’ve seen ! Thanks
good camera work, good audio, clear instruction = potentially very helpful. Great Job.
Thanks, I appreciate it! The adjustable screw inside the hose connection was what I was specifically wanting to discover this time around allowing the shift-point adjustments!
Great info. I like to review before I tackle things. It saves me from making too many trips to the parts store, as well as having to crawl out to get a tool or oil or whatever. Thanks. I've subscribed!
edpdx50 Thanks!!! I'm glad I could help! I really wanted to give a little inside info and answer questions I had before I did mine!
AWESOME VIDEO! Thank you, I just replaced mine today. I had about 1.5 qts of ATF come out when I removed the old one. No worries though, I just put a fresh batch of the same amount back in.
Is that normal,? Me to
Wondering if it's overfull?
Could be aiding in my issues?
@@ColtonLoberg Yes there will definitely be some ATF that comes out when you do this job, I guess it just all depends on how fast you move is how much will drip out
Ever find an answer if it is normal to have fluid come out. I had quite a bit come out
@@loganator78rYes, I believe it is normal. As long as you fill the trans back up with fresh fluid you'll be fine.
Sweet. My 85 M1010 just started shifting at higher rpms. Hoping it's just the modulator and not the pump. Thanks for the vid.
Was it just the modulator? My 83 c30 is doing the same thing and not wanting to shift unless I let off
@@wyatttate945 cracked rubber line was my issue
No Forward or reverse after I put the truck in the garage!?? This Video is a big help. I did suspect the Vacuum Modulator! Thanks!
Changed my vacuum modulator, had the old original style so when I pulled it out ,about a quart od transmission fluid came out . Is that normal? Never seen it before on other videos 😮😮videos .
Same... ever find an answer. I've seen post and they never say anything about a bunch of fluid coming out
It'd be cool to do a in detail vid of explaining an demonstration of adjusting it in.. like from fully closed to fully opened. 🤔 Sure closed would end up overheating trans. An fully opened would I'd guess cause gears to shift in hard at lower shift points. which I'd guess would cause gear grabbing will in time cause stress on the tail end to drive shaft, hard on u-joints , an rear end.. lol 😂 torque converter says to transmission " Are you sure about this?" As engine says " Too late"
Speak English
What we're the symptoms for replacing it?
car not shifting while driving for example stuck in first gear without upshifts and so on.
Just rebuilt my trans and I was wondering why it still shifted so rough, I will be replacing this part to see if anything changes.
I have the same issue and will try this modulator. My car is 1978, so it can't hurt to have this cheap part changed...
Saved me time and money!! Thanks for video
How many quarts of oil does it turbo 400 takes because I noticed when you put it out no fluid came out
Why did you need to replace it ?
My Jeep j10 had this as well.. i was wondering what the heck the transmission was doing with a vacuum line
Nice bro ! Good talking points
Hope this is the issue with my 1983 Cadillac hearse instead of needing a clutch. I’ll add a comment if it worked once the weather is nicer and I can get under it.
Thanks for the video, I’m going to replace mine soon I don’t think it’s shifting into 3rd hope this corrects it
Mine is doing that to did that fix it ?
@@AndrewParramore-mu1oj no my issue was because of a new carb and my vacuum hose and kick down were not hooked up.
Long shot here I guess but anyways I have a 76 GMC Vandura w/ the TH400 and one day it shifted fine the next it wouldnt go into drive yet had reverse and L1....modulator?????
Great camera work.
What exactly was your issue ?
Did transmission not upshift unless accelerating full throttle ?
I just bought a Oldsmobile f85 from 1962 with a Chevy 350 and th350 gear. it has started to leak when its not in use and i had problems getting it into gear. it drives fine when i have the car on for awhile, and does not leak when the oil reaches the right degree.
My question is, are all th350 using this vaccum method?
My other big concern is that the Oldsmobile had stick shift at the steering wheel, but since they changed both motor and gear its now converted to a floor transmission.
The oil stick that was in the car dont seem to be right, and i get no oil on it.
Awesome blazer bro. Love it
Does your line go straight into your intake with a elbow????
Hey, Thanks. You saved me plenty.
Is that in the trans ?
Thank you so much for this video so helpful
Is same the electronic modulator and vacuum modulator?
I'm taking it that your transmission wasn't shifting till a high rpm. am I correct? also if anyone out there has a problem with vacuum hoses going soft from oil in the lines you can use a good quality fuel hose instead.
breezy0037 yep, you certainly can. Make sure it's firm and won't collapse. Mine was just shifting all over the place, particularly at higher rpms than normal
Does your Vacuum modulator have a small 1 inch pin that goes inside it?
Nice! What problems where you feeling before and how was the result after this new modulator install?
I'm not the poster but you can have shifting issues like hard shifting and no shifting also if theirs transmission fluid in the line when you remove the vacuum line it's bad and if you've overfilled your transmission with fluid if you pull it out the excess will come out and immediately I found that out personally , also their are different color stripes on the modulators that determine the strength of the spring inside the modulator and you can also get an adjustable modulator that you can adjust to shift with a hobby screwdriver turning clockwise will spread the shift out a little further and firm the shift if you don't have other trouble with the transmission
@@drjohnsonhungwell5115 Thank you very much for your complete explanations! Much appreciated.
@@GJJC13No problem it's usually a no shift problem and or fluid in the line and will also make smoke as it's sucked into the combustion chambers the stripes on the modulators I believe the red and green at the stiffest springs but I have used the white , red and green on my military blazer with the TH400 , fluid loss would be very little if not overfilled or hot as well I found out about the hot and luckily I was able to move fast I overfilled it a little too much after a filter change .
@@drjohnsonhungwell5115 100% correct comment
Amazing video thank you it was helpful👍👍
Hopefully this could be what's wrong with my squarebody mine wont shift at all since I put my new 350 sbc down in my vacuum house was bad so ran a new one if this isn't it new transmission time
Did this fix your problem
Great video my dude
No need to adjust?
My 1970 turbo 400 transmission is stuck in high gear what do I do
HI, please tell me I have a 3-speed transmission when picking up speed in third gear on a straight road or up I press the pedal very slowly and the transmission immediately switches to second speed, I don’t want to accelerate at a third speed only when moving down, please help if you know and want, thanks!
It sounds like you might have a bad clutch pack in that trans on the 3rd gear. Have you checked your transmission fluid? Is it dark? It is also possible that the valve body in the trans is not doing it's job. Unfortunately I had this happen to me which is why I speak from experience. The vacuum modulator will likely not cure this particular problem.
How how do you put a bracket back on the modular
Thanks for the video it helped a lot 👍
Good stuff
I have a 1997 suburban. Where is the modulator on mine? I can’t find a video anywhere the tells me where it is.
I could be totally wrong, but I’m going to assume you have a 4L60E or 4L80E trans. If that’s the case, you don’t have a vacuum modulator unless it was modified with a vacuum modulator kit. I think you have an EPC solenoid, which is located midway on the passenger side of the trans.
great job
Gotta quick question guys, any information will be useful. I have a TH350 I’m putting in a 1980 el Camino and I understand that the 350’s shift via the shifter cable attached to the carb and 400’s shift using vacuum from the modulator valve to a port on the intake and/or carb. So then what is the modulator valve for on the 350’s?? And where do I connect it to? I’m assuming to the designated port on the intake but I’d like to know for sure? Thanks.
The th350 shifts from the vacuum line that comes off the intake. The cable coming off the car is just a kickdown cable. Ive got a 350 in my 85 el camino.
You are aware that your vehicle is not the military ordered CUCV right? All you have there is a civilian K5 Blazer.
Maybe you should look at my restoration video. It's 100% CUCV, it was desert tan, still 24 volt too. Colors alone don't make it civilian. I bought it myself from government auction too
@@OdysseyOverland4x4 Ok
Will this possibly correct early shift/no kickdown issue?
On an automatic transmission there are many factors at play. It’s cheap enough and easy enough to replace that’s it’s worth a shot. In general, unless you have other valve body or clutch pack issues, it definitely can help, but for no lockdown, if you have a TH400 (and other transmission models I’m sure) I would check to make sure your kick down switch is connected and working!
what happens if it is not working?
Great job...very help full
holà cuendo quito el modulador sale' aceite de transmission es normal ? mi caja es una th350 ( el Nivel de aceite es ok motor caliente) ,gracias (mi Espagnol es mejor que' mi Ingles.)
Badass and thanks man
Thank you!
Good information... Thanks
thank you! very helpful
great video, saved my ass from more headaches.
Glad it helped! Subscribe for more!
No atf oil comming out?
J. Jeep it depends. For me nope, but if you're unsure, you can also do it when you're in the process of replacing your transmission fluid to be safe.
I have a 6.5 Diesel installed, with a THM425 GM transmission. Problem is, I don't know where to get vacuum to control the modulator valve?
The Vacuum distributor type vacuum pump, only shows 26 in vacuum "constantly" ,
and does not drop in line vacuum as I would expect it to when accelerating.
and does not allow me to start off in D "1st Gear" , unless manually.
Jenny Rodriguez so behind the air filter on the 6.2 is where the pump is. Sounds like your pump is working well. Up in the front where the throttle valve is, there's a black plastic piece that changes the amount of vacuum. It's very possible yours is busted or not tuned properly. It's adjusted via two bolts and you simply rotate it. I believe it's called the "vacuum regulator". See if you can find out where yours is!
Great vid . Thank you
Would this same one fit my 87 cutlass supreme
Nice video. I an new to working on cars/trucks. I am restoring a 1954 Dodge truck and I am learning everything as I go by watching videos like yours. I am in the process of installing a 307 small block Chevy engine with a 400 trans. I noticed hoses and electrical plugs on the trans and I wondered if you could tell me where they hook to. Where does the vacuum modulator hook up to? there are 2 small lines that I think they connect to the rad. There is a 2 prong connection by the shifter that I don't know about and hope you could tell me. I think the steel line above the dipstick hole is a breather hole or something. If you could help me out I would really appreciate it. Thanks for sharing your video. I subbed your channel so I could learn more from you.
the vacuum modulator on a diesel will go to a vacuum pump, but since you are installing a small block Chevy, you'll have to tap into a vacuum line, usually coming off of the valve covers, which is the same vacuum that you use for your brake booster... Maybe someone else can weigh in on this, I've always been a diesel guy, but I believe that is the same port oh, as for the wires, that is the kickdown switch, you can just order a turbo 400 kickdown switch, and it just hooks up to your throttle pedal.it is a mechanical switch we're after the throttle is depressed to a certain amount a switch is activated and the transmission drops a gear, that way you are able to get more torque when passing someone for example, mine has not worked, I just manually shift down if I need to, so it's sort of optional, but if you want to do it right, you can always get one. as for the cooler lines, yes, they do go to the radiator, but if your radiator does not have provisions for a transmission cooler, just get one aftermarket, and you are correct about the breather! Make sure that that line is completely clean! Otherwise you will have transmission fluid puking out of your dipstick tube
@@OdysseyOverland4x4 Wow. This is great information. I wish I had gotten into mechanics when I was younger, but back then I nothing to work on. All my cars were new and I had no problems. Now that I am retired and wanting to restore a truck, I need help. But you know there are a lot of great people like you that are willing to help. That is a good feeling. I thank you very much for the help that you gave me today. I will save the post and print it off so I can put it my book of notes.
Good video 👍
Thanks.
Well black screen can see nothing don’t what wrong with video but it’s black out !
What does the other end of the line connect to?
For me since it's a diesel it goes to a vacuum pump. For a gasser I think it goes to the engine manifold or perhaps a vacuum collector!
@@OdysseyOverland4x4 I think it goes to the carburetor
@@GJJC13 Diesel's do not have carbs, but if it was a gasser then yes, I think you're right
Thank you
Great video.
George Garcia thanks! Glad you're enjoying my videos!
What kind of shift problems would this help with? I noticed when I went to 37s I don’t shift into 3rd until about 50-55 mph
This could quite possibly be the culprit. It is worth a try since these modulators are relatively cheap. This usually fixes late/early shifting problems. If this doesn't take care of it, you COULD be looking at a new valve body (which also happened to me). But try this first!
Adam llaneta . after finally taking my project on the road i ran into shifting problems. I have 37s & th350 , same problem as you. It engages 3rd gear till like 50 mph. Please let me know if you find the problem
Ruben Herrera what gear ratio are you running? The m1009 came with 3.08 gears. I’m changing axles to a 14bff with 4.10 gears I’m hoping this change in ratios will help the shift points
Adam llaneta changing your ratios will definitely have an effect on your shift points. I am running 3.08 at the moment (stock). If you want to change your shift points and fine tune it, make sure that your vacuum regulator is working, AND the modulator. Get an adjustable one like on this video, and you'll be good to go!
Adam llaneta not sure gear ratio I have a 14sf on my jeep
Thank u so much
I have a 1978 Ford f150 that has been parked for awhile. I'm trying to get it running again, but I can't get it to shift out of park. It's shifting from the column, and I can see she shifter arm moving at the transmission, but it's not going into gear. Can someone please help. Could this be causing the problem? I don't want to buy a new transmission if it's something easy to fix that I'm overlooking.
When the truck was drivable it would shift into drive/park hard, and sometimes be late/early when shifting out of 1st and 2nd.
I have a 1978 oldsmobile with a 350 and it has the same exact issues
@@damiankillip2611 Dang, it's a frustrating issue for sure. I still haven't figured out how to fix it. Mine was shifting when I last parked it years ago, but now I can't get it to do anything. The 302 I have in mine is still good, it starts, but won't shift. Lol.
Mine starts right up it was driving last month then it sat and now I have nothing.
@@damiankillip2611 dang, that sucks. I feel you though, the struggle is real. If you find out a way to fix it, let me know lol.
Tomorrow I'm dropping the pan and replacing the filter. Try to do that the filter kit is less than $20. I'm also going to check the linkage in the trans while the pan is off. This is going to be my first time doing it and I'm 19 so this will be something new
Me interesa mucho pero quiero ver las recomendaciones en español gracias
wey no tiene que ver el idioma nomas mira lo que esta hasiendo pon atension pareses niño quieres manual y todo
@@joepurafintapurafinta3614 Es cierto, el video es "auto-explicativo" (si es que esa palabra realmente existe)
Das goot ya.
Thx
👍
Have a 84 Pace Arrow motorhome will not go into drive will work in Reverse anybody have any ideas contact me
Thank you.
Thanks