Been trying to research an issue with my pickup which has a turbo 400. Start from a stop it seems to 'studder' almost lose forward motion for a split second and continues in first. Seems to be shaking like a vibration I feel. It does go to second but thats it. As I press gas and go faster, rpms rise and no next gear. Just sounds very loud like engine is revving higher and higher. No tach or speedo so I cant tell much other data. I am handy but no mechanic. I have read things like governor or vacuum modulator. I had a similar issue on another vehicle (stepvan) which it was the vacuum modulator. A friend diagnosed that, installed and it seemed to fix the issue. I should have asked how to install as I am not sure but seemed quite simple as it took him only a short time to do. Could anyone suggest what else to test/try first or does the info lead to one source of the issue over another? Would like to understand what I should be listening for and how I can fix myself. Sure appreciate anyone who can****ist. GP
Is this a recent problem?have you check the transmission fluid? is the vacuum line for the modulator hooked up? is the rubber hose that attaches the metal line to the modulator old and rotten? HRP
Only have truck a couple weeks. Didnt notice this hesitation and shifting issue. Fluid is full and red/pink. I dont know about the vacuum line.. will have to see about that... not familiar with it. Thanks
Look where the transmission dipstick tube enters the transmission case: the modulator is close by. it's a metal canister held to the case with 1 bolt. it will have a small rubber hose going to a vacuum source. these hoses rot. The Turbo 400 is the greatest transmission of all time, so your description doesn't sound good. Hope this fixes you up.
replaced vacuum modulator and hose which goes to intake. no change. pulled governor and looked at plastic gear. look fine to me. put back in and now this happens. from stop..i press gas and it gets going and seems to slip....then motor is revving high...almost like an overdrive sound then the the trans catches. moving along now and it just seems at 30 mph to be reallt revving high. if i stop and hit gas hard it seems to go as expected. just weird..no idea what is wrong. fluid to full line and red in color. ideas?
So how does this happen? And how to fix meanung is it better to maybe find another one ready to go or rebuild this one? Any idea what a shop should charge?
yep....sounds like clutchs are slipping/burned up. Pull the dipstick and smell the fluid on the end off it. Probably smells burnt. Drop the pan and see if you see black residue on the bottom of the pan. As to the cause.....could be several things. Run to low on fluid, plugged filter or low pressure for some reason. You might get lucky and be able to just change the filter if its clogged.
Like has been said, sounds like the forward clutch has failed, it is time to either overhaul what you have or replace it with another unit. Normally 400TH transmissions are pretty tough, but anything can fail
Hard to say what caused it beside just wear and tear. My motor home has a T400 w/454. I had to go back into it after about 14 years, but still the forward clutch was okay. I start at about at about $400, cash and carry Basic rebuild, clutches,paper, rubber ,..no hard parts
please describe the procedure you are using to check the fluid level. Is the engine running? what gear is the selector in? is the transmission warm, or cold? etc.
Start the truck andhad let it idle for about 5 mins in neutral. Drove slowly around industrial area. Then on to main road for about 3-5 mins and came back. Checked trans fluid at that point. Truck in park while checking. Right up to full line. Color looks red/ dark pink. As mentioned changed the vacuum modulator and hose. Also pulled governor and checked gears. The gears did not look stripped nor any dirt but did look discolored. Weights when flipped over seemed to loosely move. Sure could use some opinions on the condition. Pictures attached. What is odd is once i put governor back in, the problem seemed to be more obvious in first second gear...and also continued with issue of it revving high and not getting to third. What I mean is more noticing slipping when in first/second and it then the rear 'catching'. Seems it might be cheaper/easier to get another trans (locally found for about $300-400) and put that in rather than wait on a rebuild of the current one? Opinions? Thanks! GP
You need to make sure you have full manifold vacuum at the hose on the modulator. Was the gear on the governor loose? It needs to fit tight in it.
Am I checking it right at the outlet connector where the hose fits to it on manifold? What reading should I be getting? One thing I did notice on vacuum modulator after I replaced it was a tiny drop of fluid at the bottom. The clamp is tight... and I wiped it and no more showed. Maybe drop the pan to see what it shows and try filter replacement? Or is it a lost cause?
I would check it at the modulator with the engine running it should have what vacuum your engine is making I would guess around 16 to 18 inches.
If its not making that...what would be next action? could that be the issue or is it the clutches most likely. Thanks
Usually with a bad modulator or no vacuum to it, it will not upshift at all. This appears to be an internal problem
Is this vehicle new to you? Did this start suddenly or get worse over time? Old transmission, rebuilt? I've had some success with K&W Trans-X additive. If it doesn't cure the problem, it cleans everything up to make a rebuild easier. You will need to remove a quart of fluid to add it. If it doesn't help, I would pull the pan and check the filter. If there is a lot of trash, it would be from the clutches. It could be a bad seal or something in the valve body.
Been through my fair share of th400's , here's my 2cents worth. Check your kickdown switch it'll keep it hung in 2nd if sticking & no 2-3 shift will be happening, of course I am use to the chevelle style accel pedal switch , truck will most likely Have a carb mounted silinoid type but still check for being stuck. Sounds like worn out clutches, my last 400 redo had busted front drum "too much NOS hope the best but after all clutches are made to wear out. Good luck! Flux
I'm inclined to think that R&R of the governor is irrelevant. What happened is your test drive wore more clutch material and therefore more slipping than previous. I also think each test drive will show more slipping than the last. Slipping is due to lack of fluid flow or worn parts.
Okay.So we have a direct clutch working and a lo/rev band, making reverse. So again..Forward clutch is smoked. Might as well do a full kit at that point. Let's go..Yank it out of there . We're not getting any younger here!
Dad..is that you? Sounds just like my pops! Ok well I had never dropped a trans before and reinstalled. Not sure if i can do myself or tools needed to get it lowered/unbolted safely.
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