Transmission problem

[81_Chevy]

well i have two more questions for y'all.

my transmission started acting weird in the last two days, on monday morn it was fine going to school but afterschool i pulled out of the parking lot and it went up to 4,000rpms before it shifted into second, then when i turned the corner towards home it stopped in second, like i would give it gas and here the engine rev higher but the truck wouldnt go faster just the same speed, so i let off the gas and then gave it some gas and it was fine.

now instead of at like 2,000rpms to second gear and 2,500rpm to third it now shifts about about 3,000 - 3,500 rpm into second and about 3,500 to 4,000rpms into 3rd gear. im really clueless on this situation. and it is shifting REALLY hard.

the transmission is a Turbo400 all stock, it was completely rebuilt the winter of 2011. i checked the fluid level, full. not smelling burt or not any dark color. im stumped.


any help is appreciated. thanks -Nic

[VileZambonie]

The second part of your question needs to go in the suspension section.

Are you checking the fluid level in park at operating temp? Are you using the correct dipstick? If the fluid level is correct sounds like it's slipping. You said it was rebuilt a year ago, who rebuilt it?

[81_Chevy]

sorry bout that, ill move it.

ya in park at temp, as far as i know its the right dipstick same one that the truck has always had. umm im not specifically sure on the name of the shop, but my dad checked them out and the were pretty reputable and did good work. ill give him a call tonight and ask since hes out in LA on business.

[VileZambonie]

A properly maintained TH400 is pretty stout as long as it's not overly abused. There's no indication of bubbles on the dipstick or discoloration? If you manually shift 1, 2, 3 does it slip?

[81_Chevy]

no bubbles that i know of, but i will double check, and theres no discoloration still the purple/red color. the thing is i dont think its slipping because if i manually shift out of 1 2 or 3 the rpms will just increase until it shifts, like ill drop it in 1 and take it to 3,000 or so and shift up into second but it wont shift into second until it hits like 4,000 or so. 

[81_Chevy]

another question, is my truck still safe to drive at the moment?

i have other transportation to school (my jeep), but i would prefer my classic pickup 

[79gmc15]

Just throwing this out there,  is the vacuum line hooked up to the transmission? In good shape?

[81_Chevy]

i just replaced it not to long ago, so its in good shape. and as far as i know its hooked up, but i will double check this morning

[Engineer]

Just throwing this out there,  is the vacuum line hooked up to the transmission? In good shape?

This.

Check this first.

[pholliday1]

one step further... put a vacuum gauge on it and take a reading while the engine is running.. kinda sounds like vacuum modulator isn't working/ or part of the valve body is sticking.

[81_Chevy]

i will do that when i get home today from school! i have a feeling that its the modulator because there has been some fluid coming out of it in the past since the rebuild. what should i be looking at for vacuum pressure wise?

[79gmc15]

I think it's watching to see if it holds pressure. Don't go crazy on the pressure, 20# is probably more then enough. Watch the gauge though. It probably shouldn't move. If it does, dbl check your connection, try again. But if it's leaking oil then something is up anyway.

[81_Chevy]

alright i will do that today after school! 

another question, if i keep driving it like this, could there be damage to the transmission?

[Engineer]

If you have tranny fluid in your vacuum line then your modulator is bad.

Driving it probably won't kill it, but why take the chance?

[VileZambonie]

As far as late shifting, no vacuum at the modulator will cause a delayed upshift.

like i would give it gas and here the engine rev higher but the truck wouldnt go faster just the same speed

This indicates the transmission is slipping