Do i need a new trans????

[67buickss]

Ok so i was driving home the other day from school and my truck is shifting really hard and i have to let off the gas to get it from 2nd to 3rd. and as i am on the highway it doesn't want to go faster than 54mph and i have gray smoke coming out of the exhaust when i am going 54, is this a overdrive issue or should i replace the whole trans?? or what..

o and buy the way it is a turbo 400 trans

 

[Barrman]

The TH400 is a 3 speed non overdrive transmission. Check your fluid level in the transmission. If it is low, then check your vacuum module on the rear of the transmission. It could have failed, causing your shift problems and be sucking fluid out.

 

[eric_banks32]

I agree. The vacuum modulator is most likely the cause and if that doesn't fix it take a look at the governor.

 

[notsosanestan]

i think this is what has happend to me i just got it rebuilt now its slipping in reverse. i

 

[niferous]

They gave you a warranty with the rebuild right?

 

[notsosanestan]

noppee im screwed i put it in myself they said it was four quarts low when i gave it to them but the day before i went so they could look at it and make sure it was all good. it was low on fluid i filled it up with the mechanic and drove it home and bourhgt it back the next day when i could get a ride. so it lost 4 quarts in a matter of maybe 8 miles. if turns out the modulator was bad im going to refuse to pay for it because they should have made sure. never going back there again

 

[tm america]

oh no not a buick guy .i bet you parked the truck next to the buick and it caught a leak from the buick

 

[tm america]

they are saying it right probably a broken modulator.a broken diaprham will make the trans fluid go up the vacume line and get burned by the engine giving you gray smoke. also it causes a vacume leak and will make the trans shift harder and later. due to higher modulator pressure as the diaphram is not pulling against the spring in the modulator like it normally is. so it acts like it is at full or higher throttle than normally

 

[laneriverrunnerm1008]

trans

when I purchased my m1008 it would not shift into third gear, also would not even move when in reverse, I changed the screen in the trans. and put a new modulator valve on and its been running good for two years now. I would try both before sinking a money on another rebuild.

 

[joesco]

My M1008 was hard shifting. Replace, fluid, Filter, three vacuum lines and the 30.00 modulator. Total cost about $75.00. It now shifts like a new transmission! OD shows 45k miles.

 

[markinnh]

your lucky ur tranny is in one piece...looks like mine was damaged by a giant fork lift, bent rear drive shaft, bent crossmember with cracked tranny case and adapter....grrrrr oh well

 

[stampy]

mine surged and shifted hard until I replaced the vacumn line. Now it shifts SOOOOOO SMOOTH

 

[67buickss]

ok well i replaced the vacuum module and the problem is still happening. but i noticed that when i shut off my engine i hear hissing in the front of the engine for about 5 or 10 seconds, would that be normal or a sign of a vacuum leak?

 

[4bogginchevys]

not normal, check the pump at rear of engine, and check vac connections at the IP area.....the line that runs under the cdr is also a possibility...good luck

 

[67buickss]

I checked around the ip they look good, and i looked at the crd it looks dirty but seems to be working.

and the hissing from what i can tell it comes from the driver side sear the area of the power steering pump. and are there any vacuum line diagrams so i can just go along and try and check everything?

 

[Keith_J]

The THM400 was designed to be used on throttled engines. Diesel engines do not develop a vacuum so also check the vacuum pump. This is solely for the transmission modulation.

 

[67buickss]

is there a quick and easy way to check if that is bad. also is there a easy way to find out where else a leak may be?

 

[4bogginchevys]

a vaccuum guage at napa is pretty cheap and comes with instructions

 

[67buickss]

well i just tested it and during idle it is showing around 20 vacuum.

for some reason it no longer makes the hiss noise when i turn off the truck.

but i do now notice a small amount at trans fluid at the top trans line on the trans, could a little leak be causing this or what other ideas do you guys have.

 

[niferous]

I would pull all the hoses and check them all off the truck. In fact if you haven't already replace every hose including the one that goes from the metal line to the transmission modulator. I had a leak on that hose that I couldn't see until I removed it from the truck. So I had vacuum up top but not going into the trans because I hadn't gotten on my back and looked at the hose under the truck. Below is a link to the topic on that.

http://www.steelsoldiers.com/cucv/45198-hard-shifting-still-after-repairs.html