trans fluid in vaccume line to transmission! - The 1947 - Present Chevrolet & GMC Truck Message Board Network

case_bt · 10-28-2005, 02:53 PM

My truck has been smoking on me some times and I noticed there was trans fluid in my vaccuum line that runs to my trans could this cause my truck to smoke and what is bad on my tranny thats allowing fluid to get to the vaccuum line? I was wondering were my trans fluid was going it seems to be a quart low about every month i dont drive the truck but maybe once a week about 60 miles a month and my engine oil doesn't drop.

1-PU70 · 10-28-2005, 03:12 PM

Sounds like a vacume modulator

*FormerMember* · 10-28-2005, 03:12 PM

Quote:

Originally Posted by case_bt

My truck has been smoking on me some times and I noticed there was trans fluid in my vaccuum line that runs to my trans could this cause my truck to smoke and what is bad on my tranny thats allowing fluid to get to the vaccuum line? I was wondering were my trans fluid was going it seems to be a quart low about every month i dont drive the truck but maybe once a week about 60 miles a month and my engine oil doesn't drop.

What transmission is it?

Sounds like a th400?

If so, there's a modulation solenoid on the side of the tranny that line runs into. You may want to check that.

**CUSTOM/10** · 10-28-2005, 03:13 PM

That vacuum line is attached to the vacuum modulation valve on your tranny. Your modulation valve is bad ( Leaking )& needs to be replaced. The vacuum from your engine is sucking the tranny fluid up and into your engine, thus your engine smoke.

Gary

Jwill41 · 10-28-2005, 03:16 PM

what custom/10 said. this has happened to me before. I almost replaced an engine once because of the modulator.

case_bt · 10-28-2005, 03:17 PM

thanks guys is it an easy repair?

*FormerMember* · 10-28-2005, 03:19 PM

About 45 mins under your truck, mostly cursing about the crap everywhere and the fact that you didn't bring the right size wrench.

At least you have one very clean motor right now...

Sweet72 · 10-28-2005, 03:22 PM

I dont believe the trans fluid is causing your engine to smoke, you definitely have a blown diaphram in the vacuum modulator though, and this would account for the quart-a-month consumption. If it smokes under acceleration then you probably have worn rings. If it smokes on startup it may be valve seals. If the smoke is blue/gray in color it's oil, white = water/coolant, and black = fuel (running too rich).

case_bt · 10-28-2005, 03:33 PM

I do believe it is the mod because after i noticed the fluid in the vac line I left it unhooked and it didn't smoke but I wanted to check with you guys first before moving on with anything

**truckdude239** · 10-28-2005, 06:14 PM

its the mod my minivan had an bad mod and the motor was smokeing its sucksing trandfuild back into the motor and burning it off built the trans and boom had an motor that run like new and no smoke

**kwmech** · 10-29-2005, 12:46 AM

At least the top of the pistons will be clean.

Longhorn Man · 10-29-2005, 01:14 AM

Also, if left untreated, the leak will get worse and you can have one of 2 real bad things happen;
1. enough dextron gets in there and hydrolocks the motor. This can crack pistons, shatter rods, mess up valves....pretty bad stuff.
2. could actually start a fire under the hood. My old longhorn had that happen to it before I got it. Left a pretty nasty scar on the hood too.

It is a cheap item, and a very quick fix.
If it is more than 12 bucks, let me know. I have one that's been sitting in my tool box at work for a couple years. It has 2 miles on it. Installed it on a tranny, didn't fix the shifting problem it was having, so they told me to drop the tranny and have it rebuilt. I couldn't see letting that sucker go..it was brand new. So you can have it for 12 bucks. That's shipping and everything to your door.
Either way, don't drive it like this, bad things may happen.

Longhorn Man · 10-29-2005, 01:14 AM

oh yeah...PM me if interested.

modifiedGMC · 10-29-2005, 10:31 AM

I agree with the others about the modulator valve on the side of the transmission. My sister called me one time and said she needed me to rebuild her 79 pickup because it was smoking really bad. I went to look at it and cranked it up and it started smoking so bad the back of the truck disappeared. but the smoke wasn' bluish like oil smoke and wasn't really white but didn't smell like antifreeze either. I was loking around on the engine and accidently bumped the vacuum line off the intake and transmission fluid dripped out. So I went and got a new modulator and installed it. We had to drive the truck around for about an hour before all the trans fluid burned out of the exhaust but after that no more smoke.

70c10 · 10-29-2005, 11:30 AM

Not to hijack the post but when he pulls the old modulator off will it gush fluid out?. Just curious cuz I need to do this soon on my dads truck.

Longhorn Man · 10-29-2005, 06:10 PM

May get sone drippage, but nothing bad. Jacking up the truck from the rear will help too.

Sweet72 · 10-29-2005, 06:52 PM

Quote:

Originally Posted by Sweet72

I dont believe the trans fluid is causing your engine to smoke.......

What the heck was I thinking, of course it will cause it to smoke.. OIL IN THE INTAKE RUNNERS, duh! Senior moment I guess

cableguy0 · 10-29-2005, 07:49 PM

so long as you jack the truck up from the rear and not the front fluid loss will be minimal. with the truck sitting level or jacked up from the front your going to get wet

**VetteVet** · 10-29-2005, 09:16 PM

It's up above the pan so fluid loss should be minimal.

case_bt · 10-31-2005, 01:13 PM

ITs fixed lost about a quart and a half easy fix now i need to adjust it to get my shift points fixed

ChevLoRay · 10-31-2005, 03:59 PM

Transmission fluid is an oil, and it will smoke, and may burn if it gets hot enough. If anyone doubts it, pour a little of it on your hot exhaust manifold or headers. The combustion chamber is hotter.....

Just change the modulator and it probably won't hurt to change the vacuum hose, too.

10-28-2005, 02:53 PM	#1
case_bt Registered User Join Date: Jan 2002 Location: willis tx Posts: 374	trans fluid in vaccume line to transmission! My truck has been smoking on me some times and I noticed there was trans fluid in my vaccuum line that runs to my trans could this cause my truck to smoke and what is bad on my tranny thats allowing fluid to get to the vaccuum line? I was wondering were my trans fluid was going it seems to be a quart low about every month i dont drive the truck but maybe once a week about 60 miles a month and my engine oil doesn't drop.

10-28-2005, 03:12 PM	#2
1-PU70 Registered User Join Date: Apr 2000 Location: Bradenton, FL Posts: 1,036	Re: trans fluid in vaccume line to transmission! Sounds like a vacume modulator __________________ 1970 CST/10 402,700R4,3:73 posi,AC,PS,PB,TLT,PW,Buckets with heaters

10-28-2005, 03:13 PM	#4
CUSTOM/10 Senior Member Join Date: May 2003 Location: Sandown, NH Posts: 2,810	Re: trans fluid in vaccume line to transmission! That vacuum line is attached to the vacuum modulation valve on your tranny. Your modulation valve is bad ( Leaking )& needs to be replaced. The vacuum from your engine is sucking the tranny fluid up and into your engine, thus your engine smoke. Gary __________________ Gary 72 SWB 4x4 My 72 SWB Build http://67-72chevytrucks.com/vboard/s...d.php?t=259859

10-28-2005, 03:16 PM	#5
Jwill41 Registered User Join Date: Aug 2002 Location: Farmers Branch, Tx Posts: 1,009	Re: trans fluid in vaccume line to transmission! what custom/10 said. this has happened to me before. I almost replaced an engine once because of the modulator. __________________ http://www.picturetrail.com/jwill41 67 1/2 ton GMC short step side 68 1/2 ton Chevy long fleet side 72 1/2 ton Chevy Suburban 99 1/2 ton Chevy Suburban founder (and only member) of the primer/clearcoat club

10-28-2005, 03:17 PM	#6
case_bt Registered User Join Date: Jan 2002 Location: willis tx Posts: 374	Re: trans fluid in vaccume line to transmission! thanks guys is it an easy repair? Last edited by case_bt; 10-28-2005 at 03:19 PM.

10-28-2005, 03:19 PM	#7
FormerMember Account Suspended Join Date: Feb 2004 Posts: 3,051	Re: trans fluid in vaccume line to transmission! About 45 mins under your truck, mostly cursing about the crap everywhere and the fact that you didn't bring the right size wrench. At least you have one very clean motor right now... Last edited by FormerMember; 10-28-2005 at 03:20 PM.

10-28-2005, 03:22 PM	#8
Sweet72 Registered User Join Date: Nov 2003 Location: Alexandria, VA Posts: 1,534	Re: trans fluid in vaccume line to transmission! I dont believe the trans fluid is causing your engine to smoke, you definitely have a blown diaphram in the vacuum modulator though, and this would account for the quart-a-month consumption. If it smokes under acceleration then you probably have worn rings. If it smokes on startup it may be valve seals. If the smoke is blue/gray in color it's oil, white = water/coolant, and black = fuel (running too rich). __________________ '72 GMC SWB C1500 Custom, frame-off in progress. 383 SBC, 9:1CR, Comp Cams XE262H, Scat internal balanced crank, Eagle SIR 6" rods, Keith Black dish pistons, Dart Iron Eagle 72/180 heads, Weiand Stealth intake, Stewart stage I water pump, Holley 4bbl vac sec, TH350 with B&M Shift Improver Kit. 12 bolt positraction.

10-28-2005, 03:33 PM	#9
case_bt Registered User Join Date: Jan 2002 Location: willis tx Posts: 374	Re: trans fluid in vaccume line to transmission! I do believe it is the mod because after i noticed the fluid in the vac line I left it unhooked and it didn't smoke but I wanted to check with you guys first before moving on with anything

10-28-2005, 06:14 PM	#10
truckdude239 Senior Member Join Date: Sep 2005 Location: Lewisville, Nc Posts: 10,233	Re: trans fluid in vaccume line to transmission! its the mod my minivan had an bad mod and the motor was smokeing its sucksing trandfuild back into the motor and burning it off built the trans and boom had an motor that run like new and no smoke

10-29-2005, 12:46 AM	#11
kwmech Senior Member Join Date: Mar 2003 Location: Colfax-California Posts: 8,505	Re: trans fluid in vaccume line to transmission! At least the top of the pistons will be clean.

10-29-2005, 01:14 AM	#12
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: trans fluid in vaccume line to transmission! Also, if left untreated, the leak will get worse and you can have one of 2 real bad things happen; 1. enough dextron gets in there and hydrolocks the motor. This can crack pistons, shatter rods, mess up valves....pretty bad stuff. 2. could actually start a fire under the hood. My old longhorn had that happen to it before I got it. Left a pretty nasty scar on the hood too. It is a cheap item, and a very quick fix. If it is more than 12 bucks, let me know. I have one that's been sitting in my tool box at work for a couple years. It has 2 miles on it. Installed it on a tranny, didn't fix the shifting problem it was having, so they told me to drop the tranny and have it rebuilt. I couldn't see letting that sucker go..it was brand new. So you can have it for 12 bucks. That's shipping and everything to your door. Either way, don't drive it like this, bad things may happen.

10-29-2005, 10:31 AM	#14
modifiedGMC Registered User Join Date: Oct 2004 Location: Walker Co. Alabama Posts: 474	Re: trans fluid in vaccume line to transmission! I agree with the others about the modulator valve on the side of the transmission. My sister called me one time and said she needed me to rebuild her 79 pickup because it was smoking really bad. I went to look at it and cranked it up and it started smoking so bad the back of the truck disappeared. but the smoke wasn' bluish like oil smoke and wasn't really white but didn't smell like antifreeze either. I was loking around on the engine and accidently bumped the vacuum line off the intake and transmission fluid dripped out. So I went and got a new modulator and installed it. We had to drive the truck around for about an hour before all the trans fluid burned out of the exhaust but after that no more smoke. __________________ If it don't fit, force it,...If it still don't fit , modify it 'till it does fit !!!

10-29-2005, 11:30 AM	#15
70c10 67-72 Addict! Join Date: Feb 2002 Location: The TAX State! Posts: 7,857	Re: trans fluid in vaccume line to transmission! Not to hijack the post but when he pulls the old modulator off will it gush fluid out?. Just curious cuz I need to do this soon on my dads truck. __________________ Jim 1970 C/10 Fleetside w/Ghost Flames Lowered 4.5" front and 4" rear (Raked) 355/350 Turbo w/shift kit 10" Redneck Performance Verter w/2500 stall Hooker Super Comps part#2808-1 Performer RPM Air-Gap 12 Bolt w/3:73 gears- Eaton Posi Comp Cams XE262 with 1.6 Crane Energizers, Road Demon 625 and Brodix IK 180 heads

10-29-2005, 06:10 PM	#16
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: trans fluid in vaccume line to transmission! May get sone drippage, but nothing bad. Jacking up the truck from the rear will help too.

10-29-2005, 07:49 PM	#18
cableguy0 Senior Member Join Date: Apr 2000 Location: Delta,Pa Posts: 14,950	Re: trans fluid in vaccume line to transmission! so long as you jack the truck up from the rear and not the front fluid loss will be minimal. with the truck sitting level or jacked up from the front your going to get wet __________________ Owner of North Point Car Care in Dundalk Md. We specialize in custom exhaust on both modern and classic vehicles. We are a full service auto shop from classics to modern vehicles. Feel free to contact me with questions. I will give a 10% discount to any board member.



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10-29-2005, 09:16 PM	#19
VetteVet Msgt USAF Ret Join Date: Jan 2005 Location: Kalamazoo, Michigan Posts: 8,709	Re: trans fluid in vaccume line to transmission! It's up above the pan so fluid loss should be minimal. __________________ VetteVet metallic green 67 stepside 74 corvette convertible 1965 Harley sportster 1995 Harley wide glide Growing old is hell, but it beats the alternative. Last edited by VetteVet; 08-30-2010 at 08:20 AM.

10-31-2005, 01:13 PM	#20
case_bt Registered User Join Date: Jan 2002 Location: willis tx Posts: 374	Re: trans fluid in vaccume line to transmission! ITs fixed lost about a quart and a half easy fix now i need to adjust it to get my shift points fixed

10-31-2005, 03:59 PM	#21
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	Re: trans fluid in vaccume line to transmission! Transmission fluid is an oil, and it will smoke, and may burn if it gets hot enough. If anyone doubts it, pour a little of it on your hot exhaust manifold or headers. The combustion chamber is hotter..... Just change the modulator and it probably won't hurt to change the vacuum hose, too. __________________ Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was.

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