Tranny question--maybe? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Huck · 01-21-2003, 10:01 AM

MY 71 truck turbo 350 is slow to engage when it's cold. Can take like 30 seconds before you get any action in either forward or reverse. Is this a factor of old fluid, dirty filter, or other more discusting problem? It also is not the best at downshifting when you push the pedal to the floor. If you manually pull hte shifter into second, it is just fine. I did check the vacuum line to the trans and it seems ok. Thought's, idea's, experience's, guesses??? Thanks---Huck

72shadetree · 01-21-2003, 10:13 AM

mine was a weak pump it lasted abouth 6 mnths after that but i think a clogged filter will do that to good luck

JimKshortstep4x4 · 01-21-2003, 02:16 PM

I would change the fluid and filter. Also, if the transmission is a little low on fluid, it will act the same way. On the downshift, the cable needs to be adjusted. (By the carb).

Jim

jays68yak · 01-21-2003, 04:00 PM

Like above I would check fuild and filter first. Ive had a pump and a the bands go bad and give kinda the same problem. Althought the bands just wouldnt go most of the time. You could always take it down to a tranny shop and have them test drive it.

**1971Stepside** · 01-21-2003, 04:04 PM

I can almost gaurantee you that if you change the oil and filter the transmission will give up on you in the next few months. I have discussed this with several transmission shops and they all recommended that if you did not regularly change the fluid not to it at all. The fluid will build up a certain amount of particles as it ages and these particles if removed and replaced with fresh fluid will cause the tranny to not engage at all.

Did you check the fluid level. Sounds like your converter is not doing its job.

Again, from experience (the expensive way) I would ask around before you change the fluid...

my new 72 · 01-21-2003, 04:29 PM

My tranny is going out too. When I get in it in the morning I have to let it sit for about 10 minutes before it will engage, and then it slips out at the corner about 1/10th of a mile from my house and I have to sit for another minute before it will engage. I do believe mine is caused by worn bands, and possibly a worn pump.

**jamie72** · 01-21-2003, 04:41 PM

been out power braking AGAIN...now you broke it.
i`d take to a tranny shop (one you trust)
maybe the bands need adjusted,had one do that adjusted bands and drove it(hard) for a couple more years before it died,but htat was behind a big block and heavy foot.
good luck
jamie

**COBALT** · 01-21-2003, 04:56 PM

No, that doesn't sound like a converter problem. Sounds more like a front pump problem or a valve body problem.

Sounds like it's taking way too long to build up enough fluid pressure to change the fluid path in valve body - OR - there is enough pressure, but the appropriate position of the main part of the valve body is taking way too long to actuate to the right position or loosing pressure once it gets there. The fact that it will shift into L2 without any problem makes me think the valve body is the culprit since the actuation of the main valve selector is different from P to D than P to L1 or L2. Same with the detent circuit (which is used when you mash the petal).

The only thing you can do is drop the pan and check for debris. I've heard of people finding broken lip seals in their pan, which would cause a problem like this. If the main valve actuator has broken a seal then fluid pressure isn't being contained in the appropriate paths of the valve body, and can be leaking over into other circuits. That would explain the good response in L2 but bad in D.

Even if you don't find anything you may have to at least rebuild your valve body, some of which can be done with the tranmission in the truck if absolutely necessary, but messing with the front pump means it has to come out.

Also, the practice of NOT changing your fluid in fear of having to rebuild the transmission is a valid one, but usually depends on how your transmission has been wearing over time, which you can really only tell if (you guessed it) drop the pan, which means this argument is pointless anyway. If your transmission contains a bit of sludge, and an excessive amount of gray paint in the pan then changing the fluid will only cause more short-term wear (but you're stuck replacing the fluid because the old stuff is sitting in a bucket on your shop floor). If your fluid is clean, with the typical thin layer of gray paint at the bottom of the pan then you should change your fluid, because it probably means your filter is full of that same gray paint, and the wear rate probably won't be increased. If you have excessive sludge, gray paint, and debris larger than the size of a beebee pellet then you shouldn't be worried about changing fluid. You should be rebuilding your transmission. Period.

Good luck.

Huck · 01-21-2003, 05:19 PM

Thanks guys for your help. I will pull the pan and probably replace the filter is it looks kaka. Changing the fluid may help if the old is being choked out by the temp change and a dirty filter but------I'm not going to rebuild the trans as it would cost me more then buying a rebuilt or a guaranteed good one from a yard. I also have a 700R4 out of an 88 silverado looking for a home so~~~~. Thanks again and I'll let you all know what I find and do. Huck

01-21-2003, 10:01 AM	#1
Huck Senior Member Join Date: Jun 2001 Location: Shelbyville, KY Posts: 3,269	Tranny question--maybe? MY 71 truck turbo 350 is slow to engage when it's cold. Can take like 30 seconds before you get any action in either forward or reverse. Is this a factor of old fluid, dirty filter, or other more discusting problem? It also is not the best at downshifting when you push the pedal to the floor. If you manually pull hte shifter into second, it is just fine. I did check the vacuum line to the trans and it seems ok. Thought's, idea's, experience's, guesses??? Thanks---Huck

01-21-2003, 10:13 AM	#2
72shadetree KEEP ON TRUCKING Join Date: Sep 2000 Location: martinsville va Posts: 2,563	mine was a weak pump it lasted abouth 6 mnths after that but i think a clogged filter will do that to good luck __________________ 72 cheyenne 2wd lwb 71 k20 sons bassett va

01-21-2003, 04:00 PM	#4
jays68yak Registered User Join Date: Oct 2002 Location: Gilroy, CA Posts: 1,454	Like above I would check fuild and filter first. Ive had a pump and a the bands go bad and give kinda the same problem. Althought the bands just wouldnt go most of the time. You could always take it down to a tranny shop and have them test drive it. __________________ 1969 Chevy Project SWB Fleet, 20s, 5.3, t56, in the weeds. 1970 Chevy Truck cab on a 1979 Jimmy frame-8.1 liter 496 bbc/sm465/np203-jeds doubler-np205/d60/14bff Welded/42 tsls on recentered H1s 1998 Chevy Crew Cab K3500 SAS'd with hpd60, links and swayaway coilovers. 8.1l vortec DD/towrig "I like long walks, especially when they are taken by people who annoy me. "

01-21-2003, 04:04 PM	#5
1971Stepside Almost Satisfied Join Date: Mar 2002 Location: Springfield, MO Posts: 2,932	I can almost gaurantee you that if you change the oil and filter the transmission will give up on you in the next few months. I have discussed this with several transmission shops and they all recommended that if you did not regularly change the fluid not to it at all. The fluid will build up a certain amount of particles as it ages and these particles if removed and replaced with fresh fluid will cause the tranny to not engage at all. Did you check the fluid level. Sounds like your converter is not doing its job. Again, from experience (the expensive way) I would ask around before you change the fluid... __________________ 1971 C10 Stepside. LSx 6.0 with BTR Stage IV, Speed Engineering Headers, 4L80e transmission w/3200 Circle-D Stall. 3.73. Posi. Purchased this truck when I was 17. I started the rebuild (or take apart) in 1993. I have drug it around all over the country in pieces. Finally back on the road in 2021. "I can't complain, but sometimes I still do. Life's been good to me so far."

01-21-2003, 04:29 PM	#6
my new 72 faster, faster, faster Join Date: Dec 2001 Location: Houston ,Texas ,USA Posts: 1,354	My tranny is going out too. When I get in it in the morning I have to let it sit for about 10 minutes before it will engage, and then it slips out at the corner about 1/10th of a mile from my house and I have to sit for another minute before it will engage. I do believe mine is caused by worn bands, and possibly a worn pump. __________________ I'm going to Law School, wanna debate? It's good practice.

01-21-2003, 02:16 PM	#3
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	I would change the fluid and filter. Also, if the transmission is a little low on fluid, it will act the same way. On the downshift, the cable needs to be adjusted. (By the carb). Jim

01-21-2003, 04:41 PM	#7
jamie72 Senior Member Join Date: Apr 2000 Location: madison indiana Posts: 3,839	been out power braking AGAIN...now you broke it. i`d take to a tranny shop (one you trust) maybe the bands need adjusted,had one do that adjusted bands and drove it(hard) for a couple more years before it died,but htat was behind a big block and heavy foot. good luck jamie __________________ jamie72 72 BB cheyenne -- Restoration getting started.. member #807 http://www.myspace.com/whitetailobsession www.antlertalk.com

01-21-2003, 04:56 PM	#8
COBALT Senior Member Join Date: Sep 2001 Location: Seattle, WA, USA Posts: 5,817	No, that doesn't sound like a converter problem. Sounds more like a front pump problem or a valve body problem. Sounds like it's taking way too long to build up enough fluid pressure to change the fluid path in valve body - OR - there is enough pressure, but the appropriate position of the main part of the valve body is taking way too long to actuate to the right position or loosing pressure once it gets there. The fact that it will shift into L2 without any problem makes me think the valve body is the culprit since the actuation of the main valve selector is different from P to D than P to L1 or L2. Same with the detent circuit (which is used when you mash the petal). The only thing you can do is drop the pan and check for debris. I've heard of people finding broken lip seals in their pan, which would cause a problem like this. If the main valve actuator has broken a seal then fluid pressure isn't being contained in the appropriate paths of the valve body, and can be leaking over into other circuits. That would explain the good response in L2 but bad in D. Even if you don't find anything you may have to at least rebuild your valve body, some of which can be done with the tranmission in the truck if absolutely necessary, but messing with the front pump means it has to come out. Also, the practice of NOT changing your fluid in fear of having to rebuild the transmission is a valid one, but usually depends on how your transmission has been wearing over time, which you can really only tell if (you guessed it) drop the pan, which means this argument is pointless anyway. If your transmission contains a bit of sludge, and an excessive amount of gray paint in the pan then changing the fluid will only cause more short-term wear (but you're stuck replacing the fluid because the old stuff is sitting in a bucket on your shop floor). If your fluid is clean, with the typical thin layer of gray paint at the bottom of the pan then you should change your fluid, because it probably means your filter is full of that same gray paint, and the wear rate probably won't be increased. If you have excessive sludge, gray paint, and debris larger than the size of a beebee pellet then you shouldn't be worried about changing fluid. You should be rebuilding your transmission. Period. Good luck. __________________ '69 3/4 ton C20 2wd-350ci/TH400 '69 3/4 ton Custom 20 2wd-350ci/4sp Manual '99 2wd 5.7 Chevy Tahoe Seattle, WA. Last edited by COBALT; 01-21-2003 at 05:00 PM.

01-21-2003, 05:19 PM	#9
Huck Senior Member Join Date: Jun 2001 Location: Shelbyville, KY Posts: 3,269	Thanks guys for your help. I will pull the pan and probably replace the filter is it looks kaka. Changing the fluid may help if the old is being choked out by the temp change and a dirty filter but------I'm not going to rebuild the trans as it would cost me more then buying a rebuilt or a guaranteed good one from a yard. I also have a 700R4 out of an 88 silverado looking for a home so~~~~. Thanks again and I'll let you all know what I find and do. Huck



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.