1985 GMC C1500 MAKES A KNOCKING NOISE WHEN IN GEAR

  • Tiny
  • andye250
  • 1985 GMC C1500

Engine Performance problem
1985 GMC C1500 V8 Four Wheel Drive Automatic 10000 miles

Hello I was wondering if you could help me i've talked to several people and they have no clue what i'm talking about.
I just got my truck 4 months ago with 10,000 miles on the motor (rebuilt) and now I'm not sure whats making the noise the motor, transmission or transfercase, or maybe the rearend. What it's doing is making a knocking noise when you are in drive and holding the brake and giving it gas to the point that it wants to spin it's making a loud banging noise constantly but as soon as I slam it into nuetral out of gear it stops. But when I removed the transmission with the torque converter it stop cause I can't hear it anymore and when I first got it I assumed that the transmission was rebuilt and I was under the influence it was the torque converter.I'm not sure I though it was the transfer case too but not sure if it could slip and make a loud noise, cause it all started one day when I was coming home from work and all of a sudden it went out of gear, and I coasted a while, and it made a loud wining noise at that point and I thought it was the transmission and I put it in neutral and it made a grinding noise I know why that happend but why would it go into neutral
my truck has a 6 in lift
307 sbc with 350 internals
35 in tires
np203 transfercase
and th350 turbo

Oh, and when I slam on the breaks it goes into neutral in order for me to get back into gear I need to put it in 4 low and then back into 2 high for it to work

Monday, October 20th, 2008 AT 6:39 PM

9 Answers

  • Tiny
  • racefan966
  • Expert
  • 5,127 posts

Now without hearing first hand what is going on I would say my best educated guess is the transmission. As far as it going into neutral it could be linkage problems or it is just slipping and feels like it is in neutral. If you have anyother questions let me know.

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Monday, October 20th, 2008 AT 6:51 PM
  • Tiny
  • andye250
  • Member

Well I did check the fluid and it's low alot and when I took the transmission line off there is fluid all over them before I pull them off, and can a transmission realy make a loud noise it sounds like a hammer hitting concrete kinda

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Monday, October 20th, 2008 AT 6:54 PM
  • Tiny
  • racefan966
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  • 5,127 posts

Shouldn't but can and if your fluid is low then you need to fill it first. You are checking it in park and running too right. Let me know where this goes ok.

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Monday, October 20th, 2008 AT 7:01 PM
  • Tiny
  • andye250
  • Member

Yes I checked it in park while it ran and there was just a little on the dipstick, and one more question I have another motor that makes the same noise and it's low on oil could it been that cause it has a little leak out the covers and the oil pressure insert on the side of the block and I 've had somone tell me once that since the motor is under a load when it's in gear there could be a noise but when the transmission was off I could rev it to 6 k rpms and no noise perfect sound

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Monday, October 20th, 2008 AT 7:07 PM
  • Tiny
  • racefan966
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  • 5,127 posts

No it shouldn't be related see the entire drivetrain is under pressure. Now if the engine makes no noise out of gear then it should make no noise in gear unless it is pinging.

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Monday, October 20th, 2008 AT 7:27 PM
  • Tiny
  • andye250
  • Member

Wat would cause it to ping, low oil , and how would i go about fixing it add oil or complete rebuilt, cause i'm looking at it right now and i can see were it leaks and it's out of the pressure insert and the plug on the bottom cause the bottom just get covered with oil when i wipe away the old stuff


http://www.2carpros.com/forum/automotive_pictures/258998_Photo0131_1.jpg



I uploaded a picture for you

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Monday, October 20th, 2008 AT 7:30 PM
  • Tiny
  • racefan966
  • Expert
  • 5,127 posts

Ok a ping is caused by to much timing. If you set the timing to high then when you step on the gas it pings as soon as you let up and just cruise without putting it under a load the ping will stop. Now in the pic I see 2 breathers and no pcv valve this is not right and cannot run right either.
Now the breather on the right (passanger side) remove it and get a pcv valve and hook the vacuum line to that instead. As you have hooked now it's causing the engine to lean out and this can cause a ping too. So first things first get that right first. As for the oil leak I can't see it but then I am not sure where you are refering too,unless it is the breather there on that valve cover and if it is then do as I have asked and replace it with the pcv and that should help a ton. Get back to me and we will go from there.


http://www.2carpros.com/forum/automotive_pictures/249564_1985ChevySilverado350_1.jpg

Like in this pic.

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Tuesday, October 21st, 2008 AT 9:34 AM
  • Tiny
  • andye250
  • Member

Not sure if it's pinging or not but i't completely back to gether and now it makes a noise in nuetral but only once in a while when it's in neutral maybe every 2-5 minutes and it sound like a bat hitting a ball now and i've turned the timing far enough back to were it's wanting to die and it won't stay idling

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Friday, October 24th, 2008 AT 4:21 PM
  • Tiny
  • racefan966
  • Expert
  • 5,127 posts

Timing should be set at 10-12 degree's. As for the noise if I could hear it, it would make things so much easier. I don't know if it is coming from the engine or transmission or torque converter. Can you take an automotive stethiscope or long screwdriver (hold handle end to your ear) and find out where the noise is coming from? If it is from the engine is it coming from the top or bottom or what? Let me know what this brings ok.

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Saturday, October 25th, 2008 AT 8:35 AM

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