Doug Maitlen

In my 79, there is a little bit of a knock/vibration when I sit in drive or neutral at idle speed. It seems to go away when I increase the rpm slightly. Does anyone have any input? It would be greatly appreciated.

Thank you
Doug

71coupe454

2 Days after I bought my 67 GTO several years ago, It started making a low deep knock at a idle. I got a bad sick feeling in my stomach. I took it by a old guy that had a carb. shop near my house. I told him I thought I had a rod knocking in this car I JUST BOUGHT! He walked out and took a listen too it and told me before I condem the engine to check my flywheel bolts. That gave me a little hope on the way home. I crawled under the GTO and stuck a wrench up on one of the bolts and sure enough it was loose. All the flywheel bolts were about a turn or so loose. Knocking noise was all gone... dont know if this will help you or not but you saying it was at a idle is what reminded me of that problem I had as it would only do it at a idle and then go away. Good luck

Doug Maitlen

I have an L48 automatic. It knocks at low idle.

'75

What is the low idle speed and oil pressure.

Doug Maitlen

1. The tachometer doesn't work, so I would guess 400-600. It seems really low, lower than before she sat for six months. Is there a way to increase the idle speed? It is a stock rochester quadrajet carburetor.

2. The oil pressure is about 35-40 on the gauge.

I will answer any more questions needed to help solve this problem.
Any input would much appreciated.
Thank you
Doug

Doug Maitlen

Any suggestions?

bernie payne

It could very well be a universal joint. Does it seem to be coming from the front or the back?

justanotherdoe

Sounds like something is loose. My AC plumbing did this until I got it fastened, and I still have an rpm/temperature related squeek in my exhaust back at the spare tire carrier.

mdj21

Get your self a mechanics stethoscope and start searching for the location of your knock. They can be had pretty cheap from Harbor Freight. A short piece of garden hose held up to your ear will also work, but the stethoscope is better.

My car started making a knock sound at idle that would disappear at above 1200 rpm. I searched for quite a while checking things like fuel pump, water pump, alternator, ect. In the end it turned out to be a rod bearing going out on number 6 piston rod. Fourtinatly I caught it early enough that major damage was avoided. I’m in the process of fixing it my self pretty cheaply for the cost of a crank kit, a complete gasket set, and I had my rods honed.

Hopefully your knock is something less serious like having your fly wheel bolts a little loose like 71coupe454 or a bad water pump.

Do a search through the archives for “Knock” or “Engine Knock” and try any suggestions you find. You want to check the cheap and easy stuff first. If you still can’t find it, you can drop the oil pan and check for a bad bearing with a steel rod. Tap the rod on all of the bearing caps (rods and mains). Good bearings will make a more solid sound while bad ones will sound sort of hollow.

But again, try the simple, easy stuff first before you tear into your motor unnecessarily. And please do not drive your car before you find the knock. A bad bearing is a lot better to be fixing than the damage you can get from a thrown rod.

Good luck and I hope this helps.

Mike.

G dad

Remove the inspection cover at the transmission check your torque converter bolts they could be loose...