Have a 95 blazer 4x4, 4.3L. Vortec. This only happens at random, isn't a consistent noise. Sometimes when I'm pulling off from a stop light slow there is a light tapping that comes from the driver's side. But, when I romp on the gas then let back off it goes away. Any ideas? The person I got it from said it did that since they put in a new starter, and that if the cover is off it doesnt do that. But would that really be a starter tapping like that?

 

Cracked/broken flex plate?? Just a guess.

 

The noise has not happened since I replaced the brake power booster 2 days ago. The knocking has stopped completely and engine is performing great. Does a bad booster really cause that many issues?

 

The noise is back, went away for 2 days then came back. Where is the flex plate? Going to check that out.

 

It's between the crankshaft and the torque converter at the back of the engine. Some people would call it a flywheel, but that's really just a manual transmission thing. Starter engages on the ring. There is a plate on the trans bellhousing in front of it that it runs quite close to, but that plate is not removable on a 4L60e as far as I know so not sure what PO was talking about.

Type "broken flex plate" into Google and select "Images". This will give you an idea what can happen. They always crack around the bolt holes when they go. Torque converter pushes against the flex plate when running, and how hard it pushes varies with hydraulic pressure inside the torque converter. Could be why romping the gas and then letting off makes the noise go away. Maybe you are repositioning the cracks by pushing on the flex plate harder? Again, just a guess it is a flex plate. Replacement in a 4WD Blazer - definitely not fun - diagnosis difficult on a Blazer because of full surround bellhousing on a 4L60e. Take to a tranny shop for diagnosis/repairs, if you're not familiar with the problem or performing difficult repairs.

There is a hole with a push-in metal cap in the bottom of the 4L60E bellhousing in my 2001 Blazer. You might be able to work through such a hole if one is present and see if the flexplate wobbles or can be pried backward and forward, indicating it is cracked or broken.

Good luck!

 

No way in my mind can it be the starter.

Are you sure it's bottom end noise? Being you're right there with the cover off and you can't it hear it. And you said it's designated to the driver side, plus it's a "tapping" not a muffled "thunk"? If so, it's possible valve train.

Usually when the flexplate cracks it is very noticeable, almost bogs the engine when taking off or revving when it gets really bad, and imo sounds like a rod bearing about to blow out.

What is your oil pressure like when it does this? Being it goes away under throttle it could be you are not getting oil properly to the top end from time to time. Does it just tap, skip, stutter under load?

 

Pressure, temp everything is normal. It is coming from around where the transmission is. Threw it in gear and pushed e-brake all the way down and crawled under it. It's like a can-like tap tap tap tap that increases with rpms but only low ranges and when stomp the gas and go back to low rpms it goes away. Only happens from a stop with slow acceleration.

 

Could be cracked then. I'd go with what Lesmyer said and if you don't have the means of checking it take it to a tranny shop. You won't hear it under a load because when it starts to spin it is at the least point of resistance, momentum takes place. When it's at low rpm's it's not as easy to keep/get the tc and tranny turning.

 

Yeah that's what I'm thinking...gonna try to check it out tonight or tomorrow morning. Hey luckily might have a new job at Advanced Auto lol...maybe get discounted parts hahaha. Anyway one more thing...got a weird leak...i say weird because no fluid are going down at all...yet like a 6inch puddle every morning under the engine by drivers side and middle on the truck. I'm stumped.

 

I work at Advance Auto as part of management. A terrible mistake.. atleast my store. Discount is alright though.