HELP---Strange Engine Noise is very puzzling

[datzenmike]

The vent tells you nothing you don't already know. The sound is coming from the front, we all know this.

 

Put vehicle against a wall and put a load on it while you stick your head in under the hood and listen.

[raythomas]

On 12/13/2022 at 7:53 PM, datzenmike said:

The vent tells you nothing you don't already know. The sound is coming from the front, we all know this.

 

Put vehicle against a wall and put a load on it while you stick your head in under the hood and listen.

Well It finally stopped raining yesterday morning but its turned bad cold. Finally got a chance to try the truck with it held back. Got my father-in-law to do the "driving" while I listened with the hood up. The engine is still as smooth as melted butter and after crawling under the truck the noise sounds to be coming from inside the bell housing on the front side of the transmission. You can "feel" it when you hold your hand on the botom front side of the transmission case. I'm sure I'll need to pull the trans to see whats up with the clutch, or pressure plate assembly. Anybody got any ideas what I should be looking for that could make a noise there?

Thanks for all the tips and ideas so far. I appreciate every reply.

Thx

Ray

[Stoffregen Motorsports]

Inside the bellhousing. Could be a lost bolt or a rock or anything that got into the bellhousing and is bouncing around. This is actually pretty common.

[datzenmike]

Might be a pressure plate mounting bolt or one of those torsion springs from the clutch disc. 

 

Are the transmission mounting bolts tight?

[Thomas Perkins]

A loose bolt broke off in mine,and it went thru the transmission and all the fluid came out.I was coming home from work one day.Truck been running so good,then I hear a noise and I thought oh shit.Was a mile from the house,it was making a noise,stopped at the mail box,got out looked under it and had a puddle of transmission fluid,so i had 330 feet to go to my carport.I had a leak all the way there,Then it all came out.But the good thing was i had a warranty on the transmission.So I had it towed and he said a bolt came loose,the transmission was no more good and he put another one in.Here are some pics,check the date.so my transmission he replaced is now 5 years old.I use Red line MT-90 transmission fluid.Gears change so good.When the bolt went thru the transmission,i could feel the lost compression from the transmission.I would park your truck and get it fixed or it may total the transmission like mine,but who knows if may be something different than mine.I just wanted to share what mine did.I do check my fluid often,it has no leaks anywhere.

Edited December 18, 2022 by Thomas Perkins

[raythomas]

2 hours ago, datzenmike said:

Might be a pressure plate mounting bolt or one of those torsion springs from the clutch disc. 

 

Are the transmission mounting bolts tight?

Yes sir, they are. The sound started just a little bit and then got a little worse and a little worse so I"m hoping its a bolt that's backed out or something in the clutch. On an 87 model with the 5 speed isn't there a small dust cover or plate on the lower side of the transmission where it bolts to the engine?

 

I'm gonna try to pull the trans in a week or so.

Thx

Ray

[Stoffregen Motorsports]

Yes, there is a dust cover, but some of them are not removable, ie- a one piece rear engine plate. If it is removeable, you still can't get to any bolts, but it may allow enough room to let the debris fall out.

 

Removing the starter may allow enough access to get a mirror and light in there. Maybe a 12mm wrench for the clutch cover bolts too.

[datzenmike]

Manuals have a one piece engine plate. Automatics can also have a one piece plate but there is a suitably placed hole covered with a rubber plug so you can get at the torque converter bolts on the flex plate. Most automatics are two piece with the bottom half removable and bolted to the transmission. Automatic engine plates will work on manuals but not the other way round.

 

 

 

 

[raythomas]

I just had a thought. Could it possible be the starter? And if it was, could the starter still work correctly to crank over the truck and yet be broken to allow it to make the noise? Like something loose on it or something?

Thx

Ray

[Stoffregen Motorsports]

Maybe, but not likely. Really the only thing that would make noise in the starter is if the bendix hung up and is causing the gear to stay engaged. I've seen this, but it's really noisy. Not something you would ever be able to live with.

[raythomas]

6 hours ago, Stoffregen Motorsports said:

Maybe, but not likely. Really the only thing that would make noise in the starter is if the bendix hung up and is causing the gear to stay engaged. I've seen this, but it's really noisy. Not something you would ever be able to live with.

Well it rained here for like a solid week and now that its quit raining the temps have nose dived. I did get the truck in the shop. I plan to start taking the trans out over the holidays maybe. I sure hope its something loose in that clutch area.

Thx

Ray

[Crashtd420]

16 hours ago, raythomas said:

I just had a thought. Could it possible be the starter? And if it was, could the starter still work correctly to crank over the truck and yet be broken to allow it to make the noise? Like something loose on it or something?

Thx

Ray

I had a starter do that... the little gear would disengage after starting but would not stay retracted.... 

If the truck was facing down hill it would slide forward and bounce off the spinning flywheel... still started the truck fine....

This only happened once in all my years of driving so not very likely but with what you are going through I wouldn't rule it out.... 

[raythomas]

On 12/23/2022 at 6:58 AM, Crashtd420 said:

I had a starter do that... the little gear would disengage after starting but would not stay retracted.... 

If the truck was facing down hill it would slide forward and bounce off the spinning flywheel... still started the truck fine....

This only happened once in all my years of driving so not very likely but with what you are going through I wouldn't rule it out.... 

That's what I'm hoping. Something loose or bent.

Thx

Ray

[datzenmike]

Check the bottom half of the engine plate. Is it secure? or could it vibrate under load at a certain RPM?

 

Exhaust.... Grab everything and shake it hard....

 

Are all the exhaust down pipe to manifold bolts tight?

Has the down pipe heat shield come loose and is now rattling?

Is anything rubbing against the exhaust pipe?

The catalytic converter bolts to the exhaust pipe. Loose bolt? Catalyst came loose inside?

Hanger loose at Transmission?

[raythomas]

On 12/24/2022 at 3:00 PM, datzenmike said:

Check the bottom half of the engine plate. Is it secure? or could it vibrate under load at a certain RPM?

 

Exhaust.... Grab everything and shake it hard....

 

Are all the exhaust down pipe to manifold bolts tight?

Has the down pipe heat shield come loose and is now rattling?

Is anything rubbing against the exhaust pipe?

The catalytic converter bolts to the exhaust pipe. Loose bolt? Catalyst came loose inside?

Hanger loose at Transmission?

Nothing loose that I can tell and I've grabbed and twisted and shook everything under there. I've had the cat off so the bolts on it are tight. I just put it back on a few weeks ago. Also double checked ALL the heat shields on the exhaust from the header down to the cat and all are good. The sound is coming from inside the bellhousing. I got the truck in the garage over the holiday week. I'm in the process of getting it up on stand to start removing the trans by this weekend maybe.

Thx

Ray

[Stoffregen Motorsports]

When you get it out, double check the spring on the clutch release arm, make sure the ball pivot is tight and check the front cover bolts for leaks.

 

On the engine side, check the flywheel bolts (if you're removing the clutch cover) and inspect the fingers on the clutch cover for funky wear. Look to see that they are all laying flat and even with each other.

[raythomas]

UPDATE:
I finally got some time to work on the truck today. Got the driveshaft out, the electrical connectors undone, the trans mount bolts loosened, the trans cross member bolts loose and the starter off. Took the shifter out of the top of the trans. Got all the bell housing bolts all broke loose. Just need to get the trans jack in place and remove the cross member and bell housing bolts to get it out of the truck. How far will the trans need to move back before it can be lowered down? And just for my own curiosity, how heavy is a factory 5 speed manual transmission?  Hopefully all will go well tomorrow.

Thx

Ray

[datzenmike]

The 71c is around 70 pounds give or take.

 

Hope you drained it first or it will get messy. Also the clutch slave needs to be unbolted from the bell housing. Secure the piston inside from pushing out by wrapping with electrical tape.... and the speedometer cable unscrewed. (you probably did this but didn't mention it) And reverse light switch harness removed.

[raythomas]

Yes sir, I actually did all that. The slave cylinder, all electronic connectors. And the fluid was the first thing I did cause I knew I'd probably make a horrible mess on the garage floor. I also removed the positive battery cable cause I knew it might cause trouble when removing the starter.

70 lbs is a little more than I want to try and "juggle" underneath the truck. May just use a floor jack to be on the safe side.

So how far does the trans come back toward the rear of the truck before its free of the engine? And what keeps the engine from tilting back with just the engine mounts holding it after you remove the transmission? Seems like it would give some with rubber motor mounts.

Thx

Ray

[Stoffregen Motorsports]

It has to come back the length of the input shaft, which is about 4 inches. That's just to clear the clutch. It may need a tiny bit more wiggle room to get it out.

[datzenmike]

Another floor jack under the rear of the oil pan will support the engine and be adjustable. It can only drop as far as the bolt in cross member that supports the front of the torsion bars. When sliding the transmission to the rear, the engine will want to tilt down at the back making separation difficult. The 71B is 5.5" longer than the stock 4 speed so there's that extra length that has to be stuffed back past the torsion bar adjusters. You might consider removing one of the torsion bars so the transmission can be rolled on it's side slightly diagonal and drop out

[raythomas]

20 minutes ago, datzenmike said:

Another floor jack under the rear of the oil pan will support the engine and be adjustable. It can only drop as far as the bolt in cross member that supports the front of the torsion bars. When sliding the transmission to the rear, the engine will want to tilt down at the back making separation difficult. The 71B is 5.5" longer than the stock 4 speed so there's that extra length that has to be stuffed back past the torsion bar adjusters. You might consider removing one of the torsion bars so the transmission can be rolled on it's side slightly diagonal and drop out

Holy Moly, thanks for the information.

Thx

Ray

[raythomas]

Well, as my luck would have it I got the trans out and everything about the clutch looks perfect. The flywheel looks almost brand new, with almost no wear to be seen. And the clutch disc still has the grooves showing on the pads. No springs broke or out of place. Pilot bushing looks nice with no rough spots or noticeable wear. The throw out bearing spins super free with no gritty or grinding sound at all. The throw out arm moves the bearing assembly up and down freely without noise or binding. I'm so totally stumped by all this. I was hoping something was gonna fall out of the bellhousing when  I pulled it away from the engine and the culprit would be super obvious. But no such luck. Guess my next move is to remove the oil pan and see what the bottom end looks like. Oh, and you were right. I did have to rotate the trans 90 degrees to the left to get it pushed back away from the engine where I could angle it down out of the truck. Not terribly heavy, but still not a piece of cake either.

There is a cross member underneath the oil pan that has a bolt in each end. Can I remove that while the truck is up on ramps? I haven't removed the torsion bars, just pulled the truck up on ramps. Don't want to take that cross member out if its gonna be a problem with the weight of the truck still resting on the wheels and the torsion bars are under load.

If anyone has more suggestions I'm all ears at this point. And thanks for everything so far. I appreciate it.

Thx
Ray

[datzenmike]

Check that the flywheel mounting bolts are properly torqued. Remember this only happens when under load.  They are 100-116 ft lbs.

 

It's no problem to remove that bolt in cross member to get at the pan. I've removed them before. Possibly you may need to lightly hammer the bolts back in to get the holes to line up again.

[raythomas]

9 minutes ago, datzenmike said:

Check that the flywheel mounting bolts are properly torqued. Remember this only happens when under load.  They are 100-116 ft lbs.

 

It's no problem to remove that bolt in cross member to get at the pan. I've removed them before. Possibly you may need to lightly hammer the bolts back in to get the holes to line up again.

Thank you.

I will check those.

Thx

Ray