727 Loud shuddering bang/clunk noise under load going up hill *UPDATE*

[Evan Frucht]

When going up hill my 64 Fury is making a loud clunk or bang which sort of shakes and shudders the whole car as it happens. This happens when I accelerate up the semi steep hill that is my street. And it only happens for a moment and then goes away.

When car is revved up in neutral or park it sounds very smooth with no vibration or sounds whatsoever.

I thought it may have been the old ball and trunnion drive shaft which was clearly worn out. I just had a brand new custom drive shaft with a slip joint and double U-joints made and installed it. Paid 400 for it. All brand new and balanced. It might have reduced some vibation's a little, but the high load bang/clunk is still there.

The car has its original 318 poly/push button 727 combo

PO told me had the engine, trans, and rear end rebuilt but had no paperwork becase it was aparrently lost in a storage unit. I sort of believe him given how well the engine runs, but something isn't right in the transmission, or possibly rear end--but that seems less likely than trans. It isn't making any grinding or whiny noises.

The ATF fluid level may be a little on the low side but it was shifting through all the gears properly it seemed.

Could low fluid level cause a loud shuddering bang?

Any ideas what component in the transmission may be causing this?

 

[khryslerkid]

Remove the flywheel inspection cover and check for loose torque converter. Check for loose flywheel or cracks. Just something simple to check.

 

[Don Frelier]

A couple more ideas:
1. Motor / Trans mounts?
2. Does it shift hard into second on flat ground with normal accelleration?
3. It could be a bad pinion tooth or sidegear in the rear.

 

[Evan Frucht]

A couple more ideas:
1. Motor / Trans mounts?
2. Does it shift hard into second on flat ground with normal accelleration?
3. It could be a bad pinion tooth or sidegear in the rear.

-Checked the motor mounts they are solid.

- Not sure exactly how to check the transmission mounts, so that is a possibility. What's a good method to check them ?

- I live in the hills which doesn't make the whole test drive thing easy, but I can say ive witnessed it shift from first to second and that shift felt totally normal.

I'm not positive but the loud bang might be happening during the shift from 2nd to 3rd. It happens when you push the throttle at about 20mph, going up a relatively steep hill, not quite like San Franciscan streets but a solid incline.

Is this just something 727's will do under stress going up a hill? I'm also going easy on the throttle just because I'm still getting to know the car. Could that have something to do with it, maybe causing it to struggle?

It's defiantly loud and alarming and it doesn't help that I have a bunch of holes in the floor pans, rear seat out, and no carpet or anything atm.

 

[Evan Frucht]

Remove the flywheel inspection cover and check for loose torque converter. Check for loose flywheel or cracks. Just something simple to check.

My inspection cover is missing, could that let something in that would cause damage and a major issue to arise?

 

[Don Frelier]

Probably not unless you really drove through a bunch of mud/gravel for a long time. Likely the first thing that might happen would be the starter bendix might get dry and start hanging up. Don't think it would cause this problem.
But now it's easy to take a look in there...

 

[Evan Frucht]

Probably not unless you really drove through a bunch of mud/gravel for a long time. Likely the first thing that might happen would be the starter bendix might get dry and start hanging up. Don't think it would cause this problem.
But now it's easy to take a look in there...

Good to know. When I drained the oil out of the converter everything seemed tight.

 

[The Rebel]

What color is the trans fluid? Does it smell burnt? If not top it off to see if that stops it, but I doubt it will.

Does it seem like it's slipping or a hard shift.

 

[Evan Frucht]

I'm really not sure if it's slipping or hard shift. Leaning towards maybe a hard shift?

How would I tell one from the other?

With a really hard shift would it make the noise I'm describing?

 

[Evan Frucht]

I'm gonna try to drive it again when I get home from work. Maybe I can pinpoint more exactly when its happening. And also get a better description of the bang sound it's making.

Any other ideas would be great to hear

Thanks!

 

[AR67GTX]

Sort of sounds like a hard 2-3 trailing throttle shift due to poor timing of the band/clutches but the part about going up a hill kind of throws me off as that usually means you are feeding it some throttle. Checking for a loose torque converter mount bolt, or cracked flex plate and worn transmission mount are good, cheap first steps.

 

[Ron H]

Almost sounds like the differential. The trans evidently shifts fine from what you say. Suppose your gear is not a sure grip. Reckon you checked the underside making sure everything is tight since it's described the car was apart. Raise rear wheels and check for any run out. Ah...just how steep is that hill?

 

[Ron H]

Have you tried going up that hill leaving it in 1st or 2nd gear? If not, see if you still get that shuddering.

 

[Evan Frucht]

Almost sounds like the differential. The trans evidently shifts fine from what you say. Suppose your gear is not a sure grip. Reckon you checked the underside making sure everything is tight since it's described the car was apart. Raise rear wheels and check for any run out. Ah...just how steep is that hill?

Hard to convey exactly how steep it is. Not crazy steep but an average person would have a hard time riding a bike up it. Will try it in 1st and 2ND and report back.

 

[The Rebel]

How about when you come down the hill coasting.

 

[Evan Frucht]

How about when you come down the hill coasting.

When I came down that same hill, I put it in first. It acted normal going downhill in first but that probably doesnt say much. so I'm not sure.

 

[Evan Frucht]

What things can I do/try when I drive it to try to pinpoint the issue, any thoughts there?

 

[Dako]

You may have spark jump across plug wires. This is usually more prominent under load at lower rpms. Had this happen before and thought I had a transmission problem because when I would drop a gear it would go away. Took it to a trusted mechanic who told me what my problem was. Changed the plug wires and never had it happen again.

 

[Dako]

What things can I do/try when I drive it to try to pinpoint the issue, any thoughts there?

When it happens immediately drop it a gear and see if it goes away with a higher rpm at the same speed. If so...plug wires.

 

[Evan Frucht]

You may have spark jump across plug wires. This is usually more prominent under load at lower rpms. Had this happen before and thought I had a transmission problem because when I would drop a gear it would go away. Took it to a trusted mechanic who told me what my problem was. Changed the plug wires and never had it happen again.

Thanks. I sort of doubt that because the noise is so loud and the bang sends a strong reverberating jolt through the whole cabin. I have new spark plug wires from MSD, only put on a couple months ago right after I bought the car. But I'll jiggle them, make sure they are fully seated, and see what that does. The engine revs up very smoothly when in park and neutral, and never skips a beat.