More problems with engine and transmission

[Eric Rose]

Now that I have my cooling issue worked out I'm able to open the Falcon up on the highway. When I get up to speed and let off the throttle, I get a knocking sound. It sounds kind of like knocking rods, but its more of a thin, tinny sound and there's no vibration like knocking rods. I just had the motor rebuilt by a reputable machine shop and it runs very smooth, even when the noise occurs. It also runs cool and has great oil pressure (40lbs at cruising speed)

The transmission is a different story, however. It worked fine as it came in the car but when we changed the filter there was a large chunk of debris (piece of a broken band?) in the pan. We put it back together just to see what it would do. It operated good for a while but then it began leaking fluid like a sieve and now it sometimes slips when going into gear and doesn't shift right until its warmed up.

I usually cruise at 60mph/2500rpm. When I let off the throttle I hear the noise. If I let the RPM's drop some the noise will continue untill it drops down to 2000 rpm. Accelerating will make the noise go away. Shifting to neutral will also make the noise go away.

I read in another post that having a cracked flexplate can cause it to have symptoms similar to a knocking rod. I checked out the flexplate when I installed it and din't see any cracks but it was used and may have cracked after I put it in.

I'm also having a problem with starting the engine. It doesn't want to start unless I prime it with gas. Once I prime it with gas and let it get warm it runs fine. I have tried pumping the accelerator a few times both before and during turning over the starter, that doesn't do any good. How can it get gas once its running but not when I'm starting it?
:

 

[LaGrasta]

what's your read end like? It may need fluid or could be going out and now you hear it when the engine is not keeping the drive line taunt.

Hard starting could be float level... leak... clogged filter...

 

[Eric Rose]

The rear end looked good when I had the cover off to change the fluid last summer. I forget what weight I put in but I think it was 75-w-90 or something like that. I filled it up to the level of the plug.... too much?

It has leaked some kind of fluid all over the back of the car. Doesn't feel thick like gear oil though, it feels more like ATF. I will check to see if the rear end is leaking fluid. But I know its leaking transmission fluid from the area around the dipstick tube/lines/servo because theres usually a puddle under it. I can't tell exactly where its leaking from because its all over that area. I try to keep it topped up to the right level but checking trans fluid is not very accurate.

As for the starting problem, I took the top off of my carb and theres plenty of gas in the float bowl. I also checked to see that the needle valve wasn't seized. I can't tell if the accelerator pump is pumping or not when I work the throttle linkage, it doesn't seem like it is but once it starts it seems to rev fine.

 

[Eric Rose]

Anyone?

 

[Frankenstang]

How can it get gas once its running but not when I'm starting it?

I would hang a drop light and with choke open and looking down into the carbureator see if you can see steady stream of fuel as you work the throttle.

Once you get it running, where does it idle at rpm? What kind of carb? Where is the timing set?

As far as the auto tranny goes are you sure it's not the modulator valve leaking? I'd agree with LaGrasta that it sounds like the noise is coming from something in the drivetrain (flex plate, torque converter, drive shaft, rearend) if it only occurs under 'engine braking' or when you let off the gas.

 

[Eric Rose]

Once you get it running, where does it idle at rpm? What kind of carb? Where is the timing set?.

Carb is a Carter YF. Duraspark II (w/ MSD coil) is set to 12 degrees and the plug gap is .051. Once it warms up it has a stable idle at about 800 in neutral and 650 in gear.

 

[JOHN G]

Had a similar knocking in a previous car-turned out to be loose torque convertor to flywheel bolts. sounded just like a rod knock. Obviously, it would be t/c to flexplate on our engines, but same noise I suppose could be had.

 

[Frankenstang]

I don't know much about the Duraspark setup, but those idle and advance numbers don't sound bad, especially if the engine seems to run fine once it warms up.

It sounds like a fuel delivery problem, possibly pump, filter or junk in the carb, or a cold start issue.

I would check to make sure the choke is hooked up and operating properly. When the temps outside get sufficiently cold a disconnected choke or stuck open butterfly could make the engine very hard to start and extra fuel (priming) would over come that.

I like John G's idea on checking for loose t/c bolts.

 

[Eric Rose]

I haven't hooked up the choke at all. I have just left it open. I have tried closing it up some and starting it though, not much effect. I don't event get a gas smell when I'm trying to start it. It seems like gas is just not getting to the carb untill I prime it and it starts.

Edit: I'll check the torque converter bolts today, thanks for the suggestions guys.

 

[Eric Rose]

I think the knocking problem is resolved. I checked for a cracked flexplate/loose torque converter bolts Saturday and the flexplate was fine, the torque converter bolts were tight but I was able to get a little bit more torque on a couple of them. I took vac line off of the modulator and checked it for leaking fluid, I couldn't see any fluid leaked inside it so I reconnected it.

I felt that the results were inconclusive when I was under the car looking at stuff but when I drove it Sunday the problem was gone. My guess is that the line to the modulator valve was loose and when I put it back on it got a better seal. :

I am still leaking transmission fluid though, looks to be coming from around the dipstick tube even after I replaced the O-ring on it. I may have to get another dipstick tube. Will the tube for a V8/C4 work with a Six/C4?

I see a transmission rebuild being needed sometime in the future. Will the C4 from a V8 equipped car/truck work with the six bellhousing? I have a core that I think was pulled from a V8 truck.

 

[LaGrasta]

Yes, a V8 C4 is interchangabel with the correct bell housing and so are the dipsticks. Since you already have a new o-ring, try a bit of silicone seal as well and see what happens.