Weird clunk?

[Titleist16]

I've noticed that sometimes that when I'm sitting at a light and I take my foot of the brake to go the car seems to start moving very slowly and then a second or to later there will be a clunk and then the car will take off fine. It doesn't really feel like a shifting clunk but it does feel like it's coming from the trans or motor area. It's a 200 with a C4. Could a bad trans mount or motor mount be the problem? Any ideas on what it could be?

 

[james singleton]

I know you said that "it doesn't feel like a shifting clunk", but are you sure that it isn't the transmission modulator??? A bad modulator causes the transmission to clunk like that! Good Luck! Jim P.S. Modulator should be cheap and easy to replace.

 

[rbohm]

8) check the front U-joint on the driveshaft. that is the most likely culprit.

 

[pedal2themetal45]

I had the samething with my truck and when I had the rear end redone with a Detroit True trac I asked the guy what was the deal and he said the rod that holds the spider gears was broken in half.. I'd get it check soon
Tim

 

[The Plankster Prankster]

he said the rod that holds the spider gears was broken in half.
Tim

i bet that was an 8.8 axle? when mine in the f150 went out, the last 40 miles had a clunk every mile or two (at highway speeds) with a little lockup and get going again, shaft was damaged but not broke and spider gears lost half their teeth in the process (thats what that clunk-skid thing was)

but more likely is a u-joint, i've heard that the rear is more likely to fail, but check em both.

if you feel like checking your mounts, my method is to get under the vehicle and put a jack in a position to raise the tranny if youre checking its mount, or the engine to check its mounts. it should barely flex and raise the car with it.

 

[Titleist16]

how do I go about checking the U-joints?

 

[pedal2themetal45]

he said the rod that holds the spider gears was broken in half.
Tim

i bet that was an 8.8 axle? .

No it was a 9" out of a 72 F-100..

To check the U's get under the car and wiggle/shake/turn the U-joint by hand if there is any sugnifagant movement in the U joint its shot.. but I still think its in the rear end as mine acted the exact same way.. just as it would start rolling it would clunk...
Tim

 

[rbohm]

how do I go about checking the U-joints?

8) with the trans in park, crawl up under the car and turn the drive shaft back and forth. if it rotates slightly then the U-joints are bad and need replacing.

 

[addo]

Titleist16, that checking is done with the motor off!

Just in case you weren't sure...

 

[Titleist16]

Good thing you told me that, I was going to jack the car up with the motor running and car in drive and then try to grab the U-jount, lol.
Thanks guys, I'm gonna check them out today and see what happens.
If they are bad, how hard is it to replace them? I've never replaced u-joints before.

 

[rbohm]

8) titelist, if you do check it with the motor running, make sure the trans is in gear, and the rear end up on jack stands(dont want the vehicle running into the house now do we?). oh and make sure the engine is at a fast idle. then when you wake up in the emergency room, you will have a funny story to tell the doctors

as for replacing the U-joints, they are not hard to do, but you do need a vice or a press, or a really big C clamp.

 

[Titleist16]

I checked the u-joints today like you guys said but when I turn the driveshaft it moves a little but it just sems like freeplay in the trans and rear end. When I turn it you can the see the yoke turn with it, and the rear you can hear the gears move a little. I can't tell if there's any play at the u-joints themselves. Is there any other way I can check the joints?

 

[pedal2themetal45]

Rear End rod for the spider gears .. I tell ya mine sounded the same way and sence the U's are tight.. (you checked them the right way) I still say its the rear end :x just as my truck would start to roll there would be a CLUNK.... that would jurk the truck...
Tim

 

[Titleist16]

Well I'm gonna start with replacing the u-joints since they are cheap and they look pretty old. My question is, my Comet has a C4 in it not the original 2 speed trans. Will the u-joints be the same or do I have to get a front u-joint from a car with a 200 and C4 like a mustang?

 

[Titleist16]

Well today was open shop day after work so I pulled my car in to take a look at the u-joints and trans. I had my trainer help me check everything out, the u-joints are good. He noticed that the tailshaft of the trans was sitting on this homemade plate/mount that the previous owner must have made. So I jacked up the trans a little bit and that mount was loose so I tightened it up and it lifted the tailshaft up off of it so it doesn't rub on it now. Because it was sitting on that metal plate it wore a groove in the tailshaft, not through it though. I put some felt on the bottom of the tailshaft for now just incase if the plate loosens again. It really improved the ride quality and it hasn't made that clunking noise yet so I hope this fixed it. What kind of mount is supposed to be at the rear of the trans? Does anybody have a picture of the rear mount?