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Discussion Starter #1
When shifting into reverse, a very noticeable "clunk" is encountered. I thought it may be due to worn U joints so I replaced them. Same phenomena is still experienced.

Any suggestions? Is this normal? This is in a '70 Coupe with a 302 and a C4. My Mechanic suggests it is symptomatic with older Mustangs.

Could it be attributed to a worn transmission mount. I suspect that this item needs to be replaced since occassionaly the trans will slip out of Drive and into Neutral.
 

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That particular noise is usually just the slop in the drivetrain, most notably in the third member (differential) being taken up. Often, lowering the idle a bit or tuning for minimal idle drop into gear can mitigate the noise. It's more of a nuiscance than a problem, at least IME...my D-coder has done it for years, especially when the idle is high with the choke on..

You can inspect your mounts and, if one or more is broken or showing substantial cracking, they can be replaced. I'd recommend replacing all mounts, engine and trans, at the same time, unless one or more has been recently replaced. Also, check your rear end u-bolt nuts and shock mounts for tightness.

Hope that helps!
 

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Discussion Starter #3
Thanks for your prompt reply Pat.

Gee, you are up late for a "relatively speaking" newly wed. You must be a nite owl like me.

I will check out the mounts this weekend.
 

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You ring and pinion are suffering from normal wear....as the two wear into eachother there is space left in between them

this is called backlash and can be adjusted to a certain extent.

Do check all your U koints and mounts before taking on this endeavor. I would take this opportunity to switch bushings to urethane ones too.


good luck!!!
 

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I agree with the others, this is just a little slack in the drivetrain. My 66 does the same thing, but I just say its because of all the power so it wants to go. *G*

Dave
 

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Make sure the pinion flange is torqued properly. My truck used to make that clunk. Then the pinion loosened up enough to wedge itself into the ring gear. Locked the rear of my truck at 50 mph. With my new rear I have no clunck.
 

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I have the same problem with my 68 C4 hooked to a 9 inch rear. So far, haven't got it fixed but this is what I have learned, for what it's worth. My U joints have been checked and seem fine?? Had a buddy of mine, retired Ford tech, look at it and he says I have a lot of play in the differential. He arrived at this by jacking the axle up and checking slop with both wheels off the ground at the same time. Also told me that C4's are know for clunking in reverse. Lot of guys in our club confirm this but not to the extent that I have. He advised me to get the differential rebuilt by local expert. List of parts included ring gear, axle gears and a few other items that escape me right now. Before I could do this, noticed that occasionally, it didn't clunk in reverse. Can't be sure, but I don't think the car was idling lower when it happened. Now I am confused. Also the rear end expert, also a Ford tech, told me that years ago, Ford had a semi fix for customers complaining of C4's clunking which involved drilling a hole somewhere in the C4 to moderate pressure when shifting into reverse. To muddy the waters, during the course of all of this found I have 2:75 gears in my 9 inch out of a 79 Ford F100/150 half ton. A friend in the club is selling me a 3:25 center section which I believe is rebuilt?? My game plan right now is to put 3:25 gears in and see if I still have clunk. If I do, then I'm off to the rear end guy to check out the 3:25 set up, do whatever needs to be done, if too much slop, and get him to do the trick with the drill, if he can remember how. Good luck! Mark
 
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