transmission qeustion

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Aug 7, 2001 | 05:56 PM

naggy

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Joined: Jul 2001

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transmission qeustion

Got a 68 f100 that when at a complete stop, the transmission will make a thump like noise when about to move foward. Happens everytime. I've notice also that when at an incline, this clunk like noise will not occur. I've checked my u-joint and all is good. Any ideas? The trans was rebuilt 20,000 miles ago.

Aug 7, 2001 | 06:10 PM

Post Fiend

Joined: Feb 2000

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From: Brea CA

transmission qeustion

Sounds like something loading and unloading. Try checking out the motor mounts, tranny mount, torque converter to flexplate nuts, u-joints (you have two, don’t you) and the pinion yoke on the pumpkin.

Aug 7, 2001 | 06:36 PM

Like M. Fords

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From: LAT 46.55501° & LON -122

transmission qeustion

Sometimes the 9" Ford differentials that have the factory limited slip installed will do this when they start to get worn. It may also be the brakes; one shoe might be remaining partially engaged to the drum until you start moving and you hear the clunk when it releases. Does it do it after you coast to a stop without using your brakes? With the engine off and in low gear (manual) or park (auto) rock the truck back and fourth within the normal slop in the trivetrain and look for any loose u-bolts or any movement between springs and axle mounting pads that may also cause klunking on takeoff.

What transmission do you have? Is the truck a 4 wheel drive?

Aug 7, 2001 | 08:19 PM

Steve_Uzi

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From: USA

transmission qeustion

I have the same problem.. I am not sure what it is.. but it doesn't happen alot... I have brand new rear brakes (new drums, etc) still does it every once in a while.. I have 1970 F-100 w/C-6 auto

Uzi... Yamaha Sleds, Honda Bikes, and Ford Trucks....

Aug 7, 2001 | 09:06 PM

tetraruby

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transmission qeustion

What in the 9's wears to yield the clunking sound? Is this the pinion and ring gear not engaging and the gear is slipping? Or is there something else within the rear axle that contibutes to this effect?

Aug 7, 2001 | 11:10 PM

bigf150

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Joined: Jan 2001

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From: Meriden USA

transmission qeustion

somtimes it could be a transmisson shifting servo thing not getting enough vaccum
Anthony DiPietro
79 F150 Ranger

Aug 8, 2001 | 07:55 PM

Like M. Fords

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From: LAT 46.55501° & LON -122

transmission qeustion

Quote:

What in the 9's wears to yield the clunking sound?

It was the 9" that came factory equiped with limited slip in my '76 Bronco. Most rotational slop that you feel in the yolk/pinion shaft of an axle assembly is actually generated from the differential itself (worn spider gears, pins, axle splines, etc). Only a small fraction is actually generated between a properly setup ring & pinion. In my case, the clutches in the limited slip unit held just enough to contain most of this backlash from deceleration at a stop. As I started to accelerate forward again, the clutches would slip under torque, and a clunk was both heard and felt as the backlash was rest to the forward position.

A regular open differential would probably not have this problem since there are no clutches to contain some of the backlash; any backlash would easily be reset to the forward load position while stopped by the slight driveline torque generated from a disengaged clutch and/or pilot bushing.