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Discussion Starter #1 (Edited)
1990 F350 with 7.3 IDI non turbo 5 speed trans.

When i bought my truck years ago my speed odom worked then it stopped so i changed the speed sensor and the little plastic gear on it cause it was chewed up a little. It worked for a few months then quit again took it off and the plastic gear was chewed all to hell. Got a gps for speed and havent thought anymore about it. What would cause this?
 

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Hard to say when your truck info isn't in your signature.


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But my first guess would be that the speedo cable is dirty & worn. If you remove the assembly from the truck, and then remove the cable from the sheath, you can wash them both with solvent, let them dry, and reassemble using new PTFE grease. Another option would be to replace the cable, IF you can find a new one that fits.


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Discussion Starter #3
the speed cable would cause the plastic gear on the end of the speed sensor to get chewed up? i had a guy tell me there is a gear in the back of the trans that might be the cause of it. is this true?
 

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the speed cable would cause the plastic gear on the end of the speed sensor to get chewed up? i had a guy tell me there is a gear in the back of the trans that might be the cause of it. is this true?
Could be, but first and easiest step is pull your old cable from the cable housing and inspect it. They will fray and bind up causing the plastic gear to bind too and lose teeth. There's no such thing as buying a cable that fits. Most mechanic shops and parts houses have speedo cable kits with different diameter cable in bulk rolls, a choice of ends so you take in an old cable and they match length, ends, and make you a new one right there.
 

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Discussion Starter #6
another question about my transmission/clutch my stock clutch took a crap on me so i replaced it with a aftermarket one and now i have a god awful sound like gears grinding or something like that. am i the only one that has had this problem and how can i fix it. ive watched a few videos on youtube and they said its the vibrations from the motor.
 

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What these trucks came with is what's called a dual mass flywheel. It's designed in such a way that it dampens firing impulses as the engine is idling. Sounds like you had a "regular" type flywheel installed along with the clutch replacement. When that happens you get what's called gear rollover noise. Some "internet experts" overfill the trans which quiets it a bit but that's an invitation for a leaking front trans seal and you end up with an oil-soaked clutch disc. Others have used a heavier trans gear lube, but the 5 speeds have some close tolerances which is why nothing but ATF is advised by the manufacturer. The dual mass flywheels are real spendy, but when mine needs replacing I'll bite the bullet and buy one. Some guys have set the idle up a bit higher and say that makes the gear rattle less obnoxious.
 

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thank you. when i bought it. it had thick gear oil in it so i changed it back to atf. so i should go back to the dual mass flywheel? can anyone tell me a good one?
 

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That's a complicated question. Many owners on these IDI sites have replaced the dual mass with a standard flywheel and have no problem and tolerate the noise. This is a post from another IDI site from about the only guy over there who is a genuine full time mechanic:
I probably have at least 6 customers with IDI's and the LUK kit installed. I've seen enough issues with the kits over the years where I am still running DMF systems. Here's my latest finding. A little background first.
The truck is a 1990 F450 flatbed car carrier. It's tare is 11k, max legal is 15k but frequently sees 14-17k and infrequently sees 19-21k gross. 7.3 natural, 5.13 ration Dana 80 rear. It got a rebuilt ZF5 two years ago and the clutch disc was replaced then. The ZF5 required replacement of the input shaft and countershaft due to excessive wear on the gear teeth. The teeth was worn to "knife sharp" points. My suspicion of the cause is the SMF changeover.
SMF means single piece flywheel and LUK is the brand. I respect this guy's opinion, plus the dual mass flywheels are expensive so I'm sure Ford wouldn't have included them on the assembly line if their research didn't show they were reasonably necessary.
 
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