C4 Trouble -vibration and downshift - Hot Rod Forum : Hotrodders Bulletin Board
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Old 11-24-2002, 07:30 PM
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Question C4 Trouble -vibration and downshift

Just picked up a 68 Mustang w/a healthy 302 and C4 trans. Both are freshly built, but when I'm in 2nd gear I hear a low pitched vibration when I hit the accelerator pedal -even slightly. It doesn't make the sound in first gear, only 2nd and 3rd, and it stops when I let up on the pedal and let the car coast (though still in gear). Any thoughts? I would almost think the trans is a red herring, but the sound doesn't seem to be coming from the engine bay, so I figured it might be the trans. Also, the car is currently running without a kickdown lever, and after it is good and warmed up it has trouble getting back into 1st. I plan on getting the lever in, but I thought it was worth mentioning in connection with my vibration. Thank you much!

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Old 11-24-2002, 07:37 PM
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U-joint? Classic sign.
“She may not look like much, but she's got it where it counts, kid. I've made a lot of special modifications myself.”

— Han Solo
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Old 11-24-2002, 10:14 PM
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Transmission noisy checklist:
1. Check fluid level, color and condition
2. Check the manual linkage for proper adjustment
3. check the driveplate-to-torque converter bolts for loosness
4. check for cooler lines grounding on frame.

If not any of those you might need to look deeper into the trany.
1. check the oil pump for internal leakage or damaged gears.
2. check the valve body for dirty or sticking valves.
3. check for damaged bushings, planetary gear set or one-way clutch.
4. check for damaged speedometer gear.

The missing lever should have no causation to the noise problem but will cause some problem when wanting to pass someone.
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Old 11-25-2002, 09:56 PM
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Thank you much for your replies -helped guide some of my probing around.

Found out that there is play between the front driveshaft yoke and the outer oil seal (about 1/32" to 1/64") -just enough to leak and move up down/side to side. That probably means the bushing behind the seal is bad, no? Thing is, the seal looks brand new, no pitting, cracks, or other wear signs. I know that the C4 takes two kinds of oil seals for the trans output shaft (pre 67 'dual range' and 67 up), so maybe the wrong one was used on my tranny? I don't however know which one is smaller. And at any rate, if I read the exploded view correctly, the external oil seal and output shaft seal are not the same.

Any voodoo Ford-tranny-seal knowledge would be appreciated. And thank you much for your help so far.
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Old 11-26-2002, 12:02 AM
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You won't know until you pull the driveshaft and inspect the yoke where it rides in the bushing.

Either or both the yoke/bushing may be worn. If it is a recent seal, it may have been an attempt to hide the problem.

Check the front u-joint at this time. It may require disassembly to find one frozen, i.e. it may not seen loose when shaken but be binding at the crosses due to lack of lubrication.

There is a service tool to remove and replace the bushing in the car.

[ November 26, 2002: Message edited by: KULTULZ ]</p>
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Old 11-26-2002, 03:23 PM
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you may have more than one problem here!!! the low pitched vibration , may be caused by a bad u joint, also check for missing weights, dents and check for straightnes of the drive shaft. the whine noise during aceleration may be in the rear end ( rear end noise on aceleration and coast, is gear noise, and if it is there all the time it is a bearing noise.) it could be caused by worn gears, or to much back lash. also the noise could be from the trans ,( bad planetary gears.)
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Old 12-26-2002, 05:57 PM
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dklong WINS!

You nailed it buddy -rear end problem (the only mechanical part of the car that didn't look spit-shined new). After checking everything else (u-joints, output shaft bearing/seal, converter bolts, etc.) it turns out that the rear end bearings were spun and the ring and pinion gears had quite a few miles on them. All is replaced and she's vibration free.

Many thanks all for your help.
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