My 1991 F250 has an M5OD manual, and I have noticed a rattling sound that I only hear if I am coasting with the clutch depressed and i'm applying moderate pressure to the brakes. It slows down with the vehicle and seems to be coming from the tranny. It is most noticeable around 35MPH or so, in 3rd or 4th gear, haven't seen if it does it in OD. I am guessing it is the same rattle I have heard about that appears when going over bumps since my brakes put out a good amount of vibration. Could it possibly be anything else?
I normally don't coast like that with the clutch in, but I did it and noticed the noise, and it got me wondering. It doesn't make any noise at all unless the brakes are being applied enough to feel them vibrate, no sound at all just letting it coast. I appreciate any ideas anybody has!

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1991 F250 R/C L/B 4X2
300 I6 5 speed

 

Hmmm, I have a F150 with the 300 I6 & M5 tranny...

I would check the following;

1. Drop the trans fluid & refill (I do mine every 30K using Mercon III)

2. Check trans/engine mounts to see if they are worn, etc.

3. Check U-Joints, might be getting tired

4. Check Differential for fluid level

5. Check tightness of trans bellhousing bolts.

6. Last thought is it might be a throw-out bearing beginning to go.

My best guess

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Member: Never trust a person over 40 who drives a Chevy club
Flatheads ain't so bad!
Certified backyard mechanic I & II

 

Thanks beechkid. I am planning to change the tranny fluid soon anyway, and replace it with Redline D4 ATF. First I have to fix the rubber plugs on the top that are leaking, I have to keep an eye on the fluid level with those things leaking like they do. I'll check that other stuff. Thanks again.

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1991 F250 R/C L/B 4X2
300 I6 5 speed

 

Given the age of your truck, I'm jumping to a big conclusion that the clutch is old and the transmission is original.

Since you're allowing the clutch disc to 'do it's own thing' (by de-clutching), you might be hearing the disc 'chuck' back and forth with respect to the normal gyrations of the input shaft of the transmission.

Over many miles, not only does the spline-area of the disk wear (gain rotational slop), the springs that cushion the clutch from shock wear (compress and take a 'set') -- and even break -- allowing the disc to move a few degrees with respect to the hub/spline that slides over the input shaft of the transmission.

In the above scenario, you'd never hear anything at an idle -- simply because the disc is stopped (D'Oh! It's hooked to the rear axle, not the engine).

I've seen a lot of them at our clutch plant in Auburn.

Question: If you 'blip' the throttle in the gear of your choice -- do you sense a lot of 'slop' in the gear-train?

Lastly -- if you've not changed your tranny fluid in eyons, you may also be seeing the result of everything simply being 'loose' -- since the oil is the consistency of water at operating temperature -- and offers little-to-no cushioning between gears (which are also gaining a bit of 'slop' over the years).

Bottom line: If all seems 'normal' in gear with the clutch out -- and you don't hear springs grinding and flopping around in the clutch/bell-housing -- and it doesn't slip -- just enjoy the long life you've gotten out of your clutch (those tire-smoking starts probably just squashed your springs flat).

Regards,

Jim

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Y2K™ Jim - N8JG@Hotmail.com

Toreador Red, Keyless XLT SC SB 5.4L E4x4 4wDisc/ABS, 3.73LS, Skid, HD 7700# Towing, LT-245's on Chrome, Tube-Steps, Captain's, 6CD, Tonneau, named: "Nick"

 

There does seem to be a little slop in the driveline, but not much. I think the trans oil is due for a change though. Also there is no noise with the clutch engaged and it never slips, so I guess I have nothing really to worry about. Thanks for the help.

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1991 F250 R/C L/B 4X2
300 I6 5 speed

 

This is the board for ****-retentives like us, right?

One thing I've learned from years of working with mechanical things -- very little wrong causes very much noise.

Turn up the radio! ;0