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Mike Sal said:
The problem with the CAD motor theory is that why would it always stop when I slow down and why would it start at random times. If it was partially engaged, it should be grinding all the time.

I guess my next move is to start pulling it apart to see what's inside. I'll pull the cover to get rid of the oil then pull the CAD motor.
Vacuum rises "higher than normal idle reading" when you let off the pedal to slow down.
 

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If it was partially engaged, it should be grinding all the time.
It's not engaged! You have two splined shafts with a sliding collar on one of them that moves. The collar is getting to close to the other shaft(spinning at different speeds)It touches it and you hear the noise. Pull the cad and take a look!
 

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Discussion Starter #23
I'm very well versed in vacuum....I have studebakers with vacuum wipers & know how to slow them down or speed them up with the gas pedal.

While trying diagnose this issue, I've shifted the truck into neutral and let it go to idle to see what impact it would have (yielding max vacuum). No difference.
The noise wouldn't stop until I was down to less that 5mph.

Yes, the front drive shaft doesn't have any feeling of roughness or binding (in 2 wheel mode).

This week I'll be pulling the cover & vacuum motor to see what clues may be hiding there.....
 

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I'm very well versed in vacuum....I have studebakers with vacuum wipers & know how to slow them down or speed them up with the gas pedal.

While trying diagnose this issue, I've shifted the truck into neutral and let it go to idle to see what impact it would have (yielding max vacuum). No difference.
The noise wouldn't stop until I was down to less that 5mph.

Yes, the front drive shaft doesn't have any feeling of roughness or binding (in 2 wheel mode).

This week I'll be pulling the cover & vacuum motor to see what clues may be hiding there.....
Print in blue is vac "at idle" (normally say 18" ish); vac will be--
-- higher when throttle is closed after running at "higher than idle" rpm (say 21" ish), and is similar to releasing pedal at road speeds
--highest when throttle is closed at very high rpm (say 23"+)
 

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Discussion Starter #25
I've finally discovered the issue appears to have been right under my nose every time I pulled the RH axle out all along, but didn't know it.....

I opened the pumpkin & found nothing unusual. I then attempted to remove the vacuum motor & twisted off one upper & one lower screw (insert cuss words here). The shift fork looked good....the shift collar looked good.....The splines on the intermediate shaft look good....BUT....I happened to notice that the tenon which stick out of the end of the shaft looked very dry....not wet with gear lube. Hmmmm, I'm thinking I should look at the end of the RH axle shaft.

Low & behold there appears to be a bushing in the end of the axle shaft & the inside diameter is very dry & spalled (photo attached). I also noticed there was gear lubed on the lower half of the motor cover....this could be where I lost some oil back when I noticed it was low. I do wonder how the bushing is supposed to get lubricated. there's not much room around the outer bearing the intermediate shaft runs in.

So, it's to the parts store tomorrow to try & source a bushing. I'll probably waste more time trying to get those broken screws out than putting the hole thing back together.....
 

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Discussion Starter #26
Argghhhh....the downside of living in the sticks....only 2 parts stores to check (napa & autozone) & neither have a clue about the "axle disconnect inner bushing" that I need. No truck repair shops either.

The internet is full of them & the 5 dollar bushing is now on order....I sure was hoping to put it all back together tonight.....
Mike S
 

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Might wanna change the seal (with no bushing the shaft was "orbiting" pretty wild, and sounds like the umpteen shaft R+R have not likely been kind to the seal).
... Intermediate shaft "bearing"?

... Put some/fill cavity with gear oil before installing cover; consider using synthetic for quicker engage/release, especially if your in a cold clime.

... Hope that spalled bore holds the bushing ok (not too loose).
 

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Discussion Starter #28
The bushing is still present (the bore of the axle is not damaged), but the I.D. surface is rough from the spalling. I do plan to replace the seal although there wasn't any sign of leakage.

I do plan to pack the cavity of the bushing with some good grease upon reassembly.
Mike S
 

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Discussion Starter #29
Just thought I'd close this up by letting you know that changing that crummy 4 dollar bushing cured the problem. It cost as much in shipping as the purchase price. New bearings, tires, brakes, rotors, calipers, u-joints.....all replaced while it was just that stupid little bushing.....(although it needed tires & the brake pads were probably on their last couple thousand miles).

Now, on to the next problem....leaky steering box....
Mike S
 

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Discussion Starter #30
I forgot to mention that there is indeed a default position of the actuator. There is a spring within the vacuum motor that will push the collar to the "2 wheel drive" position if vacuum is lost. There had been some doubt about it in some earlier posts.
Mike S
 
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