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Need to check condition of motor mounts.


Paisano

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I have a 'thump' and shuddering from underneath my truck. It seems like classic bad motor mount symptom. But I don't know yet. It might be something else.
The motor mounts were replaced in 2015. I'm scheduled to get a warranty repair on my transmission in the coming days. The transmission shop
owner is concerned about this 'thump', 'clunk' underneath the truck (92' Ford Ranger, 2.9 V6, A4LD transmission)

Can you answer these questions please? The least I can do is check the motor mounts. Even if it turns out to not be motor mounts. It's just one more thing
I need to learn anyway.

1. Is there a simple test I can for this? If I have a friend look into the engine bay, will he see the engine block
move excessively if I move it into drive?

2. Do I raise ALL 4 wheels of the truck on jack stands, to check the motor mounts?

3. Also is it really ok to raise the engine with a block of wood under the oil pan....like the Chilton manual says? What thickness of wood?
 


RonD

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Motor mounts are easy to diagnose
Open hood
Start engine
Shift into R
Foot on the brake raise RPMs and watch for engine to lift up on one side
Take foot off the gas pedal quickly, listen for a "clunk", broken mount on the side that lifted up, if no clunk then mount is OK

Do same think but in D now, other side will lift up

Same for Manual just use 1st and Reverse and clutch pedal


Depends on the oil pan but yes in most cases
You want to spread out the weight of the engine so 3/4" x 6" plywood square or 2x4 x 6 will work
What you are trying to avoid is small metal jack head denting the pan because of smaller area weight distribution
 
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franklin2

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Even easier, leave the engine off and the trans in 1st gear or park. Lift the hood (make sure it will not fall on you) and grab the front of the truck and start rocking it forward and backward. Get it going good. If something is loose, the engine will heave up to one side or the other.
 

Paisano

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Will these two tests diagnose bad motor mounts without jacking up the engine a little on the wooden block to inspect? Either way, I am eager to do these simple tests.

For the 1st test recommended by Ron, should the engine be warmed up first?
Is Ron saying give it some gas while foot is on the brake?

I'd like to do these tests no later than tonight.
 

RonD

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No jacking up required
Engine can be cold or warm
 

Paisano

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I just did both tests.
With Franklin's test involving rocking forward and backward, there was zero movement of the engine. With Ron's test, the engine would lean slightly to either side when testing in drive and reverse. But no thump, clunk, or noise of any kind. What do you think?
 

Paisano

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Sorry I didn't respond last night. My Internet plan data renewed this morning. I spent an hour under the truck about a week ago. I could not find anything loose or any real visual defects that would cause this. So it has to be something else hidden with transmission/transmission mount, or somewhere else on the driveline .
 

rusty ol ranger

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Check your Universal joints
 

Shran

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My dad's truck clunks really hard when shifting from Park to any other gear. I assumed it was the mounts too but it was just as bad after replacing all of them. Just decided to ignore it... but I had my wife's truck in for a similar issue and they said it was caused by low oil pressure. Basically instead of just shifting into gear it has to build up pressure and when there is finally enough to complete the shift, it slams into gear.

Just what I was told anyway.
 

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Because a rear axle has to be able to go up and down relative to the frame and transmission is fixed to the frame, the drive shaft needs a slip-joint somewhere so its length can change, as the distance between rear axle and transmission end changes on each "bump"

In some vehicles the slip joint is in the end of the transmission, drive shaft slides into the back of the transmission onto a splined shaft so it is free to move in and out as rear axle goes up and down

In others its on the drive shaft, you will see a rubber accordion boot covering the slip-joint

Either if these can, should be, lubed
Ford makes a "blue" lube just for this
Dry slip-joint will cause a "clunk" noise when shifting into gear in an automatic, or when letting out the clutch in a manual
Sometimes even when accelerating or decelerating
Its metal on metal, no lube, so dry

But as said U-joints can make similar noise
And so can worn out ring and pinion gears in rear axle


Yes, an automatic runs on fluid pressure
That pressure comes from the pump at the front of the trans which is driven by the torque converter at engine RPMs
Forward gear requires about 80-100psi pressure to engage
Reverse 130-150psi to engage
This is why Automatics often lose Reverse first if there is a pressure issue, or are slower to engage Reverse
Raising engine RPMs increases pump speed so raises pressure
So if increasing RPMs gets faster engagement then there is a pressure issue
Usually from leaking Valve body gaskets or seals on the valves and/or passages
"Trans Fix" additives work by swelling gaskets and softening seals to help raise lost pressure, not really a "fix" but won't hurt anything
 
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Paisano

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Yep, My slip joint is on the drive shaft with the accordion boot. I have NEVER lubed it. I didn't know I was supposed to. What do I lube on it?
Come to think of it, I peeked under the boot about a week ago and I saw blue-colored splines.
The U-Joints seem fine. I grease those every oil change.
My rear axle assembly is only 1.5 years old. Complete rebuild. I have opened the pumpkin twice already.
 
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Shran

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This is the Ford recommended lube for slip yokes:

Blue is good, that's some sort of coating they put on there. Check the slip yoke for movement in all directions - it shouldn't "sag"... if that makes sense... it should only be able to slip apart and a tiny bit of twisting movement where the splines mesh, should have close to zero movement in any other direction. I have seen some that are really worn that will kinda sag especially at close to full extension and that would for sure cause noise.

Rebuilt rear axle doesn't necessarily mean it's in good shape, I would unbolt your driveshaft from it and see how far you can rotate the pinion. Very little is good, some movement (probably 10-15 degrees at most) is OK but if you have a lot of slop that could also cause noise. So can a carrier with worn holes where the cross pin goes through. If the holes are egged out then the pin will slap the sides of the hole and will make noise.
 

Paisano

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My truck is getting the transmission fixed for the 2nd time under warranty. The transmission place commented on the 'thumping.' They might get some insight into while they're fixing the trans. If not, I'm going to check the possible trouble spots you all mentioned here, starting with the slip yoke. In fact, I might as well replace the slip yoke just from old age
 

Paisano

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Still waiting to check the slip yoke since my truck is being fixed at the transmission place for the 4th time.
 

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