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2005 CTS-V SC
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Discussion Starter #1
I’ve been chasing the clunk since I’ve owned this car. It appears now its time to do the motor mounts since I’ve done all the bushings in the rear and the clunk as slowly returned.

Has anyone installed motor mounts themselves? I have an engine hoist floating around between friends somewhere. I was wondering what had to be disconnected and how high the engine had to be to pull the mounts. Anyone’s experience, insights or tricks would be greatly appreciated.
 

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No need for an engine hoist. The engine can be lifted high enough from the oil pan. Just be sure to put a board on the jack to spread the weight evenly.

Search for lollygagger's post on his motor mount install.
 

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2005 CTS V (long gone), 2016 CT6
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Changing the mounts can't hurt but if they're not leaking I wouldn't bother. You'll never completely eliminate the clunk due to the 50lb dual mass flywheel, rubber drive shaft coupling and the somewhat excessive amount of lash between the ring and pinion gears in the diff. At low speeds if you load that system then release it by depressing the clutch you're going to get a clunk...motor mounts won't do anything for it.
 

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Discussion Starter #4
I’ll search for lollygagger's post. I searched for quite awhile but couldn’t find anything. (maybe I should start using Google and the domain name)

As others have mentioned. The clunk seems to go away for awhile then slowly reappear. I’ll put it up on stands this weekend and take a good look at the mounts to see if they are leaking. I’ve always had a little clunk with the clutch. I tend to control that by riding it a little during release. This new clunk is noticeable getting on and off the gas at freeway speeds.

I’ve got Autocrosses for the next two weekends (two practice days and one event), and then a day drag racing at Fontana. I wonder how it will feel after that?

I have this uncomfortable feeling I’m heading towards a rear end explosion.

Moth to the flame.
 

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2005 CTS-V
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Changing the mounts can't hurt but if they're not leaking I wouldn't bother. You'll never completely eliminate the clunk due to the 50lb dual mass flywheel, rubber drive shaft coupling and the somewhat excessive amount of lash between the ring and pinion gears in the diff. At low speeds if you load that system then release it by depressing the clutch you're going to get a clunk...motor mounts won't do anything for it.
I agree that the clunk is contributed to by the drive shaft design but the ring and pinion backlash specification is only 0.008 to 0.013 inch. Why is that excessive?
 

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Platinum 2004 CTS-V
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No need for an engine hoist. The engine can be lifted high enough from the oil pan. Just be sure to put a board on the jack to spread the weight evenly.

Search for lollygagger's post on his motor mount install.
:yeah:
Thanks Cadiblk

Put a nice inch or two thick piece of wood as wide and as long as the bottom of the oilpan, and jack the engine up high enough to be able to pull the old mounts out/put the new mounts in. The pan is strong enough, don't worry. I felt the same way you do. I've done this to two Jeeps as well w/o probs....the wood will displace the weight. Don't just jack it up without the wood or you'll punch thru the pan.

It's a bitch to get to all the bolts, I won't lie. Loooonnnng extensions or it ain't happening. There's like 4 bolts holding the mount to the block on the drivers side (3 on pass side) and two or three bolts to the frame on each side if memory serves.

Remove the strut tower brace, and the headers/manifolds too. header bolts are 13mm. I think the strut tower brace bolts are 18mm.....Can't remember the MM bolts sorry!

I think that's all of it. If you have questions, poast and we'll get you fixed up.
 

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Discussion Starter #10
:yeah:
Thanks Cadiblk

Put a nice inch or two thick piece of wood as wide and as long as the bottom of the oilpan, and jack the engine up high enough to be able to pull the old mounts out/put the new mounts in. The pan is strong enough, don't worry. I felt the same way you do. I've done this to two Jeeps as well w/o probs....the wood will displace the weight. Don't just jack it up without the wood or you'll punch thru the pan.

It's a bitch to get to all the bolts, I won't lie. Loooonnnng extensions or it ain't happening. There's like 4 bolts holding the mount to the block on the drivers side (3 on pass side) and two or three bolts to the frame on each side if memory serves.

Remove the strut tower brace, and the headers/manifolds too. header bolts are 13mm. I think the strut tower brace bolts are 18mm.....Can't remember the MM bolts sorry!

I think that's all of it. If you have questions, poast and we'll get you fixed up.
I'll get the car up on jacks this weekend and take a look. I have 9 air drops in my garage and every swivel joint and extension I could find. (I don’t know how I survived with air tools before)

I'm thinking about doing headers while I'm down there. I live in CA, but the car isn't due for smog until 2011. After that it becomes a bit of a hassle to have headers in the car.

Thanks again.
 

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I agree that the clunk is contributed to by the drive shaft design but the ring and pinion backlash specification is only 0.008 to 0.013 inch. Why is that excessive?
Watch NormV's video of the input shaft of a diff on a bench where he rotates the shaft one direction then the other by hand and you'll see what I mean...if he still has it in his Photobucket.
 

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Discussion Starter #14

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I'll get the car up on jacks this weekend and take a look. I have 9 air drops in my garage and every swivel joint and extension I could find. (I don’t know how I survived with air tools before)

I'm thinking about doing headers while I'm down there. I live in CA, but the car isn't due for smog until 2011. After that it becomes a bit of a hassle to have headers in the car.

Thanks again.
Ya, I did my headers at the same time......that's the best way to do it. You'll be good with the airdrops!

Holy sloppy backlash batman! :hide:
 

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Discussion Starter #16
Just crawled from under the car. The mounts looked good so the clunking was do to the diff bushing bolt coming loose. This time I used Loctite and my torque wrench. Thought I would bleed my clutch while I had the car up, but I couldn’t get a wrench on the bleeder. I think its 8mm. The clutch feels fine, so I’ll cycle some fluid through if I do headers down the line.
 

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2005 CTS-V
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Watch NormV's video of the input shaft of a diff on a bench where he rotates the shaft one direction then the other by hand and you'll see what I mean...if he still has it in his Photobucket.
I have seen that video before in an earlier thread and the amount of shaft rotation in that video does not indicate the effect of ring and pinion clearance (backlash).
 

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2005 CTS-V
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What would be the culprit for all that play then? :hmm:
The only thing the video shows is how much you must turn the pinion flange before you "hear" a click. You will notice that when the flange turned smoothly for most of a turn you hear no sound. The internal gears are clearly turning.

Backlash, in general, is measured by holding one gear still and turning the other gear to determine how much play there is before the turning gear engages the gear being held. In the video the pinion flange is being turned but the ring gear is not being held.

The Service Manual calls for the play, measured at the pinion flange with a dial indicator, be between 0.008 inch and 0.013 inch. In the video the audible click does not occur until about an inch or so. Clearly: (a) the sound is not from initial ring-to-pinion gear engagement; or (b) that differential is out of spec to the point of being broken.

I think the click is the sound of the some other internal part such as the clutch packs in the absence of fluid.
 
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