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Hello all,

This is my first post here and i'm looking forward to getting good information from other caddy owners.

I picked up my 98 sts about 5 months ago, when I shift from park to drive or drive to reverse it takes a second to engage and its often associated with a solid "clunk."

I mentioned the problem to my friendly neighborhood mechanic and he suggests that we first check out the motor mounts.

Has anyone else been through this? What was the eventual outcome?


Thanks in advance,
 

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2005 CTS-V, 1994 Infiniti Q45
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Welcome!!!!!! Thanks for signing up :wave:

My first impression is a bad tranny mount??? Do FWD cars have tranny mounts?? If its something internal, i dont know...... But it sounds like something is hitting the tranny (or the tranny hitting something) when it shifts..... It will actually move around a little......

Dont heed my words, its just a guess.....
 

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53 Eldo, 54 CDV, 74 FWB 96 FWB (sold),1998 STS(sold), 03 ESV
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Make sure your foot is firmly on the brake while shifting. Also be sure your idle speed is not too high.
 

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I have a 98 STS with 83,000 miles. I too experienced this CLUNK going from reverse to Forward, and when accelerating from a stop. Also, test the mount while driving. While driving slowly, take your foot off the accelerator, and then reapply the gas quickly. If it makes a noticeable noise, then inspect your mounts. If it thunks, the mounts are probably bad.

With the hood raised, engine idling, and one person watching the engine from the side of the car, shift to reverse and hold the brake. LIGHTLY push the accelerator and watch the engine torque up from the rear. It should NOT move from the firewall going forward. Generally there is no problem this way.

Then select DRIVE or shift down to "1", and apply the accelerator lightly. If the mounts are bad, the engine will torque up from the side of the engine closest to the radiator, and try to lift straight up. BOUNCE the accelerator pedal a few times, and if the mounts are broken, it will move everytime.

Talking to Cadillac, they said that the most common mount to break is the one closest to the radiator. It is a bear to do, but I did it last night. It took me 2 hours because I did not have a hydraulic lift. Using jackstands, I lifted the 2 front wheels. There are mounts on both sides of the car, but they mainly support the engine and transmission assembly, and do not break often.

You will also have to take off the entire plastic cover underneath to see what you are doing, and to gain access to the mount and mount holder.

You will have to lift the engine using a hydraulic floor jack. There is a spot just for this purpose. The exhaust comes down and there is a removeable black metal support that surrounds the pipe, and ensures the pipe will not get bent in that area. Do not lift the engine on the oil pan unless you have a block of wood or other insulating material to protect from cracking the aluminum.

The motor mount is attached to its' own holder assembly. The holder has 2 bolts on the bottom around the oil pressure switch, and 2 bolts on top, where they bolt into head closest to the front of the car.) You will have to remove the plastic cover over the upper radiator hose, and move the upper radiator hose up slightly to gain access to those 2 bolts.

I am a fairly large guy, and I caught heck trying to get my arms between the frame and the engine up front. Make sure the engine is cool or cold before trying to get these bolts out. I also used my air driven ratchet to get themout. I would HATE to try to swing a 15mm wrench in that area. TOO CLOSE.

The bottom of the mount itself goes through the removeable cradle under the engine. This cradle is held in place by 4 bolts that go up into the chassis. 2 bolts are up front by the radiator support underneath, and the other two are on the back of the support near the front doors on both sides of the car. This makes up the removeable sub frame underneath the car.

You will have to drop this cradle down by removing the 2 front bolts. Put a jack under the cradle and remove the 2 large bolts, and slowly lower the jack. The engine will NOT fall out. Tug the cradle down far enough to pull the mount and mount holder out once all 4 bolts are out. The mount and holder assembly MUST come out from the bottom. It is a tight fit, but I did not want to take out the rear subframe bolts because I had only 1 hydraulic jack, and did not want to fight to get this cradle up and aligned on all 4 points.

Once the mount assembly is out, unbolt the mount from the assembly, and align the new mount in place using the dowel pin in the mount to align in the holder. I used my impact gun on this top nut. This nut is NOT accessible from inside the car. That is why the holder must be removed with the mount. The bottom of the mount will point downward, and the long stud will go back through the subframe cradle once the mount is back into place, and the subframe is retightened.

Reassembly is the reverse of the disassembly. Maybe this is the hardest mount to replace, but I am glad it was done. Use the jack to lift up the subframe, and the bottom stud of the motor mount will go right through. Tighten the 2 side bolts on the subframe, and put the large nut onto the stud of the motor mount once it goes through the subframe. I used my impact gun again to make sure it was tight. Doing everything by hand only makes this job harder and take longer to complete.

OBSERVATIONS:

The rubber mounts are very susceptable to engine oil and grease. Unfortunately, the oil pressure switch leaked hot oil for a long time, and definitely weakened this mount. THAT, plus the repeated torquing of the engine while driving, caused the mount to break at the top, but not completely separate. This extra movement was enough to let the engine lift up unnaturally.

The difference in the driving experience cannot be described. I am sure that "hotdogging" it from a stop, and spinning the front wheels after holding the car against the brakes contributed greatly to the damage of the mount. GUILTY AS CHARGED...and I will now modify my driving habits to take it easy on the mount. I will continue to run it through the gears after I am rolling, but powerbraking for me is now OUT! Not worth the effort required to change the mount.

Let me say that if the dealership charges 2 hours of labor (170 to 250 dollars), rest assured that they earned it. It is worth every penny to have someone else change it. But I am stubborn, and wanted to learn how to do it myself. It is not easy, believe me, but it CAN be done safely with jackstands, and easier with air tools.

Just my $.02

GSEREP1
 

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There is a bulletin that exists for 1998 Sevilles built before mid Feb, 1998 that states if the trans clunks and had a shift delay, replace the trans, they were built incorrectly. Good luck with trying to find a dealer to do it. Even with the bulletin in hand, they'll tell you there's nothing wrong with the trans and it's up to specs.
 

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I had no delay with my transmission...just the clunk going from reverse to forward. Nothing from drive to reverse. I could see the engine moving, so I knew I had a broken motor mount.

Good luck to those of you that have a transmission problem.

GSEREP1
 

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1998 STS
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When the mounts go, do they break internally first? I have a similar problem with my ride. I was parking it on a loading dock at work one day (backing in) and when I took my foot off the brake, the car lurched backward more so than usual. Ever since then, I have a bit of a clunk going from drive to reverse or vice versa.

I had someone shift the car from drive to reverse and back a bunch of times while I looked at the engine and it does seem to move farther than it should. I looked at the mounts when he was doing the shifting and the vast majority of the movement seemed to be happening at the rear trans mount. Looking at it though, it doesn't seem to really offer much in the way of stabilizing the drive train. Should it?


When I had it in for an oil change at the dealer, I looked the front mount over and it appears to be intact and the rubber is not broken in any place that I can see.

I was thinking of replacing the front mount behind the radiator anyway, but would hate to just throw part$ at it until it's fixed.

Any suggestions here?

Thanks,
Dick
 

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Depends on which way the engine is moving. IF the engine is trying to move UP at the side near the radiator while going forward, that mount is bad.

When you shift to reverse, the opposite side of the engine will try to move upwards near the firewall. If it does that, And you get an annoying clunk when applying and removing your foot off the pedal, then the rear mount is bad. This is rare.

That front mount is sneaky. I did not find it until I had thecar jacked up, and the engine lifted up from the floor using a hydraulic floor jack. Once thepressure was on, I climbed underneath, and I could put my finger in the giant crack in the rubber. The mount was broken, but it was not completely separated into two pieces.

I enclose two pictures. The second photo shows the big crack in the top of the rubber. The first picture shows the whole mount from top to bottom,. The top has the short shaft, and bolts to the engine standing straight up. The bottom has a long shaft, and this is the part that goes through the frame on the bottom, and finally secured with a big nut to hold it steady. When the engine rises up during a takeoff, it stretches the mount, but it holds the engine down. Myold mount allowed the engine to freely move about.

I hope this makes it clear.

GSEREP1
 

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1998 STS
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Gsrep,

Thanks for the insight. I need to jack up the engine and verify the condition of the front motor mount. I appreciate your help and your posting of the pics of your failed mount. Going from memory, do you think it would be easier to change the mount by first pulling the radiator? It looks like a real knuckle breaker in there. As I remember, from looking at it about a month ago, it seems that w/o the radiator in place, the whole front mount should be pretty accessable. Another thing I must do is to look at a good, solid rear trans mount to determine the condition of mine.

Thanks again, I really love these boards and the wealth of information that can be gleaned from them. They are a real gift to the DIYers out there.

Best,

Dick
 

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hey guys,

my 98 sts has a tranny problem that seems a little similar to this discussion on motor mounts. i sometimes coast through uncontrolled intersections, and even down the road if i find myself speeding. anyway, when i re-apply the throttle, it feels as if i just let the clutch out too fast. nice little jerk. could this be one of the motor mounts? i am several hundred miles from my car right now, so i can't do the described test.

thanx!

rash
 

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DICK 98STS,
Thinking back, I believe that the radiator was a limiting factor in removing the front mount and bracket it is attached to. That was because it was so hard getting to the top 2 small bolts in the bracket attached to the mount.

However, I DO think that the mount won't come up through the top, even with the radiator out,but I may be wrong. I think lt has to come from the bottom.

I will look it over again, but I am glad I did it the way I did instead of removing the radiator, fans, ect. The radiator and the fans are designed to come out of the car as one assembly...just disconnect the two fan wiring harnesses (one for each fan), and unbolt the radiator. It should lift right out together. Once the radiator is removed, then it has to be refilled, and the pellets willhave to be reinstalled in oneof the big hoses.

Good luck with changing your mount. Let me know if I can be of more assistance.

GSEREP1
 
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