Hi Everyone,

Today I am test driving a '98 SLS. I am in love with it. it has 74,000 on the odo. Everything about this car is great, but i have one question.

While i am driving if i let my foot off the gas for a bit to coast and then apply the gas again, i feel a sort of "thump" as the rpms go up. the thump lasts for barely a second. is this normal? i dont ever feel it when the car is accelerating after i feel it for the first time.

The transmission fluid was just changed i believe, since the DIC says 100% of life left.

i flipped through the manual this morning but the previous owner did not record any maintenance to the vehicle.

I am going to ask the dealer to do a compression test tomorrow if possible before we discuss payment options.

thanks a million for any advice! :yup:

.... The transmission fluid was just changed i believe, since the DIC says 100% of life left.
Does not necessarily mean the fluid was changed. Anyone could reset the message to 100% at anytime.

My '98 still indicated 100% life remaining at 125,000 miles and I can guarantee the DIC had not been "accidently" reset.

JimD, this is true, they could reset it, but i hope they wouldn't have! The sales rep, told me it had just come out of getting its service check up. That is amazing that at 125,000 miles yours still stated 100%. that must be a good thing, right? ;)

It also comes with (though it doesn't mean squat) a 30 day / 1,000 mile warranty, whichever comes first.

My 2000 STS has that slight bump when you reapply the throttle. As long as it isn't too long or harsh, I wouldn't worry about it. Check the codes and see if there are any set for the trans, engine, suspension system, etc.

thanks for your reply. the bump is very, very short.

i just did a carfax report on the vehicle, i have never used carfax before, it is great! I now know a lot more about the car.

Has had 2 owners, 1st was Corporate Lease Vehicle, 2nd i am guessing was a 'normal' person. Everything checks out on the carfax report.

lists "vehicle serviced" every 3-4,000 miles so i am *hoping* those were oil changes! Shows the A/C was serviced once, at about 53,000.

I am thinking about asking the dealer to perform a compression test tomorrow... my old '89 lost compression in one of the cylinders at 230,000 miles, but, the transmission went out on my parent's jeep grand cherokee at around 100,000 miles.

This car however seems strong! :)

I wouldn't bother with a compression test. With those low miles, the engine I'm sure is fine. As long as it's not smoking or running rough, you'd be wasting your money with a compression test.

i may take your advice. my urge to have this car *now* is rushing through me.

quick question, how do i access the service engine codes? it was OFF + WARM on my '89 deville. not sure how it is on this seville! i didnt find anything in my manual.

never mind to that, i found it, searching a few more times. i knew it had to be here. http://www.cadillacforums.com/forums/showthread.php?t=27840

i'll check that out in a little bit. gotta do some work first.

Hold the Info up and on/off buttons.

That thunp is just the engagement of teeth from all the different gears in the tranny. Whe you let off the gas and coast, there will be a little bit of slack in the drivetrain. When you reapply the gas, it spins up all the gears, and that's what the thump "usually" is. I have it in my 1998 STS, and it runs like a champ. It's similar to the noise you get from the axle of a rwd car, when you reapply the gas after coasting. You will tend to notice it alot more when going uphill, than going level or downhill.

thanks for all your responses! I am done with my test drive tonight at 5pm, at which time i will be meeting with the dealer to discuss possible payments and a few things i'd like them to do on it if i purchase from them! :)

The slight drivetrain bump you are noticing is normal. Lots of the FWD cars have that. It is partially lash in the driveline and partly the engine moving on the cradle. With transverse engines and transaxles the engine moves a bit like that ...it actually rocks back and forth...which is perfectly normal.

The trans fluid can easily last 100K miles with no problems. Basically the trans is filled for life so it never really needs replacing but at 100K it is a good idea to drop the bottom pan, drain the side cover with the hidden drain plug, clean the pickup screens and fill with fresh fluid. Don't be scammed into a transmission "flush".... The trans oil life will stay at 100% unless the trans is overheated or the trans oil has been running at high temps due to towing or other heavy loads. The fact that it is at 100% is a good sign.

The engine in that car likes to be exercised. Give it an occasional WOT blast when merging or on the expressway to keep the carbon cleane out and the rings exercised. It likes it.

Speaking of cradles, mounts ans such. Bbob, I remember you telling me that the newer engine and tranny mounts were designed not to soak up as much power, in order to transfer more to the wheels. If this is the case, what do you think of RSM's aluminum engine and tranny mounts that use Polyurethane bushings. Do you think that these would be to harsh on the drivetrain, or would they work better than the '98-'99 ones. They claim "15 more lb ft of torque at the wheels", but as we all know,this will not be the case. I do think that a firmer mount would make a differece when transferring power to the wheels more efficiently. Any thoughts on this would be great. Thank's Bbob. :D

Speaking of cradles, mounts ans such. Bbob, I remember you telling me that the newer engine and tranny mounts were designed not to soak up as much power, in order to transfer more to the wheels. If this is the case, what do you think of RSM's aluminum engine and tranny mounts that use Polyurethane bushings. Do you think that these would be to harsh on the drivetrain, or would they work better than the '98-'99 ones. They claim "15 more lb ft of torque at the wheels", but as we all know,this will not be the case. I do think that a firmer mount would make a differece when transferring power to the wheels more efficiently. Any thoughts on this would be great. Thank's Bbob. :D



The change in mounts from the dog bone style torque struts to the lower mounting package in the 98 and later sevilles was mentioned....but that has nothing to do with "soaking up engine power"...

Engine mounts are not going to give you power...they hold the engine in place and isolate the car from engine vibrations and movement but there is no power there....

Can't understand how a poly bearing or bushing could give more power...hmmm....

Since it takes energy to move the whole engine and transmission, wouldn't more power be quickly transfered to the wheels instead of moving the engine and trans with a more solid mount?? Make sense to me, but I don't know if it would be worth 15 ft-lbs.

:yeah: . That's what I was reffering to. Not adding power, but transferrring the already existing power more efficiently to the wheels. I know a mount isn't going to add power, I just wondered if it would help keep the drivetrain, from absorbing power by moving.

My 98 has the "bump" and it's like nothing I've ever had in any FWD car, including Northstar Cadillacs. It's not the front mount, that's been changed. It feels like excessive lash in the differential. The car also has a delay into reverse after 1/2 hour + use. Now, there's a fast little flutter in the gas pedal after the 2nd to 3rd shift at anywhere from 25 to 40 mph. This is not normal. I've been going back and forth with the dealer on this for quite some time. It took them 30,000 miles and the right tech to admit there's something loose in the front end. They finally changed the left front hub and the steering rack.

I had a bump that seems similar to what you describe. Going from no throttle to medium to heavy throttle, while the car was already rolling, would lead to a noticable bump. Also, the whole engine had sounded just a *bit* rough for a couple of weeks. Subtle, but obvious to me. I took it to the dealer and had a cracked engine mount replaced, and both problems immediately went away. I think this was about a $300 job by the time it was all done though. Luckily I have 1100 miles and three months of warranty left.... gosh I sure hope I can come up with a couple more repairs to get done in the next 12 weeks!

Point is, you might take a look at the engine mounts and see if they're damaged. As I understood it, mine was just cracked a bit and the repair was not critical. Under warranty the repair was a no brainer... whether it's worth paying for I dunno. Mine's a 2001 SLS, by the way.

My car has been to the dealer at least a half a dozen times on the trans problems. The bad mount was changed three visits ago and the "bump" is still there. There's a bulletin on the delay into reverse which says to change the trans and reflash the PCM. The dealer still finds no problem. I'm calling Cadillac Assistance so they can start a case on the car. Let them deal with the dealer.

thanks for all the input from everyone. i really liked this SLS, but the dealer salesman has been not friendly to me, since i told him i was not making any move until i father came to look at the vehicle also. my dad has a 98 Deville. I also wanted my dad's 'blessing' so to speak. He also liked the car, a lot, but when i made an offer to the dealer, expecting him to counter-offer, he refused and basically told me to "go to hell".

I half expected him to call me back today with an offer, and he has not. I will not call him either. I feel insulted, and i feel that half of the fact is my young age. I am only 23. I was approved for financing, on the sticker price, without any money down or a co-signer, but I refuse to pay sticker price on a used vehicle.

and with the comments on the motor mounts possibly being cracked. I will wait and look elsewhere or hold off until the end of the summer, and perhaps get a new model year.

Well, there's plenty of used Cadillacs out there! If this dealer doesn't want to work with you, it's his loss! I've had pretty good luck with dealers being friendly and willing to talk, I'm 23 as well and have a 2000 STS. It could just be you were working with an @ss of a salesman.

:yeah: . That's what I was reffering to. Not adding power, but transferrring the already existing power more efficiently to the wheels. I know a mount isn't going to add power, I just wondered if it would help keep the drivetrain, from absorbing power by moving.

Mounts can't transfer power more efficiently or less efficiently. They are actually springs by physics law. They give back all energy "absorbed". Because of that, no energy wasted. Otherwise, if some energy was wasted in mounts they will be hot as hell. In reality only energy spent is the energy of internal friction, which is minimal.

Wouldn't mounts that are more solid not allow the engine to rock as much when under heavy load. It's this action that I'm reffering to. When you accelerate hard, the engine will move on the mounts, before it applies force to the wheels. This is because the torque of the engine is allowing it to spin a little till it uses up the slack in the power train, at which point it engages the transmission. This slack is partialy absorbed by the engine mounts. Harder mounts would help prevent the engine from rocking under heavy load, thus helping to transfer the power more efficiently. I'm not sure how well it would work with a northstar, but it definitely helped the 289 in my Mustang. With the orinigal mounts, the enigne would tend to jump when I stepped on the gas. After I bought heavy duty mounts for the engine, it doesn't move as much, and now engages the drivetrain faster, increasing my acceleration.

If anything, solid mounts could improve reaction times!

Let's just remove mounts at all! It will increase acceleration!

It will not increase acceleration (may be just for time spent to move engine around split of a second), it will only FEEL harder and make more stress on parts.
Mounts installed for purpose, not like a fancy thing. I beleive GM spent a lot of time disign mounts to make ride comfortable, with no vibration.

Drag racers do that! They use solid mounts to keep the drivetrain stable. It decreases the reaction time.

Well, there's plenty of used Cadillacs out there! If this dealer doesn't want to work with you, it's his loss! I've had pretty good luck with dealers being friendly and willing to talk, I'm 23 as well and have a 2000 STS. It could just be you were working with an @ss of a salesman.

well i was shocked. the dealer called me back and said they'd sell me the car for the price i gave them.

they are doing the compression tests today, and if that passes, they will do a few other minor things, and i should be signing off today or tomorrow!

I am just waiting for a dealer in my old home town to get back to me with what the results *should* be. :D