I recently bought a used 2004 Nissan Sentra Spec V with 54000 miles (standard transmission). The test drive went great and I noticed no problems and a basic inspection gave me the OK to purcahse the car. However recently I have begun to notice a scraping/metal-on-metal noise when I let the car slow down in gear. Just as it reaches the range of RPMs where a downshift is warranted the noise begins to emanate from underneath the car. It is alleviated when I press the clutch. It happens in all gears though not as noticeable in higher gears such as 5 or 6. I'm bringing it in to a good mechanic but I'm worried this might be the start of a transmission problem.
It is not easy to understand what noise is being emitted and coming from where. From symptom description, I don't think it is a transmission problem, more likely the drive trains.
Manual transmission seldom gives problems when decelerating, and more often symptoms would be present when accelerating or cruising.
Let the mechanic check and see what he has to say.
July, 11, 2011 AT 10:52 PM
The mechanic said that the exhaust system is very rusted and that he recommended a pretty extensive replacement. I am going in to look at the car to see the extent of the rust damage. Unfortunately this car was driven in MA for most of its life so its not shocking that there is rust on it but I wasn't expecting this much rust. He said the catalytic converter needs to be replaced. I asked him what was the max cost and he replied that if he were to get all factory parts it could be around 2000 and maybe more. He said he's looking into finding the best possible price scenario. Does this seem like a lot? How much should a skilled mechanic charge for an exhaust replacement?
July, 11, 2011 AT 10:55 PM
He said the noise was coming from one of the mounts that had rusted off. I would think this would give more of a rattling noise then a scraping noise that I had described. He didn't mention anything about the transmission over the phone but like I said I am going in to see him.
July, 12, 2011 AT 11:56 AM
For normal exhaust change it should take about an hour but for rusted components, it might take much longer than that and might require some cutting of seized pars.
When miounts breaks, they can cause scraping noise if the component it is holding is tilted away from the mount and brushes against other body parts.
July, 12, 2011 AT 3:19 PM
Yea. It definitely sounds like that could be the cause of the sound. And the fact that it happens at the same RPMs in every gear makes me think that at a certain resonance frequency the exhaust vibrates.
He said that he has to get all factory parts to keep the car California emissions certified and that the entire job to replace the resonator, cat, pre-cat, and muffler would be $2080 (parts, labor, tax). However he told me that there is a warranty still on the car for Emissions Defective parts (there was a recall a long while back on the pre-cat and cat components although it had already been replaced) and that it might cover the the pre-cat and catalytic converter which would take $700.00 off in parts. He would rather I do that and save money if possible and get the work done at Nissan.
He seemed pretty genuine but I would thing that you could find a decent muffler and resonator for pretty cheap. I can see how the pre-cat and cat would cost an arm and a leg as they usually have to meet certain specification in California. Does this seem like a reasonable price even if the rusted parts require extra labor?
July, 12, 2011 AT 3:30 PM
I am in no position to comment on the cost due to my location but from your description and some understanding from fellow experts, I would say the price seems reasonable.
I understand that the regullations for California is the strictest in the world and the part about getting genuine parts should be heeded. If you were to save some money now but fail to pass smog test, it is going to cost you more later.