mikeg75

Hey all - I've done some searches on this site and around the web looking for some possible sources of the annoying light thud that is heard after the ac is run on my car and when we drive over any bumps, accelerate, or slow down thereafter. Really - any light bump or shift in the engine seems to make this little thud.

I don't want to go replacing or buying parts without having it narrowed down significantly because it is a '95 Maxima and cash flow is tight at the moment.

One thought was that it was related to the belts / pulleys, however, after reading a thread on another forum, I thought it might be the fan bumping or rattling after it has engaged in the process of cooling the engine.

I know that the radiator support bar is rusting so maybe the front is loose and when the fan engages, it flops more than it is supposed to. Does this seem logical and has anyone had a similar issue or might have ideas as to how to diagnose the problem.

My mechanic is a neighbor who owns his own shop but we have a language issue in that he is foreign and he also doesn't seem worried about something until it breaks. He is a great mechanic and has fixed things for free or cheaply in the past and I trust him a lot. I want to get some ideas before I tell him to check this out.

Lastly, the noise only occurs in the summer when we use the ac. It doesn't occur in any other season, so it must be related to the ac, belts, pulleys, or the fans, in my estimation.

Thanks in advance for any help!!

DennisMik

iTrader: (2)

I can't think of anything related to the A/c that would do this if everything is bolted down tight like it should be. I'm thinking you should check your motor mounts. especially the front and the passenger side.

mikeg75

Wouldn't problematic motor mounts make noise at any time, not just after the ac was run?

I guess I can see the connection in that if the fans cause vibration, maybe the engine then starts to wobble because of it.

Is that what you had in mind? Thanks!

DennisMik

iTrader: (2)

I don't think the fans are it at all. They do not mount on nor touch the engine. If a fan motor goes bad it makes a loud, constant low pitch grumbling noise, not a thunk.

I still think the motor mounts are suspect. It could be that as the engine heats up everything under the hood, the rubber material gets softer and allows the engine to move around.

Sicarius_Vis

iTrader: (2)

I had a strange noise when I turned on the a/c a few days ago. It ended up being the splash guard rubbing on the belt, right under the compressor.

The motor mounts might be worth looking into. I just did mine after experiencing clunking noises and a lot of engine movement. I'll be replacing the lower radiator support soon as well, as the crossmember bolts are barely hanging in there due to rust. My fan is fairly loose as well, but I secured it until I can replace the support. Are you sure the noise isn't there when the a/c is on? You might not be able to hear it with all the fan noise. Just a thought...

mikeg75

My wife primarily drives the car and she confirms that the noise occurs when the ac is on as well as after it has run. Maybe the heat does cause the engine mounts to soften and then it starts to shift around more, making the noise. How much should it cost to have them replaced by a mechanic?

Thanks guys, for your insights.

cashoit

the ac hose from the drier to the evap connection makes a "L" path around the firewall side of the engine. That line runs beneath the battery and could be hitting there. Check to see if the line is secure.

Sicarius_Vis

iTrader: (2)

I'm not sure how much a mechanic would charge. If I had to guess, prob at least 200 for labor. I did them myself with the help of a Haynes book and some threads on here. I don't consider myself to be a great mechanic either. If you're a decent mechanic, you can pull it off.

The hardest part, for me, was removing the actual mounts from the crossmember once it was out. The bolts were rusted on there pretty good. Mind you, I don't have any air tools. Just pb blaster and a braker bar.

If you do decide to change the mounts, I suggest going with Energy Suspension PU mounts. I couldn't believe the difference it made...less wheel hop, engine movement, etc. Just a little more vibration, being the downside. There's a guy on here, MaximaJoe I believe, that sells them for 200. It was well worth it, imho.

mikeg75

I will try to take a look to find this hose, tonight. Thanks for your input!

mikeg75

I have a set of wrenches and not much experience using them. Took a couple parts out and cleaned them (TB, for one), and once put in an EGR solenoid but that is the extent of what I've done under the hood, aside from screwing in new hood lifts.

I don't think I could do anything with engine mounts, myself. May give that a try after trying Cashoit's idea.

mikeg75

New idea after trying to find the hose Cashoit referred to...

I think the low pressure AC hose is not properly aligned and tightened to where it is supposed to go through the firewall. It seems like something needs to be screwed down / tightened right there at the firewall. I'll have to take a picture and maybe then you guys can tell me if that could be the source of the annoying thud we hear.

Here is a diagram and I think it is #6 that might be the problem -> http://www.cardomain.com/ride/748507...-maxima/page-7

Maybe it's this part -> http://cgi.ebay.com/ebaymotors/A-C-E...item56446959da

I really don't know much about the way the air conditioning works but from a quick scan of the diagram on that guy's car domain page, these seem to be the parts that are misaligned on my car.

cashoit

the evaporator and expansion valve is inside of the car behind the dash.

THe ac lines both run to the evaporator as shown in the diagram u provided. Both low and high pressure side screw into the evaporator high and low side ports.

If they arent screwed in tightly, 1) Your refrigerant would be leaking, 2) I dont think the knockin or noise from the hose shifting would be loud eonugh or audible in the cabin. 3) Are u sure u cannot recreate the thud u hear with the ac off??

I find it hard to believe that any noise other than a bad compressor bearing or compressor clutch being audible.

In fact, that is prolly the problem. Ur compressor is on its way out. Does the compressor whine?

dundun

iTrader: (1)

I've been tryna figure this out for like 3 months now

mikeg75

After doing an experiment in the driveway where we put the AC on a while, and then I rocked the car, I couldn't get the noise to come on. Then, I put the AC on high, and heard some kind of click, valve opening, or something else engage (maybe a belt). Then I drove the car a little and immediately started hearing the noise. I went around the block and the noise could be heard every shift in the engine weight (e.g. starting off, stopping, turning, etc).

After a little while trying to hear specifically where the noise was coming from, with my wife driving up and down the driveway with the hood open, and me listening and walking alongside it, we noticed that the noise seemed to come from around where the clutch area is. It also became hard for her to put the car in gear. Is there a pump which supplies pressure to the clutch? Why else would it become hard to shift? Maybe I need some fluid. I'm going to do some more searching and see if I can learn a little about how the clutch, transmission and related parts work to see if I can help narrow down the problem.

It's the original clutch in the car (@ 175,000 miles), although once the slave cylinder of the clutch was replaced (@ around 110,000 miles).

mikeg75

I have been reading around more in these forums and after thinking about the way the engine looked with the hood up when my wife was going back and forth in the driveway, I definitely remember it shifting around a bit to the front and back, and that must mean the motor mounts aren't holding it in place as well as they are supposed to.

Suppose the noise is the motor mounts, how can I tell which one it is? I took a look under the hood and can readily see the one on the passenger side and the front one, but I couldn't even see the back or other one (trans mount I think its called).

Would it make sense to replace only the front and back ones, or should all four be replaced? If this work was being done, might it also make sense to do the alternator and clutch, two other items high on my list since both are originals and this is a '95 SE. I'm thinking that the labor in putting in the motor mounts would be high so may as well get it all done at once.

Thanks again for all responses guys.

DennisMik

iTrader: (2)

I don't fully understand what you mean by putting the AC on high. But it doesn't matter. The AC under the hood only works one of two ways. It is on or it is off.

Inside the car, you have different fan speeds and you have temperature control. And again, this is inside the car and has nothing to do with what is happening under the hood.

There is no pump for the clutch itself or the hydraulic cylinders that operate it. The hard shifting could be because the engine is not sitting properly lined up and is causing the shift linkage to bind.

If you can see the engine moving, you have an engine mount problem.

You have to be able to see the engine mount to check it. Depending on how bad it is, sometims you can visually tell by the way the mount is not symetrical as it sits there. Sometimes you have to use a prybar and see if you can move the engine.

Should you replace all of the mounts? Lot of different opinions. If you have either the front or rear mount bad, I say replace them both and leave the sides alone. If you have a bad side mount, replace them both and leave the front and rear alone.

Talk to you mechanic and negotiate to see if he would give you a break on the labor by having everything done at one time. I think you should get a break with engine mounts and clutch job but it's up to your mechanic to give you a break or not. The alternator is the same amount of work by itself or with the other stuff.

Sicarius_Vis

iTrader: (2)

To test your motor mounts, pull the e-brake up firmly. Start the car up and put it in first and slowly let the clutch out to put load on the engine. You can do the same in reverse as well. There should be relatively small movements in the engine. If you see it lifting up, the mounts are most likely worn.

I would also suggest checking your tranny fluid as well if you're having trouble shifting into gear. If you decide to change it, Amsoil GL-4 is a good brand from my experience. There's a plug in the trans that takes a 1/2" ratchet end iirc. You should be able to stick your thumb in there to feel the oil. It shouldn't come pouring out either.

It wouldn't hurt to ask your mechanic for a bit of a price break. A clutch, alternator, and motor mount job will not be cheap, imo. As for the motor mounts, just replace the front and rear if they need it. The sides really don't do a whole lot.

mikeg75

I haven't had a chance to test this yet but I appreciate your advice.

I'm still puzzled at why the noise would only occur after the car has been driven say 20 min. or so (it takes longer to hear the noise if the AC is not run but we found that it does occur after a longer drive, even if we don't put the AC on). Is it typical for worn engine mounts to only make noise after the engine is warm enough to make the rubber softer?

If the only issue is the noise I hear, I may just leave the motor mounts in and save the cash for a real repair like the alternator or clutch.

DennisMik

iTrader: (2)

Your engine mounts are probably just reaching the point where they are weak enough for the thudding noise to be heard under harsher conditions. The rubber is deteriorating and will only get worse. The thunk will turn into a knock and then into a metallic clank as the rubber disappears. If the movement gets bad enough, damage to the exhaust system is likely, broken y-pipe, cracked exhaust headers at worst case.

mikeg75

Can someone recommend an online store where I can get new motor mounts? The site I had bookmarked and priced the parts when I last posted in this thread no longer has them (www.buynissanparts.com) for my car. That store seems to only have 96 and later mounts, which have a solenoid attached. I had the same experience doing a search on ebay so I thought I'd throw the question out here...

Anyone know a good place to get new (after market) 1995 motor mounts? It's a manual transmission.

Br0nz

rockauto.com best prices and if advanced auto has the same part the will price match(have to call) but you will save the shipping costs.

Sicarius_Vis

iTrader: (2)

If you are interested, I have both, front and rear motor mounts with the original bushings. You could replace them with stock bushings, or Energy Suspension PU ones.

I found it easier to just buy used motor mounts and replace the bushings. My Maxima is my daily driver, so when I replaced the mounts, it was a quick swap. Let me know if you're interested.

mikeg75

Hi - thanks for the offer. I decided to search for new parts on ebay and found a set of three new ones made by DEA products for just over $75, shipping included. There is a fourth mount for the manual transmission that I didn't buy but may get later if these three don't do the trick.

Thanks everyone else for your help. Will keep you posted on whether the new motor mounts help get rid of the squeaks and vibrations that seem to be getting worse. Once these are in, I think I'll worry about another clunk that the left front is making, then come back to the rear power locks. Every week something new seems to be going on - must be the car doesn't like the change in the season.

Hopefully the time I'm investing in trying to solve these problems myself will be worth it!

NHMAX603

iTrader: (1)

had a problem this past summer lol i washed my car when i sprayed under the car the force of the hose blew one of the heat shield upward and lodged it against the ac compressor easy fix.

mikeg75

Update - the 3 1/2 year old cheapo motor mounts are failing and the clunk is back, now that the weather is warm and I'm using the AC again. I've ordered just the passenger side one b/c I can see the rubber is shot.

I'll update the thread again once it's installed, in a couple weeks.