Ok, I know I come up w/ some off the wall crap sometimes but I wanted to get some opinions on this thought that came into my mind today.

My 4Runner has over 220,000 miles on it and runs like a champ except for a few small things that bother me. The main thing that gets on my nerves is the fact that once the motor warms up, at idle, the exhaust will vibrate pretty bad when it is in drive or reverse. It also seems to shift with a thud only when warm and generally feels like slop in the drivetrain when standing on the brakes and then getting back on the gas.

None of these problems are manifest when I first crank her up, which I had just attributed to the fast idle that occurs until the motor is warm. But now I am living near Boston where it is much colder. I noticed that the colder it is, the less slop I feel and the smoother she shifts. I also replaced the rubber hangers for the exhaust and it still rattles enough to feel and hear it in the cabin.

I am wondering if I need to replace my motor mounts... I mean, all they are is big piece of rubber sandwiched by two metal plates bolted together to keep them from seperating too much right?

My theory is that the cold rubber is firmer and thus performs better than the hot rubber. Is that even remotely possible?

And it's most probable that these things are worn out. I have jumped the truck a couple times back in my younger days and I remember hearing a loud slam when I landed (motor coming down on mounts?) And the truck is starting to age being a 97.

Alright, I have talked enough. Anyone think it might be worth my while to drop the front diff and replace the motor mounts soon based on my little story?

 

Oh just to add,

I dropped the rear driveshaft to eliminate the possiblity of warn u-joints or binding slip yoke. Still noticed the symptoms.

The rear gears were removed and taken to the best gear guy around the columbia area who reset the backlash. He said the gears looked pretty darn good.

 

#1: Essentially, yes. Rubber adhered to/between the 2 plates.

#2: No. Not enough that you could possibly tell the difference, IMO.

#3: Worn out? I doubt it. Why? Because...Mine lasted 20 years on my 88. At least 1 of them did did, the other(pass.side) is still in good enough shape, didn't bother replacing it.

#4: Check them first, then replace if needed(jumping the truck may require it ). Lift up on the engine somehow(bottle jack under the tranny worked for me)and see if the rubber is seperated from the plates. The usual suspect being the side that gets pulled more often than squished under torque. The driver's side unless you drive in reverse alot.

 

Checking them sounds like a good idea. Round here, people always say check your mounts but I have never gotten a reply on what to check for until now. Thanks MudHippy, I am going to take a look soon.

So the cold hard rubber theory doesn't fly though. I thought it might be a stretch but it sounded good when I first came up with it. I do swear that it runs smoother when it's really cold out. (Even with the motor at running tempurature)

 

I wouldn't know about '97 4Runners, but on my '86 Runner my transfercase mount was shot(half serperated) and my driver side engine mount was toast(competely seperated). The passenger side mount still looked in great shape...I definately don't drive alot in reverse!!! I replaced all three mounts and it made a differnce.

 

Well, I still have'nt checked my mounts yet but, I cleaned the MAF sensor at lunch today and I think that helped sooo much. I used to run an amsoil filter which I probably over-oiled way too much. I am sticking to paper filters from now on.

The vibs at idle are still there but are a little bit better. The main thing is I feel like I have low end torque again which makes driving so much better in heavy traffic. I think what I thought was slop/slipping in the drivetrain was actually just no low end torque.