Deathbots

Bear with me here - long post but the results could mean that I'm not paying back an auto loan for the next 2 years on a junk car. I really need some help from the experts.

I looked at this 86 gxl today to buy, and overall everything runs great. The engine is supposedly rebuilt, and it sure runs like it. The trans is supposedly rebuilt, too .. BUT

I get in and shift into first, drive away to take it for a test drive. It starts making this noise, though. Imagine rocks hitting a thin metal? But it's not rocks. It's wierder than that, and honestly I don't remember it all that clearly. It also started out pretty roughly, like it had a bad U-joint or something was my first reaction. It doesn't make the noise unless I hit the gas. If the clutch is engaged and the trans is spinning, it doesn't do it. It did this noise after accelerating through second, too until I got up to speed. After that, everything was fine. Even up to 90 mph, where I finally decided to stop accelerating on the small, near one lane country road. I'm telling you, apart from this noise, it runs beautifully. No Horrendous vibration at 90.

I was scared that it was the trans, though. The thing is, it probably really was rebuilt - the clutch is perfect, and the cars in good shape, so the owner seemed like he took good care of it.

The guy said it was his son's car, and he was just selling it for him, he didn't know all that much about the car. This seems to check out, since it had colorado plates and I'm in illinois. But there was a greenskeeper (he was golfing and this car was in a golf course parking lot) who was a mechanic, and I asked him to take a ride and tell me what he thought. So I said, trying to be all worst case scenario - it sounds like the trans. And he goes - it's definately not the trans, sounds like the U-joint.

Now I've never heard of a U-joint making noises before, and I don't know all the specifics of what happens when a U-joint fails. So can any of you tell me whether or not this guy was lying? Can a U-joint make a noise like that when it's failing? Any noise at all? Overall, the car shifted smoothly, and like I said, I got up to 90 with no problems after like 25. It wasn't gear specific because it did it in 2nd and 1st. But I have to know if it was the trans or not to make my purchasing decision. I hope it's not, because it's a nice car and I really want my Rx-7! I can afford an aftermarket driveshaft, not a rebuilt trans

Thanks for reading this far!

Taranis

Sounds like your mechanic friend got it right. But I'll ask you a couple questions anyway.

When you're starting out from a dead stop, do you hear a clank from the rear center of the car?

Another way to check the differential is to climb under the car with the engine off and shake the driveline, and try to turn it. If it turns, even a little, the u-joints are bad.

To answer your question, the u-joints can and sometimes do make a rattling noise when the're getting ready to go bad.

Hope that helps...

One last thing: How's the differential fluid? Is it full?

Josepi

I had the front U-joints on my driveshaft fail me after 183K miles. Not too shabby. On www.mazdatrix.com under the tranny/driveline section there is a troubleshooter which may help. But I had this problem: increasing noise matched with rpm that would make a "whine" and a "clunk" when applying power (pushing the go!!!! pedal ). As soon as you let off the gas, it would seem to go away, but after a few k or 2 miles it just made more and more noise. Swapped it out with a 18.50$ driveshaft from the junkyard, noticed that one of my bearings had exploded. Yippers; result being smooth and QUIET ride. Driveshafts are REALLY easy to take out yourself, I had a lengthy step by step detail on it but it got killed with the board wipe. So if you got a Haynes manual, good. If you don't spend the 20$ and follow it. It should take you longer to jack your car up on jackstands than to remove the driveshaft.

Joe

Deathbots

thank you for all your help folks. I don't know about the diff fluid. I wouldn't even know how to check. the car does have 186,000 miles on it, i don't know if the ds has ever been replaced. I talked to a mechanically inclined friend of mine who owns an rx-7 and he said that he's sure it's the U-joints. So I'm going to buy the car with confidence.

I've heard conflicting reports on how easy it is to get the driveshaft out. I'll give it a go. Some say you have to remove the whole exhaust system, and if that's the case, I'll probably have to have it done. I don't have a garage or many tools. I'll pick up a haynes manual for sure.

I don't remember a clanking noise when starting out, but we'll see. My friend found a post on these forums and someone was describing this noise, and described it exactly as I first did - sounded like pebbles hitting the catalytic converter heat shield. his problem was U-joints.

I love these forums!

jeff88

Pulling the driveshaft is not too hard. I took the exhaust off for mine, so I don't know if it can be done with it on. once the exhaust is off you can go right at the driveshaft, just unbolt it and pull it out and have an oil pan there so catch the gear lube.

HAILERS

Download the factory manual from the web at www.fc3s.org and do yourself a favor.

tman701

It is the U-joints for sure.
I have the same noises, metallic clunking noises coming from my car.
It happens when I first accelerate. it clunks and tehn squeeaks.
It goes away as my speed increases. I thought it was the pilot bearing or throw out bearing making the noise.

I also thought that maybe the front diff. mount was broken.

I jacked up the car this weekend and checked the diff mount and it looks good. I went to check the front ujoint and it has a lot of play in it. I moved it with my hand and it moves sideways, up-down, and wherever I push it.

So just get the drive shaft replaced. And you do have to take the exhaust off to do it.

Tman
90GXL