Thump. Thump. Thump. What is IT?

[AxiOn419]

OK, finalized everything with the rb20 swap this weekend and now have some kinks to work out. Right now, my major concern is this thumping noise I am getting when driving. I will give as much info as possible:

Car: 1991 s13 hicas w/ rb20

-Thumping noise is especially noticeable when starting off in 1st gear and accelerating, but the noise persist when in other gears.

-Once at cruising speeds, I do not really notice it, drives pretty smooth.

-When I hit a bump in the road, I think the bump noise can be heard even more, as if something is hitting the underside of the car from hitting a bump in the road.

-Its the same feeling you would get with a loose exhaust system hitting the underside of the car but I have pretty much jumped on the tailpipe and can not get it to reproduce the noise.

-I think the noise is more prominent when accelerating and taking a sharp turn.

-Does NOT make the thumping noise when stopped.

If I had to guess I would say the noise is coming from the rear center or rear passenger side.

Things I have done:-Checked exhaust system, it does have 1 broken hanger that I am going to replace but I do not think this is the issue as the exhaust system is very sturdy. Also, the noise seems way to developed when starting in 1st for it to be a shaky exhaust.-Had someone lay on the road and look under the car as I drove off, did not see anything out of place, yet it was still making the noise.-I do not have my shift boot on at this point so I can see the tail end of the transmission, it looks fairly stable, nothing out of the ordinary.

Could it be?:

-Universal joint?-Carrier bearing?

How do I test this?

As a side note, when working on the engine swap, I had jacked the car up by the differential in order to get under the car. While it was jacked up I heard a slight "pop" sound, it could have been the car "settling" (like an old house you know! ) but can not be for sure. I have slid under the car and looked for anything out of place or anything that could be broken but I just dont see it.

Sorry for the lengthy post, just trying to provide as much info as possible.

Thanks in advance!

[240z4u]

Sounds like you broke one of the subframe bushings or diff bushings.

makes a banging noise.

Jack up the car, dont put stands under the subframe, put them under the pinch welds. Start prying around with a big prybar.

My car was like that when I got it.

[s14 2510's]

what he said. I took my subframe out and pressed in solid motgomery poly bushings. The factory ones are fun to get out but it feels way better now.

[AxiOn419]

How involved is it to change this out? I have my wrecked s13 as a parts car with the entire rear end in perfect condition. I could pull it from that. Is there a difference between the hicas and non-hicas model bushings?

On my way to work today I paid close attention to the noise.. it really just feels like something rattling around on the underside of the car. It is wierd, yet very annoying and noticeable.

Would jacking the car up by the dif put stress on that bushing causing it to break?

Also, if I continue to drive the car if that is indeed the problem, will it cause any significant damage?

[USMCgetsome]

driveshaft carrier bearing if u used your old ka driveshaft. Felt like a damn horrible rumble when it completely went out. jack up the car and rattle the driveshaft. Also check your transmission mount.

[240z4u]

The fact that you heard it "pop" made me wonder if it was the bushings.

It is kinda dangerous, it could upset handling etc.. at a bad time

Otherwise its a huge pain, and thats it.

Evan

[AxiOn419]

I used the driveshaft that I previously used in my old s13 w/ rb20. Its a 180sx driveshaft I believe. It worked just fine before, but maybe after sitting up for so long it dry rotted. I hope that is all the issue is. That would be a pretty easy fix considering I have my old driveshaft I could pull the carrier bearing off of.

This may be a stupid question, is it a bad idea to jack the car up from the diff and actually start it and give it a bit of gas to check how the driveshaft is spinning? Would not having a load on the wheels grenade the diff?

Is there a good way of diagnosing driveshaft issue. I have shook the driveshaft while under the car and it seems pretty normal to me.

[AxiOn419]

Hmm.. Funny you should mention something about handling.

Yesterday was my first full day out driving the car and I drive it quite a bit. On two occasions, the steering was pulling hard to the right. Like the alignment was WAY off and unless I held the wheel, the car would shoot right. It was really strange. I hit a bump in the road and it knocked it straight and drove straight as an arrow witohut my hands on the wheel.. Not sure if that is related in any way, but a concern none the less.

[240z4u]

Search subframe bushings. its very common.

Jack your damn car up and check already.

And holding your car up by the diff with a jack while its in drive is the worst idea ever. It may not rumble anyway.

Evan

[rb25drag]

Jack the car up put it on jackstands by the frame, Start the car put it in 1st gear and see iof you hear or see anything popping. Only solution, Like the other guys said sub frame bushings, Carrier bearing, Possible U-joints.

[AxiOn419]

But wait.. 240z just said that is a terrible idea and then you recommend for me to do it.. Which is it?

I did search and have already collected as much information on it as I could. I would jack the car up if I werent sitting in the office here at work. Thats why I am asking all of these questions, so I can get a good idea for what to look for.

So let me bother you with one last question. For the subframe bushing, where exactly am I looking and what am I looking for?

[240z4u]

You COULD jack the car up and listen but honestly there is a good chance it wont make any noise.

Its okay to support the car by the frame with jackstands, its NOT okay to hold the car up by the diff with a jack like you had suggested.

Your going to need to pry on the subframe and diff to see if there is any excessive movement. IMO ANY movement is bad.

I was just giving you a hard time about doing it. Speculation is useless without more info beyond what we have.

Evan

If you do decide to listen for sounds with the back in the air, do NOT get underneath it. Its VERY dangerous. Also don't do this without chocking front wheels and having someone ready in the drivers seat if something goes sour.

[AxiOn419]

Alright, thank you for clearing that up for me. As soon as I do this I will post back with my findings.

Thanks everyone

[DriftX]

ball joint, tie rod ?

[AxiOn419]

Ehh, after a lot of research and asking around. I think my problem is the fact that i have a non-abs driveshaft in an ABS car. Anyone have a 5-speed ABS driveshaft for sale?