Engine Shuddering

[SlowNsteady]

1 hour ago, datzenmike said:

 

The S12 from '84-'88. The '87 model introduced the VG30E engine replacing the CA18ET and continued through '88. This was the same engine used in the earlier 300zx non turbo through '87. The '87 and '88 also had the CA20E NAPS engine. What'd you get???

I haven’t gotten it yet but there’s one available within an hours drive from me for hopefully around 500$. Gonna go take a look this weekend but I wanted to do some researh on what to look out for on these guys. I’m already seeing very little aftermarket, community and spare parts around Atlanta. I think the 200sx got overshadowed by the s13 240sx but I’m not looking to turn it into a drift missile. The body looks good no dents and I can’t see any rust on the pictures. Interior not horrible but I gotta take an actual look in person 

[SlowNsteady]

Question. This part of the driveshaft seems to be causing some vibration when I put the car into first gear from a stop. It doesn’t make any other noise at any other speed but when I get going I feel the vibration. Any way I can fix this? Also worth noting I just lowered my truck using 3inch blocks and it started happening after I did that 

[datzenmike]

 

If it vibrates under load or when starting to move from a stop the rubber surround has likely rotted away. Normally it supports union where the front and rear drive shafts meet. There is a bearing that allows the outer part to remain stationary while the inner part spins. The bearing never goes bad but the rubber can. Without support the drive shaft can flop around in that yoke. I fixed mine by cutting a long strip of conveyor belt rubber and wrapped it around the drive shaft like a jelly roll and clamped it down. I was going to replace it but it worked so well I left it.

 

That said if the vibration or hum started after lowering and it's constant, that's a different thing. The angle formed between the front and rear drive shaft must equal the angle between the rear drive shaft and the differential. On a drive shaft, the angle in must equal the angle out for smooth running. By lowering the body (and the front of the driveshaft) you have inadvertently altered those angles.

 

 

 

 

I had a loud low frequency HUMMM at lower speeds after lowering. The pinion angle did not agree with my transmission/driveshaft angle. I loosened the leaf spring U bolts and slipped a 1/8" shim on the back side and got it right on the first try. Hum gone.

 

[SlowNsteady]

12 hours ago, datzenmike said:

 

If it vibrates under load or when starting to move from a stop the rubber surround has likely rotted away. Normally it supports union where the front and rear drive shafts meet. There is a bearing that allows the outer part to remain stationary while the inner part spins. The bearing never goes bad but the rubber can. Without support the drive shaft can flop around in that yoke. I fixed mine by cutting a long strip of conveyor belt rubber and wrapped it around the drive shaft like a jelly roll and clamped it down. I was going to replace it but it worked so well I left it.

 

That said if the vibration or hum started after lowering and it's constant, that's a different thing. The angle formed between the front and rear drive shaft must equal the angle between the rear drive shaft and the differential. On a drive shaft, the angle in must equal the angle out for smooth running. By lowering the body (and the front of the driveshaft) you have inadvertently altered those angles.

 

 

 

 

I had a loud low frequency HUMMM at lower speeds after lowering. The pinion angle did not agree with my transmission/driveshaft angle. I loosened the leaf spring U bolts and slipped a 1/8" shim on the back side and got it right on the first try. Hum gone.

 

Yeah the rubber is for sure rotted away. How did you clamp down your conveyor belt jelly roll? I might just have to replace it since I. Don’t have access to any rubber components that would be a suitable substitute. 

 

 Lucky for me it only vibrates on start up and not at any other speed. I bought the lowering blocks with the 2degree taper which is what I imagine you achieved with the shim. 

[datzenmike]

 

I made it slightly larger around than the two piece top and bottom support shown above. Once tightened down nothing moved. I may has used a few turn of stove pipe wire to hold it together while tightening it down.

 

 

 

 

[SlowNsteady]

Hey y’all another question. The truck I have was rear ended before it got to me. Happened a long time ago by the looks of it. The bracket/frame rail has been pretty badly bent. Any ideas on how I can fix this? I don’t want to take it to a shop but if I need to I guess I will 

[Stoffregen Motorsports]

Can't really see what's going on in the pic. Is the piece removable? Or is it the actual frame?

 

Frame rails are heat treated and will not go back into shape without some major muscle, but the problem is, when you apply that muscle, you can knock the frame out of whack in other places. The best way to remedy a damaged frame rail is by cutting and welding. You can either cut in spots to be able to bend the metal back into shape and then weld it back together or cut the piece off and weld on a replacement, either fabricated or scabbed from another frame.

[SlowNsteady]

Yeah that’s a bad picture…..  my bad. This one’s a little better but still a little hard to see 

[SlowNsteady]

I think I’m going to have to cut and weld 😕 this might be just a little too bent beyond repair 

[NC85ST]

It is a little hard to see, but it looks like you might be able to use a jack on the end where it is bent and use a sledge hammer on the bend. A torch would be very useful in straightening it out.

[SlowNsteady]

5 hours ago, NC85ST said:

It is a little hard to see, but it looks like you might be able to use a jack on the end where it is bent and use a sledge hammer on the bend. A torch would be very useful in straightening it out.

That’s exactly what I was thinking to try and straighten it out. I’m just worried it won’t do the trick. I have to take the bed off again to sand and prime everything for painting so I will try to fix it like that. I tried to do it last time I took the bed off but my torch was malfunctioning. 

[SlowNsteady]

Also here is a better picture.  Just took it as I was throwing out the trash. 

[datzenmike]

If it's not holding or supporting anything just leave it.

[SlowNsteady]

16 minutes ago, datzenmike said:

If it's not holding or supporting anything just leave it.

I don’t have a bumper 😕 I need to straighten it out to get a bumper on my truck. That’s why I’m looking to fix it 

[NC85ST]

If you have an acetylene torch and heat it red hot, you should be able to straighten it back out. 

[datzenmike]

9 hours ago, SlowNsteady said:

I don’t have a bumper 😕 I need to straighten it out to get a bumper on my truck. That’s why I’m looking to fix it 

  

Ah... of course. Take the bed off. Gas tank is mounted to the frame but filler pipe to the box. There is a small round 6 pin connector at right rear of box on or near, the frame that disconnects the rear lighting and the box is free to lift away. With the box off you can safely and easily get some major tools in there to work on it.

 

Do you have a bumper so you know when to stop bending/adjusting? 

[SlowNsteady]

I do have a bumper. I took the bed off last week to do some sanding behind the cab and replace a fuel line that was busted so luckily I can take the bed off without too much of a problem. I don’t have access to an acetylene torch just those small propane torches. Would that be too small? 

[NC85ST]

A propane torch won’t get it hot enough. It needs to be cherry red to bend that back in shape. It would probably be easiest to use a piece of 1/4” plate and weld it or if no welder, bolt it to the frame to support your bumper.

[datzenmike]

Once hot a really large crescent or pipe wrench is good for bending the softened metal. Sledge hammer too.

[SlowNsteady]

Hey yall. So I’m looking at options for my bumper situation, I haven’t been able to try and fix the bracket cuz of work and there’s less sun light after I get home. Long story short I was looking at roll pans. I don’t plan on having my truck tow anything and I don’t have any practical use for the bumper. Does anyone have a reputable source for a roll pan or any advice for it?