[zegnaguy]

What is the problem and what needs to be replaced?

Rear end sloppy moving left and right. Only happens under Excelleratio. Rear of car immediately feels like it sloshes to the right then to the left as power in the Open diff transfers.

Happening on 93 sc300 NA -6spd. (Miles 245K) Noticable everytime you hit the gas semi hard. Rear of car immediately feels like it sloshes to the left then back right, side to side the rear wheel must still be going straight. Only evens out when you let off the gas. Happens at low speeds and highs even scarier.


History Suspension and Drivetrain work:
-All 18 oem suspension bushings replaced with Diazen poly bushings. Front, back, lower, upper, sways.
-Tein flex Coilover.
-Diff (4.27 auto no LSD) drained 300 miles ago before problem. replaced with oem recommended 80-90diff fluid. no gray liquid or shavings.
-Single solid drive shaft from 6spd to custom diff adapter.
-Alignment done 300miles ago

When first installed 6spd this problem didn't occur it progressively started happening until really bad right now.


What is the problem and what needs to be replaced? What are the signs of axels/joints going out? Could it be the diff pumkin bushings wore out front or rear. wouldn't think they would cause this much flex more wheel hop if anything.

what kind of tests can I run to find out the problem?

Na-t comming next month so need to solve this before even more power than stock.



Everybodies Input is appreciated!!

 

[FLZ_Boy]

It can be a combination of factors:

1. If you haven’t done an alignment yet, please do it before doing the rest bellow.
2. Are the spacers on each plane of the differential new or old?
3. There is a small rubber part on the rear subframe that connects to the rear differential, has that piece been replaced?
4. On the NA MKIV’s, on the rear subframe, there is another larger diameter circle that is missing a solid rubber piece. The TT and Auto TT”s will have this piece connecting to the rear differential. To strength stability of the rear differential, you can add this piece (I’m assuming the SC300 has the same rear subframe as a NA MKIV).
5. Because the 6-Speed gearing for the transmission is much higher than the W58, your gearing is very high with a 4.27 rear end. Therefore, you probably notice the acceleration is much better, but you will also notice your RPMS will be very high at highway speeds. In a sense, your speedometer will be off, unless you had it calibrated.
6. Given that you have an open differential with some astronomical gearing, I’m not surprised the car getting wiggly. Maybe an LSD might help distribute the power equally to the wheels to prevent most of the side to side motion.

This is only my speculation of the problem your having. I would do an alignment first before thinking of the other steps as a possibility.

 

[zegnaguy]

It can be a combination of factors:

1. If you haven’t done an alignment yet, please do it before doing the rest bellow.Yes done 300miles ago.
2. Are the spacers on each plane of the differential new or old?all four bushings on differential have 245k on them.
3. There is a small rubber part on the rear subframe that connects to the rear differential, has that piece been replaced?NO I was and the drivers side that has the 2bolts had breaks in the rubber. 245k. I was was thinking of welding those solid replacement in place but didn't know if that would help just yet or the root of the problem.
4. On the NA MKIV’s, on the rear subframe, there is another larger diameter circle that is missing a solid rubber piece. The TT and Auto TT”s will have this piece connecting to the rear differential. To strength stability of the rear differential, you can add this piece (I’m assuming the SC300 has the same rear subframe as a NA MKIV).I beleive the Na rear ends are the same however mine has the subframe bushing connected to the diff on the driverside with 2 bolts and on the passenger side with 1 bolt (the bushing i thought wasn't supposed to be there is infact there)
5. Because the 6-Speed gearing for the transmission is much higher than the W58, your gearing is very high with a 4.27 rear end. Therefore, you probably notice the acceleration is much better, but you will also notice your RPMS will be very high at highway speeds. In a sense, your speedometer will be off, unless you had it calibrated.
6. Given that you have an open differential with some astronomical gearing, I’m not surprised the car getting wiggly. Maybe an LSD might help distribute the power equally to the wheels to prevent most of the side to side motion.

This is only my speculation of the problem your having. I would do an alignment first before thinking of the other steps as a possibility.

Do you think most of my problems are comming from lack of LSD or Worn out Differential bushings front and rear with 245k on them?

since i've replaced all the control arm bushing you don't think that worn out ball joints would cause this magnatude of a problem would you.

 

[FLZ_Boy]

Do you think most of my problems are comming from lack of LSD or Worn out Differential bushings front and rear with 245k on them?

since i've replaced all the control arm bushing you don't think that worn out ball joints would cause this magnatude of a problem would you.

I'm thinking another possibility are worn out wheel bearings, however, they should be making a loud noise if they went bad. In addition, you can check for worn out wheel bearings by jacking up the car and grabing the wheel and wiggling them around to see if they have alot of play. There shouldn't be any play (at least the rear wheels shouldn't have any play).

Some other thoughts that crossed my mind are how new are the tires and are the suspension set to stiff or soft?

I don't think you need an LSD yet to solve your current problem, I would check wheel bearings first and the ball joints you have mentioned first.

 

[muchoboosto]

i had a buddy with worn out bushings in the IRS of his vette, and it did the exact same thing. just my .02

 

[zegnaguy]

Keep the IDEAS comming

Seems to be drivetrain releated.

Rear end sloppy moving left and right. Only happens under Excelleratio. Rear of car immediately feels like it sloshes to the right then to the left as power in the Open diff transfers.

 

[FLZ_Boy]

Another idea that poped into my head is your custom driveshaft balanced? I'm afraid I can't help you on how to balance a driveshaft as that is out of my league.

An idea you might want to try a lift and hoist the car up ( I don't recommend jack stands) and run the car through 2nd gear and see if you can visually see where the vibration is comming from. You will need 2 peeps for this. However, I rather you safely have this done at a shop, safety is important .

 

[zegnaguy]

Good thought. the one piece driveshaft is used but was balanced and replaced u joints when check out. The cnc custom alum driveshaft adapter should also be balance when made.


I'm going to take off the rear tires this weekend and check all the torque settings for the rear control arms etc. I'm also going to look and see if I can see the bushings that connect the subfram to the frame.


I don't know how much the Differential front and rear bushings are having a play in this. only the two rear one that are cracked and very worn after 245k are connected to the rear subfram or at lease move around in the big bushing in it.

I'll report back.

Other thing I'm not noticing any thing wrong with my wheel bearing but maybe it would be smart to replace them anyway. Any body have instruction on how to do this at home without a press ie: C clamps or anything else. Can it be done or you need a press machine?

 

[zegnaguy]

Problem solved, I retorqued all the rear end bushings and found that the poly bushings had settled a little. Also the rear lower control arm camber adjustment side was torqued way to low from the alignment guy. Drives the way it should again. Thanks everyone!