Shaking/bouncing rear when dropping the clutch to initiate.

[Blackie1337]

So the car has new adj. 4 links (w/poly bushings) and a new panhard bar, heim joints.. New sway bars w/polys. A Kaaz 2 way, and new MCNSport coilovers all around. (not overly stiff). I've also been having trouble with an rpm dependent vibration that shows up at around 2.5-3k rpm when coasting/braking on the gears.
The centre driveshaft bearing has been replaced. An act clutch and unorthodox racing flywheel (If I remember correctly) was fitted a while back.

And I THINK these problems showed up after the clutch/flywheel change. (I hadn't driven the car much at all before the change so I didn't notice)

My question then is, could the clutch/flywheel cause the rear end to feel like its shaking to pieces when clutch dropping on snow? (The shaking was there before the LSD change, I expected it was the LSD's fault). And what ELSE could be causing the rpm vibration and the shaking/bouncing of the rear?

and BTW. the clutch is nasty hard, and VERY "on/off", its a 6 puck sprung clutch.. If thats any help..

[gbogho]

Did you have the flywheel/clutch/pressure plate balanced together before you installed it? I would also look at the driveshaft balance.

[Blackie1337]

No I did not, I'm not sure I have somewhere to do that here.. :/

[gbogho]

That's where I would look first if I'm reading this right. I have taken brand new clutches/flywheels/pressure plates to be balanced and seen noticeable weight added/removed

[allencr]

No.
How'r the motor mounts?
U-Joints loose and/or notchy?

[Blackie1337]

No what?
I actually retightened one of the engine mounts when I was searching for the cause of the rpm vibration, so those should be tight enough.
Not sure what you mean by U-Joints..

I'm gonna have another look at the gear mount the next time I have it off the ground though, one of the bolts had stripped the threads in the hole.. I just had to add locktite and leave it as tight as I could.. Still, the other bolts were tight enough..

[allencr]

'No, what? :0 ' No is the answer to the OP - 'My question then is,...'
Engine mount condition usually has nothing to do with how tight their metal plate is tightened.
I mean U-joint condition, ya got 3 of'em.
gear mount = transmission mount?? Again, the bonded metal plate is not the part of the mount you should be concerned with.


I believe you're describing got axle tramp caused by soft/worn/broken engine mounts.

[Blackie1337]

Ok, so you don't think the clutch/flywheel could be the culprit? Good to hear, bacause thats a crap job to have to redo..
I'll check the rubber on the engine and transmission mounts, not sure if they have ever been changed. But shouldn't the shake feel like it's coming from the front if the mounts are worn out?
The u-joints on the driveshaft feel fine, no slop in any of them.
It feels like axle tramp/hop yes.

BTW. If I'm gonna change the transmission mount and the engine mounts, do you have any recommendations on what to buy?

[allencr]

Clutch can't have any vibration because of balance that it doesn't have when sitting still & being revved.
Solid suspension joints are excellent for transmitting all the vibration & shakes & noise that the OEM joints absorb.
U-joint's needle bearings only move back & forth, never completely rotate, so they always wear in one spot. That spot gets changed with suspension height changes and/or suspension link changes, so the u-joints can vibrate as they now move back & forth between worn & un-worn surfaces.
Does the shifter move side to side when the rear is shaking? Feels like the clutch is being pumped/engaged & not engaged almost 60 times a minute?

[Blackie1337]

The only solid joints I have are the panhard bar.. everything else has poly bushings in the back. In the front everything is mostly stock except for the dampers, but they of course have poly bushings..
The u-joints have probably had minor changes in angle, as I've been adjusting the 4 links and ride height..
The shifter has minor movement when the hopping occurs, it feels like its moving at the length of the car though.. Its small enough to make it hard to tell.. But the engine mounts could still be crap.. And I guess it could feel like pulsing the clutch on and off. I'm gonna have to get the car up on stands to check the mounts. The garage is occupied atm. though, so it will have to wait for a few days.. I'll get back with my findings...
BTW is there an easy way to check engine mounts without taking them off the car? Without any reference as to how stiff they are supposed to be..

[allencr]

If the shifter isn't moving much then the mounts are OK.
All factory mounts are soft to begin with & age & oil make'm softer, that lets them wind up just like a spring to give the axle tramp/wheel hop effect when the tire/s break traction.
Despite the poly bushing advertising, they are pretty much solid enough to make/transmit noise & vibration that wasn't obvious before installing.
Sorry, I'm outta ideas. Good luck.

[Blackie1337]

Damn.. Anyone else want to chime in? Gearbox internals? Wrong pinion angle? Diff?

[jondee86]

Just a few random thoughts....
- Did you match the length of the adjustable links to the OEM links ?
- No chance you shortened the new links enough to cause the spline in
the back of the gearbox to bottom out ??
- Pinion nose pointing down ??
- Driveshaft been assembled without "phasing" the U-joints correctly ??
- Wheels out of balance ??
- Poly bushes loose or missing inner sleeves (if they are supposed to have them) ??
- Legend has it that some AE86´s had a bump stop above the differential or
pinion nose... if you had one of those and you dropped the car down so that
the bump stop was banging on the rear axle, that could be a problem

Cheers... jondee86

[Blackie1337]

Sorry about the very late reply, been busy with other stuff lately..

The links are adjusted to get the pinion into the right angle against the gearbox.. sort of. And I have traction brackets so the length can't be the same as stock.
I very much doubt that, but I will have a look the next time I'm under the car.
Pinion nose pointing up slightly if I remember correctly, and the gearbox down slightly..
Driveshaft remounted without making sure the links are at the same locations. (even if that would make it vibrate, it would vibrate all the time).
Wheels not out of balance, and again its an rpm dependent vibration, not speed.
All bushings in the back are new poly, or rose joints. No missing sleeves.
I have that bumpstop, but I havent been able to see if the pinion is very close to it.. And even if it was banging on it, it would be worse when accelerating, because that would push the pinion upwards and put weight on the rear suspsnsion. The problem occurs when the rear is breaking, which should transfer the weight forward, lifting the rear.

I am however considering changing the engine mounts, but I don't really know how to tell if its a bad one..
All I can see is that the engine is moving slightly more when clutch meeting in reverse than in 1st with the handbrake on.
sadly I don't have any reference to how much it "should" be allowed to move..

[totta crolla]

"The problem occurs when the rear is breaking, which should transfer the weight forward, lifting the rear."
Did you mean to say braking as in slowing down or breaking as in breaking away ?
Whichever it is it sounds entirely different to " shaking/bouncing rear when dropping the clutch to initiate"

[Blackie1337]

Braking, as in when the rear wheels are engine braking/locking up. That is when the bouncing occurs..
I'm not sure I understand what you are trying to say.. :/

[phanist]

I would take everything apart and reinstall them carefully making sure everything is sone correctly.
Tighten every bolt correctly. Check your suspension , shock bushing spring sitting correctly... Etc... U may have some thing not line up correctly.

[16v Justice]

When I did a clutch/flywheel replacement on my 4AG many moons ago it did the same thing. It "buzzed" when decelerating in gear. It didn't do this with the stock flywheel and clutch. I drove it for 4 or 5 years lke this until I swapped to an F20. It's annoying, but kinda normal so I wouldn't worry too much about it unless it's really bothering you.

[Blackie1337]

The only thing that hasn't been done after changing all of my rear suspension is the alignment, which, fair enough is important, but to my knowledge shouldn't be able to cause this problem..
And it's more than a "buzzing", like mentioned, it feels like the whole rear is bouncing.. (one side at a time)
Well, I'll leave this topic still until I have a chance to have a look under the car again, too much other stuff going on to get it done.
But by all means, if someone have experienced the same problem, or have any idea whats causing it, feel free to post it..