PeterFeix

iTrader: (1)

Hi all.

Hope someone can help me out on that:

I have a 383 Gen1 SBC (86+) which should be external balanced (Neutral Front, Weight at the Rear), that is what the engine builder told me.
Some years ago I converted the car from Th700 to T56 , got a complete assembly from a LT1-Fbody donor car. All stock parts, Valeo clutch etc.
I'm driving this for ~3-4 years now ( let's say about 3000mls within that time span, most of the time just cruising ).

Once I hit around 4000rpm the engine (or transmission) starts to vibrate.

I was first thinking of worn out u-joints from the driveshaft, replaced them, no success.
Replacing the Energy-Suspension Transmission mount (with preload plate) with an Prothane mount (without preload plate) didn't help either.

Today I checked the Flywheel if there is "no weight" , but it seems that my Flywheel is the right one for my application.

Does anyone have some suggestions what to do next?
I could just buy a new fw, clutch, fork, pilot bearing/bushing and hope the vibrations stop, but that will cost 1grand+ that may just be unnecessary right now.


Here are some pics from the assembly 3-4 years ago:




Step1



Step2



Step3



Step4



Flywheel inner side



Flywheel inner side


And I have taken a small video , hope you can hear whats going on as soon as the engine reaches 4000rpm you can hear it relatively good.

https://dl.dropboxusercontent.com/u/.../T56/video.mp4


Thanks
Alex

jmd

iTrader: (4)

Does it do it while the car is parked?
Does it do it with the accessory drive belt(s) removed?
Does it do it while the transmission is removed?
Does it do it if you replace the flywheel with an automatic flexplate for 86-92?
If yes to all, the engine balance may be in question.

It looks like you put together a nice build, by the way.

PeterFeix

iTrader: (1)

I will try whis as soon as the roads dry up here :/

But if I remember correctly the time I had the 383/Th700r4 combo, there weren't any uncommon vibrations other than a slight roughness of the engine (compared to a stock engine).

After converting to T56 I first used a cheap rubber transmission mount - The transmission was "diving" alot under torque , so I replaced it with an Energy Suspension poly mount. I think the vibrations started here or at least got worse. I did some research and removed the preload plate which was included with the transmission mount. Last year I replaced it with a Prothane Poly Mount without Pressure Plate. Didn't help either.

In the next days I'll try a stock rubber mount.... hopefully that works.

Haven't tried removing the belt yet, this will be another step once I replaced the transmission mount.

PeterFeix

iTrader: (1)

Update:

I replaced my poly transmount with a stock rubber one.
First thought once I reached 3000rpm in first gear "this feels differrent..... smoother than ever before..... hmmmmm"
After the engine reached operating temperature i took it on the autobahn and floored the pedal..... shifting at 6000rpm , stopped accellerating at around 160mph and still had no uncommon vibrations. Not bad for a stock steel driveshaft.

Strangely the whole engine feels stronger.... and that with outside temperatures of around 95*F

So: Problem solved !

jmd

iTrader: (4)

That's almost as cheap and easy as finding you have a powertrain code on an OBD-II vehicle and find it's just a cheap new gascap needed.