Drive Train "Tuning"

Drive Train \"Tuning\"

Now that I am driving the car, I have noticed a surging feeling /ubbthreads/images/graemlins/confused.gif while driving the car at cruise (neutral throttle) – that is not accelerating and not decelerating. It looks like the engine is ever so slightly bucking – back to front. It may be my imagination but it seems to occur after driving over a small bump or depression in the road. If I accelerate it immediately smooths out! It also seems to go away if I depress the clutch. Not like anything is shaking – doesn’t feel like an imbalance in the engine or the half shafts.
I have checked all the suspension, mount bolts and even the transaxle stays – everything is tight. Do any of you guys have ideas as to what might cause something like this?

I plan to try different adjustments of the shocks. I get the feeling something starts to rock (back to front) and gets into a “resonant frequency”. At present my only solution is to always accelerate!

Thanks in advance
Re: Drive Train \"Tuning\"

Engine mounts?? adaptor plate to engine mount brace??
See uncle Pete @ gt40 aus. He'll save you
Re: Drive Train \"Tuning\"

Colin check that the driveshaft yokes are aligned properly they can be the cause of velocity surging Regards denis
Re: Drive Train \"Tuning\"

I would quess you are on the right track in checking the shock settings. Because of the drivers location you really sense the movement of the car when the front or rear gets a little bounce to it.
Re: Drive Train \"Tuning\"

Colin the centrelines through the bearing cups on each end of the shaft should be perfectly aligned this can be altered by pulling the splines apart and rotating them until they line up- I hope that is clear enough I know what I am trying to say But if I was better at this computer stuff I would pst a drawing Regards Denis

Dave Bilyk

Dave Bilyk
Re: Drive Train \"Tuning\"

Colin, another thing to check is your throttle cable. If it is anchored in such a way that engine movement can modulate the throttle, this could cause this symptom, and especially if the drive shaft yokes are not properly aligned.
Hooke joints or Hardy Spicer joints, need to be 90 degrees rotated at each end of a shaft. If not, when the drive shaft is articulated, there is a 2x per rev oscillation superimposed on the output rotation for a constant input velocity of rotation.
This doesn't happen with a 'Constant Velocity' Joint which is the reason for the name.
Re: Drive Train \"Tuning\"

It now seems likely that the problem stems from my engine mgmt system. After a lengthy shake down a couple of days ago (oh what fun! /ubbthreads/images/graemlins/smile.gif ) I narrowed the problem to a finite engine rev range (1800-2200), therefore implying it is the SDS EMU. Likely that the computer is sensing a high vacuum and momentarily shutting down the fuel then adding fuel when vacuum drops thereby causing surging which manifests itself in the powertrain.

I did check though and my half shaft yokes are aligned.

Thanks for all your suggestions.