Classic/Antique Car Repair: Shadow 2, transmission fluid change, shadow 2

Question
QUESTION: Hi Vern, I have a shadow 2 that got several problems that our RR experts can't fix, first, the car has a thud when going into gear, the idle is a low as you should go but it sometimes gets this thud that makes you cringe, I have got under the car and think its in the turbo 400 but not sure, second the car has a thud when going over bumps in the rear passenger side,it also gets the same thud if you but the power on and off, over bumps you would thinks its a shocker rubber but the power on off thing is confusing, the RR experts have had it on the hoist and stuffed around for a few hours and could not find any bushings etc that they could fault. It maybe their not so informed?

ANSWER: Hi Andrew:
You are most likely correct. The TH-400 transmission on these cars are literally bullet-proof, but they will develop the "Thud" behavior over time. I suggest you have the transmission fluid change with a heavier fluid or a heavy (longer-life) additive.

Not sure about the other Thud when going over a bump. There are covers over the top of the mufflers, but that should be more of a rattle than a thud. If you are not getting a vibration when you accelerate with passengers in the rear seat, then your shocks and hydraulic unit is working fine, otherwise it time for shocks.

When was the last time you put shocks on it and had the TH-400 serviced?

---------- FOLLOW-UP ----------

QUESTION: Thanks for the reply, gearbox serviced about 1000 km ago, I've had rear springs changed and cross member mounts changed, I've discovered the horizontal compliance cushions feel soft and probably not doing what they should, I've ordered new ones in any case,and it looks like a nightmare job? the shocks don't sound noisy when I bounce the car, I've tried checking the trailing arms bushes using a jack and can't detect any movement, there is a bit of back lash in the diff, about 5mm, how does that sound?

Answer
The Thud may be the differential. When you put her in gear, the diff will engage. If there is play in the diff, you will hear a clunking sound. Also, disc brakes will developing a similar sound when the car come to a stop if there is play in the calipers.

However, turning the power on/off should not create a Thud of any kind. The thing that happens when the key is in the ON position is the fuel pump engages, but if it was going bad, it would develop a humming noise, not a thud.

Make sure all electrical items are off before you start her (e.g. Radio, A/C, etc.)