Thursday, May 31, 2007

AMG C36 - A 14-Month Long-term Update (83'312 km)

The C36 was due for its 4'300km service on 5/19 immaturely since I had to go with Eddie with his X5 (also due for the service). I live no longer in the Chai Wan area so going to Pak Lok Auto is going to be a chore. So I will just go when I have a chance. Plus I suspect the engine oil was not going great since I had a couple weeks of engine overheating a month or so earlier.

Also I have the factory MB spark plugs replacing the TM plugs. It turned out to be a bad idea. Not only I lose power but also torque and responsiveness. I will put the TM plugs back in during the next service or earlier if I can find a chance. The mighty C36 engine now turns into a silky, creamily smooth C320.

Also I learn that the wiring to the transmission has hardened and therefore due for a replacement. The front pair of upper A-arms are also getting more and more frequent clunking noise whenever they are subject to some serious suspension travel or lateral loads. Those two expensive repairs will be on the list for the next service.

Otherwise the only complaint I have is the tendency of minor understeering. This can be solved either by changing to a stiffer and stickier front tires, or lifting the rear ride height by 10mm. The ride is perfectly acceptable to me now, provided that the front tire pressure is not above 32psi when cold. I especially enjoy the firm and controlled way that they flow over the speed bumps of all sizes and shapes.

Tuesday, May 29, 2007

Changing Spring Rate on C36 Update 3



I understand the last update (2) was not an update but some useful information. However this one is. After spending a week with the H&R I springs I felt there was room for improvement.
The H&R springs made the C36 handle a lot better. And the ride was very good for the first one or two inches of spring travel. However after that due to its progressive or variable-rate nature they became awfully hard when compressed. It gave a hard time to the shock absorber especially during the rebound. Simply the shock absorber could not cope with the higher spring rate (or rebound). The H&R springs was shorter by more than an inch and two coils less, compared to the original springs. It would be nice if the H&R springs were of the same height of the original springs. This way it would add perhaps one more inch of usable spring travel and suspension compliance. Also it would help to increase the ground clearance much needed to clear the ramps, dives, dips and rises of the HK roads and parking. Most of the time I had to slowing down to a crawling to clear.
So on a Saturday morning Shing Gor of Pak Lok Garage and myself set out to the Mercedes part store to look for alternate solution. I brought my original springs to compare. We searched the database and found out that the original springs in my C36 were from the first of the listed springs of the two generations recorded in the part database. Quickly the store provided the second generation springs for some comparison. Eureka! The two new springs were of the same spring height but with one coil less turn compared to the original, both front and rear. This would mean the new springs would have around 10-15% more spring rate. We examined further a few other points and concluded that it might just work for me.
The fitting took more than two hours. I chose the thinnest spring pads front and rear. My initial impression was the loss of sparkling handling but a return of the Mercedes classic ride I had been longing for since the days of C200. The front springs now sat a tad lower a few days later. The ride was surprisingly more compliant and compliant over rough roads. There seemed to be boundless amount of spring travel. There was a new found stability and firmness in the ride. It seemed to me that the original springs were indeed a bit soft and would not work with the new shock absorbers (AMG-Bilstein) that was installed 14 months ago. The new factory springs did work better with the shocks now and hence provided the much needed improvement. It was now a joy to ride the car in both smooth and rough pavement. There was reduced nose dives in each of the corner when the front wheel found its way into pot holes. There was the tuneful and muted bump thumbs alike the W126 that I remembered. The body movement was gentle and slow when the car floated through low frequency dives and crests at high speed.
It made me remember the ride in the C200.
Mercedes Part Number Reference:
Old Factory Spring came with the C36: Front (202.321.1204), Rear (202.324.1104)
New Factory Spring for C36: Front (202.321.1804), Rear (210.324.3104).