Vintage Cars: 450SL 1979, especally, floor pans

Question
QUESTION: Dear Ron,

I am considering purchasing a 1979 450SL.  I tried one today that is in really good condition.  However, the transmission knocks quite hard when it shifts, especially from 1st to 2nd.  Also, when shifting from P to D, the wheels may spin if one don't press firmly on the brake pedal.  Is this something that can be fixed with an adjustment, or should I just forget about the car?  Could you also let me know what type of gasoline I should put in a vehicule like that.

Thank you very much.

ANSWER: is it shifting hard because the idle is too high? In nuetral it should idle around 8-900 RPM.  Some folks raise the idle to mask other issues.
1 to 2 should be firm but not knocking , P to R should be smooth.
Trannys on these cars can be adjusted as they are vacuum driven
How many miles and does it have any service history, a MUST if you are looking at one of these cars.  Also look for rust, especally along frame ,jack points, shock points , floor pans and trunk.

The more info you give me the more I can help
Good luck!
Ron

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

QUESTION: Dear Ron,

Thanks for the answer.  I noticed that the engine ran pretty fast (I didn't pay attention to the RPM though).  The owner told me the tranmission knocked like that ever since he bought it, some seven years ago.  The car does have a service history that could easily be checked.  It's 110 000 miles and I haven't seen any rust on or underneath it.  It appeared to me as a very carefully maintained vehicule, both inside and outside, hence my interest.  The asking price is about 11 000 US$, which is probably high according to US market value, but a 30 year old car without rust in Canada is a very rare thing.

Thanks again

Answer
110,000 is not a lot of miles, the 450 is a solid car with a solid engine, normal tranny is best described as firm, into all gears, no flaring or slop. park to drive and reverse should be smooth, holding foot on brake is probably due to high engine idle, but again all these symptoms may be comming from a vacuum leak.  These cars are prone to them.
At 110,000 miles , ask about injector service, valve lash service, renewing  under hood rubber. timing chain service .Make sure AC and heat work, that can be a big headache. Brakes and rubber OK?
You really need to do your homework on these ol gals, because you can get into being over your head quickly, it is always good to be handy with wrenches!
11,000 $ US is a huge amount of money for that car, it should be in nearly perfect condition ( including the tops) for that price
Good luck