1974 280C Newbie Questions - PeachParts Mercedes-Benz Forum

grubby65 · #1 12-31-2012, 08:43 PM

I recently purchased a 1974 280C for my wife's Christmas present. I am not new to cars, but most of my restorations have been performed on American models. My most recent work was a 1947 International KB-2 pickup. Now I have gone from the ultimate in simplicity to something that is not. Here are my questions:
1) When I got the car none of the dash lights, temperature or fuel gauges were working. I read about the rheostat, but I started with the fuse box. The number one fuse was missing so I installed one. The dash lights came on, but they won't go off. My initial thought was to replace the light switch. But, before I go down that path is there something else I should check. The temp and fuel gauges still don't work.
2) The car idle was set around 1500 rpm when I got it. But after replacing some vacuum lines I got that issue fixed. But, I went to set the timing and it was set at 30 degrees b.t.d initial. I backed it down to 4 degrees a.t.d. Is that the correct setting with the vacuum line hooked up to the advance? There is only one line going to the vacuum advance.
3) Both lines from the vacuum pump were disconnected. There is now a hose running from the intake manifold to the brake booster. Is it o.k. to leave like this or should I rebuild the vacuum pump. If not should the vacuum pump be removed?

I will probably be back on the forum alot. I purchased the Shop Manual on CD, but it isn't the most user friendly.

Thanks,

mbdoc · #2 01-02-2013, 08:27 AM

Welcome, I'll get you to the vintage forum.

alabbasi · #3 01-02-2013, 10:05 AM

Welcome

Quote:

Originally Posted by grubby65

1) .....The number one fuse was missing so I installed one. The dash lights came on, but they won't go off. My initial thought was to replace the light switch. But, before I go down that path is there something else I should check. The temp and fuel gauges still don't work.

Probably a good place to start and probably why the fuse was removed.

Quote:

Originally Posted by grubby65

2) The car idle was set around 1500 rpm when I got it. But after replacing some vacuum lines I got that issue fixed. But, I went to set the timing and it was set at 30 degrees b.t.d initial. I backed it down to 4 degrees a.t.d. Is that the correct setting with the vacuum line hooked up to the advance? There is only one line going to the vacuum advance.

I think it's about 18-20 degrees advance at 1500rpm. The settings are in the CD manual for that particular car.

Quote:

Originally Posted by grubby65

3) Both lines from the vacuum pump were disconnected. There is now a hose running from the intake manifold to the brake booster. Is it o.k. to leave like this or should I rebuild the vacuum pump. If not should the vacuum pump be removed?

Yes, you need the big vacuum hose to the power brake booster in order to have power brakes.

Frank Reiner · #4 01-02-2013, 02:31 PM

Re: Vac pump & brake booster

The vacuum pump was eliminated in 1976. You can use the "direct to manifold" arrangement that you describe, with this caveat: install a check valve in that vacuum line (as was done originally) that allows air to move only FROM the booster TO the intake manifold. There are two reasons for the check valve; 1. prevents fuel vapor from entering the booster, 2. prevents a backfire from damaging the booser diaphram.