Mercedes-Benz Forum banner

1 - 13 of 13 Posts

·
Registered
Mercedes Benz W126 500SEL &380SEL W116 280SE
Joined
·
75 Posts
Discussion Starter #1
I would like to add a tacho to a NA 300d . Has anyone done this before? How?
thanks Hank
 

·
Registered
'73 450SL, '83 300CD, '01 E320 4matic
Joined
·
2,446 Posts
The 'easy' way to do it would be to find a turbo 300D in a junkyard, 82-84 with the tach amplifier. You'd need the tach, the amplifier, the terminal base for the amplifier, the pickup near the crankshaft balancer, and the bracket that holds it in place.

Wiring it up is fairly straight forward, if you have the schematic. I'd be happy to post it for you if you do not have it.

The 85 model uses the pickup mounted in the rear of the engine, and would be quite a bit more difficult to install with the engine/trans assembly mounted in the car.
 

·
Registered
1983 240d AT1993 e320 AT
Joined
·
2,270 Posts
The 'easy' way to do it would be to find a turbo 300D in a junkyard, 82-84 with the tach amplifier. You'd need the tach, the amplifier, the terminal base for the amplifier, the pickup near the crankshaft balancer, and the bracket that holds it in place.

Wiring it up is fairly straight forward, if you have the schematic. I'd be happy to post it for you if you do not have it.

The 85 model uses the pickup mounted in the rear of the engine, and would be quite a bit more difficult to install with the engine/trans assembly mounted in the car.
Hi. I have an '83 and said to already have an EGR and would not require a tach amp. Is this true? Nonetheless, I would like to have a copy of the schematic. Thanks.
 

·
Registered
Mercedes Benz W126 500SEL &380SEL W116 280SE
Joined
·
75 Posts
Discussion Starter #5
As we never had the turbo cars imported in Oz, I can't go to a pick&pull. Is there a kind soul who has this in a parts car and is willing to part with it for a price? Of course I will pay postage as well.
Hank
 

·
Registered
'73 450SL, '83 300CD, '01 E320 4matic
Joined
·
2,446 Posts
 

·
Registered
89 300CE, 62 220SEb
Joined
·
272 Posts
Maybe this is a terrible question to ask, but what if Hank were to go with an aftermarket unit? Easier bits for him to find, would wiring be more simple?

Sorry if this is a dumb question...
 

·
Registered
Mercedes Benz W126 500SEL &380SEL W116 280SE
Joined
·
75 Posts
Discussion Starter #9
Maybe this is a terrible question to ask, but what if Hank were to go with an aftermarket unit? Easier bits for him to find, would wiring be more simple?

Sorry if this is a dumb question...
If that is a dumb question than I must be a dumb person, I thought about it, honestly. The reason I like the ones from the later cars (the original one), which will of course not be original in my car, but it will look original and I like it that way.

I like practical improvements, like the W116 ventilated front disks she has now. And I would love to get one of the Turbo engines to use, but who is dreaming.

Question. -- Thanks for the replies but it brought up a question which has always been in the back of my head. If the pulley on the crank is one size and the one on the alternator is smaller, how do the pulses from the alternator which are clearly out of sinc with the speed of the crank be translated in the right amount of revs?

Its wet here, floods all around me, we are high and dry, but my pit has 15cm water, so we have some hosing to do.

Hank
 

·
Registered
2001 Volvo V40
Joined
·
2,954 Posts
Question. -- Thanks for the replies but it brought up a question which has always been in the back of my head. If the pulley on the crank is one size and the one on the alternator is smaller, how do the pulses from the alternator which are clearly out of sinc with the speed of the crank be translated in the right amount of revs?
It is a question of calibration.
 

·
Registered
2001 Volvo V40
Joined
·
2,954 Posts
But what I would like to know is, how is this calibration done.
You use a potentio meter. You run the engine at a reference speed (for instance idle or full load) or use a laser tachometer to determine the speed, and then use the potentio meter to calibrate the tachometer.

Have a look at some documents Google is able to find.
 

·
Registered
Joined
·
12 Posts
This is an easy modification, when using original Benz parts from a 300D turbo. I've done it and it's been working well for over a year. Get used parts --- diagnostic socket with bracket, tach amp, magnetic pickup "crank rotation sensor", 2-pole or 3-pole socket (matching tach plug) and some wire. I cut pieces of wire and the black plastic tubing from a scrapped W123 harness. From the tach amp, through firewall grommet, use plastic tubing over wires. From the junction at fuse block up to tach, two wires are covered with cloth tape. This is the stock factory configuration. Brown from tach amp grounds behind cluster using large ring terminal, with other return wires. Black wire from tach amp connects, via ring terminal, to fuse 14. Black w/ Red from tach (+) terminal gets a ring terminal and is attached to fuse 12. Install pickup exactly as is done on turbo variants, handling the gray wiring harness carefully; it's a shielded two-conductor cable. No calibration is required. This is a plug-and-play conversion. Use Deoxit D5 or similar anti-corrosion protector on tach amp terminals, to increase reliability.
 
1 - 13 of 13 Posts
Top