Has anyone figured out the tach-amp on the benz and how to wire it up to an aftermarket tach. I have had no luck finding any info at all. I need to know soon so I dont leave a key part on the doner car before it is gone.

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Hey John I just picked up a cherokee the same year as yours 2.8 auto, and I could'nt feel the converter lock-up when I drove it home. So on that trans it may be to subtle to feel.

 

I have played around with my tach, have not got it to work yet. I kept the sensor and the amplifier from the donor car. I have the wiring schematic for it, but i'm not sure if the amplifier is even good. Congrats on your purchase!! Keep us posted on your progress.

John

 

I'm in the process of fabbing the t-converter adapter for the 700r4, it has an 12in conv. It is almost too big, barely is going to clear the starter snout. I have cut the end out of the benz conv and using it as the adapter. Once I get that done I will fab the bell adapter. I will take pics and start my own thread soon












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I love these engines i have 2 an 84 300sd and a 85 300d pumps cranked on both just blew something in the 300d's trans fluid just poors out but yea great build also which turbo created more boost the kkk or the air research i have one of each and only one boost gauge it's showin 10-12 tops on the kkk

 

What wires go where from the amp. I think there are three last time I looked. Did you try to wire it to a non benz tach?

 

I can tell you a little abut the tach. In 83 and older cars the tach signal comes from a sensor mounted up by the crank pulley. From there it goes to the tach amp, which is a little cannister looking thing just over an inch in diameter and about an inch and a half tall, mounted under the hood on the driver's side fender well. This tach amp is NOTORIOUS for failure, but they can still be purchased new for a hundred dollars or so on eBay - or you can pay about double that through a Mercedes dealer or parts house. IIRC there is a guy on peachparts.com (formerly mercedesshop.com) who has built an updated version with modern electronics that works very well.

For the 84 - 86 cars they did away with the tach amp on the fender and incorporated it into the EGR computer. Instead of using the sensor mounted next to the crank pulley, the newer one uses a sensor mounted on the driver's side of the bellhousing towards the top.

BTW the XJ with the 2.8L auto (Chrysler Torqueflight A904) doesn't have a locking converter according to everything I've read about them. They are just a straight 3-speed with hydraulic and vacuum controls.

 

Thanks for the info. I have the sensor/amp ***. from the benz, I was wondering what the three wires that leave from the amp go to. Short of tracing the loom in the benz(82), I was hoping someone had a diagram or had aleady rewired it to an aftermarket tach. Not sure weather I should save the benz tach, don't think it was working before I yanked the motor. On the 904 trans, accordig to what I have read it does have lock-up but mine is such a slug it could be worn out. What do you expect for 350, but hey I drove it home and the body is really clean and straight. Nobody wants the 2.8 so they go cheep

 

According to the schematic I have, the black wire is 12V + The brown wire is 12V -
The green/black wire goes to the tach. I hooked mine up to the factory tach that's in the dash of the Jeep, it would not work. Either the amplifier is bad, or the Jeep tach is not calibrated properly for the signal. I have an aftermarket tach ,I need to hook that up and see what happens.

John

 

Sorry, never looked into the older system at that level of detail since mine is an 84 with the newer system.

Well, the old dog learns another new one. Some additional research on my part reveals that they indeed did produce a variant of the A904, which they actually called an A909, that had a lockup torque converter, and they indeed installed them in some 84-86 Jeep Cherokees. Funny but my 84 with the 4 cylinder had the straight A904 without the lockup converter - probably because the little 4-banger with the auto was such a slug to start with the converter wouldn't be able to stay locked...

 

Thanks John , I still have the benz tach so I'll try that too. The aftermarket tach I have has a switch on the back for 4-6-8 but no 5 so calibration could be it.