I've got the "bouncing tachometer problem" that has been reported elsewhere in this forum (i.e. the yips). The tach and the oil pressure guage intermittently and simultaneously drop to zero for awhile and then back to normal for awhile.

This is a known problem in the 140 chassis. Technical service bulletin of 4/28/97 recommends replacement of the electronic circuit board of the instrument cluster when the intermittent tach/oil pressure guage problem is present.

However, the instrument cluster is a $1400 item and ought to be a testable/repairable item. The circuit board is loaded with test connectors--as if the board is capable of being plugged into a testing device.

Does anyone know of anyone who tests/repairs MB instrument clusters?

Something is common between the tach and the oil pressure gauage--but can't figure out what. All other gauges acting normally. Just those two bounce--and they bounce in sync with each other. I've studied the wiring diagrams and can't identify any input common to the tach and oil pressure guage. I've cleaned the ground involved (W1; behind instrument cluster) since that is a common link. Problem persists--so I figure it must be internal to the instrument cluster.

Beckman Technologies 919-381-2700

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Sounds like you may have a problem with the source of the power for your Inst. Cluster .....We always Remove and Replace all of the FUSES About once a year .(under routine Maint.)after removing the fuses take a "small" wire brush and clean the contacts where the fuses seat. for some reason they get a film on them and could drive you up a wall trying to resolve the problem...We were using an after mkt fuse. for years but went back to MB fuses (specal alloy) which resolves the problem . But we still remove Clean and replace fuses . Belts and hoses at different intervels..It is why MB are so reliable and will practally last forever if you keep up on the MAINT>(Somewhat like the Aviation Industry) We Treat our cars like we treat our Airplanes. Hope it helps .Let me know if it resolves your problems.

I had my cluster rebuilt at a place in Tenn. Contact by email.
The address is:
george murphy
E-mail Address(es):
george_murphy@compuserve.com

Gabby,

Fuzes? What a great idea! I'll try it and let you know.


All others,

Thanks for the sources for instrument cluster repair/rebuild.

I had a '92 140 chassis where the instrument cluster would flash its warning lights whenever the turn signals or wipers would be on. Very annoying so I sent the cluster to Programa in Florida for the repair and drove the car while it was out watching the speed limits carefully and filling the gas tank before removing!
Have also heard that b/c there were so many problems with these that MB has them rebuilt/exchange.

Good luck....
Tobias MB
4 MBs

Tobias MB,

Just for completeness of our discussion here, do you have any contact information or a website reference for Programma?

Just yesterday, I asked the parts people at the MB dealer (Signal Hill, CA) about repair services for the instrument clusters. They said there is no repair available--and the replacement units are $1,400. Apparently, MB thinks that MB owners have so much money--that they're willing to throw away these instrument clusters.

You are correct. MB did have lot of problems with these instruments clusters and there were replacement circuit boards available at one time according to a July 1996 Technical Service Bulletin (Ref. MBNA 54/44A).

The TSB mentions six different part numbers--three for the 129 chassis and three for the 140 chassis. For the 140.032 chassis (up to 11/93 production) the part numbers are: 140 540 80 47 91 (W/O ASR) and 140 540 80 47 90 (W ASR).

Unfortunately, the dealer says the parts are no longer available.

I'm on the way to wire brush the fuse sockets as Gabby suggested. It makes sense. I sure hope it works.

Ed

If you are trying to save money, I would recommend resoldering all the joints on the circuits involved, it's an easy and enjoyable task to do.

I had a simiar problem with my 94 plymouth acclaim, resoldering the cluster fixed it right away. I'm still having the same problem with my curise control computer in my 190E, after I resolder it, it works for 15 minutes but that's because of the brake light bulbs

I don't use CC anyway

Might want to try it.

I fixed all the electrical problems in my car this way.

xp

__________________
1985 190E 2.3L - a constant project.

Ed,
The link to ProgRama is www.programainc.com and their land line # is 800-668-8843. They are located in BocaRaton, FL and when I sent my cluster in the charge then was $300 with a 3 year warranty. Turnaround repair time is 48 hrs max.
BTW the easiest way to remove the cluster without breaking anything or having special tools is to remove the the left side air/heat vent and the duct tubes behind it. This way you can put your hand up in there and push the unit out from behind. If it has never been out it may be stuck in there and you don't want to crack the lens by pulling on the edges of the cluster.

Good luck in your repair...
Tobias MB
4 MBs

Gabby,

I think we may have a fix!

As you suggested, I cleaned the fuze sockets. I targeted fuzes related to the instrument cluster (i.e. fuzes 17, 23, and 24 in Fuse Box #3).

I brushed each fuze socket with the wire brush. And I also noticed that the fuze contacts were oxidized. So, I cleaned up the contacts on each fuze by scraping the contacts clean with the edge of a sharp pen knife.

Well--I took the car out for a 15-20 minute test drive and the tach and oil pressure guages never once dropped to zero--as they had been doing.

I'll continue to monitor the situation. This is miraculous if we do, indeed, have a fix.

Actually, your suggestion may have even fixed problems that I didn't even tell you about. I had one DTC being set in the Cruise Control/Idle Speed Control module (DTC #10) saying that the TNA signal (engine speed) was bad. That signal (TNA) also goes to the tach. So now that the tach is acting normally--I'm hoping that the CC/ISC module is happy too. The engine, by the way, is idling much more evenly--no variations in idle speed as it had before.

Can this be possible? Can dirty fuzes and dirty fuze sockets really cause all this trouble? I shudder when I think of the costs involved with other possible diagnoses of this problem. Instrument cluster ($1,400), air mass sensor ($800), base module ($2,500), or CC/ISC module ($2,500) all could have been implicated. If the problem has gone away after cleaning up the fuzes and fuze sockets, it's a genuine miracle! No doubt about it--a miracle!

A big, big--even huge--thanks to Gabby. I'll let you all know if it continues to be a successful fix (i.e. tach working, oil guage working, and DTC #10 from CC/ISC is gone).

Ed

The light for the fuel gauge keeps going out on my S350. A tap on the dash at the side of the housing usually brings it back on. Also, the light for the ambient temp readout is out. I still get the temp but I can only see it in daylight. Is there a fix for this? Will unplugging the instrument panel generate any fault codes? I just got my SRS light working right and do not want to mess that up trying to fix something else. all things being equal, I can solder with the best.

__________________
N. Hodges
1994 S350
1987 300 SDL (for sale)

N Hodges,

Assuming that your S350 is anything like my 400SE, I can answer a couple of your questions based on my recent experience.

There is a twist-out light bulb for the ambient temperature display. The best way to get the instrument cluster out is to remove the LH vent, reach in, and push the cluster out from the back.

Unplugging my instrument cluster did not generate any DTCs. Out of curiousity, I did start the engine with the cluster out and everything worked pretty much as usual.

It sounds like instrument cluster removal and a few light bulb changes will do the trick for you.

Ed

All of the twist out bulbs are new as of Friday. Are there any bulbs on the circuit board? I did not see any of the bulbs that are controlled by the rheostat... the ones that actually light up the instruments. I did see all of the bulbs for the warning lights. Does any one have PICs of the cluster? A schematic?

__________________
N. Hodges
1994 S350
1987 300 SDL (for sale)

N. Hodges,

I did partially disassemble my instrument cluster but I didn't see any bulbs on the circuit board itself. All bulbs in my cluster (i.e. warning light and illumination) seem to be the twist out variety.

The AllData electrical diagrams cover some--but not all--of the instrument cluster wiring. (Some wires lead to a rectangle and the details of what goes on inside the rectangle are unknown.)

A detailed MB schematic of the instrument cluster would be a great thing to have.

Ed

ED Hannah

Every light in mine was identified on the plastic surround. That's why I thought that they may be on the circuit board. Are you sure that the bulbs are twist out? I will look again. The dealer cleaned mine and replaced all of the bulbs...or so the service writer said. I would really like to tackle this problem. The light for the fuel gauge is intermittent. I can get it to come on with a slap on the side of the dash but the ambient temp light does not come on at all. The schematic does exist. Can anyone on the forum supply one or point me in the right direction.

Nap

__________________
N. Hodges
1994 S350
1987 300 SDL (for sale)