Jerky Cruise after Performa amp rebuild
 

I searched the archives for jerky cruise controls but got nothing. I'm sure I'm not the first guy to get this but I thought I'd throw it out to pool the great experience base of this forum.

My cruise did not work so I sent the amp to performa to be rebuilt. They had it back to me in 5 days!

Cruise now works but is jerky.

My speedo is a little bit wobbly at slow speeds (below 40mph) but higher speeds seem quite steady.

My flex disks are new and in good shape.

Any chance this is something other than the speedo cable?

Any suggestions on cable replacement?

Thanks,

Bob Kopicki
Massillon OH
'97 VW Cabrio (POS)
'93 Miata
'87 300e
'76 GMC C15
'67 TR-4a

When you say the cruise control id "jerky" do you mean that while the crusie controlis engaged, the car will alternate between speeding up and slowing down creating a sort of rocking motion or jerking you forward and back? If this is the case, the rebuild was not sucessful. My current crusie amp was doing the rocking motion symptom prior to my resoldering all the connections inside. A good resolder and the problem was gone. I have had two amps do the same thing. The crusie will set, accelerate, decelerate, resume, etc. But either after a while of operation or immediately upon turning the crusie on ( just depending on the day, temp, etc) the rocking motion would begin. A good resolder rebuild and the problem was gone. I have rarely seen the amps go "bad" they just get funny symptoms due to failing solder connections. They can manifest in all sorts of problems...turning off on their own, the rocking motion, not operating at all, etc. I have not ever had one completely DOA, they have all beun to work again after a good resolder session. I would recommend returning the amp to the rebuild shop, they dont seem to have done the rebuild quite right in your case. Good luck.

The speedometer cable and the cruise system are seperate systems. A bad speedo cable will likely cause your speedo needle to bounce at a certain speed and it will usually clear up at higher speeds. A bad speedo cable will not effect your crusie control as far as I know. A broken speedo cable would be an issue since the cruise system uses a speed pickup sensor at teh back of the instrument cluster at the speedo cable connection. It reads the rotation speed and uses the signal to maintain the desired speed. Unless the speedo cable is just doing something crazy it would not effect much. It would have to probably actually start rotating and then come to a stop and start again to cause any major jerking motion. I dont think that is really a possible situation. I think you have a bad rebuild

Chris,

Thanks for your reply. The "jerky" motion is fairly rapid. The car does not noticibly accelerate or decelerate, but feels like someone quickly tapping the gas pedal maybe every second or so.

Guess I'll give proforma a call on Monday.

Thanks,

My experience in the "jerky" motion with the cruise engaged is maybe not quite so severe, but it sounds the same. maybe every 2 seconds so I think you still may have a bad rebuild. Good luck.

Chris,
I'll be calling proforma on Monday. I started looking at the other parts of the system, and since the amp is already paid for (with a 3 year warranty) I hope that is the troublesome part.
Thanks,
Bob

Cruise control
 

My 1989 300E cruise control does the same thing. Please give us an update on what you find.

Where is the amp located and how much was the cost to rebuild?

The amp is located under the steering column and to the left. It cost $140 to rebuild by Proforma, $15 shipping and comes with a 3 year warranty. I've attached 2 pics of my amp before I sent it to proforma to be rebuilt. I pulled the amp and tried the resolder that many have written about on this and other forums, but it did no good so off it went to the pro's.

Thanks,

Whoa! I'm fairly certain that the rebuilders won't warranty an amp that has been 're-soldered' by anyone other than them, prior to the re-build, nor will they accept a re-soldered amp as a core trade-in. If this is not correct, please let us know.
I have re-soldered the amp in my '85 380SE twice, and both times, it has been about 90% functional for the spring/summer/fall seasons that I use the car, only on long road trips though. It does seem to get buggered up from sitting unused for awhile, maybe the extended sub-zero temps of a Canadian winter aren't easy on those solder joints, I dunno.
The amp in my '86 560SL doesn't work at all, so now I'm debating a re-solder or send it off like you did for a 'pro' rebuild. I'd really like to hear how you make out on the warranty, as a shot at re-soldering myself is worth it if I can still get them to rebuild it later if it doesn't work.....

Perhaps this is a don't ask don't tell situation. They didn't ask me if I resoldered it and I didn't offer that info. (it would have been very obvious to any electronics tech that the unit had been opened and soldered)

However, if they have the bench equipment to "rebuild and test" a circuit board, what does it matter what someone did to the board before they rebuild it? If they get it to work, it would seem to me (and apparently them too since they put a "warranty void if broken" tape across the cover) that it would only matter what you do after they repair the board.

Either way, I'll be calling them Monday morning to see where we go from here.

Thanks

One thing to check...
 

I had a similar symptom in the 300SD. I found that the nut holding the lnkage to the servo was very loose. Once I tightened it the problem went away. I think the servo was hunting to compensate for the linkage being loose

Worth a shot anyway...

Yes,

Worth a shot. I've been out of town this weekend but I'll be getting home tonight. I think I'll check the linkage before I call programa.

That's why I like this forum, want to try to cover all the bases whenever something goes wrong.

Thanks,

Just a quick follow up. Proforma says they'd be happy to look at the amp again since it is covered under warranty but their tech support could only suggest checking the wiring and connections.

Guess I'll be looking for a loose linkage or bad connections and if I don't find anything, back it goes.

Cruise Control
 

Good luck!

i get that crap too ... jerk jerk jerk ... now my speedometer is bouncing too .. bahhhh .. i love this mercedes but dam it would be nice to not work on it or a while