I just bought a 1987 300 SDL ... - Page 3 - PeachParts Mercedes-Benz Forum

tstarr · #31 08-17-2003, 07:04 PM

Peter,

I'll check that when I get back from the beach. I spent some time before going replacing rubber all over the place. I have a couple more pieces of rubber to change, but I'm still not getting much in the way of vacuum. I blocked off everything on the right side, drew a vacuum and it held, so that's good. I drove it after replacing most of the rubber and it shifted into high, but then stopped and I limped back in 3rd. A little more rubber to replace and that's eliminated.
If the vacuum pump weren't working, wouldn't I be having problems with the brakes? That was when I knew I was having vac pump problems on my 82.
Anyway, some more grunt work when I get back.

- Ted

psfred · #32 08-18-2003, 08:06 PM

Ted:

There are separate taps on the vac pump for the booster and the control system vac on the 603. If the line to the vac pump for the control system is plugged, you won't have vac.

Do what I did, pull the 5-way T off and check for vac from the pump first, and get that fixed if you have a problem (bad line, plugged restrictor), then see what you have. I have a rubber hose from the pump to the T -- I think the original plastic line was replaced.

Peter

tstarr · #33 08-19-2003, 06:28 PM

Peter,

Here are this afternoon's diagnostics.

1) I attached the vacuum gauge directly to the vacuum pump (no restrictor) and got about 20 inches. Don't recall exactly, but I knew from looking at it that I was getting vacuum.
2) On the other side of the restrictor, the same.

When I hook the gauge in next to the vac amp, it goes up to 4, then starts to bleed off back to 0.
Then I thought I would take the 3 lines off of the tranny control (mounted to the IP) and use the Mityvac to draw vacuum. It held, telling me that there are no more vacuum leaks in the lines and that the trouble is probably in the tranny control. Does that make sense?

I have now replaced all the rubber vacuum connectors with new or rigged ones from rubber hose. THe connector that goes into the tranny control is molded and was totally shot. I trimmed down a piece of vacuum hose so it would slide into the hole in the box and it seems to hold OK. Not the perfect solution, but it should be holding vacuum better than before. Still, same results.

Is there a reasonable way to confirm/deny that the tranny control is the problem? I haven't seen anything in the CDs on testing any of this stuff...

- Ted

tstarr · #34 08-19-2003, 06:31 PM

Upon reading my previous post, I wanted to be clear on one of the checks. I disconnected the tranny control from everything else by disconnecting the hoses and blocking them each with a tee. Then I pulled a vacuum from another spot in the vacuum hose "circuit" (with the tranny control OUT of the circuit) and it held vacuum. Sorry for the confusing description before.

- Ted

psfred · #35 08-20-2003, 07:57 PM

Ted:

Did you check the entire vac circuit for the tranny control, including the low temp switchover valve?

If so, I'd agree that the tranny amp is bad, replace it.

I did all the vac line connectors, and solved the big problem by plugging off the lines to the air recirc and EGR valves pending new vac actuators -- mine were both blown.

Verify, if you have not, that you get 17" or so of vac on the line labled "vac" on the amplifier -- if not, you still have a leak somewhere.

I have the diagram of the entire engine vac system if you need it, but cannot scan it in here.

Peter

tstarr · #36 08-20-2003, 08:21 PM

Peter,

Yes, I disconnected all 3 vacuum lines from the tranny control, blocked 2 of them with tees and pulled vacuum on the 3rd. Everything was there except the tranny control and it held. I got a good price on a new one locally, so I'm going to pick it up at lunchtime tomorrow and pop it in. I'm going to have my fingers and toes crossed...

I'm having similar problems with my 82 SD, but not as bad. It's a non-glamorous job to block off this and that to narrow down the vacuum leaks. But at least the SD will shift into high gear with some coaxing...
By the way, I found a link that contains some good info on tuning the transmissions, including vacuum diagrams. I hope this goes through, but here it is.

http://www.mercedesdismantlers.com/diesel_vacuum_system#Diesel%20Vacuum%20System%20Troubleshooting

Sorry, I don't know how to make a cute link text, so this should work. Thanks for helping out on this. I'll let you know how it goes tomorrow.

- Ted

psfred · #37 08-21-2003, 12:18 AM

Ted:

Adjust the Bowden (kickdown) cable on the 603 to be all the way out but not loose for correct shift point -- the vac only controls shift feel on this tranny, not shift point.

The cable works backwards to most -- it is all the way out at closed throttle, goes back into the tranny as the throttle is opened, unlike the usual system of all the way in at closed throttle and pulling out as throttle is opened.

If the cable it too tight, you may no want to go fast enough to get it to upshift -- I've hit 80 in 3rd at wide open throttle. Also, check to make sure the kickdown switch isn't stuck closed, that will make it shift VERY late as well.

Peter

tstarr · #38 08-22-2003, 09:39 PM

Peter,

This problem is about to kick my butt. I have replaced ALL of the rubber in the engine compartment and replaced several parts that I thought were leaking. I did check underneath the footpedal and the kickdown switch was NOT stuck down. It was up and I could click it down and it would come back up. It took a pretty good amount of effort to push it in, which made sense to me.
I'm going to continue fiddling with the bowden cable and see if I can get the shift point working right. Is there any chance that it's the kickdown switch solenoid? I wouldn't really know how to check.
But I'm going to have to put it off until Sunday. We have something pretty cool going on with the local MB club tomorrow. One of the local dealers is opening up their shop for us and giving each of us 2 hours on a lift and they are going to have a number of MB mechanics walking around to help and keep us out of trouble. My son and I are going to take on a number of undercarriage tasks with the 82 300SD, including changing the transmission wiring harness. Fun! I'm looking to knock off a number of our "to do" items on that car tomorrow. I've been driving it the last couple of days while trying to figure out this shifting problem.
THanks for the tips. I'll let you know how it goes from here. DId I mention that I hate vacuum???

- Ted

tstarr · #39 08-24-2003, 09:56 PM

Peter,

An interesting thing happened this weekend. I kept fiddling with the Bowden cable to no avail, then thought I would get a different T to check vacuum. Then I did as you ended up doing (blocking off the EGR and air recirc valve) and the vacuum was fine. For some reason, it checked out OK the other day but not now.
What I find is that the shift point seems to be completely insensitive to the Bowden cable adjustment. I have run the nut all the way out to the bracket, and run it way back toward the firewall and I'm not really seeing any appreciable difference.
I'm a bit confused, given that I'm not seeing results, but should the white nut be run back toward the firewall or toward the front of the car for proper shift point? I'll continue moving it that direction a couple of turns at a time to see what happens.
Also, just to make sure I didn't have a kickdown switch issue, I pulled the carpet out of the driver's side so that there wouldn't be any chance of carpet catching it. It looks as if PO cut some of the carpet away - I cut away more.
Anyway, I'll continue moving the nut in the direction you tell me. Thanks!

- Ted

psfred · #40 08-24-2003, 10:05 PM

Ted:

The bowden cable on the 603 is a bit screwy -- it is all the way OUT at closed throttle, and goes back into the housing under spring tension from the tranny as the throttle is opened.

It should be comletely extended with just enough tension on the small spring on the engine end to keep it from rattling at closed throttle. Likewise, it should not be fully retracted until you get to full throttle.

You may be way off -- what do you have, very late shifts or very early ones? I've got mine set to upshift to fourth at about 30 mph or so under light throttle, and it will run up to 80 or so floored before it shifts into fourth.

Peter

Peter

tstarr · #41 08-24-2003, 10:10 PM

Peter,

My shifts are very late to non-existent. And this happened all of a sudden. My wife and I drove to Costco without incident, then it wouldn't shift up to 4th coming home.
So it sounds to me like I need to continue to run the white nut back toward the firewall. I believe that's the direction that pushes the cable back out. That being the case, I'll run it back there many turns tomorrow morning and try it again.
I also want to look more at what the vac is doing when I drive as well.

- Ted

tstarr · #42 08-24-2003, 11:01 PM

Peter,

My shifts are very late to non-existent. And this happened all of a sudden. My wife and I drove to Costco without incident, then it wouldn't shift up to 4th coming home.
So it sounds to me like I need to continue to run the white nut back toward the firewall. I believe that's the direction that pushes the cable back out. That being the case, I'll run it back there many turns tomorrow morning and try it again.
I also want to look more at what the vac is doing when I drive as well.

- Ted

tstarr · #43 08-25-2003, 02:55 PM

Today's saga of the transmission -

First, I gave up on moving the Bowden cable nut (white one) toward the firewall and adjusted back out. Seemed to help a little, but not much.

I checked vacuum after the blocking of the EGR and other valve, and it went up to 15 slowly. It got there, but it took probably a minute to work its way up to 15. I believe I've read elsewhere that means that there is a restricted line somewhere. I replaced one line which was old and I thought might have been restricted, but no change. Plugged off the line to the tranny to see if the pressure would come up faster, but no. When I hit the throttle, the vacuum drops, but I've only seen it drop to about 5. I thought it had to drop to close to zero for a shift.

Then I come in (after taking the other car out) and notice transmission fluid on the driveway. I haven't climbed underneath, but there isn't any obvious leakage around the modulator, but I'll see when I can get some ramps (natch - left those at the beach...).

I'm also getting some flaring as we go forward. I'm driving along and then it seems to shift into neutral, then eventually catch again. I have a filter and gasket, so I'll go ahead and change that while I'm down there since it's due.

Sigh...

- Ted

PS - Peter, thanks for patiently listening to my latest tale of woe.

tstarr · #44 08-25-2003, 03:20 PM

Peter,

One other thought, since the car hasn't shifted into 4th gear in a week, and the Bowden cable adjustments don't seem to matter. Could I be having the dreaded B-2 piston issue? I bought the car in December and haven't yet serviced the transmission. That was actually one of the items I was going to do this past weekend at the DIY session. I don't know if that has been replace by the PO or not.

- Ted

psfred · #45 08-25-2003, 08:57 PM

Ted:

B2 piston causes second gear to fail (its the servo for second gear band).

Unfortunately, refusal to upshift is usually a dead tranny valve body. Swap for a rebuilt, don't bother to have it done, that tranny is fairly rare and no one will know how to do it correctly.

On the other hand, check the linkage to make sure you don't have a missing bushing so it is popping into third rather than drive... Also check to make sure the kickdown switch under the throttle isn't stuck down or shorted. If it is, you may have to run up to 80 or so to get it to upshift.

Peter