Readying the PUB-mobile

[twistedtree]

As you may have gleaned from some other posts that I have made, I'm trying get one of my SLs in suitable condition to be my PUB-mobile.  I really don't want to show up driving my daily BMW.  I'm currently contemplating two problem, and would welcome and input.  The good news is that I've put about 50 miles on the car and didn't have to walk home even once.  Not bad for a car that hasn't really been driven since 1979.

Problem 1 - Mixture is still out of whack.  I have carefully set the linkages, and rechecked them a number of times, so am confident they are correct.  I have also rectified a number of vacuum leaks including a damaged intake manifold gasket and a badly leaking brake booster.  I'm pretty confident that I don't have any more vacuum leaks, but can't be 100% sure.  I've sprayed around all the joints and that typically will surface a leak pretty quickly.  My FIP and CSV have been recently rebuilt by H&R.  The CSV, WRD, etc are all working very well.  However, right from the get-go after installed the FIP, the car was running lean. In consult with Hans at H&R, I richened it up via the main rack screw.  That made for an engine that ran well and reved up in neutral which was all I could do at the time.  Just recently I've fixed other problems and have now been able to put about 50 miles on the car on the streets.  I also have an AFR meter rigged up so I can see the instantaneous AFR while I drive.  Under full load about 3000 RPM, if anything the mixture is a tad rich at 12% or so.  Partial load at 3000 RPM looks pretty good in the 13% range.  But at light load in the 1500-2000 RPM range the engine runs really lean in the 15-16% range, and surges.  At idle I've got it adjusted to run well, but that's really moot since it will get readjusted once everything else is correct.

My interpretation of this is that I need to adjust the light load screws on the FIP.  That's what the data seems to suggest.  However I'm surprised to find the miture off on a newly rebuilt FIP - not just the light load, but the main rack as well.  I've got a few days here to contemplate this before I start making adjustments.  And don't worry, I keep careful track of all the adjustment that I make so I can get back to where I started if needed.  Anyone have any other ideas?

Problem 2 - Trans doesn't downshift under load.  In all other respects the transmission is working well.  All 4 gears are there, it upshifts at the right points, starts in 2nd, kicks down to 1st, etc.  Coming to a stop, it downshifts gently as expected.  I have checked the 3 position solenoid for proper operation, and also confirmed the operating pressures in each of the 3 positions.  The one problem is that it won't downshift under load.  So, for example, if I'm running in 4th and start to climb a steep hill.  I can give it full gas just short of the kickdown switch, but still keep losing speed because of the climb.  But the trans never downshifts.  If I move the selector lever from 4 to 3, it downshifts right away.

I'm thinking this problem must be related to the vacuum line and modulator since that's what would control a downshift under load.  Sound right?  There is no sign that trans fluid is getting past the diaphragm.  I checked the vacuum pipe up at the manifold and it's dry.  There also is no smoke.  So I'm guessing it's not ruptured, but perhaps stuck or something?  Does this make sense or do you think it might be something else?  I'm pretty certain that I have a replacement diaphragm so my plan is to take it apart and do a quick rebuild.  At the same time I'll check to be sure I'm actually getting a vacuum reading down at the trans end of the pipe.  I suppose it could be crushed somewhere and not passing the vacuum signal.

I welcome any thoughts before I dive into these two issues in a couple of days.

Thanks

[ja17]

What procedure did you use to set up the IP timing for installation?

[twistedtree]

I used whatever the documented procedure is.  If memory serves me, you set the crank pulley to something like 20 deg ATDC, then align the notch on the FIP and install.  It was a couple of years ago so I don't recall it exactly, but I do know I followed the documented procedure.  Doesn't mean I didn't screw it up.  Would that make the car run lean only at light loads?

[ctaylor738]

I don't want to dump on the pump rebuilders, but my experience has been the same as yours.  I have worked on two cars with pumps from rebuilder A.  One I had to do a rack adjustment three clicks rich to get it to stop backfiring under medium load, like pulling away from a stop normally, and one was so bad it had to go back for a do-over.  The pump on my 280SL was done by rebuilder B and it needed two clicks rich to get rid of a stutter under light load.  Gernold told me he usually needs to adjust rebuilt pumps as well.  So I'm not surprised.  I think the Bosch specs are no longer totally correct for today's gas.  If you have the patience to do the partial load adjustment, go for it, just be prepared for the gush of oil when you take the rear plate off, and a lot of fun trying to get the screwdriver positioned.

WRT the transmission, mine will not downshift from 4 to 3 under partial load either, but otherwise works fine.  I do the shift from 4 to 3 manually and have learned to live with it.  You can try fiddling the modulator adjustment, but be sure to keep track of where you started.

Good luck.

[twistedtree]

Interesting that yours doesn't downshift either.  I wonder if others will report the same thing.  I could easily move that to the "sometime later" list.  Repairs sways carry the risk of creating a bigger problem.

It's also interesting to hear about the FIP mixture.  Right now. Think I just need to suck it up and make the adjustments.

[badali]

My car shifts from 4 to 3 under a light load up to about 45 MPH.  If I am on a rural winding road where I can not stay above 45 then it shifts back to 3 a lot.

[ctaylor738]

I looked at the BBB and found the following on 27-5/2:

Shifting Down with Partial to Full Throttle

Decelerate vehicle in selector lever position 4 to approx. 40 km/h, then apply full throttle; the transmission will shift down to 3rd speed for acceleration.

[kampala]

Chuck,

How do you interpret the BBB quote?  Does that mean that it will only downshift automatically from 4th to 3rd with full throttle since the kickdown switch gets activated?   Or does it mean that it will downshift prior to the kickdown switch being pushed on?

Thanks.

[ctaylor738]

I think it means full throttle but not kick down.  In another section "kick down" is referred to as "beyond" full throttle.

Also, I think that manifold vacuum needs to go really low for the modulator to cause a downshift.  That's what would happen under the conditions described - low-ish rpm and full throttle.

[twistedtree]

Ready or not, the PUB Mobile is done.  I don't have enough confidence in it yet to drive to PUB, so will trailer it and drive locally in Ohio.

For those who may have missed the back story about How One Pagoda Turned Into Four http://www.sl113.org/forums/index.php?topic=12033.0, this car is part of a four car, four rooms of parts "barn find" from nearly 5 years ago.  One car was brought back to life, fixed up as a respectable "driver", and sold.  Another was never touched and sold as-is.  And I kept two; a '64 230 and a '70 280.   One very early example, and one very late example.  I plan to fully restore both over time, but for now have gotten the '64 driveable and plan to use it for a while to see what I really have and confirm that I want to go through the restoration.  Same with the '70 280, and I'll probably keep one driving at all times while the other is apart.