Save my 81 300SD - for sale - Page 5 - PeachParts Mercedes-Benz Forum

JamesDean · #61 04-03-2011, 02:47 PM

Transmission Modulator Adjustment Cap?`

ashedd · #62 04-03-2011, 03:30 PM

The cap on the modulator is air/vacuum tight. The modulator will not work if it leaks. Just find the vac line by the IP that goes to the modulator, plug in your mitty vac, then see if the modulator holds vacuum. If not, look at the cap.

Once it's all sorted out it will shift like warm butter. And yes it will shift hard as heck w/o the modulator working. They say it's not bad for the transmission, but it sure does feel odd.

JamesDean · #63 04-03-2011, 04:02 PM

I was told there is a snap ring that could be removed and it could be taken off neatly. However I couldnt see one on mine, so I just pryed the thing off and ordered a replacement rubber-cap style one. It was only $30, so you're mechanic might be correct. This was the first time I've ever run into the plastic cap type ones. I prefer the rubber one.

tyl604 · #64 04-03-2011, 05:28 PM

James - with the mityvac I found the only vac leaks were the two lines that go to the EGR. After looking at your picture I left the EGR on the valve cover but disconnected these two lines at the Y's and I used golf tees (temporary only) to close the rubber Y's - both the lower and the upper. So I should have the same vac path that you now have. I also notice you took both lines off the oil pressure sending unit (at least I think that's what that is) and just left them open.

However when I started the engine the oil gauge is now pegged out at 3 and will not go down. What the heck? I put everything back together in the original configuration and started it again and still get it pegged out.

Any idea what could be the matter? Did the gauge just conveniently go out while I was working or could my adjustments have done something to it. Does your gauge still work with no vac hoses attached as shown in your picture? I have changed it back to your configuration but do I dare drive it around the block to test the shifting with the oil gauge pegged out?

JamesDean · #65 04-03-2011, 05:40 PM

Quote:

Originally Posted by tyl604

James - with the mityvac I found the only vac leaks were the two lines that go to the EGR. After looking at your picture I left the EGR on the valve cover but disconnected these two lines at the Y's and I used golf tees (temporary only) to close the rubber Y's - both the lower and the upper. So I should have the same vac path that you now have. I also notice you took both lines off the oil pressure sending unit (at least I think that's what that is) and just left them open.

However when I started the engine the oil gauge is now pegged out at 3 and will not go down. What the heck? I put everything back together in the original configuration and started it again and still get it pegged out.

Any idea what could be the matter? Did the gauge just conveniently go out while I was working or could my adjustments have done something to it. Does your gauge still work with no vac hoses attached as shown in your picture? I have changed it back to your configuration but do I dare drive it around the block to test the shifting with the oil gauge pegged out?

Your connections look good, configured the same as mine. The lines that are in the front of the engine are not for oil pressure. The lines that go to the blue plastic fittings in front of the EGR area are thermo-vacuum switches for enabling/disabling the EGR. They've nothing to do with oil pressure. I believe the oil pressure send is somewhere near the oil filter housing.

tyl604 · #66 04-03-2011, 05:51 PM

Any idea why the oil gauge is now pegged out? Dare I drive it?

ashedd · #67 04-03-2011, 06:08 PM

drive it and see how it shifts. You know for a fact it has good oil pressure, no worries. I have no idea why it would just peg like that.

JamesDean · #68 04-03-2011, 06:39 PM

I cannot recall exactly but the gauge will peg under certain conditions. If the wire to the sender gets disconnected or the sender goes bad..it will either peg or show nothing. I cant recall.

tyl604 · #69 04-03-2011, 08:21 PM

James - I took Ashedd's advice and took it for a drive. It worked fine. Pegs under acceleration and goes back down at a full stop. That's when I realized that the tranny mechanic must have set up the idle without telling me.

So that problem is resolved.

The tranny also shifted slightly better but I am getting rubber in second and third. That can't be right with a 300SD.

JamesDean · #70 04-03-2011, 09:21 PM

Are the shifts smoother? If not adjust more, if you hit flaring, back it off.

tyl604 · #71 04-03-2011, 09:35 PM

Probably tomorrow. Will have to climb under the car to pop off the white cap. Right now I am getting rubber when it shifts into second and third.

That can't be in spec.

ashedd · #72 04-03-2011, 10:21 PM

Quote:

Originally Posted by tyl604

Probably tomorrow. Will have to climb under the car to pop off the white cap. Right now I am getting rubber when it shifts into second and third.

That can't be in spec.

My SD only did that a handful of times when floored. Your mechanic probably has that modulator turned up pretty high. Did the downshifts improve?

Probably should ask a moderator to move this to the diesel section

You will get more traffic/info.

suginami · #73 04-03-2011, 11:08 PM

Quote:

Originally Posted by ashedd

Probably should ask a moderator to move this to the diesel section

You will get more traffic/info.

Done.

JamesDean · #74 04-03-2011, 11:49 PM

I agree, adjust it more CCW soften it up. Might want to verify that your getting the proper quantity of vacuum too.

tyl604 · #75 04-04-2011, 08:28 AM

James - yesterday I found that the two lines going to the EGR seem to be the only vac leaks. So I plugged them off. I have been using the mityvac with the engine off. Are you suggesting that I start the engine and check the lbs. of vacuum? What should I expect for good vac - 10-15 lbs? With the engine off should there be exactly zero vac leak?