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  #1  
Old 12-18-2003, 04:46 PM
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Join Date: Mar 2000
Location: cool ca
Posts: 109
plastic valves

well i need some help have a 1983 300sd was having trans. shifting problems. I did the search for information. no luck. Heres the problem. These valves are located on top of the valve cover.{ take off the black box top and there they are with short hoses running to a plastic manifold ] this is hooked into the vacume lines also into the egr which is pluged. The question are these valves need for anything?
One of the plastic valves is broken and also the plastic manifold was broken i had a vacume leak. I by passed the whole thing.I am not useing them now. Will this hurt any thing?
I was getting a flare in first gear, like the tras. not being in gear.
Took it for a test drive seams to shift ok. don't know about the flare yet.
Bill
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Old 12-18-2003, 05:16 PM
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Join Date: Aug 2001
Location: Evansville, Indiana
Posts: 8,150
Those valves control the shift speed ('feel') and the EGR.

You will need a replacement if they are broken, as bypassing can cause the EGR to be on all the time (although you'd notice that) and very soft and sloppy shifts. The latter will ruin the tranny sooner or later. If you plug the vac line, and have no vac on the modulator, the tranny will shift VERY hard -- this is rough on the rear end, the tranny, and the flex disks.

Peter
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  #3  
Old 12-18-2003, 08:35 PM
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Join Date: May 2002
Location: Central Oregon
Posts: 1,004
If you plug the transmission directly to the vacuum pump you will have extremely soft shifts and very fast like 1 then 2 then 3 at about 20 miles per hour...

The vacuum blocks perform a couple fo functions but the primary one is adjusting the shifting based on throttle position. it does the same thing for the egr but since you don't havet o worery about that...
When at idle or slight throttle there is full or nearly full vacuum to the transmission providing soft shifts in slight acceleration. When pedal to the metal there is very little if any vacuum at the tranny causing hard (solid) shifts so you get acceleration into the next gear.
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