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-   -   Decelerator valve/shift on the fly (https://forums.off-road.com/jeep-short-wheelbase/2058-decelerator-valve-shift-fly.html)

**DONOTDELETE** 11-02-1999 07:05 AM

Decelerator valve/shift on the fly
 
I pulled my Carter and most vacuum tubes and vacuum solenoids preparing for the Weber install. My engine is apparently from California and according to the vacuum routing chart it has a Decelerator valve. The vacuum hoses that route to the decel valve also eventually operate my shift on the fly 4wheel drive.

Question 1: Can I remove the decelerator valve and attached tubing and run direct manifold vac to the shift on the fly?

Question 2: What is the function of the decelerator valve and is it necessary to leave it installed?


dorfs 11-02-1999 07:51 AM

Re: Decelerator valve/shift on the fly
 
The decel valve, or gulp valve, will help prevent back-fire under rapid decel conditions. When the air injection reaction manifolds inject air into the exhaust, the engine will have a tendency to back-fire under rich conditions. Under rapid decel, you will have high manifold vacuum, and very rich conditions. The decel valve will since this condition, and create a momentary large vacuum leak under the base of the carb, and lean the mixtures, and try to prevent this from happening.

If you removed your air manifolds, there should be no reason for leaving the decel valve, however, this falls under the federal emission tamperiang laws.


**DONOTDELETE** 11-02-1999 08:52 AM

Re: Decelerator valve/shift on the fly
 
Thanks for the info dorfs. Do you know if I can run direct manifold vac to the "shift on the fly" 4WD, bypassing the maze of hoses attached to the decel vlv? I notice that the 4wd vacuum hose tees from the line routing from the decel valve to the vacuum reservoir, through what looks like a small check valve.


CJDave 11-02-1999 09:08 AM

Re: Decelerator valve/shift on the fly
 
[img]/wwwthreads_images/icons/tongue.gif[/img] Wouldn't you be better off WITH the decel valve since gas engines puke away fuel on hard deceleration and breaking the vacuum would do two things: (1) make your Jeep engine hold less on deceleration, producing a "roller skate" effect and contributing to higher fuel mileage; (2) reducing the amount of fuel sucked into the engine while deceleration and thereby wasted?[img]/wwwthreads_images/icons/crazy.gif[/img]

CJDave

**DONOTDELETE** 11-02-1999 09:29 AM

Re: CJDave - Decelerator valve/shift on the fly
 
Since I am vacuum systemly challenged, that sounds reasonable to me. I'm not opposed to keeping the decel attached, however if I do keep it with the hose maze, et. al., attached, how does it hook up to my new Weber?

....Doug


xjy173 11-02-1999 04:17 PM

Re: CJDave - Decelerator valve/shift on the fly
 
Hey Doug,
I think dorfs and CJ Dave are giving you good advice on the decel valve/air injection thing. If you remove it and allow some raw fuel into the exhaust manifold you could backfire and the raw fuel will do your cat convertor damage.
I think it would be a bad idea to put manifold vacuum to the axle shift servo, too, because the high manifold vacuum generated during slow speed might do damage to the servo diaphram. There is vacuum to the front axle servo in both 2wd and 4wd mode in order to keep the shift collar in the desired position.

Good Luck!! [img]/wwwthreads_images/icons/smile.gif[/img]


**DONOTDELETE** 11-02-1999 04:24 PM

Re: Decelerator valve/shift on the fly
 
No matter what you end up doing with the decel valve, why don't you get the cable accuator for the front disconnect from BDS. This will
solve any problems with that trobulsome unit.

Gary

**DONOTDELETE** 11-02-1999 04:46 PM

Gary - cable accuator
 
Enlighten me, What is it, what is its function, where do I get it, and why do I want it? I'm assuming you refer to a mechanical control device for the 4WD.

...Doug


**DONOTDELETE** 11-02-1999 05:34 PM

Re: Gary - cable accuator
 
It's a cable accuator kit that replaces the vacuum disconnect motor and vacuum can. The cable mounts to the front axle and comes
into the interior and mounts the knob on a bracket to the bottom of the dash. Positive mechanical engagement. It's made by a com-
pany called BDS. They used to be called Big Dicks Suspension.

Gary

xjy173 11-02-1999 11:28 PM

Re: Gary - cable accuator
 
Actually, the real problem in my experience with the front Dana 30 disconnect is not the vacuum system at all but the shift collar getting stuck on the splines due to loss of lubrication. What I do every year is remove the servo from the axle and grease the splines/collar with axle grease. Whether you have a vacuum or cable actuator, it is a good PM to do. Since I started doing this on my 86 XJ about 5 years ago, my front axle shifts into and out of 4wd very easily. [img]/wwwthreads_images/icons/wink.gif[/img] [img]/wwwthreads_images/icons/smile.gif[/img]



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