Question about underdash vacuum line


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Rusty Driver
Rusty Driver

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Post Fri Jan 04, 2013 9:52 pm

Question about underdash vacuum line

I am curious as to what is missing from from under the dash of my 1949 KBS-5. As you can see in the attached picture, I have a capped vacuum line on the inside of the fire wall that leads out to the control valve for the two-speed axle. Could someone fill me in? Thank you in advance.
oldbike99
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Golden Jubilee
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Post Sat Jan 05, 2013 10:18 am

Re: Question about underdash vacuum line

It is for the ratio adaptor that should be on the input of the speedo. It changes the cable speed when shifting the rear axle from low to high. It is necessary to keep the speedo reading correctly with two different ratios in the rear axle. Without it connected the speedo will only read correctly in one of the two ratios.
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Rusty Driver
Rusty Driver

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Location: Grand Forks, N.D.

Post Sat Jan 05, 2013 11:12 am

Re: Question about underdash vacuum line

Thank you. So the speedometer cable was originally two sections?
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Golden Jubilee
Golden Jubilee

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Post Sat Jan 05, 2013 11:25 am

Re: Question about underdash vacuum line

No, the ratio adaptor was on the back of the speedo. It screw into the speedo where the cable normally goes, and the speedo cable screw into the adaptor. It is likely that someone removed the adaptor and screwed the cable directly into the speedo. If you have a device on the back, then you have the device, if not then you need one.
Later trucks used an electrical ratio adaptor and these were often mounted somewhere on the firewall and used a two piece cable.
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Golden Jubilee
Golden Jubilee

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Post Sat Jan 05, 2013 3:15 pm

Re: Question about underdash vacuum line

the problem with the vacuum two speed adapter is there is a tiny, about 1 inch in diameter lil diaphragm and when that dries out and splits the adapte is toast,

I have yet to see where you can buy a replacement diaphragm, I bought a few instrument clusters thru the years just to get the adapter off the back,

if you don't have it, it isn't really that big of a deal, the speedo isn't that far off and it ain't like your gonna get a speeding ticket in that truck,

keep an eye out on ebay, they do come up,,

looks like this
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Rusty Driver
Rusty Driver

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Location: Grand Forks, N.D.

Post Sun Jan 06, 2013 4:25 pm

Thanks for the help

I appreciate all the help this forum has been. Someday I my be able to return the favor.
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Golden Jubilee
Golden Jubilee

Posts: 4837

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Location: Bothell, Washington

Post Mon Jan 07, 2013 7:25 pm

Re: Question about underdash vacuum line

here is one on ePay, this is not mine just sharing,,

http://www.ebay.com/itm/41-42-46-47-48-49-INTERNATIONAL-PICKUP-TRUCK-SPEEDOMETER-GEAR-REDUCER-ADAPTER-/120890595102?pt=Vintage_Car_Truck_Parts_Accessories&hash=item1c25a4171e&vxp=mtr

you can find one cheaper in my opinion,

I bought a rusty hunk broken instrument cluster for $10 on ePay, it had one on the back, threw the cluster away, it was that bad, but reducer was fine,
Gentle Men! you can't fight in here! This is the war room!

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