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Author Topic: jake brakes on a 8v71 what 2 look for  (Read 4208 times)
johnjem
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« on: July 05, 2007, 01:15:48 PM »

i was reading 1 of the old papers in my bus and it said for sale 1970 gmc 4905 8v71/with jakes and it is for the bus that i own must be old anyways so i get to looking for the jake brakes no wires coming out from the valve cover stunned  do i even have jake brakes and what is a tell tale sign that i have them ,i have a few switchs on my dash that i dont know what they do??
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DrivingMissLazy
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« Reply #1 on: July 05, 2007, 02:29:26 PM »

If you do not have a wire coming from each valve cover, then that will be the first place to look.
Does not matter how many switches are on the dash.

Pull the valve covers and see if the Jake solenoids are there. If so, then start your wiring from there with a wire thru each cover. You will probably have to drill that hole for the wire.
Richard

i was reading 1 of the old papers in my bus and it said for sale 1970 gmc 4905 8v71/with jakes and it is for the bus that i own must be old anyways so i get to looking for the jake brakes no wires coming out from the valve cover stunned  do i even have jake brakes and what is a tell tale sign that i have them ,i have a few switchs on my dash that i dont know what they do??
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« Reply #2 on: July 05, 2007, 02:47:01 PM »

Number one is to see if you have the tall valve covers.  Normal valve covers are about 2 inches tall compared to the valve covers for Jake brakes that are about 5 inches tall-or you could have the 2 inch tall valve covers with a 3" spacer below.  If you do have the tall valve covers, just take one of them off (lower one is easiest) and see if you have them (only two bolts).  If all you see are 3 rocker arms per cylinder, you don't have them.  If you see two big double castings covering the rocker arms, you have them.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
johnjem
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« Reply #3 on: July 05, 2007, 06:45:43 PM »

hey i found the wire for my jakes lookes just like a temp sending unit it goes thru the head not the valve cover nice thanks    johnm
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Dallas
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« Reply #4 on: July 05, 2007, 06:51:51 PM »

hey i found the wire for my jakes lookes just like a temp sending unit it goes thru the head not the valve cover nice thanks    johnm

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chris4905
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« Reply #5 on: July 05, 2007, 07:39:24 PM »

John,

Look for the jake buffer switch.  I've included a picture from my old 8V71 with the buffer switch installed.  If it's installed it will be on the top edge of the governor.  It can either be round or square depending on how old it is, but regardless it will have two electrical pigtails or blades, where wires can be attached to the switch.
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Chris & Cheryl Christensen
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« Reply #6 on: July 05, 2007, 09:23:05 PM »

That's also a good picture of the high valve covers for the Jakes.  Do yours look that tall?  Good Luck, TomC
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« Reply #7 on: July 07, 2007, 04:15:05 AM »

yes i have the tall boys vavle cover lookes just like that and the buffer switch with three wires coming from it 1 to each head single wire black and 1 yellow  going to the fuse panel above the engine ,the jakes are hooked up to the reverse switch on the left side of the dash because,the bus used to be a standerd .i also pulled the valve covers off and saw both sets of jakes pretty neat ,john
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DrivingMissLazy
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« Reply #8 on: July 07, 2007, 05:47:48 AM »

Sounds like you found everything then? Do they work?
I do not understand your statement
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the bus used to be a standard
Richard

yes i have the tall boys vavle cover lookes just like that and the buffer switch with three wires coming from it 1 to each head single wire black and 1 yellow  going to the fuse panel above the engine ,the jakes are hooked up to the reverse switch on the left side of the dash because,the bus used to be a standerd .i also pulled the valve covers off and saw both sets of jakes pretty neat ,john
« Last Edit: July 07, 2007, 05:50:08 AM by DrivingMissLazy » Logged

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johnjem
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« Reply #9 on: July 07, 2007, 06:03:57 AM »

sorry the bus used to be a standerd shift  so they put the jake switch  on the dash where the rev switch used to be
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« Reply #10 on: July 07, 2007, 08:42:07 AM »

If you have an assistant that can stand next to the engine, with the valve covers off (you can here them with the valve covers on if it is quiet) you play with the wiring in front until your assistant hears the jakes click on.  You'll have to jump the buffer switch to do this.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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« Reply #11 on: July 07, 2007, 09:04:58 AM »

My vote is to take the rear valve cover off. Quick, easy, and will eliminate all doubt. Off, inspect, on in less than a minute.
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« Reply #12 on: July 07, 2007, 02:34:47 PM »

If you're still looking for the wires in the covers, John, here's how mine's hooked up (v-drive 8V71).

HTH,
Brian B.
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Brian Brown
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« Reply #13 on: July 07, 2007, 02:47:06 PM »

I should mention, that it's also a good idea to check for voltage drop across the solenoids, since one with a bad coil will take down the whole system. Use a VOM from the buffer switch and check voltage. Something between 12v and 13.8v (for 12v solenoids, anyways) is good. Double that for 24v solenoids. Apply the voltage to the solenoids (listen for the click) then check the voltage. Start disconnecting them one by one (you should have two on each bank) and see if any one solenoid is dropping voltage too much.

I had to replace one of my solenoids last fall. About $100 from Stewart Stevenson. I also bypassed my buffer switch because it was acting up. Now, I can't leave them on all of the time the way I used to, at least until I replace the switch. But it's better to have "Jakes on demand" than "Jakes every now and then", esp. facing a Colorado 7% downgrade, etc.

HTH,
Brian B.
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Brian Brown
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Nick Badame Refrig/ACC
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« Reply #14 on: July 11, 2007, 08:23:12 PM »

Hi Brian, Tom C, & Richard,

I purchaced a used set of Jakes from Bill Keller and they were out of a truck. I know that I need certain things like, throttle buffer, dash switch, ect..

I had the jakes sent to an Amish Detroit Diesel shop in PA to have everything serviced, so I'm waiting on that stage.

The Jakes are 12v set-up and that will be easy. I'm having Keith Crawlford from Crawford Custom Coach near Harrisburg PA install them.

Question, I never having Jakes before, what would be the best way to set them up with my 8V92T [silver] and HT740?  Switch, Throttle, or both?

Thanks
Nick-
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