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??
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
Quote from: johnjem 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??
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
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
Quote from: johnjem 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
That's not it.
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.
That's also a good picture of the high valve covers for the Jakes. Do yours look that tall? Good Luck, TomC
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
Sounds like you found everything then? Do they work?
I do not understand your statement
Quotethe bus used to be a standard
Richard
Quote from: johnjem 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
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
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
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.
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.
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.
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-
Nick i have mine on a 2 postion switch where you can have a high and low
QuoteQuestion, 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?
I might not understand your question correctly but the switch with a high low selects the level of braking the jakes do. Low runs one bank (1/2 braking), high, two banks (Full braking). The position of the throttle turns it on/off. I find that having to remember not to completely let off the throttle is annoying at times, mostly on the interstate. I like the jakes the most around town (yes I know that is where you're not supposed to make all of that racket). In addition to the panel switch, I want to add a foot switch to my system that would allow me to only activate them when I briefly need them. It would be a momentary switch that would look like a high/low dimmer foot switch. This would allow me to activate them when going down a long steep hill if I needed them, and allow coasting down smaller ones when I didn't, all the while not having to feather the throttle. For most flatlanders they wouldn't have a problem with the traditional setup, but I spend most of my time driving up and down here in the mountains.
Barn Owl, don't you have an on/off switch for the jakes? The reason they want the jakes to come on only when the throttle is released is because if you don't the fuel system will still deliver some fuel while jaking, which produces alot of smoke.
Lloyd
Nick, if the buffer switch is set up correctly, you should be able to leave the switch on and then the use of the throttle will turn them off. My Jakes do not have the two-position switch and I'll be adding this feature soon because mine provides a LOT of braking force with both banks going... great for going down steep grades, but too much for going down slighter ones and for slowing in traffic. A turbo motor like yours won't provide quite as much braking power due to lower compression, but I'd still opt for a hi-lo switch.
You'll also want to get a feel for when your tranny is in lockup, since any of the torque-converter ranges won't provide effective engine braking. Left on, the Jakes should slow the coach enough for it to downshift all the way down to your hydraulic 2nd or even 1st gear (depends on how your tranny downshifts), and then the service brake provides the rest when you need to come to a compete stop. Used properly, a Jake will add years to a set of brake linings (in RV service, anyways). I'm often able to come down winding roads and Interstate off-ramps with the Jakes alone, moderating speed with the on-off switch, all the way down to 15mph or so. My foot is always ready to apply the service brakes should the need arise, the linings and drums stay nice and cool.
Speaking of on-off switch, I like your idea of a momentary switch, Laryn! One foot on the service brake, one on the Jake... would save me a lot of fumbling for the switch. Love that busnut ingenuity!
Brian B.
Thanks for the replies guy's.
Brian, I thought someone mentioned about a trans device... what is this that I need for my 740?
Nick-
With the 740, all you need is a
properly adjusted Buffer switch.
Although I've said it before, the most important part of the Jake installation is the location of the HI-LO-OFF switch. I had to move mine from the dash to the side switch panel because I had to lean forward to reach it. It should be within easy reach while you are in your normal driving position without having to fumble around or search for it in the dark. Properly used I think you will find it the control that you use the most while out on a trip.
Richard
Quote from: Nick Badame Refrig. Co. on July 12, 2007, 03:59:38 AM
Thanks for the replies guy's.
Brian, I thought someone mentioned about a trans device... what is this that I need for my 740?
Nick-
QuoteBarn Owl, don't you have an on/off switch for the jakes?
My switch is set up like Brian's, either off or on but no high/low. I would like to change it to select one or two banks for the same reason Brian has stated. My current setup, all or nothing, makes it uncomfortable for some driving situations. It's like I've dropped anchor or something.
I believe the tranny that Brian has (V730) acts significantly different than the 740 tranny that Nick has and that I had in DML.
There was really no way to detect when the tranny was in lock up or not.
Significant braking is provided even with a turbo. If the Jake is left on in normal driving, this braking is very annoying and the ability to easily switch between HI and LO as well as OFF is, in my opinion, mandatory.
I stress that the proper adjustment of the Jake valve clearance and that of the buffer switch is of extreme importance.
Richard
Quote from: Buffalo SpaceShip on July 11, 2007, 11:30:00 PM
Nick, if the buffer switch is set up correctly, you should be able to leave the switch on and then the use of the throttle will turn them off. My Jakes do not have the two-position switch and I'll be adding this feature soon because mine provides a LOT of braking force with both banks going... great for going down steep grades, but too much for going down slighter ones and for slowing in traffic. A turbo motor like yours won't provide quite as much braking power due to lower compression, but I'd still opt for a hi-lo switch.
You'll also want to get a feel for when your tranny is in lockup, since any of the torque-converter ranges won't provide effective engine braking. Left on, the Jakes should slow the coach enough for it to downshift all the way down to your hydraulic 2nd or even 1st gear (depends on how your tranny downshifts), and then the service brake provides the rest when you need to come to a compete stop. Used properly, a Jake will add years to a set of brake linings (in RV service, anyways). I'm often able to come down winding roads and Interstate off-ramps with the Jakes alone, moderating speed with the on-off switch, all the way down to 15mph or so. My foot is always ready to apply the service brakes should the need arise, the linings and drums stay nice and cool.
Speaking of on-off switch, I like your idea of a momentary switch, Laryn! One foot on the service brake, one on the Jake... would save me a lot of fumbling for the switch. Love that busnut ingenuity!
Brian B.
Richard,
How does one adjust the speed at which the Jake disengages? Is it done by the buffer switch, or oil pressure, etc?
Laryn
I should have mentioned that mine drops out around 35mph. I guess engine rpm might also have something to do with it. I would like mine to disengage at a lower speed, like Brian's 15mph.
Brian, are you letting your transmission shift on its own or are you using the TomC's method of shifting to get down to 15mph before your Jakes let go?
Quote from: DrivingMissLazy on July 12, 2007, 07:05:27 AM
I believe the tranny that Brian has (V730) acts significantly different than the 740 tranny that Nick has and that I had in DML.
There was really no way to detect when the tranny was in lock up or not.
Richard, the torque-converter Allisons are all designed similarly enough to make some observations about lockup and how it affects braking and deceleration. Brian Diehl even went so far as to make an override solenoid on his old HT574: http://home.earthlink.net/~diehls0792/HT754TorqueConverterLockup.html , a brilliant device, IMHO. If one has a tach and observes rpm drop or rise vs. the same in mph and compares throttle position to the same, it will soon become obvious if the tranny is locked-up or not. Noting the shifts of the tranny and when it goes in and out of lockup (and whether manual shifts make any impact on lockup... mine does) makes driving a coach, esp. in hilly conditions, much more safe and enjoyable.
Case in point, there's a long 10% downgrade into the Palo Duro Canyon (in TX) with sharp turns limiting speed to 15mph max. In hydraulic first (non-lockup mode) the Jakes were of no help, the tranny just "free wheeling" down, and I had to maintain heavy service brake use all the way down. Once I learned how to lockup my tranny in first, the Jakes could work along with the engine and I barely had to hit the service brakes at all. Huge difference.
For most flatland driving, lockup is not that big of a concern, but for coming down or even going
up hills (for tans. cooling sake), it makes a
huge difference being "locked-up" or not.
My $0.02,
Brian Brown
The Jakes disengage automatically as the engine oil pressure drops to the point that it is too low to hold the Jake' open. In my case it was in the 800-1,000 rpm range.
In reality, the Jakes generally disengaged when the tranny dropped out of lockup and quit spinning the engine. This generally only presented a problem on extremely steep grades in 1st gear when I had to go so slow (below 15 mph) that the tranny would not stay engaged. I believe there is some modification that can be made to the 740 to prevent this dropout, but I do not know what it is.
Richard
Quote from: Barn Owl on July 12, 2007, 08:00:51 AM
Richard,
How does one adjust the speed at which the Jake disengages? Is it done by the buffer switch, or oil pressure, etc?
Laryn
Quote from: Barn Owl on July 12, 2007, 08:11:14 AM
I should have mentioned that mine drops out around 35mph. I guess engine rpm might also have something to do with it. I would like mine to disengage at a lower speed, like Brian's 15mph.
Brian, are you letting your transmission shift on its own or are you using the TomC's method of shifting to get down to 15mph before your Jakes let go?
Laryn, the V730 in "D" mode is very "dumb" when it comes to shifting up and down. It was made for transit busses that seldom even hit lockup mode nor seldom climb hills. First off, if you don't have a tachometer,
get one. Short of the temp. gauge, it's the most important gauge on an automatic-equipped coach IMHO. Ironically, I drove a stick-shift 4106 for years without a tach, and still wouldn't need one, since you shift 'em by the speedo and the 1:1 relationship it has with rpm.
The short answer is that you
can control when it goes in and out of lockup with the shifter
and the accelerator. The shifter determines the gear range and throttle position (on air modulators anyways) determines when and how the transmission will lockup. Usually just backing off the throttle a bit will allow it to lockup. If you have an hour and can find some empty roads, you'll get the
feel of lockup and how it affects driving.
When going up hills, shift down at 1600rpm and up at no more than 2200rpm. Once you know when she's in lockup, try to climb hills that way to avoid heating up the tranny unnecessarily.
The absolute best thing to do would be to build Brian Diehl's solenoid lockup override mentioned above. Living here in the hills (and you have 'em, too), it's definitely on my short-list.
HTH,
Brian
Need someone that is very familiar with the various Allison transmissions. I feel certain the my 740 went into lockup while still in first gear, at about 15mph, and remained in lockup thereafter as it it shifted to 2nd and then on up, while still locked up. But, I could be wrong. Would not be the first time. LOL
Richard
Quote from: Buffalo SpaceShip on July 12, 2007, 08:26:38 AM
Quote from: Barn Owl on July 12, 2007, 08:11:14 AM
I should have mentioned that mine drops out around 35mph. I guess engine rpm might also have something to do with it. I would like mine to disengage at a lower speed, like Brian's 15mph.
Brian, are you letting your transmission shift on its own or are you using the TomC's method of shifting to get down to 15mph before your Jakes let go?
Laryn, the V730 in "D" mode is very "dumb" when it comes to shifting up and down. It was made for transit busses that seldom even hit lockup mode nor seldom climb hills. First off, if you don't have a tachometer, get one. Short of the temp. gauge, it's the most important gauge on an automatic-equipped coach IMHO. Ironically, I drove a stick-shift 4106 for years without a tach, and still wouldn't need one, since you shift 'em by the speedo and the 1:1 relationship it has with rpm.
The short answer is that you can control when it goes in and out of lockup with the shifter and the accelerator. The shifter determines the gear range and throttle position (on air modulators anyways) determines when and how the transmission will lockup. Usually just backing off the throttle a bit will allow it to lockup. If you have an hour and can find some empty roads, you'll get the feel of lockup and how it affects driving.
When going up hills, shift down at 1600rpm and up at no more than 2200rpm. Once you know when she's in lockup, try to climb hills that way to avoid heating up the tranny unnecessarily.
The absolute best thing to do would be to build Brian Diehl's solenoid lockup override mentioned above. Living here in the hills (and you have 'em, too), it's definitely on my short-list.
HTH,
Brian
The only time Allisons will lock up in first is if the shifter is in 1st. If it is in 2-6th, it will start in 1st converter, go to 2nd converter, then 2nd lockup up to top gear. This applies to HT740, HT754, HT755, HD4060, B500. The MT640, MT643, locked up in 3rd. There were some derivations to this, but only on truck Allisons, like the HT750DR that had a real granny low and would normally start in 2nd. Then it would lock up in 3rd. (they had a programming that would have each gear go from converter to lockup, so a four speed would be 1C-1L-2C-2L-3C-3L-4C-4L. Kept the engines more wound up, but worse on mileage). Good Luck, TomC
Tom, based on that would you then feel seven shifts (for a 740) if everything was working properly?
I never felt more than three.
And was there ever something like a 740-HD? I got charged for that when I had my 6V92 upgraded to an 8V92. The shop in Tucson (Arizona Transmission & Engine exchange?) stated that I had to have the heavier duty tranny. As i recall it cost me a few thousand dollars extra above th original quoted price.
Thanks again for all your valuable information and the time it takes to answer all the questions you do.
Richard
Quote from: TomC on July 12, 2007, 08:58:14 PM
The only time Allisons will lock up in first is if the shifter is in 1st. If it is in 2-6th, it will start in 1st converter, go to 2nd converter, then 2nd lockup up to top gear. This applies to HT740, HT754, HT755, HD4060, B500. The MT640, MT643, locked up in 3rd. There were some derivations to this, but only on truck Allisons, like the HT750DR that had a real granny low and would normally start in 2nd. Then it would lock up in 3rd. (they had a programming that would have each gear go from converter to lockup, so a four speed would be 1C-1L-2C-2L-3C-3L-4C-4L. Kept the engines more wound up, but worse on mileage). Good Luck, TomC
The 4 speed that had the 7 converter and lockups was only for a truck. On a 4 spd you should feel 4 shifts-one being the converter lockup and then the 3 gear shifts.
The only "heavy duty" HT740 I know of was the HT748 that was designed for transit buses. It had a more robust torque converter with hardened input shaft to take the hundreds of starts and stops per day. The normal HT740 had a factory rating that easily could take the power of the 8V-92TA-I know this since this was an option when I ordered my first truck in '79 with the 8V-92TA ($8,700 extra said I got the 13 spd instead-but always pined for the Allison). Hate to say it about the price you paid for the "heavy duty version"..... Good Luck, TomC
Tom, then if I understand correctly my 740 would start out in first, it then would lock up at about 15 for the first shift I felt, then on to second, third and fourth, for the four shifts I felt.
Regarding the work I had done in Tucson, it was before even the internet and of course no bus boards or anyone to ask questions of. I took it in with an initial estimate of $8,000 to change the engine. It cost me over $25,000 to get it out of there. Boy, what a bunch of crooks.
Richard
Quote from: TomC on July 13, 2007, 08:46:05 AM
The 4 speed that had the 7 converter and lockups was only for a truck. On a 4 spd you should feel 4 shifts-one being the converter lockup and then the 3 gear shifts.
The only "heavy duty" HT740 I know of was the HT748 that was designed for transit buses. It had a more robust torque converter with hardened input shaft to take the hundreds of starts and stops per day. The normal HT740 had a factory rating that easily could take the power of the 8V-92TA-I know this since this was an option when I ordered my first truck in '79 with the 8V-92TA ($8,700 extra said I got the 13 spd instead-but always pined for the Allison). Hate to say it about the price you paid for the "heavy duty version"..... Good Luck, TomC
All Allisons, including your 740, start in first converter, then shift to second converter, then into second lockup, third lockup, fourth lockup. The only time you can get lockup in first is by pulling the shift selector down into 1st. Good Luck, TomC
OK, thanks Tom. I have always wondered what the shift pattern really is.
Richard
Quote from: TomC on July 13, 2007, 10:57:23 PM
All Allisons, including your 740, start in first converter, then shift to second converter, then into second lockup, third lockup, fourth lockup. The only time you can get lockup in first is by pulling the shift selector down into 1st. Good Luck, TomC
wow 701 veiws guess it is a good subject 2 talk about!
hi
JohnJem,
Hi back atcha. It was a great post, really.
There is something missing here, though. There was a post, including pics and detailed instructions, relating to "forcing" the trans to "stay in lock-up" even below 15 MPH. This would seem to allow the Knut that was picking his way down a really winding steep hill the ability to keep his Jake engaged. It involved putting in a copper hyd line and a couple fittings. It got rave reviews at the time. I hope that data gets added to this as it would make an already outstanding thread even better.
Thanks for the memories,
John
John,
Here is my information on what I did when I had an Allison in my bus:
http://home.earthlink.net/~diehls0792/HT754TorqueConverterLockup.html
It worked awesome!
Of course, I now have an Eaton Autoshift and can keep it in any gear I want. The above allowed me to accomplish the same with the automatic.
Any reason that wouldn't work on a V730?
Brian,
That is the mod I was referring to and everyone else thought it was a SUPER good mod. I first saw it posted by another Knut cause I remember the pic of the copper tube was from directly under it and it traveled diagonally across the pic. Maybe you invented it first!!!!! No matter, it is an idea whose time has come.
Thank you for sharing that,
John