Engine/Transmission (1994 - 1998) governor pressure affected by kickdown?

["Mad Max"]

Howdy folks -



I have a '93 Ramcharger 4x4 that I've converted to diesel using a '91 6BT and a '95 47RH (and a 241, D60/D70). Lock-up and overdrive are controlled via a pair of adjustable hobbs switches plumbed into the governor port on the 47RH.



At speed/pressure 'x' the respective switches close, completing the ground circuit, activating the lock-up and overdrive. I also have switches in the cab to disable the curcuit in case I want to prolong the particular gear. It actually works pretty well..... so long as I don't completely lift off the throttle. Therein lies my problem -



Upon a normal acceleration run, 1-2-3 is perfect, then at ~35 mph the lock-up engages, and then at ~45 mph the overdrive engages. Works great and propells my Ramcharger right on down the road.



-- BUT --



... . if, while cruising along at 60 mph or so... (any speed with both l. u. and od engaged) if I lift all the way off the throttle, the overdrive (and maybe the lock-up as well - hard to tell exactly) - one or both of them disengage..... and then if I get back into the throttle one or both re-engage per normal.



Now... the hobbs switches are activated via governor port pressure which... I thought... was only dictated by vehicle speed, not the kickdown linkage system. But because of how the thing is acting, my question is, is governor line pressure affected in any way by the kickdown linkage system?



Sorry for the long discussion but I felt I had to explain the system as it is set up in order to ask the question.



Any help regarding this kickdown -vs- governor pressure issue would be hugely appreciated.



- Sam

 

[cerberusiam]

Pretty much, you got it. The amount of gov pressure available is controlled by TV pressure which is a direct result of throttle position.



The amount of gov pressure that is seen in the circuit and ultimately the VB is a function of output shaft speed on an RH. RE's use wheel speed and electronically set the gov pressure, an RH has a governor in the output shaft that controls the pressure by rotation. Drop the amount of pressure available and the amount registered also drops. Works fine in gears 1-3 but there are others things in place to make the shifts a bit more predictable.



You now know why OD and lockup has always been under computer control in these transmissions. The Hobbs switches work great in normal acceleration modes but lack adjustability and intelligence to compensate for lots of pedal movement at other times.

 

["Mad Max"]

thanks Alan, that's what I was afraid of. But still... I know there is a way to do this fully 'automatically' (har har) without the use of the near-extinct factory computer. I'm going to find it - a way to use 'speed' - speedometer signal for example, to control the transmission. Apparantly the hobbs switch is not the ideal answer.



Lemme ask another question here: The lock-up and overdrive system(s) - can the kickown system be 'bypassed' where l. u. and od control are concerned yet still be functional for throttle kickdown and down/up-shifting?



I'm looking at aftermarket speedometer signal generators (Autometer, etc), and speed 'switches' - a adjustable/programable switch that will actuate on or off based on speedo signal input.



I know there's a way... and I haven't found it yet... but I will.



- Sam

 

[chipster]

I had the same problem with my 47rh set up. I used adjustable hobbs switches, and when I lowered the lock-up pressure to lock-up at 28 mph, and raised the O/D pressure to engauge at 55 MPH, the problem went away. I found some adjustable pressure switches at McMaster Carr that have a differential on and off setting. they turn on at a set ( adjustable) pressure and turn off at a lower pressure,a percentage of the set pressure (I think it was 15% lower, but not sure) I think they would be better than the hobbs that turn on at a set pressure and off when the pressure gets lower than the set pressure. I just have not got arround to getting a set yet. I really liked the feel when the lock-up was at 38 MPH and O/D was at 55Mph, but did NOT like the feel of what unlocked when I lifted all the way off the throttle. some A/C pressure diffenteral switches would work if you can find them to turn on at a pressure to suit you. a GM switch turns on at 45 lbs and off at 22 lbs. if you can check your line pressures as the speed increases,and what the pressure drops to when you lift all the way off the throttle, you will have a better idea of what switch you would need to turn on and off the lock-up and O/D.

 

[cerberusiam]

Like chipster said, different differential switches set to what your prssures are doing would work. You just have to track whats going on under all the driving conditions and build accordingly.



ATS has the box they call the commander but not sure it controls OD, just lockup off a VSS signal. With a VB that has not been modified the Hobbs switch to get to OD and then another box for lockup will work also. The 47RH will upshift locked but unless you change the VB it won't downshift. As long as the TC is locked up it will stay in OD.



At one time I think Art Carr had a box capable of some of these functions also. The electronics to do it is really simple, getting them to work together with some logic around it is where it takes time to develop solution.



To have a controller that has enough brains to say speed is 70 mph and you went WOT throttle, hold OD and lockup or even drop lockup but hold OD, or, speed is 55 mph you went WOT throttle and I need to down shift to drive and lockup again is what is needed. Thats all logic that has to be loaded into a controller. You cannot simulate that with a series of switches and make it seamless.



Now, if you wanted to go to an RE unit both ATS and Suncoast have fully programmable stand alone controllers that allow this to happen AND you can customize it to your liking. Any more, its easier to RE solutions because they were a longer lived unit. The 46, 47, and 48RE were used across a broad line of vehicles in a lot of years and they all function the same way.

 

["Mad Max"]

- hey have a look at the 'easy adjust high-pressure switches'; NEMA-1, #3427K2 - that might be the proper one(s) to use, one-each for l. u. and o-d, eh?



McMaster-Carr



- Sam