Hey everyone, 

 

I have been playing with my 47re with my pacbrake. I'm starting to wonder what is a good healthy line pressure when engine braking. 

 

Right now I'm seeing 80-85psi at idle in drive, and driving down the road were about 110 with my foot out of the throttle. In the throttle I'm seeing about 125psi. 

 

When I'm engine braking I see about 115psi going from 2,000 to 1,250rpm.

 

When I'm downshifting and in 3rd, I can move it to M2 and it will downshift at 32.5mph 1,250rpm. 

 

I have a lower stall torque converter and it seems to brake hard even on second.  I was looking to see having the TC lock up when downshifting in second, but dynamic supposedly built it to do that, but so far the pacbrake hasn't done it.

 

That's another issue I need to deal with. 

 

Any advice or input here, @Doubletrouble

I have a @Dynamicbuilt trans and a Pac PXRB and do get engine braking in 2ed but it turns off with slow speed and low RPM and not very useful.  I've never tested my line pressure with the exhaust brake on, but I know the line pressure is similar to yours going down the road.   

 Unfortunately I don't have much experience with automatic transmissions or pacbrakes on these trucks, sorry.

1 hour ago, IBMobile said:

I have a @Dynamicbuilt trans and a Pac PXRB and do get engine braking in 2ed but it turns off with slow speed and low RPM and not very useful.  I've never tested my line pressure with the exhaust brake on, but I know the line pressure is similar to yours going down the road.   

I guess that is a good thing to know. Would you consider running a gauge off the middle test port and letting me know what your seeing with the pack brake on, and off?

 

When you downshift into 2nd you don't get much holding pressure? Is that locked or unlocked?

 

Mine is unlocked and it seems to have good holding pressure.

Edited August 15, 20222 yr by pepsi71ocean

1 hour ago, pepsi71ocean said:

Would you consider running a gauge off the middle test port and letting me know what your seeing with the pack brake on, and off?

Yes, but it may be a while before I can get to it.

 

1 hour ago, pepsi71ocean said:

When you downshift into 2nd you don't get much holding pressure? Is that locked or unlocked?

 Not sure.  I drop it in to second when I'm below 40MPH and the brake turns off quickly after that.

7 hours ago, IBMobile said:

Yes, but it may be a while before I can get to it.

 

That would be great. I want to put together an article about this.

 

7 hours ago, IBMobile said:

 Not sure.  I drop it in to second when I'm below 40MPH and the brake turns off quickly after that.

 

Do you know by any chance what the speed is that your truck down shifts into second at if you put it in manual too at 40 miles an hour?

 

My other question is do you know if you have a slow stall speed converter or is yours a stock stall speed converter?

 

See I think the stall speed on the converter being lower on mine might be why mine engine brakes so hard even when the transmission is not locked up. But I could be wrong.

 

 

Found this list of line pressures when the transmission was first installed after Dynamic rebuilt it.

 

Line pressure, transmission in drive:  no throttle stopped   85 PSI       

                                                          light throttle  2ed gear 105 PSI

                                                          light throttle  3ed gear  110 PSI

                                                          light throttle  4th gear   120 PSI @ 2200 RPM

                                                          W/O throttle  1-2 shift   180 PSI @ 2800 RPM

                                                          W/O throttle  2-3 shift   175 PSI @ 3100 RPM 

                                                          W/O throttle  3-4 shift   150 PSI  

                                                          W/O throttle  4-3 shift  150 PSI  

                                                          100% throttle 4th gear TCC locked @ 70 MPH 160 PSI

                                                          0% throttle 3ed or 4th gear TCC locked down hill slowing 100PSI

                                                          reverse gear stall test 330 PSI

1 hour ago, pepsi71ocean said:

Do you know by any chance what the speed is that your truck down shifts into second at if you put it in manual too at 40 miles an hour?

When the E brake is on, and the transmission is in 4th it will not down shift until truck is stopped unless I manually downshift.  When the transmission is manually downshifted the E brake kicks off and will reengage if throttle is applied.

 

1 hour ago, pepsi71ocean said:

My other question is do you know if you have a slow stall speed converter or is yours a stock stall speed converter?

It is a low stall speed, about 800RPM.

My E brake shuts off at 1,000 rpms. I’d have to double check the speed. If memory serves me correctly I can manually grab second gear and the E brake will remain engaged till 1,000 rpms. I’ll  double check all that today on my way home from work. I’ve just got Dynamics valves body. I have a billit converter that came with the truck so I have no specs on it. 
 Ok. 3rd gear locked the  E brake disengages at  30 mph.  Second gear locked is 18mph. The rpm on both is 1000.  While it’s still in 3rd locked I have to manually downshift to second before it disengages otherwise it won’t stay locked and engaged  in second. 
I hope that makes sense. 😆 

Edited August 16, 20222 yr by Threadzy
Tested exhaust break in second gear.

What I would like to do is use the momentary switch, that is on my shifter, to engage the EB when the Pac Brake controller won't let it.  I think I can wire it so the solenoid will put air to the piston but lock up of the convertor may be a problem.  I tried running the EB with my mystery switch set up and the convertor would not unlock on command unless the engine was shut off and restarted.

Well I made it to Florida with the truck. Of course when I was 15 mins away from the house in Florida I lost manual 2nd with the engine brake on. It still shifts fine however. 

 

I think maybe the fluid was really hot, or maybe low. I'll check it out in a day or so. But I bet now blow something out.

Keep me posted...

 

Well everyone I checked the fluids cold, and later hot. I took it for a spin and it shifted just fine with the engine brake on. 

 

I also discovered that the pacbrake locks the torque converter in manual 2nd and when I'm driving with it I can keep it locked up. Very bizarre behavior, as I did not expect the torque converter to be locked and second gear. However during road testing today I did confirm this. Even with the current load it seems to be breaking so quickly.

 

I suspect that the gearing in the truck means that even at the truck's current combined load of 18,400 lbs it is still not enough weight to determine whether or not second gear is required when breaking. But the truck will if you keep it in manual 2nd it will stay locked. 2,000 rpms on the tack at 30 mph. You can tell it's locked based on the rpms not jumping at all between braking and accelerating.

 

I suspect the is the possibility that I was charging the intersection when I was breaking at the very tail end of the drive, maybe because I was rushing caused the truck to not want to shift fast enough? I'm at a loss of words here. I know charging intersections with an engine brake is not recommended. 

 

However over 2 hours of testing today have not shown the same symptoms at all. The only thing that needs to be addressed right now is the fact that the trans temperature gauge is not reading at all. 

 

I'm doing a PM tomorrow to check the other fluids before heading home. I did shoot some video porn for y'all! I'm going to upload it as we speak. 

 

VIDEOS 

 

Here is a video of about 30% throttle, which is fairly aggressive for acceleration in my truck.

 

https://youtube.com/shorts/tDB2zxEWBgw?feature=share

 

 

Here is a video of 50-60% throttle unloaded

https://youtube.com/shorts/cIz5JmQW5-k?feature=share

 

Here is engine braking into 2nd gear

 

https://youtube.com/shorts/m9hhUEduo88?feature=share

 

Here is the 2nd gear lock up that I was talking about.

 

https://youtube.com/shorts/arSP-41cf4g?feature=share

 

Here is a loaded acceleration video of the trick at 18,400lbs

 

https://youtube.com/shorts/rS90zobfgpQ?feature=share

 

Here is a 5% grade going over the twin span.

 

https://youtube.com/shorts/hh_bB723BQg?feature=share

 

 

 

 

Edited August 21, 20222 yr by pepsi71ocean

She’s ripping it up that grade!  

Finally had time to install a pressure gauge to the transmission and check line pressure with E-brake function.  It didn't matter what gear the transmission was in, or the speed the truck was going, line pressure was always 100psi with the E-brake engaged or not when decelerating.  I even had it locked up in 1st gear.  Second gear is a bit tricky because sometimes the E-brake would come on and other it would not engage or lockup; this is why I want to put a "command on" switch in the system.   

At idle, Line pressure @ 81°F was 90PSI and @190°F was 80PSI.

All pressures were reduced by 10PSI when operating temperature was reached.

Edited August 22, 20222 yr by IBMobile

On 8/21/2022 at 6:56 PM, IBMobile said:

Finally had time to install a pressure gauge to the transmission and check line pressure with E-brake function.  It didn't matter what gear the transmission was in, or the speed the truck was going, line pressure was always 100psi with the E-brake engaged or not when decelerating.  I even had it locked up in 1st gear.  Second gear is a bit tricky because sometimes the E-brake would come on and other it would not engage or lockup; this is why I want to put a "command on" switch in the system.   

At idle, Line pressure @ 81°F was 90PSI and @190°F was 80PSI.

All pressures were reduced by 10PSI when operating temperature was reached.

 

This mirrors what I am finding on line pressures. I'm seeing 110 going down hill at idle, but in running about 90 hot. 

Based on the ATSG specs on line pressure:

unmodified valve body of course

line pressure in drive with gauge in the accumulator (middle) port at idle should be 54-60 and stall 90-96.
 

I can’t comment on stall psi but my idle psi is about 85psi at ambient temp of about 80 or 85 with the shift kit installed by the transmission shop. I also don’t have an exhaust brake just trying to help.

 

i think the lower pressure at operating temp is due to the fluid expanding and thus becoming “thinner”

On 9/18/2022 at 9:57 AM, 2000Ram2500 said:

 

i think the lower pressure at operating temp is due to the fluid expanding and thus becoming “thinner”

 

One of the weird things about automatics. They run a super thin fluid and expected to lube, cool, and be a hydraulic fluid for handling bands and clutches. I know some others have experimented with using tractor hydraulic fluids to better lifespan for performance reasons. I've seen several dump the ATF+4 and use tractor fluids. Again this will only work with modified transmissions. Don't take this as a working solution but I've seen people looking for fluids that don't thin as much with working temperatures under heavy stress. 

 

Side note (all manual transmissions) this is why I dropped the factory 75w-85 transmission fluid (actually 10w-30 engine oil for viscosity) in NV4500 in Beast and switch to 50 SAE Trans Fluid its actually 90 weight gear lube GL-4 rated. Same reason I don't want to have it thinning out under heavy loads. Another reason I'll be dumping the ATF+4 out of Thor (G56 Trans) and reloading with 50 SAE trans fluid. Better cling to the gears and bearings and doesn't thin out under heat of heavy stress.

 

Just looked up the viscosity of ATF+4...

 

Quote

Properties and Specifications ; Kinematic Viscosity @ 100 C (212*F), mm2/s, ASTM D445. 7.5 ; Kinematic Viscosity @ 40 C (104*F), mm2/s, ASTM D445. 34.4 ; Pour Point, °C, ASTM D97.

Which is like like so thin... Look below at 40*C is 34.4 which is like 15W engine oil, then at full temp 100*C it falls off the scale at 7.5. 

Edited September 20, 20222 yr by Mopar1973Man

5 hours ago, Mopar1973Man said:

 

One of the weird things about automatics. They run a super thin fluid and expected to lube, cool, and be a hydraulic fluid for handling bands and clutches. I know some others have experimented with using tractor hydraulic fluids to better lifespan for performance reasons. I've seen several dump the ATF+4 and use tractor fluids. Again this will only work with modified transmissions. Don't take this as a working solution but I've seen people looking for fluids that don't thin as much with working temperatures under heavy stress. 

 

Side note (all manual transmissions) this is why I dropped the factory 75w-85 transmission fluid (actually 10w-30 engine oil for viscosity) in NV4500 in Beast and switch to 50 SAE Trans Fluid its actually 90 weight gear lube GL-4 rated. Same reason I don't want to have it thinning out under heavy loads. Another reason I'll be dumping the ATF+4 out of Thor (G56 Trans) and reloading with 50 SAE trans fluid. Better cling to the gears and bearings and doesn't thin out under heat of heavy stress.

 

I’m agreeing with what your saying

 

I tried telling a dealership mechanic about how gear oil and engine oil are weighed on different scales etc.. as a parts guy working in the same store as him so he already knows me… and it was like talking to a wall.

 

Nobody seems to understand the science here

 

i tried to tell him that at a certain temperature a 10w engine oil and a 75w gear oil are gonna behave the same (not knowing the exact science or numbers I tried to generalize for him) and he all but laughed me out of the room because sure gear oil is like honey and engine oil is like water by comparison.

 

So I don’t blame someone at the surface but an axle will see high temperatures and pressures as the bearings squeezing the fluid out. I think there’s a lot involved in the additives that isn’t necessarily broadcasted to the public that may help the thinner fluids stick to parts much like the thicker fluids do naturally.

 

I’ll have to double check myself at work but I’m pretty sure mopar superseded the G56 fluid to ATF+4 a while back. That’s when I got the lecture from the BG chemicals guy about how fluid viscosities aren’t measured the same as what they seem to imply with the obvious thickness of gear oil and kinda scary lack of thickness in ATF. 

Edited September 21, 20222 yr by 2000Ram2500
Below post

31 minutes ago, 2000Ram2500 said:

I tried telling a dealership mechanic about how gear oil and engine oil are weighed on different scales etc.. as a parts guy working in the same store as him so he already knows me… and it was like talking to a wall. Nobody understands this

 

You might want to look back at my post I did look up the viscosity of ATF+4 and its thinner than you think. I was editing my post to add this information. Yes I do understand the viscosity differences between gear oil and crankcase oils. Still in all I do understand that thinner oils do create less drag but do they cling to parts under stress and protect at extreme loads and highway speeds or are they just slung off the parts from centrifugal forces? Like when I look back towards true racing they use some seriously thick fluids to keep everything lubed up. Just food for thoughts... 

Edited September 20, 20222 yr by Mopar1973Man

4 hours ago, Mopar1973Man said:

 

You might want to look back at my post I did look up the viscosity of ATF+4 and its thinner than you think. I was editing my post to add this information. Yes I do understand the viscosity differences between gear oil and crankcase oils. Still in all I do understand that thinner oils do create less drag but do they cling to parts under stress and protect at extreme loads and highway speeds or are they just slung off the parts from centrifugal forces? Like when I look back towards true racing they use some seriously thick fluids to keep everything lubed up. Just food for thoughts... 

I edited mine also.