Transmission temperature with retarder

[jack14r]

I have recently made two round trips to Asheville,NC and returning from Asheville I must descend Black Mountain.I know that it is nothing like the grades out west but it is about as big as we have in the east.The grade is as much as 6% and it is 6 miles long.My coach weighs 53,800 and I was towing a 4 door Chevrolet truck with a golf cart in the bed and I would estimate my total just above 60,000.On the first trip the outside temperature was 70 degrees and the transmission temp started at 196 and ended up at 213 degrees,the second trip the outside temp was 62 and the transmission started at 193 and ended at 206.I used the 4,5,6 positions on the retarder mostly with the speed between 35-50MPH depending on the curves,I never touched the brakes going down the mountain and I could always decelerate with the retarder if I wanted to.I am impressed with the small rise in temp and the dramatic breaking ability.Some have said that they would not want the retarder because of the temp rise,I would say that I want the retarder because it is effective in controlling speed.

[Kevin Erion]

Jack,
I agree that the retarder does a good job controlling speed. My problem was in the summer, outside temps near or above 100 degrees and I would see 215-220 very quickly and I didn't like that high heat. I did have transynd fluid and I would change it way to often but it still bothered me.
FYI, I have an 07 4 door GMC 8' bed PU and I weighted it with nothing in the bed, a little over 7000lbs.

[Pete]

Jack, do you run synthetic or regular transmission fluid?

[dalej]

Good post Jack!

Did you happen to remember the climb? with that much weight, how does your bus preform going up the same hill?

[jack14r]

I do have transend synthetic fluid in the transmission.On the climb I started out at 65 or so but I was down to 37 at the top.

[Gary & Peggy Stevens]

Even though I don't have the transmission retarder, I have a Jake brake, I have always been a big fan of the retarder over the Jake. But that is just me. ;)

What should the high end limit temperature be in the transmission? And for how long?

I would think if a 213 degree temp was met and even maintained for say 10-15 minutes, and then the temp lowered after getting down the grade, would it adversly affect anything?


Gary S.

[Jon Wehrenberg]

It sounds like Jack did it right. When we went to Pahrump last spring we encountered hills which were long and steep and that required the retarder.

We were able to negotiate them without using the brakes and we easily managed the temps. I think the outside temps were in the seventies or maybe the low eighties.

I simply geared down, and in my coach forth gear tops out at 55 MPH. So as I approached a steep descent I geared down to about 50 in forth gear, and I used the second retarder position, usually going back and forth between the three lowest positions to hold the speed to just below 55. I was concerned about truckers running up my tail, but that concern was never to happen. The truckers out west were gearing down and holding the speeds to the same ones I was using.

The temps as I recall stayed between about 210 to 220 as best as i could determine on the small analog gauge.

I do know that our coaches have a sensor on the fluid output on the retarder section of the transmission. The set point is 300 as I recall and once the fluid reaches that the retarder is automatically reduced to keep temperatures from exceeding the 300 degree limit. I can find nothing published that indicates the temperature range of Transynd or Dextron III, but my gut tells me that the further we keep our fluid temperatures from the 300 degree limit the longer they will last. One problem with our coaches is that we have no red lines or limit markings on any of our instruments which would be a far simpler way of alerting us to the acceptable range than requiring us to find the limits in owner's manuals (none in my Prevost manual) for the various components such as the engine, transmission, etc.

[Jerry Winchester]

Jon,

Might be a couple of good questions in here for the Allison transmission guy at OKC.

[Jon Wehrenberg]

Jerry, I agree, and similar questions for the Detroit folks.

I have a number of limits I would like to know. The obvious ones are limits for temps on our engine, our transmission and for those with the gauge, differential. We know when our fans kick in, and we know our bus starts to lose power by virtue of DDEC stepping in as temps rise, but what are the limits? What is the normal range?

But how about voltage limits? We discuss voltages in terms of when to charge and battery life, but how low will DDEC allow the voltage to go before it shuts down. Someone in Podunk trying to nurse a coach to a safe spot needs to know at what point the computer just quits.

What about upper voltage limits? Apart from battery life, at what point does the voltage impact the electronics so folks know to shut the engine down and disconnect the failed regulator field wire?

I don't think it is a bad idea for someone to tell us the upper and lower limits for safe operation for air pressure. We know that at some pressure on the low side it's all over because the emergency brakes are going to engage. But what is a safe lower limit for driving? What if my system has a leak and I need to get somewhere safe. If it is capable of holding 75 PSI and I can release my parking brakes am I good to go? What happens if someone turns up the regulator so my air pressure is sufficiently high to raise the front airbags without having to lift the tag axle to get the front up? Is 135 OK? What about 140?

For guys with the 8V92 is there a max pyrometer limit?

Does anyone really know what red line should be for engine RPMs? What if I am in a lower gear on a very steep hill and I let it get up to 2200? Is that OK? What about 2400? 2500?

Does everyone have a 75 MPH speed limit on the tires? How does an owner find out?

There is a correlation between these limits and the life of fluids and components. Not all limits mean you are going to break something, but they may mean you will shorten something's life.

[dalej]

Jon,

Your the answer man.... what's with all the questions! :)

[Jon Wehrenberg]

This is a pop quiz..............close your books and answer the questions above.