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Jake Brake or Transmission Retarder, or Both
11-18-2014, 15:56
Post: #1
Jake Brake or Transmission Retarder, or Both
Now that I have 6K miles on my bus, I am a retarder convert. I was of the other camp having put many miles on my Jake Brake equipped Blue Bird. Both are excellent and both would be nice to have. Each has its advantages, but who can argue with 600hp of braking power at your fingertips. I think the manufacturers have the heat thing pretty well sorted. Transynd is up to the challenge as is the generous transmission cooler that Prevost installs. The trick is to descend the long grades a little slower than you otherwise would with a Jake. It's important on long grades to keep the speeds such that the heat generated by the transmission is being fully sunk by the cooler and radiator, an equilibrium needs to be met and an equilibrium is possible. But, for those moments as you describe, the full 600hp of braking can instantly be applied. In these cases, transient heat sink in excess of the coolant system's capability can be accommodated.

I often noticed in my BB how full Jake power resulted in about 15 to 20 psi of turbo boost. That extra intake charge compression gives us the full 350hp of Jake Brake power capability. I had my preselect moved from 4 to 5 because of what I considered engine over-revving. I'd commonly see in excess of 2350rpm on the tach during downshift to 4th and under full Jake Brake power. The DD S60 no load max rpm is 2225 and full Jake is hardly a no load condition.

david brady,
'02 Wanderlodge LXi 'Smokey' (Sold),
'04 Prevost H3 Vantare 'SpongeBob'

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11-29-2014, 10:51
Post: #2
RE: Jake Brake or Transmission Retarder, or Both
David,
We had an 04 Foretravel U320 with the transmission retarder and in my opinion that was the best feature of that coach. Before the Foretravel we had a 03 Country Coach Intrigue with a Jake brake. I felt the transmission retarder did a better job of slowing the coach down versus the Jake brake.
Reese



Now that I have 6K miles on my bus, I am a retarder convert. I was of the other camp having put many miles on my Jake Brake equipped Blue Bird. Both are excellent and both would be nice to have. Each has its advantages, but who can argue with 600hp of braking power at your fingertips. I think the manufacturers have the heat thing pretty well sorted. Transynd is up to the challenge as is the generous transmission cooler that Prevost installs. The trick is to descend the long grades a little slower than you otherwise would with a Jake. It's important on long grades to keep the speeds such that the heat generated by the transmission is being fully sunk by the cooler and radiator, an equilibrium needs to be met and an equilibrium is possible. But, for those moments as you describe, the full 600hp of braking can instantly be applied. In these cases, transient heat sink in excess of the coolant system's capability can be accommodated.

I often noticed in my BB how full Jake power resulted in about 15 to 20 psi of turbo boost. That extra intake charge compression gives us the full 350hp of Jake Brake power capability. I had my preselect moved from 4 to 5 because of what I considered engine over-revving. I'd commonly see in excess of 2350rpm on the tach during downshift to 4th and under full Jake Brake power. The DD S60 no load max rpm is 2225 and full Jake is hardly a no load condition.
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01-07-2016, 21:06
Post: #3
RE: Jake Brake or Transmission Retarder, or Both
Ernie,

Heat is definitely an issue with the retarder. My H3 has a huge transmission cooler plumbed just upstream of the S60 water pump. With the retarder on, when the transmission fluid hits around 230 deg F the S60 radiator fan comes on which gives the system a lot of head room to absorb additional heat. I can say I Death Valley tested the system on my way home from Kamloops CN. I entered Death Valley on the west end and descended from 8500 ft to -200ft below sea level in about 3 miles and in 100+ deg F ambient temperature. It was a challenge to keep the transmission fluid below 250 deg F which is the point at which the Allison will throw a code. At one point I had to pull off the road to let things cool down. So, you do have to watch the temps on long steep descents.

david brady,
'02 Wanderlodge LXi 'Smokey' (Sold),
'04 Prevost H3 Vantare 'SpongeBob'

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01-08-2016, 09:14
Post: #4
RE: Jake Brake or Transmission Retarder, or Both
Thanks David. I had a transmission retarder on my 88 Wanderlodge. I could really see the temps rising and made sure it did not overheat.

Ernie Ekberg
97 Liberty Classic
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01-08-2016, 13:16
Post: #5
RE: Jake Brake or Transmission Retarder, or Both
Ernie,

Having had the three stage jake on my LXi and having only the retarder on my H3 I can say that you can descend faster with the Jake. With the retarder I need to keep my speeds down below what I normally would in my LXi to achieve a balance between heat generated by the retarder and that rejected by the cooling system. As you know, the heat flow needs to be in equilibrium or else temperatures will climb.

The nice thing about the retarder is that it puts out more stopping power and it'll produce that stopping power all the way to virtually a standstill whereas on the LXi the jake would disengage at 15mph or so. Also the six stage retarder on my H3 works in conjunction with the brake pedal. The harder I push on the pedal the more retarder stopping power dialed in. It's a wonderful system, especially for stop and go traffic or around town. Truthfully, I'd like to have both the jake and the retarder. I can't do without my retarder; it's that good on the Prevost, but for long, long 6% descents on a hot day you can't beat the jake and the jake will get you down 5 to 10 mph faster.

david brady,
'02 Wanderlodge LXi 'Smokey' (Sold),
'04 Prevost H3 Vantare 'SpongeBob'

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01-08-2016, 17:22
Post: #6
RE: Jake Brake or Transmission Retarder, or Both
The 3 stage Jake on my previous Wanderlodge LXi worked beautifully to slow the coach and it was so dependable on downgrades. I found the 2 stage Jake on my Prevost Marathon not quite up to the performance level of my LXi's Jake. So I had it and the S60's valves adjusted which did improve its performance but not that much.

Now I don't know exactly what the difference is between the two Jakes. Theoretically, given that both bus's weight and gearing is similar they should slow the bus speed in a similar fashion but I believe the LXi's Jake did it more quickly at stage 3 or full on. The full on stage 2 Jake on my Marathon's performance is similar to the stage 2 (4 cylinder) performance of the LXi's 3 stage Jake. This makes me wonder if the 2 stage Jake on my Prevost when set full on is only working on 4 cylinders of the S60.

Does anyone know if a 2 stage Jake at full on operates on all 6 of the S60's cylinders or only on 4 cylinders?

Regarding the comparison between a Jake or a trans retarder, I have driven Prevosts with both and I like the Jake best. That could be because I've had a lot of experience driving busses with Jakes and not mush driving busses with trans retarders.

Truth is both braking systems if used improperly by the driver can result in overheating. That being the chassis brakes on a bus equipped with an engine Jake brake or overheating of the transmission fluid on a bus equipped with a transmission retarder. Both work well if operated properly by the driver.


Chuck & Tela Millsap
Arizona
2003 Marathon XLII S/S
2000 Wanderlodge LXi S/S
2004 Wanderlodge M380 D/S
2000 Wanderlodge LXi N
/S
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01-08-2016, 19:12 (This post was last modified: 01-08-2016 19:42 by davidbrady.)
Post: #7
RE: Jake Brake or Transmission Retarder, or Both
I can't say for certain how your bus is setup Chuck, but the owner's manual for the 2002 XLII says:

Press down rocker switch to the first position to actuate system to 2/3 engine brake and press to the second position for a full application of engine brake. Refer to "Other Features" chapter 4.

It seems to imply the first position uses 4 cylinders and the second uses 6.

Attached is a trouble shooting guide from the Jacobs Brake website:

BTW for those of us with retarders, the folks at Prevost Service in Richmond BC told me if the Transynd reaches 300 deg F the fluid is toast and should be changed. As long as the Allison isn't throwing a temperature code, you're okay. Like I said, mine throws a code at 250 deg F. My bus doesn't have an individual dash mounted transmission temperature gauge but there is an electronic gauge in the Message Center Display (MCD, which is the graphical display that reads DDEC info across the CANBus). There's a gauge mode which displays battery voltage, engine oil temperature, and transmission fluid temperature.
─░mage

The combined automatic retarder action with service brake application is something to be relished. It's like driving a car with a brake servo-booster versus one without. They feel like power brakes. Smile


Attached File(s)
.pdf  Jake Brake Troubleshooting Guide.pdf (Size: 4 MB / Downloads: 2)

david brady,
'02 Wanderlodge LXi 'Smokey' (Sold),
'04 Prevost H3 Vantare 'SpongeBob'

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01-08-2016, 20:33
Post: #8
RE: Jake Brake or Transmission Retarder, or Both
it sounds like what I have been doing with the bird will mirror what I need to do with the Prevost.

Ernie Ekberg
97 Liberty Classic
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