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05-12-2009, 15:04

Perhaps someone with an 85 can address specifics about handling the retarder in your year coach. (I have an 'exhaust-based retarder' and it has different issues.)

In general, coming down grade, you do shift down to match your engine to the speed you're traveling -- but the retarder (electric or ??) may have specific instructions. The primary concern is heat build up in the retarder, so watch the appropriate gauges carefully. On the up grade, watch (1) oil temperature and (2) water temperature. If you approach the "red line" with either one, pull off and run at high idle until normal temperatures return (usually about 3 minutes).

Brakes should be used to bring the coach to about 5 mph below your target speed. Then roll under retarder control until your speed increases to the target or slightly above. Then use the service brakes to bring the coach speed bat to about 5 mph below the target speed.

Do keep an eye on the air in the system. If you seem to be running the air down faster than it recovers, then slow way down or stop until the air pressure builds up. (Shifting down should run the compressor faster to recover the air pressure.)

You absolutely do not want to overspeed the engine. Recheck your manual, as different engines have different specs. My S-60 has a 2100 RPM red line under power, but allows a maximum 2400 RPM while traveling under jake brake down grade. If things are getting "close" then use the service brakes.

Note, do not 'pump' the brakes (that just bleeds off excessive air), the brakes are designed to handle controlling the vehicle. The slow below and build up procedure gives time for the brakes to cool (somewhat) between applications.

If it seems like you're building excess speed too quickly, then set your target speed lower.

A rule of thumb is to go down hill at about the same speed you came up the hill. However, it's often OK to go down a little faster than the up hill run, if the highway conditions permit. Keep in mind, not all grades are the same on either side of the hill. Often, (in the western mountains) one side of a pass will have a steeper run than the other. For example, the downgrade from Donner Pass, west to the foot hills is about 40 miles. From Donner Pass, east to the Nevada border is more like 10 miles. The actual grade (e.g. 6%, 7% etc.) is about the same, but the "intensity" and curves are a different experience.

Enjoy your trip.

Pete Masterson

'95 Blue Bird Wanderlodge WBDA 42

El Sobrante CA

"aeonix1@mac.com"

Photos:

http://picasaweb.google.com/Bluebirdzoom/PeteMasterson#

On May 12, 2009, at 7:32 PM, jburgessx2 wrote:

I'm getting ready to take my Bird on a trip from SoCal to Oregon. I haven't really driven hills too much and was looking for some advice on how the coach handles on hills and how to control the speed (if necessary). I have an 85 PT40 with the 6V92 and transmission retarder. Does down shifting help control the speed going down hill without increasing the rpm's too much? Should the retarder be used rather than down shifting?

I really don't want to over rev the engine or stress the retarder too much so I need some tips on how best to control a BB on the hills.

Thanks.

Jerry
85 PT40

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