New Crown

[rdt9910]

Thanks. I spent some time reading through a lot of the posts regarding crowns before I even bought the bus. Getting it home was an adventure. I still need some practice driving it, especially downshifting. I find myself having to come complete stops to get going again. Any tips in that area would be appreciated.

I did read through your conversion as well a bit back and certainly like the progress you made. Although, some of this bus is coverted, it is likely going to be a gut job, but it has good bones and should make a great starting point.

And any help with manuals is greatly appreciated. Thanks for reaching out.

[Tejon7]

I also need more practice driving and downshifting, so I'm not the best person to be offering advice. This is the internet, though, so I won't let that stop me Any critiques from the pros are welcome and maybe will help us both out.

I've found that float shifting is generally easier than double clutching. As mentioned earlier, a light touch on the shifter is all it takes - if the RPMs are correct for your speed, it'll drop easily into gear. Going up through the gears, float shifting seems like it's always the way to go (at least in my bus). I also find float shifting down through the upper 5 speeds to be fairly straightforward.

Where double clutching really helps me is downshifting in the lower 5 speeds. This only happens in city driving. I normally start out in 3rd gear from a stop, so I'm only in the lower 5 at very slow speeds. Maybe it's my imagination, or maybe I just need more city driving practice, but it seems like my bus only likes to downshift into 5th or 4th if I double clutch. Double clutching or not, the RPMs still need to be pretty close to correct for it to side into gear. That means after clutching out of the higher gear, bump the accelerator to get RPMs back up before clutching into the lower gear.

After struggling through my first day of driving, I did some math to figure out what speeds the bus liked for each gear. If you figure out your gear ratios, axle ratio, and tire diameter, you can make a chart of road speed vs engine RPM for each gear. This was really helpful for me to get a general idea of what gear I should be in at a given speed. A table full of numbers didn't make me a good driver, but it helped me understand my bus a little better.

It seemed like my bus likes to shift somewhere around 1700 and 2200 RPM (though my tach is fritzy, so that's just my best guess). Using those two values and the stuff I mentioned above, I came up with the following speeds:

3rd gear: 8-11 MPH
4th gear: 11-15 MPH
5th gear: 14-19 MPH
6th gear: 18-24 MPH
7th gear: 24-31 MPH
8th gear: 31-40 MPH
9th gear: 40-52 MPH
10th gear: 51-67 MPH

I never bothered putting in 1st or 2nd gear because they're just for creeping along. These numbers won't be the same for you, but I'm guessing they're pretty close. For reference, my transmission is an RT11610, my rear tires are 41.6" diameter, and my rear differential is 4.10:1.

PS thanks for the pics - she's a beaut! Somebody put a good deal of work into that partial conversion, but I would also want to start from scratch.

[rossvtaylor]

That, Tejon7, is spot on and mirrors my experience in a not-Crown bus (a similar, but not-Crown... Gillig). Mine also has a 10-speed, which I love. And like you said, I generally start in 3rd. 1st is way too low to start, for general driving. And, like you, I prefer to float the gears. Upshifting, I float them all. Downshifting, as you mentioned, works well in the upper half. I'm not adding anything new, but hopefully reinforcing your observations with mine.


The only downside of floating the gears is that you can't do it during your CDL road test. Other that that, as long as you're not mashing and grinding, it's the way to go. Two fingers, match the speed to the RPMs, and it'll slide right into gear.


Since our Gillig has a Cat, which revs up and down more quickly than our Detroits do, I do have be be pretty quick and light on the pedal when I downshift. I ground a lot of metal, I'm sure, while learning...

[Tejon7]

That's reassuring to hear that your experience is similar. I was half expecting the next reply to be something like "NEVER float gears! ALWAYS start in first! You're destroying your transmission!"

Maybe that reply is still coming...

Here's a question that hopefully isn't hijacking the OP's thread too much - should you always downshift through all the gears? I remember reading that it's safer to always have the transmission in gear, which makes sense in case your brakes give out. A hay truck driver I asked about this scoffed at that idea. According to him, if you're coming up to a stop sign, it's ok to pop it into neutral and just use the brakes to slow down. His argument was that downshifting to a full stop every time is unnecessary wear on the transmission.

[Tejon7]

Oh, and back to the question of equipment manuals. For everything but the engine, I've been finding that many parts still have freely available maintenance and service manuals floating around the internet. If you climb around under your bus for a while scrubbing off grime, you'll likely find a little metal embossed ID tag on almost every part. Type the model number into AskJeeves or Netscape or Bing or whatever the kids are using these days, and voila! Manuals aplenty.

[rossvtaylor]

Originally Posted by Tejon7

Here's a question that hopefully isn't hijacking the OP's thread too much - should you always downshift through all the gears? I remember reading that it's safer to always have the transmission in gear, which makes sense in case your brakes give out. A hay truck driver I asked about this scoffed at that idea. According to him, if you're coming up to a stop sign, it's ok to pop it into neutral and just use the brakes to slow down. His argument was that downshifting to a full stop every time is unnecessary wear on the transmission.

You are correct, it's safer to have the vehicle in gear. In fact, in Arizona at least, it's illegal to coast down a hill in neutral (or with the clutch disengaged, in a commercial vehicle).

[Tejon7]

Ah, now I remember where I read that about always staying in gear... The CDL manual!

I'm guessing the fellow I talked to got complacent after driving hay bales on country roads in the middle of nowhere.

[Ronnie]

I do remember when I used to drive Dad's truck with a 10 speed we started in 3rd when empty and on the flat. As far as shifting down in each gear often not slow down to idle in top gear then let the brakes do the rest. Now if the stop is planned versus a stoplight changing and you have time to go down through the gears it is a gentle and nice way to stop. I do it in my bus coming off exit ramps. My bus has a 5 trans and two speed rear. Normal driving is just the main with the rear staying in high. Heavy towing then split shifting.

[wireguy]

If you want to learn about 2 stroke Detroit diesels follow THE BUS GREASE MONKEY on youtube. All he works on is Detroit diesels mostly in the old Greyhound buses.

[oberrw]

Look-up the Facebook group "Crown Coach Junkies".

Randy Ober

Originally Posted by rdt9910

Hello -
I just recently picked up a 1990 Crown Super Coach and have some initial questions regarding the Detroit 6-71T.

First where would be the best place to pick up service manuals for this particular bus? Not finding a whole lot online.

Secondly, I was told this particular bus doesn't have a governor. Not sure if that's by design or failure but how could I verify/fix this issue. I am new to driving the 10 speed and I am afraid of over revving this thing if I haven't already.

Can anyone suggest a fair/honest Detroit mechanic in the Billings area?

[flattracker]

Welcome to the club!
I have two Crowns myself. The "old Crown" is a 35 foot version with a Detroit 671 turbo and an Alison trans. The "new Crown" has a Cummins big Cam I 400 upgraded to a III, with an Alison trans also. I had the gear ratio changed in the new Crown for better cruise speed.

Crown used truck parts for their chassis, so those won't be super rare.
The bus kid used to post some Crown manual pages in the net. Search her out.
I didn't see enough details about your layout to see how the conversion was done. I could give you some ideas though. One tip though, don't block the over engine cover in the middle of your bus as some engine parts are accessed through there.
Also use straight 40 wt oil in your engine. Please give some more info about your Crown.