'04 Report

[GM0406]

Well we put 300 miles on the '04 this weekend.  Although we have had this coach for over 5 years, we haven't used it much.  It spent two years in a repair shop and this run was the first real test run.  She ran fine and well able to run at 70 mph up to 77 mph on the gps.  But get her on any kind of a serious grade and you are down to 35 mph in no time.  And this is the big block engine with a 5" blower intake, 4 valve head and N-65 injectors! 

A little concerned about the ride.  I have realtively new tires and they are at 100 lbs.  Going up 99 from Stockton to Sacramento we hit many nasty bumps courtesy of J Brown construction!!  Please avoid that road until the tire killing, suspension shocking, bumps are fixed.  It is worse than having to drive in the right hand lane on 80!  In Nevada we have seen many "Bump" signs over the years.  We don't pay much attention to them.  But on 99, they mean what they say, every sign!  The sign should read "Dangerous Excessive Tire and Suspension Endangerin Bump"  Anyway, what is the correct ride height for this coach?  I may be too low and if so, could that cause rough ride?  I thought if I kept it a little low, the ride would be softer.

Bill T.  04 & 06 

[Len Silva]

How does the ride compare to your '06?

The ride height should be set by the book, measured from the rubber stop bumpers to the frame.  I don't think messing with the ride height will affect the ride over bumps.

Tire pressures seem a bit high.  You would have to weigh each axle and refer to the tire manufacturer's charts, but I think a typical 4104 conversion, if it is not overly heavy, could run 70 psi in front and maybe 80 in the rear.

That, and good shocks, should get you as good a ride as possible.

[RJ]

Bill -

I agree with you about NB 99 between Stockton & Sac - Ouch!

I'm making a similar run soon, and will be cutting over from 99 to I-5 using Hiway 4 in Stockton, much smoother that way.

I also agree with Len, your front tire pressures may be on the high side.  Run your coach across a set of scales to find out the front/rear axle weights in "ready to run" load, to thus determine the correct tire pressures F/R for the size tire you're running.

The ride height spec is in the Maintenance Manual, but a quick check is from the ground to the top of the bottom step of the entry way, and to the top of the floor of the exterior compartment underneath the driver.  IIRC, this should be 14" when the ride height is adjusted properly.

You may have to readjust the rear, too.

FWIW & HTH. . .

[GM0406]

Thanks for the replies on height and pressure.  I think the '06 would have responded the same to the bumps on 99.  What about 70 in front for both coaches and 90 on the 06 and 80 on the 04?  I got a new air compressor and thought 100 would be good for fuel mileage.  RJ, remember the '06 has an air seat, so I am not a good candidate for how hard the bumps are when driving that coach.  But the grandchildren complained that they were bounced off the floor in the '04 yesterday!! 

We don't use the '04 very much and are still driving on $1.50 fuel waiting for the Odumma inflation to end.  She holds 225 gallons so we haven't been hurrying to the station to fill her up.  If sane times return, we could get back on the road.  The '06 has been used more, and it scared me the other day when it looked like it was down to 1/3 tank.  Filling it cost $130 so it looks like that big engine with the turbo is not as hard on fuel as I thought it was. 

Still trying to get used to these coaches and am quite sensitive to any noise.  We went to Seacliff beach a week ago with the '04 and I really got discouraged when I heard a very bad sound which could best be described as the driveshaft rubbing on something.  I realized that I had the suspension way too high and think the angle of the drive shaft may have been too great.  I have a two speed between the trans and rear end.  Lowering it seems to have gotten rid of the noise.  Bill T. 

[Bill in KS]

Curious about your 2 speed before the rear end.  Is it something you built ?

Thanks
Bill in KS

[TomC]

GM0406-as weird as this may sound and it will sound in reverse-the higher the ride with more air in the air bag, the softer the ride will be (unless it is all the way at the top).  With lots of air in the air bag with it up, you have a bigger cushion of air for the bumps to react against, compared to if the bags are down, then the air cushion is minimal and the bumps will react faster making for a rougher ride.  But-especially on the rear, you should run so the driveshaft is at the correct angle.  I have a transit with a much longer overhang in the back, so I'm alright with my drive angle and my suspension being up higher then normal. I would try raising the front up a bit though.  Good Luck, TomC

[RJ]

Tom -

The 4104 and the 4106, altho both suspended by air, are different.

The '04 originally came from the factory with double-convoluted air bellows utilizing large air chambers, similar to early MCIs and the Scenics.

The '06 is more like your transit, with rolling lobe bellows and no air chambers.

I haven't seen Bill's '04, he'll have to chime in and let us know if his coach still is using the air chambers, or if they've been plated off due to leakage and it now has rolling lobe-style air bags.

Anyway, the point I want to make is that GM spent a LOT of time and engineering on the original air suspension system (it came out on the '04 before they started building transits with this design), and the ride heights specified for the '04 GMC determined to be the best compromise between ride, handling and driveline dependability.

Seven years and 5065 coaches later, with lots of field mileage and experience under their belts, GM switched to the rolling lobe air bellow for the parlor cars, after introducing it on the "Fishbowls" two years earlier.  Much more simple in design and maintenance, without the troublesome leaking air chambers, yet with similar ride characteristics.  (Altho some folk feel the '06 rides a little rougher than an '04 - Ford vs Chevy debate-type thing.)  They still utilized four air bags per axle on all their models up until the introduction of the RTS.

IBME that additional ride height in the front of an '06, '07 or '08 tends to make the coach a little squirrelly, and more prone to front end shimmy around 50 mph.  Alright for around town, or squiggling into a campsite, but somewhat annoying on the freeway.   You probably don't notice this because the extra five feet of length your coach has tends to dampen the front end more, just like the 40-foot 4905s.


Bill -

I would still run both coaches across a set of scales to determine the weight on each axle.  That's the only way you're going to ascertain (college word!) the correct air pressure for the weight being carried.

That and setting the ride height to specs should make the coach much more enjoyable for driver and passengers.

Be careful setting the ride height - best on ramps or over a pit.

FWIW & HTH. . .

[GM0406]

Hi Again,

Much good info here, so will reply best I can.  Not sure if this coach has been modified or not.  I can tell you that never in the time I have owned this coach have I seen the pressure guage George Thornhill has to monitor the reserve pressure go below 120 PSI!  Day or night running or not.   The other guage goes down in about 6 hours or more after shut down.  What I don't have is a guage for the left and right rear wheel bags and one for the front bags to know what pressure is in those bags. 

How can I know if George modified it to not use the original chambers?  This coach came from Arizona Charter, which means it spend all of it's life in the Southwest and therefore should be rust free.  I see no signs of rust on this coach. Unfortunately we can't ask George about the suspension as he passed away a few years ago.  But George had several friends in Western GM and maybe some of you here knew him and know the coach.  I am learning all the time, but a great deal of respect should be shown by all for those of you who know these coaches and have done your own work.  If or one am very grateful and very teachable when it comes to someone who has experience.  I learned a long time ago that there are a lot of tricks that are not in the book.  A friend who knows can save you a lot of headaches or busted knuckles if you know what I mean.   

George installed a two speed box between the axle and transmission that has a splitter switch like a truck on the spicer shift stick.  I have a hard enough time matching engine and transmission speed let alone trying to shift that box on the fly.  I mainly use the low range for moving the coach around here at the bus depot!  Bill T. 

[TomC]

RJ- I fully agree with you and did know about the difference between the double convoluting on the '04 and rolling lobe on the '06.  I suggested this since my AMGeneral has double convoluting air bags bus with what looks like big (almost twice the diameter of the air bag) aluminum cans at the top of the air bag for increased air volume.  Once again to increase the volume and to make the ride softer.  Interesting-when I picked up my bus originally from the first mechanic that worked on it, I asked if I should change to the rolling lobe since either was an option.  He said both rode the same-so don't bother.  I know this-when I had all the air bags replaced a few years ago-the mechanic said it was a real bitch getting the air bags to seat into the aluminum cans.  The bus companies had a special compression tool for this-of which of course none exist anymore.  But at least all 8 of my air bags are relatively new now.  And-I enjoy the ride of my bus.  Good Luck, TomC

[fe2_o3]

     I am also very interested in the gear splitter between the axle and trans. When I bought the bus there was a paper that mentioned a gear splitter and had a phone number on it. After the engine rebuild I wanted to call it but couldn't find it. I hope some one can bring this back from the dead. With the angle of my driveway, something like this could save us several clutches...Cable

[Kevin]

Bill,

I wonder if you have one of those rare two-speed custom-built rears that a gentleman engineered for the angle-drive GMs many years ago. I would love to have one for my '04.

Word is that the gentleman passed away, his kids have the plans (or blueprints, whatever) but have no intention of building any rears or sharing/selling the plans. Too bad.

Anyone else have any info on this unique two-speed rear for GM?

Anyone ever successfully incorporate a "Brownie" two-speed auxilary between angle drive and rear on a GM?

The more gears the merrier with our beloved DD 2-strokes!

Kevin

[zimtok]

Bill,

I wonder if you have one of those rare two-speed custom-built rears that a gentleman engineered for the angle-drive GMs many years ago. I would love to have one for my '04.

Word is that the gentleman passed away, his kids have the plans (or blueprints, whatever) but have no intention of building any rears or sharing/selling the plans. Too bad.

Anyone else have any info on this unique two-speed rear for GM?

Anyone ever successfully incorporate a "Brownie" two-speed auxilary between angle drive and rear on a GM?

The more gears the merrier with our beloved DD 2-strokes!

Kevin

There used to be a drawing floating around the bus forums that showed what was done to the diff to make it a 2 speed.
I thought I had copied it but I can't find it in my files....


.

[Len Silva]

I posted that years ago on GMC Busnuts, but there is not a lot of info there and it would be a major undertaking today.  There are indeed, a few two-speed 41xx buses running around with this arrangement.

http://autos.groups.yahoo.com/group/gmc-busnuts/files/GM%20Two%20Speed/

[Bill in KS]

this is the second two speed gear box befor the diffe that I've read about , there is one on a '04 in California ( blue / raised roof ) been for sale on craigslist for a year or better.  No information or help from him.

Then GM0406 spoke of his and caught my interest.  

I'm mainly curious if it is a adapted setup or a fresh trans case casted and a 3&4 gear setup out of a donor spicer trans.  could be something totally different.  I'd love a few photos.  

Probably people on this board have the info they just don't want the brush fire associated with the post and I understand.

Bill in KS

[Kevin]

Thanks, Lin, for posting the drawing and instructions.

Very intriguing! Wish I had connections to an excellent machine shop and someone who could interpret and recreate what is illustrated. I would choose the under-drive route so I might negotiate off-road (desert dirt-biking) terrain a bit easier... a snail's pace in first would be pretty sweet. And it would make life much easier starting on a steep incline, etc.

This drawing and the instructions give me something to dream about... It's been done before, so...

Thanks again Lin!

Kevin