PD4104 from Highway traveler to Highway Hauler

[roadrunnertex]

Many years ago I bought a 1960 PD-4104 serial number 5025 ex Peoria Rockford coach.
Before it was converted to a motor home and just a shell we would take it on vacation and long trips lot's of fun back then.
It had the high speed rear end and 12R/22.5 tires and the engine was running around 2000 rpm give or take a few.
On flat interstate like I-10 it would run in the Monfort/left lane with out any problem.
Fun part would be passing a Greyhound MC-9 or a Trailways model 10 Eagle and watching them fade away in the rear view mirror.
Had a bus buddy follow me with my Toyota one day and he said that the old PD4104 would leave him and go out of sight and he was doing over 80MPH trying to stay with me.
Sad to say I converted the coach and sold it an I now own a P8M4905A with a V730 and it's 65mph cruse now it tops out at about 75 mph with the foot feed aganist the stop.
Good luck with your 4104 you to can now run in the Monfort Lane.
jlv

[gg04]

running 3.55's with 11r24.5's same dia as original 20's..671ta ddec set at 2800rpm top.. torque and hp turned up..have only put on 86000miles since swap but..11.46mpg average and boy is it fun to drive down the road..rdw....

[HB of CJ]

How about a nice 750 hp / 2200 tor Cummins Big Cam 855 governed at a mild 2500 rpm turning 2.76 rear gears with a .75 OD 10th gear running heat treated 11R X24.5 tires.  Works out to around 150 mph!  Only problem is I sold my Crown Supercoach.  Oh well.  HB of CJ (old coot)

[johns4104]

gg04,
That sounds like a nice set-up. and only 86k miles on it! LOL

[gus]

John,

I'm just going by my experience in the 4104 for five years and 75,000 mi. I got caught a few times when I had no choice but to slip the clutch and it hurt to have to do that, diesel engines are very hard on slipping clutches. What I did was kind of rock it so the clutch didn't slip but an instant at a time. It doesn't take long to get smoke. It keeps one alert!

Most of my problems were in RV parks, at state parks and at stop signs on steep inclines.

It is really nice with the AT in the 4107 not to have to worry about it anymore!

I used to know the rear ratio on it but have forgotten but it is pretty much a stock bus.

I think that the original 11-20 bias tires are about the same diameter as the 11-22.5. The 22.5 only means it is tubeless.

[luvrbus]

Johns4104 gg04 does have a nice setup the 6L71 DDEC set a 330 hp will get there on less fuel fwiw they are not hard to build you really don't need a DDEC 6L71 engine or the 6L71 ECM either to build one, come to valley in May I am getting ready to build one for a guy but it's going to be a right hander with a air to air charger not a aftercooler we are going for 400 hp

good luck

[johns4104]

Gus,
The 11-22.5 are actually equal to the 10-20's tube type wheels. 12-22.5 are the 11-20's.

Cliff,
I may just have to come up and see it.
I bought my parts bus with a fresh rebuild, 4 valve head, and a turned down blower speed for a turbo set-up.
In fact it didn't run too well because it was not sucking enough air. lol

Thanks,
John

[gus]

John,

You are probably right but I'm too lazy to go out in the cold to check what the originals were. I thought they were 11:00 x 20 but maybe not.

Since 11:00 it the max tire width it makes sense not to change that.

Strangely, the GMC bus specs website doesn't list tire sizes?

[RJ]

John & Gus -

The OEM tire size on the 4104 (and 4106/07) were 11.00x20.  It's listed in the sales spec sheets.  When radials came out, 12R22.5 became the OEM tire on the GM Parlor Cars.

But more importantly, you need to know that the whole powertrain was based on tires that turned 495 revs per mile.

So, regardless of whether you want to use 11R22.5, 12R22.5, 11R24.5, 295/75R22.5 or 315/80R22.5, you need to look at the manufacturer's specs for the revs per mile, as well as the load range for the appropriate weight capability for your coach, when buying tires.

Using tires that turn MORE than 495 revs/mile will lower your top speed, as well as increase your fuel consumption somewhat.

Using tires that turn LESS than 495 will have the opposite effect.  (Might make incline starts a little more challenging, too.)

FWIW & HTH. . .

[zimtok]

My 1960 4104 has a top speed of 62mph on a flat road. (GPS speedometer)
I get about 8.5mpg on the highway and about 7.3mpg local driving.

I don't know the rear end ratio or the RPM that the engine is governed at.
The tires are 295/75-22.5R Toyo.

It has a 4 valve head with N65 injectors.
It still has the original 4 speed transmission.

I guess I need to find a way to connect a tachometer and see the RPM of the engine.

[gus]

When I got my 4104 it had 11:00 bias tubeless tires. I changed to Toyo 11:00 radials which had plenty of weight capacity and they seemed to me to be the exact same size. 12:00s seem too large to me, they look OK on the 4106 though but it is also a bit heavier. I could tell no difference in speeds or speedometer readings.

It did not like speeds over 62-65 mph. It would go faster but the engine sounds told me it was too fast!