I can't drive past 55! Governor/limiter question

[MilesOriginal]

I'm crafty and mechanically inclined, but I have never had the time or place to take apart an engine and learn its secrets, do what may be old hat to many of you is still a mystery to me. I am especially dumbfounded by diesels, and now we have one.
It's a c8.3 in a 97 ElDorado National Escort RE, don't know what transmission yet as I haven't looked for the nameplate. Drove it with the pedal to the metal for an hour straight with no issues, but it's governed out limited to 55mph. It holds steady at 2250rpm, and there's no electrical on this engine, so I'm pretty sure it's a mechanical limiting device that may be removable.
Our mechanics have not looked at it yet (no plates, and their shop is by the Tacoma Police fleet station), but when I mentioned the speed limiting and possibly adjusting or removing it, they got that look that mechanics get when you mention something that will cause certain death. They both spoke of vehicles unexpectedly taking off after the limiters were removed, one being in a shop when it happened.
I trust our mechanics, they're family, but I can't wrap my head around the scenario. Is this possible? Is there a way to prevent it? I just want to be able to hit 60mph!
The previous owners told me all kinds of things that they had done to the bus, like an in-frame rebuild and replacing the differential so that it can go up to 70mph (the first exposed lie, though I bet it could without the limiting).

[o1marc]

Need lots mor einfo, what rear gear does it have, what transmission. Usually the older motors were governed with a mechanical spring set up that senses load, the more load you apply the more it slows the engine.



Here's a previous thread on the subject.

http://www.skoolie.net/forums/f36/8-...n-15247-3.html

[MilesOriginal]

Thanks for the link, I couldn't get any good results from searching the forums.
I'll have to get that info on the transmission, and I have no idea how to figure out the rear gear info.

[o1marc]

Originally Posted by MilesOriginal

Thanks for the link, I couldn't get any good results from searching the forums.
I'll have to get that info on the transmission, and I have no idea how to figure out the rear gear info.

Get a VIN#, the dealer site can tell exactly what's in it.

[Sehnsucht]

I think that brand/model was much more designed as a city transit or shuttle bus, not a highway cruiser. Therefore it may not be geared for much more than 55 even if you defeat the limiter. Especially if you're already turning 2250rpms at 55mph, unless there's some hidden top gear I think that may be all she's got. A prior owner says they regeared? Not sure what that got them, maybe now we know why they unloaded it.

[MilesOriginal]

The prior owners had it for 11 years and used it as a church shuttle for their seniors. The driver of the bus worked for the city transit, and he unloaded on me for about an hour, all of the things he replaced and rebuilt, as well as what he didn't do and why. The problem with all of that is that he said he replaced the differential and that it could now do 65-70 on the freeway. One lie makes me wonder how much of the rest of what he said he did was actually done. But, doing 55 at 2250rpm, I'm sure it could do 65-70 (until it pops).
Does it seem unreasonable to be expecting 60mph at 2300rpm? Wouldn't that be in the sweet spot for rpms, or is it different with a diesel?

[PNW_Steve]

I would suggest looking closer to the engine. The 8.3 went electronic in '96.

It could be that Eldorado bought a '96 chassis and finished it in '97 but there is a good chance that you have an electronic engine and the governor is set in programming.

The 8.3's Max rpm varies by application but is around 2500-2600rpm.

[MilesOriginal]

No electronics on this one.
I had no idea how different the rpms are from a car, that's an eye opener.
So, if I'm maxed out at 55mph - 50mph on I-5 inclines - am I going to be dragging along at 40-45 with a tow vehicle?

[PNW_Steve]

Originally Posted by MilesOriginal

No electronics on this one.
I had no idea how different the rpms are from a car, that's an eye opener.
So, if I'm maxed out at 55mph - 50mph on I-5 inclines - am I going to be dragging along at 40-45 with a tow vehicle?

Probably not.

I have an 8.3 in my full size Bluebird. From the Eldorado's that I have looked at, I suspect that yours is lighter.

I packed a houseful of stuff in the back of the bus when I moved to the East side. I mean packed. I pulled Snoqualmie pass at 55. Not because of a lack of power. It was in the high 90's outside and I was not in a hurry. On the steep bits the coolant temps started climbing a bit so I backed out of the throttle a bit.

Last time I was in Tacoma I was attending a training class hosted by TPD. Nice folks.

[coolcraftnet18]

He probably has the AT545 which isn't geared high enough to hit 60

[EastCoastCB]

Originally Posted by coolcraftnet18

He probably has the AT545 which isn't geared high enough to hit 60

My 545 sure doesn't have a problem going 55+. In fact mine will do 80.
The transmission and the final drive are two different things.

[magnakansas]

Some things come to mind......

1. with the engine rpm listed..... I would expect you be able to move at a faster pace , if the other bits are in place to do so.....

transmission type.... gonna have to get under the bus and verify.... be sure to block the bus up so that there is absolutely no way it can sit down on you. Air suspensions have a wicked way of getting people killed when they get under them.........

axle gear ratio..... good idea to get a helper for this one.... there are ways to figure this out, with just one set of wheels in the air, but I have always found both ends of the axle up in the air is least troublesome.

2. Verify tachometer is correct, would not be the first one I have seen not set up correctly

3. Low on power? I would first have you put a boost gauge on this so you can read Intake manifold pressure. No air = no power.

4. I think this engine uses the bosch P7100 fuel injection pump. Very very tunable for more poop at the rear wheels. But as an example, I spent $1000 to have mine rebuilt, balanced for flow, governor springs, and modified for a bit more power. And this pump was in good working condition. Costs go up when there are damaged parts. My point is ... My 200 hp cummins 5.9 is able to to make about 425 hp at the flywheel now...... so you having a bigger engine to start with should get some good torque numbers cause you got two more liters than I do.....

start with the information about the kind of transmission and rear end gears and then go from there...

william

[MilesOriginal]

I hope someone sees this.
I have finally had a chance to look at the transmission plate, it's an Allison MT643, which sounds like a beast from what I'm reading around here.
I once had a Ford crown Victoria with a vacuum leak. It decided that it no longer needed to shift into 3rd or 4th after a couple of weeks. It got impounded before I could get anything looked at, so it may have been something else. This makes me wonder: does the air system that runs the breaks and the doors (that only open properly when they want to) also have some influence over the transmission or -somehow- the top speed?
There is an air leak or 20 in the system. It gets up to operating pressures in 5 or so minutes, but it drains out over the next 2 days until the doors can't hold themselves shut.
I had absolutely no issues driving it for just over an hour on the freeway, other than being stuck at 55mph. Seemless shifting, good torque, surprisingly good breaking.
I know the best way to get an answer is to get it to a mechanic, but the past year has left us short on that type of cash, so I'm hoping to get an idea of what I'm looking at. Any info advice or tips are greatly appreciated.

[cadillackid]

gears are everything.. but 2250 im pretty sure is what was factory max RPM on these engines. most everything ive seen for these is a 2100 max rating fir power.. red line is usually a couple huindred or less above so the governer is likely set there..



you can probably safely alter the governer to wind it out to 2500 RPM however you are just going to shorten its llife and burn lots of fuel...




there are 2 devices which determine the shifting of a 643. the governer and the modulator.



they work in coinjunction.. the modulator is on the side and has a cable which pulls out and opens a valve as you press the gas pedal.. this increases the shift point and pressure (firmer shift for more power)..


the governer has weights, springs and a gear.. the faster you drive the weights control a valve..


so now onto shifting.


if the governer gear breaks (where the governer doesnt spin) then you'll get no shifts.. it will be stuck in 1st gear..


if a spring breaks in the governer then all of your shifts are crazy early.. you feel like you have zero power because all it does is shft..



if your modulator cable breaks or stretches, all of your shift points are early..


if your modulator gets stuck pulled out then all of your shifts will feel late even at part-pedal throttle youll feel like "why doesnt the damn thing shift".. but it will still shift if you punch it..



so now onto driveability..


start our in D from a stop.


punch it to the floor and keep it there the whole time,



first gear is somewhat short in a 643 youll feel the 1-2 shift as a bit of a back flare then a forward push and notice a drop in RPMs.



second gear youll gain speed nicely and RPM.. the 2-3 shift is a modest feel.. its a bit of a close gear ratio with the converter unlocked. . you'll have to pay attention for it and notice a small drop in RPM going in.


third gear.. about halfway through 3rd gear. you will get a very noticeable Surge and drop in RPM.. this is the lockup converter engagement.. you are still in 3rd gear not 4th. since your turbo is nicely spooled youll feel a good amount of power in 3-locked.

shifting into 4th is a pretty major drop in gear ratio and another very noticeable drop in engine RPM..


fourth gear - this is it you are in top gear take it to the moon. (or to 2250 RPM)....


since you mention good solid torque and power till you reach 55.. I suspect low rear end gearing.. gearing is a 2 way street.. really low gears give you great low end torque and a quick feel off the line to accelerate but they top out early... I suspect this is your case...


Taller (Low gear NUMBERS) give you great top end speed and fuel economy but they have less torque getting up to speed..



I suspect your bus has the common Local / city bus 4.78 rear end ratio or possibly a 5.13,

[MilesOriginal]

This is some golden info, Cadillac Kid. I only hope that I can done day be as familiar with the behavior of my drivetrain as you are with the MT643. Thank you.