Speed limiter and 545 transmission.

[schooliefiend]

I purchased a 1995 Thomas full sized bus and at the end of this month I fly out to go bring it home. I've got to drive about 2300 miles in it and unfortunately, it has a limiter keeping the speed below 55 MPH. I do plan to replace the transmission with a 5 or 6 speed after I get it home, but for the trip home, I'm wondering if I shouldn't go ahead and get the limit removed. Driving 55 and below (going up hills) on the interstate doesn't sound like a good time to me, but I'm wondering how the transmission will be impacted on the drive home if I push the speed to 65 or 70MPH? What are your thoughts about the impact to the bus if I get that limiter removed?

 

[turf]

enjoy the slow drive and save your money for the trans swap. can you identify which component is limiting the speed? my guess is, its the 545.

my 545 bus never went faster than 67mph. after the trans swap, i've been over 80 and too scared to find out top speed.

i wouldnt worry about "pushing" the trans. if its limited like that, its been pushed to its threshold its whole life.

 

[Mr P]

My dt466/545 bus was limited to about 67 mph, due to the engine RPM governor of about 2700. I do not think my trans had anything to do with limiting speed.

There is one connection between the 545 and the engine, it's a cable from the "throttle" linkage to the trans. I think it's only there for the pedal position to alter trans fluid pressure, NOT for the trans to affect any RPM limit.

 

[nikitis]

Your 545 is the limiter here. What engine do you have?

55 is the max you're gonna wanna go on the Interstate with that Trans. And even that is pushing it. Most software limiters put on are set to 45, so if you are going 55mph you're already past the traditional software limiter and at 55 you'll be pushing anywhere from 2400-2600 RPM already which is up there for a long period of time, so you definitely do not want to go any higher than that for long periods of time on such an older engine. Do 45 when you can and 55 on interstate. You are a school bus, people will know why you are going so slow, and get it. Just sit back and enjoy it.

I'm in the same boat. I got the 55MPH. I can go 65 but then I'm at 2800-3000 RPM at 65 MPH with a 4.78 Rear Axle.

You need to find out what your rear axle ratio is too as that helps a lot in determining top speed.

 

[schooliefiend]

Your 545 is the limiter here. What engine do you have?

55 is the max you're gonna wanna go on the Interstate with that Trans. And even that is pushing it. Most software limiters put on are set to 45, so if you are going 55mph you're already past the traditional software limiter and at 55 you'll be pushing anywhere from 2400-2600 RPM already which is up there for a long period of time, so you definitely do not want to go any higher than that for long periods of time on such an older engine. Do 45 when you can and 55 on interstate. You are a school bus, people will know why you are going so slow, and get it. Just sit back and enjoy it.

I'm in the same boat. I got the 55MPH. I can go 65 but then I'm at 2800-3000 RPM at 65 MPH with a 4.78 Rear Axle.

You need to find out what your rear axle ratio is too as that helps a lot in determining top speed.

Here's the info sheet, if that helps.

 

[nikitis]

Ok, so you have the T444E like me and Same Trans, so yeah all I said applies and is true. You won't get much more speed out of it with that transmission. I wouldn't worry about removing speed limiter software if you can reach 55mph, there's no point.

If you live near by I could do the unlock for you for free but again it won't matter until the transmission is swapped.

If you do ever swap it, and want it unlocked, and are near Charlotte, NC let me know.

 

[Mr P]

Your 545 is the limiter here. What engine do you have?

You need to find out what your rear axle ratio is too as that helps a lot in determining top speed.

So, I might be splitting hairs, but how does the trans limit speed any more than the rear gear ratio? Or tire height? Or governed engine speed? Any one of those can be changed for more top speed.

Of course, for now the "take it slow and enjoy it" advice is spot on. And a different trans is most likely the best modification for more speed.

 

[schooliefiend]

Ok, so you have the T444E like me and Same Trans, so yeah all I said applies and is true. You won't get much more speed out of it with that transmission. I wouldn't worry about removing speed limiter software if you can reach 55mph, there's no point.

If you live near by I could do the unlock for you for free but again it won't matter until the transmission is swapped.

If you do ever swap it, and want it unlocked, and are near Charlotte, NC let me know.

Hey! I appreciate the offer, but the bus is in TN and I'll be traveling the opposite direction. Thanks again though!

 

[Mr P]

So, the build sheet says the engine is limited to 2500 RPM, and there is also a 55 mph electronic limiter. At 55 mph what is the engine RPM?

 

[Mr P]

And Ford truck 7.3 engines turn what max RPM? Google the image of a 7.3 power stroke tachometer...they redline at about 3700 RPM.

IMO, you should look into turning up the RPM limit if that's what's keeping you at 55.

 

[turf]

a trans swap gives you overdrive. the 545 is 4th gear is 1:1, an allison 2500 runs by memory 4th 1:1, 5th 1:89 and 6th is like 1:.84.* iirc. the trans swap alone gets you regeared to a higher speed just by having 5 and 6.

if your plan is to change the trans then do that and dont mess with the rpm until after the swap. that just adds more complications to a hard project.