s2mikon
Senior Member
What are you trying achieve with your re-gear?
BarnYardCamp
Senior Member
4.88 to 4.10 is about a 16% difference.
Ad 16% to 52 ends up with just a tad over 60.
maybe your bus has a governor holding the top speed down. Maybe that money would be better spent on upgrading the tranny.
Swapping out the rear end gears is a lot of work and expense to gain so little.
Ad 16% to 52 ends up with just a tad over 60.
maybe your bus has a governor holding the top speed down. Maybe that money would be better spent on upgrading the tranny.
Swapping out the rear end gears is a lot of work and expense to gain so little.
cadillackid
Senior Member
best thing to do is get your VIN, call bluebird and see if they can generate you a build sheet, line ticket, etc of your bus.. there are dozens if not more different rear end carriers used in school busses.. they are most all some variant of spicer and maybe you can get lucky and find a tag on it with some numbers you can cross reference against a list online.. and the best method for re-gearing is to find a like-axle, and buy the whole 3rd member(good used one) and just swap it out.. you dont even have to take the wheels off.. (its heavy but theres jacks for that)...
cadillackid
Senior Member
what size tires are you running? im guessing you must be running a low profile 22.5 or a 19.5" rim size?
post your tire sizes
post your tire sizes
s2mikon
Senior Member
Are you up against the governor now at 52mph? What size tires are on it? You have to be careful when re-gearing a truck or bus with the AT-545 to not over do it because of the non locking converter. An additional oil cooler will have to be added to the project. My bus is 4.1 ratio with large rubber and is good on the highway.
BarnYardCamp
Senior Member
what bus do you have?
My bus, with the freightliner FS-65 chassis has 5.71 rear gear. no problem going 65mph.
My bus, with the freightliner FS-65 chassis has 5.71 rear gear. no problem going 65mph.
cadillackid
Senior Member
Barnyard you prob have an Allison 2000/3000 transmission which has a pretty steep overdrive. His 94 has a non OD trans
BarnYardCamp
Senior Member
I have the 2000 tranny.
11R22.5 then has a H-302 on it? They are like 42 or 44 inches tall, its a log truck tire. I can go faster than 52, I have seen 60 but that's running at like 2800 or 3000 so not hitting the rev limiter if it has one. It's a TC2000 about 36-38 foot long seems like. Front engine. If I could get a just a third member with the 4.10 gears that wouldn't be too bad to swap out as long as it was the right one.
La Camioneta
Senior Member
I'm in the process of a 545 to A-1000 swap in a 1994 5.9 B700. Could have gone the 3rd member regear but locking tc and o/d made the trans swap more desirable. If you use .74 as your OD multiplier same rpms should net you 70mph with the A-1000 +whatever 545 non-lockup losses.
Would recommend the Killer Dowel Pin fix for you. https://www.motortrend.com/how-to/what-is-killer-dowel-pin/
My road speed was around 60 stock. Went from 10/22.5 to 11/22.5. Added #8 fuel plate, 3k GSK kit for more rpms, increased timing on p-pump. Getting the trans wiring and programming sorted and torque converter made before the swap. I post updates on my build thread.
Would recommend the Killer Dowel Pin fix for you. https://www.motortrend.com/how-to/what-is-killer-dowel-pin/
My road speed was around 60 stock. Went from 10/22.5 to 11/22.5. Added #8 fuel plate, 3k GSK kit for more rpms, increased timing on p-pump. Getting the trans wiring and programming sorted and torque converter made before the swap. I post updates on my build thread.
Booyah45828
Senior Member
You need to find the axle make/model for us to help you. Saying it's a bluebird w/ cummins and at545 doesn't tell us anything. You likely have an n175 or n190, but only you can look on the axle's data tag to see what you really have.
Regardless of the axle, something isn't adding up with what you say.
A 4.88 rear ratio with 11r22.5(42" tall) tires, 1:1 at545, and 3k rpm should get you around 75 mph. If you're only at 60 with that, something is wrong. Either your numbers are or your trans/torque converter is slipping.
Verify your numbers and run the data again. A 6bt had a governed speed of 2600 rpms, so unless your pump has been modified, you're likely not running at 3k rpm. I'd also be surprised if you had a 4.88 axle, as most buses came with one that is in the 5.xx range. There were some outliers out there that were built to run interstate speeds, but the majority of buses weren't, as they were on route duty picking up/dropping kids off, and didn't need to hit interstate speeds.
For instance, 2600 rpm, with a 5.63 ratio, 42" tall tires, and a 1:1 at545 would get you around 58mph, which is something that I've seen a lot more often. Even a 5.38 axle ratio would make sense as it would put you at 60mph with those tires/trans/rpms.
If your numbers are correct, you have a lot of slip in the trans or torque converter. And that needs to be addressed before you look at the rear axle. Changing the gear ratio in the rear axle isn't going to help anything with that. In fact, it will likely make it slip worse.
See what model axle you have, verify the ratio, and then come back and we can go from there.
Regardless of the axle, something isn't adding up with what you say.
A 4.88 rear ratio with 11r22.5(42" tall) tires, 1:1 at545, and 3k rpm should get you around 75 mph. If you're only at 60 with that, something is wrong. Either your numbers are or your trans/torque converter is slipping.
Verify your numbers and run the data again. A 6bt had a governed speed of 2600 rpms, so unless your pump has been modified, you're likely not running at 3k rpm. I'd also be surprised if you had a 4.88 axle, as most buses came with one that is in the 5.xx range. There were some outliers out there that were built to run interstate speeds, but the majority of buses weren't, as they were on route duty picking up/dropping kids off, and didn't need to hit interstate speeds.
For instance, 2600 rpm, with a 5.63 ratio, 42" tall tires, and a 1:1 at545 would get you around 58mph, which is something that I've seen a lot more often. Even a 5.38 axle ratio would make sense as it would put you at 60mph with those tires/trans/rpms.
If your numbers are correct, you have a lot of slip in the trans or torque converter. And that needs to be addressed before you look at the rear axle. Changing the gear ratio in the rear axle isn't going to help anything with that. In fact, it will likely make it slip worse.
See what model axle you have, verify the ratio, and then come back and we can go from there.
Booyah, Thanks for the info. Well I'm pretty sure on the gear ratio unless it has been changed since new. Thats what the tag inside the bus says by the front door up above the window. Maybe the speedo and rpm gauges are off.
When I took it to eastern Oregon and back on I84 I had to run about 26-2700 rpm and speedo said 52-54 range, I got passed by everything but the amish!
I'll investigate further. I was hoping the Bluebird only ran maybe 3-4 different axles so it wouldn't be so hard to find out what I got so I could check pricing on 3rd members.
I had a buddy turn up the pump a little bit by adjusting the plate but how much I don't know?
When I took it to eastern Oregon and back on I84 I had to run about 26-2700 rpm and speedo said 52-54 range, I got passed by everything but the amish!
I'll investigate further. I was hoping the Bluebird only ran maybe 3-4 different axles so it wouldn't be so hard to find out what I got so I could check pricing on 3rd members.
I had a buddy turn up the pump a little bit by adjusting the plate but how much I don't know?
Booyah45828
Senior Member
Well, here's the link for a simple mph calculator.
https://spicerparts.com/calculators/transmission-ratio-rpm-calculator
4.88 R&P, 42" tall tire, 2600 RPM, 1:1 trans ratio calculates out to 66 mph. Quite a ways off of 52 mph. Being an at545, you'll have converter slip due a non-lockup design and the fact most factory converters are on the loose end. But 14 mph is way outside of acceptable IMO. Something is wrong, whether it's your numbers or the trans.
Turning up a p7100 doesn't gain you any rpm afaik. You'd have to swap governor springs to gain more then stock.
I wouldn't be certain on any tag to give me the ratio, unless it coincides with what I'm seeing with my mph. Your's isn't, so I wouldn't trust the tag. If you can't count ring and pinion teeth, spin the wheels 10 revolutions, while you count the driveshaft revolutions. If you truly have a 4.88, you'll get 48 3/4 driveshaft turns, whereas a 5.xx will give you 50+ turns.
https://spicerparts.com/calculators/transmission-ratio-rpm-calculator
4.88 R&P, 42" tall tire, 2600 RPM, 1:1 trans ratio calculates out to 66 mph. Quite a ways off of 52 mph. Being an at545, you'll have converter slip due a non-lockup design and the fact most factory converters are on the loose end. But 14 mph is way outside of acceptable IMO. Something is wrong, whether it's your numbers or the trans.
Turning up a p7100 doesn't gain you any rpm afaik. You'd have to swap governor springs to gain more then stock.
I wouldn't be certain on any tag to give me the ratio, unless it coincides with what I'm seeing with my mph. Your's isn't, so I wouldn't trust the tag. If you can't count ring and pinion teeth, spin the wheels 10 revolutions, while you count the driveshaft revolutions. If you truly have a 4.88, you'll get 48 3/4 driveshaft turns, whereas a 5.xx will give you 50+ turns.
Copy that. Well I have buried behind a few rigs right now so no way to get to it so I can jack it up. Ill get some info off the axle and see if it has a tag as well with the gear ratio.
3rd members for N175 or N190 run from $500 to $1000 bucks looks like from what I found.
3rd members for N175 or N190 run from $500 to $1000 bucks looks like from what I found.
Spicer rearend. Model J190 S. R44AF108-2. SN 20394B tag on axle housing
Tag on 3rd member reads - H-R44CA103-5X. SN C6194
3rd tag on axle tube closet to wheel only had #9453252
Tires are about 41-42 inches tall
Off of tag above door Chassis # 61956
Rear Axle Diff #H-R44CA103-5X
Rear Axle ratio - 4.78
MFR- 08/94
Tag on 3rd member reads - H-R44CA103-5X. SN C6194
3rd tag on axle tube closet to wheel only had #9453252
Tires are about 41-42 inches tall
Off of tag above door Chassis # 61956
Rear Axle Diff #H-R44CA103-5X
Rear Axle ratio - 4.78
MFR- 08/94
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