Model of differential

prevost82 · August 29, 2007, 11:37:35 AM

Hi all ... I have a Rockwell diff in my 82 Prevost. I am looking at going to a 3.30 : 1 and I have a 3.70 : 1 now. Does anyone know a model number of the diff?
Ron

tekebird · August 29, 2007, 02:46:11 PM

crawl under...should have a tag. or a call to prevost with your serial number will get you what it was sent out of the factory with

TomC · August 29, 2007, 04:08:30 PM

Ron- if you have 12R-22.5 at 485rpm and Allison transmission with direct as high, your present 3.70 will net you a top speed of 70mph @ 2100rpm. Switching to the 3.30 will raise the top speed to almost 79mph. I think you should ask yourself, is all that money for a new rear end and the trouble to change it worth the extra 9mph you're going to gain? Personally I don't think so.

What would be most effective would be to get rid of the HT740 and get either the B500 or HD4060 with low profile oil pan (B500 is the HD4060 or 4000HS with a low profile oil pan). Using your present 3.70 gear ratio, your top speed with the .74 (5th gear) and .64 (6th gear) overdrives in the B500 will increase to 95mph in 5th and 109mph in 6th. Or to get more realistic, your 75 mph cruising rpm will be 1660rpm in 5th and 1435rpm in 6th-of which it might not even get into 6th until more closer to 80mph! The B500 is about the same size as the HT740. Good Luck, TomC

prevost82 · August 29, 2007, 04:39:49 PM

Tom ... I running an 8V92ta @ 475 hp and a 6 speed stick tranny. I trying to get my RPM's down at cruising speed (60 MPH). I'm not trying to go faster. With a 3.3:1 ratio I'd be doing around 62 at 1600 RPM, instead of 1750 RMP and that should improve my fuel mileage a bit.

I live in the mountains and need all the gears I can get, there's not a 6% grade out of this town, on 3 highways, and not just one 6% grade either. The other option is to put a 10 speed in with 10th gear as an overdrive. Putting 4060 or B500 wouldn't work for me because I'd still have to change the diff ratio, to use 6th gear. So that option would be WAY more money.
Ron

luvrbus · August 29, 2007, 05:42:05 PM

My 8v92 loves the new gear switch from 370s to 336 ratio and i do too

rdbishop · August 29, 2007, 06:18:32 PM

Say luvrbus,

What was your top speed with the 3.70 ? Mine was 74 mph at 2250 rpm. I want to go to 336 also, but I have to find a good pumpkin housing first. I really liked the 370's in the mountains.

Richard

luvrbus · August 29, 2007, 06:28:53 PM

Richard, thats about where i ran i can not see any difference in the mountains but i can see a little difference in the braking power of Jake brake

rdbishop · August 29, 2007, 06:36:27 PM

luverbus,

Does that mean the jakes won't be as strong.

Richard

luvrbus · August 29, 2007, 06:45:43 PM

mine seem as strong just not in 4th gear it might just be me

rdbishop · August 29, 2007, 06:49:20 PM

Maybe they can be adjusted to compensate. (hopefully)

Richard

luvrbus · August 29, 2007, 07:11:36 PM

Richard, you will love the extra rpms you have when you need it

rdbishop · August 29, 2007, 07:19:51 PM

luverbus,

Sounds good!! I'm trying to get mine done before the Texas round-up. My pumpkin housing is all mess up,so I need to find one and get the 336 installed at the same time.....which is getting short.

Richard

rdbishop · August 29, 2007, 07:35:34 PM

Prevost 82,

I talked to a diff. company in ft worth, tx. today and he said he needed a number off the pinon shaft where the yoke nut is. Said I would probally have to take the driveshaft loose. Also said I would have to wirebrush it to get the numbers. The gear ratio is there also. I'm going to look for mine tomorrow as it looks like I need another pumpkin housing. I'll let you Know what I find.

Richard

Merlin-PV · August 29, 2007, 08:58:19 PM

If memory serves me correct it is"sqdd"

TomC · August 30, 2007, 12:16:36 AM

Ron- once again, I'll repeat-don't spend the money, time and effort to change from the 3.7 to 3.3 gears- it just isn't enough of a difference to make much fuel difference-probably wouldn't ever pay it off. What will really make a difference in your fuel mileage would be to change that 6 speed to a (these are all Eaton Transmissions) 7spd overdrive (with a .75 overdrive and still in one stick with no air splitter), or a 9 spd (which I personally like the best) with either a .73 or.74 overdriver, or a 10spd with a .74 or .75 overdrive (don't like the 10spd because of the U shifting from 5th to 6th). With the .75 overdrive of the 7 speed, you'd get your cruise rpm down. With 3.7 and 485 tires (12R-22.5) you'd be doing 1794 at 60mph-which is fine. Go to 65 mph and you'll be at 1944-which is starting to get a bit high. Shift into 7th and you'll drop to 1458 at 65, 1570 at 70 and 1682 at 75-all of which is not to low for the 8V-92TA. You'll really get fuel mileage results and quite possibly cost you less since I know there is alot of transmissions around compared to bus rear ends. Good Luck, TomC