| Author | Message | ||
| Joe (Frtnkr)
Rating: N/A |
I need to get some more speed out of my 87 Flx Metro. I am considering changing out the rear end. I will post the gear ratio tomorrow after I find out what it is. There is a 3 speed allison trans, I beleve it is a V731 and the rear end is geared for city driving. I have heard that highway gears are hard to find for this V drive bus, however turning up the engine and adjusting the govner or putting larger tires on the back, sound like half a** solutions as they will eat more fuel and put extra strain on the already under powered engine. I just want to be able to do 50-55 up hill, but I am no speed deamon. My questions to you all are... Has anyone ever done this with there bus, flx metro or other similar bus, and if so what gear and pinion did you use, and how did it work when it was all said and done? Also, where is the best place to find new gears and pinion? Will doing this affect fuel mileage and hill climbing ability positivly or negitivly? And, are there other options that would help other than changing the gear and pinion? I am getting about 60-65 MPH flat ground, but I am really loosing speed on hills. I have a new engine going in the bus right now and a newer transmission, so i am thinking that that may get me some more power on the hills. | ||
| james dean boggs (Jd_boggs)
Rating: N/A |
Joe, I've been trying the same thing until I found out the price. I was first quoted $1450 for the gears and installation. Then when I dug out the axle part number and got a better accuracy the price jumped to about $5,000. The gears cost $2600 and labor plus a few bearings and new seals that may need replacing. Get the part number off the rear axle it should start with a number of 730 or 733 then call around for pricing. They will know what ring and pinion gears you need. I'm looking for 4.10 gears. My bus 1981 Flex Metro has 4.56 gear and your's maybe the same. Post the axle part numbers here then I will post the numbers I have. You could also search the RTS bus nut and the GMC busnut board there is alot of activity about gears there. RTS, GMC and Flex use the same axle. | ||
| james dean boggs (Jd_boggs)
Rating: N/A |
PS don't go under the bus without proper blocking the body and wheels. There are blocking points on the under structure. | ||
| Greg Peterson Rating: N/A |
Before I bought my MCI I was looking at the old Flex buses. You didn’t say but I would bet you have a DDEC 6v-92ta engine. The v731 was designed to work with the DDEC computer. The third gear ratio was .88:1. The buses I looked at would only top out at about 60 mph. You will need to change the rear end gear ratio but finding a used set of gears is not easy. I think it needs to be around 4.1. A new set of gears is over $1000 and as I recall something else had to be changed in the rear end in order to make it work. I don’t understand why you are losing speed on the hills. The low gear ratio should pull very well up any reasonable hill. Maybe you have small injectors in the engine and have low horsepower or the lockup on the torque converter is not working. If the torque converter is slipping you could lose speed on a hill. What size tires are on the back? | ||
| Greg Peterson Rating: N/A |
I just remembered one other thing I did not like about changing the rear end gear ratio The first gear is like 1.7:1 for a v731 as compared to 3.7:1 in a HT740 4 speed. If you cut your rear end ratio down will you have start ability problems? | ||
| JW Smythe (Jwsmythe)
Rating: N/A |
From everything I've seen, mechanically (engine, transmission, etc) you'll find the Flxible to be VERY similar to the GMC RTS II. There are many folks who are helpful here, and there's a Yahoo group on our stuff too. I have a GMC RTS II. I'm far from an expert, but I've been reading a lot on the subject.  Pete can get the gears. He's on this board, and will probably be posting a reply soon. I posted his pricing message at the end of this message. The 4.10 gears should get you up to 75mph. Changing gears for higher speeds will reduce the power that you're putting out to the wheels, but will increase your road speed up to the limit that you have power for. From what I've seen, all it takes to upgrade the power on our buses is to swap out the injectors. Your bus should have about 260hp now. 9G90 injectors should bring it to 350hp, and 9G95 injectors should bring it to 375hp. I'm quoting Geoff from an old post on those numbers. There have been other posts on the subject, search the archives. http://www.busnut.com/bbs/messages/233/2901.html Personally, I'm changing the gears out for the 4.10 gears, and changing the injectors. I'm leaving the actual mechanic work to a truck shop. My bus in stock form was peppy enough to move almost ok on the highway, but at 60mph (full throttle, hitting the rev limiter) people were buzzing past me like I was standing still. The check has been sent off to Pete, so I'm in the limbo of waiting for them to arrive. === From this message === http://www.busnut.com/bbs/messages/11/13482.html === === I sell both 4.10 and 4.56 Rockwell 59000 series V-drive rear end Ring and Pinion Gear by Arvin Meritor <>The 4.10s Ring and Pinion Gear Set (A-38152-1) are $1957 and include shipping - but require 90-120 day lead time <>The 4.56s Ring and Pinion Gear Set (A-38158-1) are $1489 and include shipping - I have 2 available to be shipping immediately === end Pete's gear post === | ||
| Geoff (Geoff)
Rating: N/A |
Joe-- you are saying you are putting in a new engine/transmission? Can you find out and post what it is? If it is a stock transit engine you may not see any improvement in power, and if it is a DDEC engine you are not going to be able to upgrade the power very easily. And if it is an MUI (mechanical engine) it may be one of the EPA smog engines that are also hard to upgrade for power. The information from JW above is correct-- you really need to upgrade the power before you change rear end ratios or you will be worse off trying to climb hills. And kudos to JW Smythe-- he is a good student who learns fast and listens! I have seen a rash of new posters on the board who do a little bit of independent study on 2-stroke Detroits and try to tell everyone wrong information. BTW, the old post that JW linked where the guy was going to change out his engine for more power and jakes turned out well-- he took my advice and just upgraded his injectors and installed jakes on his engine and solved his power problems-- he thanked me later for saving him thousands of dollars. --Geoff | ||
| JW Smythe (Jwsmythe)
Rating: N/A |
Geoff, Thanks! Ya, I try to listen and learn. Right now, I'm in a waiting period, where my bus is sitting in one place, I'm in another, and I'm waiting for a few things to happen so I can progress. It's actually very nerve racking. Many days, I wish I could go out to the bus, and at least do SOMETHING to it. It's giving me a lot of time to read and research. I'm on eBay on a regular basis looking for the killer deals on a few parts (air conditioning, generator, etc). So far, I've bought a set of BDU's, and night vision goggles. Ok, they're not bus stuff, but that's what I get for shopping. The night vision goggles are VERY cool though. Lots of things apply from my knowledge of automobiles. In a sports car, something like 3.23 gears are great for street and racing. If you want pulling power or are drag racing with tall fat tires, 4.10's are good, but you lose top speed, and fuel efficiency. If you want fuel economy you can go with an even lower numeric value to keep the RPM's down, but you lose power. For sports cars on the street, we want as much power as possible, while keeping our top end ability. Good milage is good too. My car does this with a 6 speed transmission, two gears being overdrives. Exactly the same applies to our buses. The same goes with the injectors, except you'd usually want to do more stuff to the engine first before injectors. I haven't run across performance parts for the DD motors yet, but that's understandable. Most of our engines are in commercial vehicles. There isn't a huge demand for performance parts on commercial vehicles, since most companies can't use them (insurance, and longevity). I'd like to know that I could put in a performance cam and heads. Then again, if the injector change bumps the power up so well, performance replacements of other parts is simply unnecessary. | ||
| Pete/RTS Daytona (Pete_rtsdaytona)
Rating: N/A |
Hi I'm just about to place my gear order - let me know if your interested in new 4.10 or 4.56 gears (before Arvin Meritor raises there prices AGAIN). I also have (3) 4.56 Flx Pumpkins stored near Nashville Tenn for $750 each + shipping (450lbs) Pete RTS/Daytona 386...672..0571 or hawk_ii_mail at yahoo.com | ||
| Joe (Frtnkr)
Rating: N/A |
Thanks for all the great info so far, sorry about the lack of details. My bus had a 6V71 and it is getting a 6V71. I bought the engine from Blacksburg VA transit. They had it remanufactured by Detroit in 2000, installed it on the cradle, and there it sat untill I bought it. I am 90% sure it is not a DDEC as it has a mechanical govner. The info the mechanic gave me off the axle tag is...Rockwell model 59733WX30 Customer number, 97-5358-31 Serial Number NKA 86060364 He has all my manuals and I am waiting to hear from him on what gear ratio it in there now. If you can figgure it from the model number let me know. Sorry that I have not done more research on this before asking a bunch of questions, but I am on the road right now and the mechanic started work earlier than I expected so time is of the essence. So thanks...I'll get some more spacifics later today. Also, I heard that changing out for larger injectors will create more hear and require a larger cooling system, how true is that in your experiences? | ||
| Greg Peterson Rating: N/A |
You really don’t have enough HP with the 6v-71 to go any faster. The reason you are slowing down on the hills is your lack of HP. The 4.1 rear end will be worse. Take a look at that Cat RV performance that I posted earlier. You need about 150 wheel horsepower at 60 mph. At 72 mph you will need about 200 wheel horsepower. (40,000lb gross vehicle weight) You probably have no more than 238 engine hp and maybe less depending on injectors. The 238 is when the engine is at high rpm anyway. Cat takes off about 12% for drive train efficiency that would reduce your engine HP to 209 HP. We have to subtract the power to drive the fan and other accessories about 20 HP which leave us with 189 wheel HP. That is good on the flats at 60mph but pushing it at 72mph. Now look at the graph of HP needed to climb a 6% grade versus mph. You need 200 HP or more to go 30 MPH. This is all theoretical HP from Cat and I would not post it here if I could not back it up with real data. My father had a truck with a 4-71 (150hp) he used to drive 70 miles up route 55 to Chicago. Anybody that has been on this road knows it is about as flat as it can get and low altitude… maybe 600-700ft above sea level. The 4-71 truck with 10 speed trans could do about 50 to 55 mph. The truck was about 43,000 lb. GVW. My father later bought a 1962 GMC with a 6-71 (238). This could go 60 to 65 mph. It was about the same weight and had a 10 speed trans. I remember riding with him and remembering he used many of the 10 gears when it was loaded. When we came home empty he could probably get close to 70 mph with no head wind. This is very close to what you would predict from reading the Cat data. I think anyone that is going to buy a bus or re-power and re-trans would learn something from looking at the data. The 10-speed transmission really helped in the truck. In a head wind condition he could drop one gear and go fairly fast. In your case with only 3 speeds you will lose a lot when you drop into second gear. My dad would sometime higher a local trucker to help out with the hauling. That guy had an 8v-71 in his truck and even though my dad and he would leave at the same time he always got back first. The two extra cylinders must of let him go 70mph, this was way back when the speed limit was 70mph on route 55. Hope this info helps….. but do it your way as they say. | ||
| JW Smythe (Jwsmythe)
Rating: N/A |
Oh, I didn't know it had a 6v71. 426ci is painfully less than 552ci. Greg's probably right, you could have the gearing to go fast, but not enough power to do it. Someone on here may have experience with upgrading injectors on the 6v71 to give you an experienced opinion on what it'll do. I can't say that I recall reading about anyone doing it. I'm sure someone's tried though. | ||
| Joe (Frtnkr)
Rating: N/A |
I have not opened up the rocker covers to make absolutly sure, but acording to the information printed on the engine the injectors are G60's which I understand are quite small. The engine is already set to run at 2200 RPM's and I am quite sure, after reading your posts and talking to some mechanics that changing the rear end will not benifit over all preformance especially climbing hills. I am fine with crusing at 55-65 mph, however I am still interested in changing injectors if I am sure the engine can burn all the fuel I am giving it and the stock cooling system can handle it. Thanks for all the great advice... | ||
| Greg Peterson Rating: N/A |
According to my super DD Field service data book if you have N60 injectors you will get 195 HP at 2100 rpm. With C65 injectors you will get 238 hp at 2100 rpm with 1.484 timing. N70 injectors give 249 hp at 2100 rpm and 252 hp 2300 rpm. I would put in the N70 and set the governor so it revs up to 2300 rpm. This will give you more top speed and sure solve your hill climbing problems based on the Cat data. Even with 40,000 lb, you should be able to go up that 6% grade. Look at the post on the fans. You may want to use the 8-blade fan in order to help cool it. Maybe you can set the v730 shift points higher in rpm in order to take advantage of the engine horsepower at 2300 rpm. You probably need to set the unloaded engine governor speed to about 2400 rpm. With all that fuel and rpm that old 6v-71 should really sound good. ZEE RRRRR Good luck and if it blows up contact me I know where you can get an 8v-71TA for a flex bus. | ||
| RJ Long (Rjlong)
Rating: N/A |
Joe - Check the emailbox listed in your profile. | ||
| Greg Peterson Rating: N/A |
Joe I forgot one other thing. My dad’s 6-71 truck had the 65 injectors with the 238hp rating and did not smoke. However, he ran it at fairly low altitude. It appears that the 65 injectors causes smoke on an 8v-71 in Colorado based on a previous post. I don’t know if you are going to run the bus at high altitude. If you run near the coastlines maybe the N70 injectors won’t smoke to bad. This is just a guess I have not seen an engine run with them in it. The HP numbers are impressive with them. Good luck and hopes this helps…. I know how hard it is to get any info on this stuff. |