| Author | Message | ||
| Rusty Thompson (Rusty)
Rating: |
I took the plunge and purchased my first Bus Conversion. A 1960 GMC PD4104. I live in Oregon but the most complete... cheepest one I could find was in Michigan so I bought it. Needless to say it was a long dirve. After 5 days, 2400 miles, two diesel leeks (fixed the first one left the second one), a sore rearend, and having the bus struck with lightning ( ya lightning) I'm home, and I have a few questions. The First is that on the highway I could only get the bus to go about 50-55 miles an hour in 4th gear. For the trip this was fine since it was my first time driving anything close to this size, and not being able to speed down the highway was probably a blessing. I've looked around the forum and it seems that most people can get at least in the 60's. I had a friend who was a diesel mechanic look at it and he said that it seemed to run fine, but hasn't worked on diesels for so long that he couldn't tell me why it was so slow without doing some reaserch. Anyway the question is, does anyone have any clues as what the problem could be so that I can fix it... or have it fixed. My second question is how to change the bus to a negative ground I know it can be done but I don't know how. The third is where I can get some new body panels for the bus. some of the panels in the rear are corroded and need replaced. Even sheets of corrigated aluminum that are the same as on the bus would be fine. Any help would be greatly appreciated, thanks a lot you guys (girls) are awsome. | ||
| TWODOGS (Twodogs)
Rating: N/A |
fuel filters ( ! ) | ||
| John that newguy Rating: N/A |
How fast does it go in 3rd? | ||
| Brian (Bigbusguy)
Rating: N/A |
What size tires? Have you checked on the gmcbusnut yahoo group? If you go the the rally in Oregon. http://www.busnusa.com/ You should be able to find others and lots of good info there. Where in Oregon? Brian 4905 Oregon? | ||
| sherryd4104 Rating: N/A |
Rusty, Our 04 did the same thing and we lengthend the lock nut and unscrewed the clevis about 4 threads. This would be the acellerator(sp) rod or cable to lengthen it. Hope this helps..Sherryd4104 | ||
| Rusty Thompson (Rusty)
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John ... it goes maxs out at about 30 in third gear | ||
| Linda-4104-FL Rating: N/A |
Rusty, you can get 4104 body panels from International Bus Parts in Apopka Florida. Ask them to send you a catalog. I don't have their number handy, but probably you can find it easily on the Internet (Google, etc.) or Directory Assistance. They are nice folks. HTH Linda-4104 | ||
| Jim Bob Rating: N/A |
Rusty, The 4104 has two possible gear ratios. One (4.125:1) is a "hill climber" and limits the bus to about 60-65 mph. The other (3.56:1) is a good "flat land" gear and lets the bus run about 72-74 mph. It sounds like you may have the hill climber. You need to buy a maintenance manual for the bus & the engine. Next, you should get someone with an accurate car speedometer to check your bus speedo. Once you know it is correct the full throttle shift points are close to 20, 30 & 50. You will know it's time to shift when the governor reduces the engine's power. Sometimes the engine is set up to turn less than the book setting of 2100 RPMs. If I were setting up your bus, I would first disconnect the throttle linkage at the end of the cable in the rear. (There is a clevis and pin) Then I would get a helper to fully depress the throttle & hold it there. Then you open the engine throttle by hand (engine off) & verify that when the pedal is fully depressed, the engine is at full throttle (the holes line up). Next, you would need to find someone with a "photo tach", a hand held tachometer that reads a little pice of reflective tape you stick on the flywheel or dampener. Engine should turn 2100-2150 max no load rpm. Standard tires were 10 x 20 tube type on split rims but many have been changed to 12 x 22.5 tubeless which are the same diameter. Some people change to 11 x 24.5 like the big rigs & gain some MPH. Those might be fine for the 4.125 ratio but I am certain they would be too big for the 3.55 ratio. The gear ratio is stamped into the end of the pinion gear shaft and can be read as two numbers (like 8/33) after removing the front end of the driveshaft that connects to the differential. Once you know the actual gear ratio, tire size, max engine rpm etc, you can use Daris' calculator program to figure how fast various changes will make your bus. By the way, going that distance including some mountain climbing in a just purchased bus with no REAL problems is quite remarkable! You got a good one! Sounds like you got the shifting sorted out too! Welcome to the hobby/addiction! Jim Bob '59 4104-4039 | ||
| Richard Bowyer (Drivingmisslazy)
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Most of the old time diesel mechanics I have talked to suggest 2300 rpm as a no load full rpm for the DD's. That is what I run my 8V92 at for 15 years. Under load it is generally somewhat lower than that while driving. 200 rpm makes a considerable difference when chugging up a hill. When I first got my 4104 I had a similiar problem, and it ended up being the fuel pickup in the fuel tank was plugged. I hooked an air hose up to it and blew back into the tank and never had that problem again. Richard | ||
| Jtng Rating: N/A |
His 6-71 doesn't have the pizzaz of the v's. 238hp at 2100.. It should still provide enough to go over 55, though... Diesel engine specs: http://www.adieselengine.com/new_page_1.htm | ||
| Jim Bob Rating: N/A |
JTNG, if it is the original 2 valve engine, it doesn't have 238HP. The 4104 book says the original engines were 170 HP due to the head & small injectors. I am suspecting that the engine may not be getting full throttle or it is not tuned properly, etc. Top speed is more about RPMs & gearing than HP. Horsepower governs what gear you go up the hill in. My 4104 would only go about 55-60 when we got it but it goes 74 now. But mine has the "tall" 3.56 axle ratio. | ||
| Jim Bob Rating: N/A |
Just went to Daris B's speed calculator. Assuming 11 x 22.5 tires (10 x 20 is actually a little larger diameter), and the "hill climber" 4.125 ratio, 2050 RPMs would give 62.7 mph, 1950 = 58.2 & 1800 = 53.7 mph. From the looks of it, assuming the speedo is correct (Don't Assume!), the engine must not be reaching full RPMs. Now if the bus has larger tires or the higher ratio, it should be going even faster. | ||
| gusc Rating: N/A |
You can easily determine the rear end ratio by jacking up one rear wheel, turning the jacked up wheel until the drive shaft makes one complete revolution and then dividing the number of wheel turns by two. Not exact because of the difficulty of accurately measuring the wheel turns, but close enough to tell the difference between 4.1 and 3.5. I am very interested in this thread because I,too just purchased a 4104 and am soon going to drive it from VA to AR, about 800 mi. Since mine was originally bought by Tamiami Trails Trailways it probably has the tall gearing but I haven't checked it. | ||
| gusc Rating: N/A |
Jim Bob, I will disagree with you about HP. HP is about how fast it will go but torque is what gets it up the hills. Torque is work and HP is how fast the work gets done. | ||
| Tim Hoskinson (Tdh37514151)
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There seems to be a mith about the 4 valve heads on the 671. According to detroits own publications there is no H.P. difference between 2 valve and 4 valve engines. Four valve heads were used in answer to EPA regs. Cylinder ports, pistons, and injectors made the difference in H.P. 671 238 H.P. were built with both 2 and 4 valve heads. | ||
| Jim Bob Rating: N/A |
Gus, if you are talking about an ungoverned engine on flat ground, then top speed IS about horsepower vs wind resistance. But if the engine can not turn more than say, 2100 rpms, then gearing & tire diameter govern top speed since few of us would argue that these engines have enough horsepower to get the bus to governed top rpm in 4th gear. I can tell you from experience that my tall geared 4104 will get to max rpm even with a 20 mph headwind on flat ground. (but it takes a LOONGG time to get there!) Torque is definitely work and horsepower & torque is what gets you to that top speed quickly. | ||
| gusc Rating: N/A |
Jim Bob, Glad to know your 04 gets up to good speed because I suspect mine is the same ratio as yours. RPMs, tire diameter and gearing all have to do with bus performance but the basic definitions of torque are work and the rate of doing work in that order. In other words torque is the work done and HP is how fast it is done. Tim, I always suspected what you say. None of the DD manuals or specs I have show any difference between 2 and 4 valve engines. From what I can deduct the 4 valve head allows for the installation of a Jake brake and is probably a bit more efficient but not any difference in engine output. | ||
| Craig Craddock (Gs4)
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You can install a Jake on a 2 value head. Just requires one special cap over the value and delete the Jake value bridge. There is a less common 3.875 rear end ratio for 4104's A friend ran a 4104 for years with 55 injectors, 3.54 rear end. Was very happy with it except for starting on steep hills or backing up in soft dirt or hills. Reverse is second gear ratio. | ||
| Tom Caffrey (Pvcces)
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gusc, I think that calling torque work is not really right. Work is force times speed for a given period of time. Horsepower is just force times speed. Torque is just force. RPM is Speed. A KWH is an amount of work. A KW is a rate of work. If something uses 2 KW for 1/4 hour, that's 1/2 KWH. This is why your utility charges you for KWH used. People often mix up these terms. The horsepower delivered to the rear axle will be limit the top speed that can be made on a grade unless there is enough horsepower delivered to reach governed speed; then RPM and gearing will limit top speed. This happens all the time with transits. For what it's worth. Tom Caffrey PD4106-2576 Suncatcher | ||
| Rusty Thompson (Rusty)
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I would just like to thank everyone for their valuble suggestions. I will check into all of them to see if I can find the culprit. Since the fuel lines are fairly rotten, and I had to replace part of one to stop a diesel leak on the way back it might be the fuel filter, or some other kind of restriction along the way. This might be compounded by not reaching full throttle since I was only getting 45 until I tightened a nut in the throttle linkage that was loose and slipping sidways when I pressed down on the peddle. I will get back to you and tell you how it goes.... About the speedo not being correct I drove by one of those convienet millage watch dogs on the side of the road that tells your speed digitaly and it showed the same speed as my spedomiter so I think it is correct | ||
| Tim Hoskinson (Tdh37514151)
Rating: N/A |
Hey Rusty remember to look at the return line as well Detroits are picky about return pressure and that can greatly effect power. Best of luck to you with your bus I have a 4104 of my own and they are a very nice vehicle especially for their age. Tim | ||
| Jim Bob Rating: N/A |
Craig, I have a friend with a '57 4104 that has a tag on the axle that says 3.875:1. I thought it was a transplant or a mistake as "Da Book" says only two ratios. I drove that bus on flat ground & found it peppier off the line than mine. I think that would probably be a better ratio than either of the stock ratios. I haven't calculated the speeds on that axle. (His bus is not running right now.) I think it could use 24.5 tires which would give it a good top end but it would still be low enough in first or second to climb big hills. | ||
| Jim Bob Rating: N/A |
Rusty, at the risk of being a nag, you need a 4104 service manual. Do the maintenance & adjustment of the throttle cable/linkage & governor linkage & you might be surprised. (I'll bet the throttle cable hasn't been removed, cleaned, lubed & properly adjusted in 30 years!) | ||
| Richard Bowyer (Drivingmisslazy)
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And to add to that Rusty, I sincerely doubt if the rack is being fully opened due to lack of linkage service. I know I had that problem with my 4104 also. Richard | ||
| john w. roan (Chessie4905)
Rating: N/A |
Too bad somebody doesn't remanufacture the parts for the Hydrashift again... with a 4:55 rear axle ratio, it would be the perfect setup- able to back up by just idling and letting out the clutch, able to split the shifts and 85 at 2200rpm for top speed. | ||
| DMDave Rating: N/A |
Dont forget the pickup tube screen in the tank! | ||
| gusc Rating: N/A |
Craig, You are probably correct but I was told by a bus converter in CA that 2 valve heads couldn't have Jakes added. As a newbie I really don't know but assumed he was the expert. Tom, Torque is a measure of work. Torque is measured in pound-feet. If you move a pound one foot you have done work. Force is not work, the pound in pound-feet is a force, it is not work. If you apply one pound of force to a one foot wrench and don't move it you haven't done any work, you have expended energy. If you move one pound 550 feet in one second (If I remember the numbers correctly) you have produced one horsepower. The amount of torque determines if you get up a hill and gives acceleration, HP determines how fast you get up the hill. A KW is a thousand watts. A watt is a unit of electrical power, simply put, amperes x volts. If a bus doesn't have enough torque to get up to governed speed it can never develop its potential HP. As I remember a 671 Detroit develops max torque at 1600 rpm and max HP at 2300. Not sure that is exact, but it is close. | ||
| Craig Craddock (Gs4)
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gusc, There has been a myth about not being able to install Jakes on 2 value heads for a long time. I have 12 of the adapters and have installed them on several 671's. I also have the Jacobs instruction manual on exactly how to install them. This dates back to the early 1970's. In my opinion they work just as good as the 4 value jake. I have the parts manual for this in my computer I will be happy to e-mail it to you. | ||
| gusc Rating: N/A |
Craig, Thanks. My email is egusDOTcATpokynetDOTcom. Wish you were closer I'd have you install one for me. I just bought the bus and really don't know what head I have. You must work at NAS Lemoore? I have an old high school chum in Bakersfield that we visit every Spring. We might be able to work something out yet. I see you have a 4104 with an 8V71TA, that must be quite a mover. I am contemplating installing a 671TA in my 4104, I am very partial to straight 6 diesels. What is the advantage of 4 valves over 2? | ||
| Craig Craddock (Gs4)
Rating: N/A |
gusc I do not think I got your address correct. Mine is CraigC at direcway dot com |
