| Author | Message | ||
| Gary Stadler (Boogiethecat) (68.7.217.217)
Rating: N/A |
Took another great trip this weekend but had a repeat of a mystery occur...twice this trip. The trip was 12 hours of continuous driving, hot outside (100+) mostly above 4000'. Twice while coming down 6% grades, the engine died at the bottom. This exact same thing happened two years ago...exactly... Ok: Going down the grade with the exhaust brake on. Keeping the top RPM's slightly below the governor max (2400) by stab-braking as necessary. All three times I *think* I may have let the RPM's go above 2400, or at least aproach 2400. All three times, when I got to the bottom of the grade and stepped on the throttle, the engine was DEAD. All three times I pulled over and coasted to a stop, waited about 1 minute and the engine started up normally and I drove on (which at least gives me some confidence that nothing disasterous is happening) All three times, putting the clutch in, letting the engine stop turning, waiting, and popping the clutch- wouldn't start it. I had to pull over. All three times, pulled over but prior to that one minute waiting period, trying to start with the key it did nothing, and it sounded strangely like there was little or no compression. My first thought was maybe the exhaust brake floated the intake valves and the hydraulic lifters inflated to keep them floating...but the engine doesnt have hydraulic lifters. So it may simply be because the engine was hot and I never start it when it's that hot, that I'm just not used to how it sounds in this state. So I'm somewhat miffed. It's definitely NOT electrical (ie the fuel solenoid). My guess is that there may be something hydraulic in the PT fuel pump that gets pushed too far if I let the motor go above 2400 while coasting down, and in thinking that it's governing, it goes overboard and shuts the fuel clean off, and it takes that minute to leak down into reality and let things run again. But I'm kinda clueless... any thoughts? | ||
| TWO DOGS (63.185.83.77) Rating: N/A |
I'd try it without the exhaust brake....seems like that might be the culpret... to each his own....I don't like stab brakeing...as you crest the hill lite pressure all the way down,if it gets close to 2400 a little more pressure...you did not say,automatic or standard... (not bragging,but I drove over a million miles,never had a jake brake)80,000 pounds | ||
| Gary Stadler (Boogiethecat) (68.7.217.217)
Rating: N/A |
Standard. I dont like stab breaking either, or breaking at all down hills. The exhaust brake usually takes care of everything just fine but this time I was towing a big trailer and the bus was fully (I mean FULLY) loaded, so the grades were worse in both directions than normal. Yup, this trip has me considering Jakes... | ||
| BrianMCI96A3 (205.188.116.135) Rating: N/A |
As a Diesel Mechanic of 25 years I read "stab braking" and cringe. By stabbing the brakes you can, and often do, create hot spots or hardened areas on the inside of the brake drums, as the drum wears, the hardened areas do not wear at an equal rate, pretty soon the hardened areas are high spots and you will experience a shudder when the brakes are applied, over time as the the drum wears, the high spots will only get higher and the shudder worse. Not to mention that a HOT brake drum can in fact distruct explosively (though it doesn't happen often, I've seen the aftermath) if you stab the brakes at the wrong instant, lets say just before one of those high spots comes around. Brian | ||
| madbrit (67.136.110.65) Rating: N/A |
Brian, I beg to differ, long slow braking can generate just as much heat, may be more. With stab braking one is primarily holding the vehicle back on the transmission and motor and only using the brakes to keep it within the safe speed bracket. It really is a matter of choice and often the best method is the way one is taught and feels comfortable and confident. The reason for drum failure is most often caused by someone machining the drum too thin, but as you say, a very rare occurrence. I have heard of more brake disc failures than drums exploding. I can't see how a spinning drum can get hot spots, surely with it spinning at speed, the heat is spread evenly around where the shoe makes contact. Now if the drum has varying thicknesses, then that may cause this situation. Peter. | ||
| TWO DOGS (65.179.192.146) Rating: N/A |
stab brakeing....: let up & you expose the hot shoes to air....combustable + air = fire of course ...nobody here has seen brakes on fire ever seen those melted areas in the road on the side of the highway...that's where a vehicle burned | ||
| BrianMCI96A3 (205.188.116.135) Rating: N/A |
Peter, I can assure you that hot spots are caused when the brakes are stabbed and the hot spot is caused at the point of first contact. The fact is the shoes pivot from one end so you are not going to have uniform contact. I am not suggesting that you use only long slow braking, instead, I am suggesting that you do not STAB the brakes, apply them normally THEN increase pressure to slow the vehicle as quickly as needed. Brian | ||
| Henry R. Bergman, Jr. (Henryofcj) (63.224.197.10)
Rating: N/A |
Gary, my uneducated best guess here leads to four (4) possibilities. In order of probability... ...the exhaust brake is floating the exhaust valves a little bit. Enough to stall the mill. Try the downgrade(s) at the same rpm WITHOUT the exhaust brake and see what happens. Ask the Williams company (?) if they have a booklet listing the max back pressure in the ... ...exhaust system for various mills and see how it compares with your potatoe brake settings. Second possibility. Just plain overreving unrelated to the exhaust brake. 2500 is not... ....even close to a Big Cam max rpm, but for a 743, I do not know. Try the same downgrade... ...(if possible) at 2200 or 2300 without the exhaust brake and sees what happens. You may just have tired valve springs or maybe the 743 can not handle high rpm that well. Try 2200 to 2300 WITH the exhaust brake to determine if this theory is true or not. Third possibility. Something not quite right with the injector pump governor settings... ...which may be "hanging up," shutting off the fuel when freewheeling at high rpm with no throttle. Thus you have no fuel when you try to restart the mill. The mill will then really crank easy. This may give the sound and feeling of the mill sounding like it has no compression when... ...it is cranking. No fuel introduced into the cylinders will make a Cummins sound like that. A forth possibility. Do you have fixed timing, or something called variable mechanical timing? I do not know what non-turboed 743 mills had, or if the factory turboed 743 had something... ...different. I will ask Fred our local friendly, (mostly) master Cummins mechanic. Sorry I can be more more specific. My Crown conversion continues. Yours is DONE! CROWNS FOREVER!!!  | ||
| madbrit (67.136.110.65) Rating: N/A |
Brian, A misunderstanding on the term stab, I am used to what you described as the stab method, in otherwords, one applies the brakes slowly and progressively to reduce speed, then release them and when the vehicle achieves the higher allowed speed, then one reapplies the brakes and so on. Still not convinced on your hotspot theory, I can see hotspots on the shoes where not all the shoe is in contact with the drum, but whatever part of the shoe is touching, all of the spinning drum's braking surface will be touching it at one point as it spins. Check out some of these test films and you will see the whole drum is one uniform color of red from the heat. From your example, it would mean the shoe would have the hotspot not the drum, all the drum's braking surface will pass over the spot where the shoe contacts it and so spreading the point of contact to the whole drum. Brake shoes should be profiled to each drum to make as much of the shoe touch the drum as possible. Ideally the shoes and drums should be replaced as matched sets to get the best from your brakes. Out of round drums are often caused by the vehicle standing for long periods with the park brakes applied and the shoes being pressed against the drum but not uniformally due to the angle that the shoes contact. I was told brake fires are caused by the over hot brakes catching something on fire, like oil from a defective axle seal, having leaked into the brake area. As far as I know, brake dust and shoes will not burn. Exposing them to air will also not cause combustion, air is what cools them. Peter. | ||
| doughtebonifiedbusnut (24.62.99.43)
Rating: N/A |
I'm with you Madbrit, Like TD's I drove for a lot of years and never used the stab method except when I was in a very slippery condition. No matter how quickly you hit the brakes you will not put a hot spot in a small area of the drum. The wheel will be turnoing to fast. Gary's problem was intreging when He first talked about it. Got to be something to do with the pump governor it could be turning the delivery of fuel off at an unususlly high rpm.I am pretty sure unless you have had work done to your pump it is governed at 2150 rpm. After that no fuel. Then you got to stop and replenish the system. But thats just ta guess on my part. Will be interested to find out what it is. | ||
| Soulin Heath (66.82.50.1) Rating: N/A |
Stab Brakeing as discribed in Ca. DMV "Hand Book. NOTE: Scrol down to near the bottom of the page. http://www.dmv.ca.gov/pubs/cdl_htm/sec5_a.htm CA CDL Handbook< . S.M. H. | ||
| Tom Caffrey (Pvcces) (65.74.66.104)
Rating: N/A |
Brian, I've done quite a bit of brake work in the past and I've seen the hard spots, as well. I'm talking about the ones that you have to use a grinder on because they are too hard for a lathe to cut. The ones I've seen were brought on by heating and cooling, alright, but the local hardening was caused by impurities or variations in the drum metal. Most of the drum will not harden excessively, but if the metal is right and the drum reaches 1000 degrees, then spots in it will if the drum cools quickly enough. Stab braking on drum breaks was still the approved method of braking on grades when I last checked the Alaska CDL handbook. I doubt if it helps much with disc brakes, however. For what it's worth. Tom Caffrey PD4106-2576 Suncatcher | ||
| madbrit (67.136.100.24) Rating: N/A |
Well Guys, That Ca DMV webpage was interesting. They list stab braking for emergency stops and their Proper Braking Technique is what I was always told was stab braking. There was no mention of the 'constant light pressure' method. So I don't think I would travel down a hill using their stab braking method of locking the wheels each time......... LOL. Peter. | ||
| TWO DOGS (63.185.73.74) Rating: N/A |
this subject has been discussed many times here...do it your way...people need to have something to point and laugh at ...at the bottom of the hill | ||
| Gary Stadler (Boogiethecat) (68.7.217.217)
Rating: N/A |
Well guys, so much for my problem... I wasnt needing advice on braking....I want to figure out what's going on with my engine! But I guess you guys would rather preach on an off topic subject rather than come up with any help for the problem I asked this thread to address. Thanks Henry Doug and Two Dogs, at least you guys stuck to the topic! BTW, my governor limit has been reset to 2500 Gary | ||
| madbrit (67.136.123.77) Rating: N/A |
Sorry Gary, But how many times has a thread not wandered around and strayed from it's original subject line. Hey, you got some response, that's better than some threads........ LOL. Peter. | ||
| TWO DOGS (63.185.65.220) Rating: N/A |
I think you are trying to go down the hill too fast...slow down....turn flashers on...right lane | ||
| Gary Stadler (Boogiethecat) (68.7.217.217)
Rating: N/A |
Well, yeah, threads always morph. But I'm really looking for a old dog who knows Cummins 220s who has seen this before, not advice on how to brake or come down a hill. In the cases where the engine failed, all three times it was at the bottom of about 6 miles of 6% grade, going down in exactly the gear and speed necessary so that the exhaust brake would hold me back with maybe 2-3 minimal applications of the brake over the entire hill. Usually this is about 35mph. In the right lane...Definitely not too fast... | ||
| TWO DOGS (65.177.145.141) Rating: N/A |
6 miles at 6%...what do the signs say...25 or 30 | ||
| Derek (Derek_L) (24.83.196.239)
Rating: N/A |
ButButButBut... You mean it's not a good idea to be running down a 30km (never mind 6 mile!) 6%~8% grade at 170km/h with a Series 60 doing 2800RPM??? (I once rode on a Prevost H3-45 driven like this on the hill descending into Kelowna, BC, Canada.) (TWO DOGS, did you ever come into Western Canada with your trucks? If you did, you've probably seen that hill...) ------Americanized!------ ButButButBut... You mean it's not a good idea to be running down a 18.6 mile (never mind 6 mile!) 6%~8% grade at 105mph with a Series 60 doing 2800RPM??? (I once rode on a Prevost H3-45 driven in this fashion on the hill descending into Kelowna, BC, Canada.) | ||
| Henry R. Bergman, Jr. (Henryofcj) (67.136.241.239)
Rating: N/A |
Gary, I did talk to our local friendly (mostly) retired Cummins Master Mechanic and he told me while 2500 rpm is kinda high for a 743, it should NOT HURT it a all. He also said that it is possible that the injection pump governor is sensing the 2500 rpm on a contineous basis (going down hill) and shutting off the fuel. And...not resetting or whatever goes on inside a 743 injection pump. He did not expand upon this notion and I have no idea. This would let the mill appear to be dead and NOT restart. Then, if you flop the gas pedal several times, then the governor lets go and the pump resets to the fuel position letting your mightly 743 start?? And he confirmed what I said about... ....a Cummins cranking without fuel will sound like it has no compression. Seems there is enough fuel injected in the start position to really slow the starter down. He did NOT think the valves were floating nor did he think the exhaust brake was floating the exhaust valves. It said it was possible but unlikely. Anyway, good luck. CROWNS FOREVER!!! | ||
| Tom Caffrey (Pvcces) (65.74.66.104)
Rating: N/A |
Sorry about wandering off topic, Gary. For me, it was mostly caused by inattention, and some concern about misleading information. I don't have any idea how to help you with your engine. I think you were right to ask if anyone else had run into your problem. We have owned Cummins engines, and still have a small bore like yours. I never noticed it sounding like it didn't have compression if the fuel was turned off, so I don't know what Henry is talking about. If you pulled the compression release on ours, it sounded like an electric motor turning over. With it released, you had no problem hearing it come up on compression on every cyclinder. For what it's worth. Tom Caffrey PD4106-2576 Suncatcher | ||
| Henry R. Bergman, Jr. (Henryofcj) (67.136.241.239)
Rating: N/A |
Oh come on Tom...I tried my best to says it was our local friend (mostly) retired Cummins master mechanic who said that stuff and not me. Have YOU ever heard a 743 Cummins crank WITHOUT the pump being in the "RUN/START" position? Without getting ANY fuel? I have not either. However...he he he, our local friendly (mostly) retired Cummmins MASTER MECHANIC probably has dozens of times and I take his word for it. Gary, the mechanic still thinks your governor is not quite right and not possibly "releasing" or "resetting" to the fuel-on position. In his opinion this would make your mighty 743 turboed Cummins spin faster and sounds like the compression was down. Try pumping the gas... ...several times to see if then the mill will start. Again, he does not believe it is the exhaust brake or the valves floating. And...I will ask him also if it could be something to do with the manual compression release that is hanging up actually causing... ....you mighty 743 not to have any actual compression and sound that way like you described. We are trying to fix your... ....problem and at this point anything is still possible. We need to eliminate the improbable like Sherlock. CROWNS FOREVER!!! | ||
| Tom Caffrey (Pvcces) (65.74.66.104)
Rating: N/A |
Henry, I understand what you're talking about when you say that you were just passing the information along. The fact is, I had to crank the engine over with no fuel because of doing the timing on it. When I said that I didn't remember that symptom, that's just what I meant. I think I would have remembered it if it had sounded like there was no compression, so I was kind of surprised by what you said. It's been at least 20 years since that happened, so who knows? It just seemed kind of odd, to me. Tom Caffrey PD4106-2576 Suncatcher | ||
| Henry R. Bergman, Jr. (Henryofcj) (63.224.197.10)
Rating: N/A |
Finally got more specific stuff from my mechanic. He says it is a possibility that the fuel transfer pump is also cavitating and not passing fuel to the mill when running down a hill at 2500 rpm. To fast for the pump to keep up. This would let the mill act and sound like it is getting no fuel, which in a way is true. After cranking the 743 for a while, or just letting it set, the nature of the pump is to restablish... ...prime on its own. This would allow the mill to restart on its own which seems to be the situation. Or...he said it could be combination of the transfer pump cavitating and the governor not working properly. He also said again that in his opinion 2500 rpm may just be too high for a 743 Cummins which is not like a 855 Big Cam at all. Just his opinion which I am passing along. Thank you Tom, I understand what you are saying. It is difficult to get specific and correct information third hand, which is what we are trying to do here. No disrespect intended. CROWNS FOREVER!!! |