I just got my 98' Kenworth last october and I had zero experience with anything above a 7 spd eaton before it. I taught myself to drive the 13 spd with a little input from the owner of the trucking company we use. He pretty much just gave me a basic description of ghost shifting and told me about the clutch brake. Well, I've gotten pretty good so far, I've hauled about 10 full loads with it this spring and I'm starting to wonder if the things I'm doing or issues I'm facing are "normal". First thing is that I was told not to use the half gears when down shifting, which I assume is the norm? I can downshift using half gears, and do quite often to keep a certain speed. But, I'm curious as to what the majority of people do? Also, the truck has an 800,000 mile 425hp C-12 in it, and with no past experience with trucks I'm unsure of the performance of it. For example, if I'm on flat ground loaded going 55mph in 8th direct or 12th basically, cruising at 1500 rpms and I drop to 7th direct, I'm now at 1800 rpm and I really don't slow down at all, very slowly at least. I just feel like I end up using my brakes way to much to slow down when I don't have the jake on high. Another example: Today I was coming down a 3 mile 6% grade with a truck speed limit of 45mph. I was about 68,000lbs gross weight so not that heavy. I was in 7th Direct with the jake on full and it was holding me right at 45mph at about 1700 rpm with no brake input. Basically I just feel like the truck doesn't slow me down enough without the jake blaring, and even then when I'm hauling machinery at 87,000 with the jake blaring I would think I still need a lot of brake. Is the truck just due for an overhaul or am I doing something wrong? Thanks.
I used to drive a 98 KW T-800 transport for a equipment rental co. It had an N-14 Cummins, 460 horse, 13 sp, 3:73 rears. Maybe it was the differance in engines, Cat vs. Cummins, and 35 more hp which is also 35 more braking hp. I used the jakes on full power 99% of the time I had plenty of stopping/slowing power with out riding the brakes. I've never had a problem with blaring the Jakes, actually I kinda like it!! Even with heavy loads 70,000and up 100,000 as long as I was in the right gear all went well. As for down shifting a half a gear at a time, I've never been told NOT to do that. For instance, if you're climbing a hill, the beauty of the 13,15, and 18 speed IS that you down shift 1/2 a gear at a time. As for coming to a stop, I just shift 'em how I need to. I can't imagine that shifting 1/2 or 1 whole gear at a time really makes a differance. Maybe I'm wrong and someone on hear can correct me. But by all means use the heck out of the Jakes... as a matter of fact may I recommend 8'' straight's they have a really nice low rumble, and when they are really working.... man that's good stuff!
Yeah I guess I'm a little conservative with the jake. Mine are definetly loud though. Sounds like a pretty similar truck too, I have 3.90 rears though. I guess my question breaks down into two main things that are bothering me: 1. Is downshifting when your truck is at 1500 rpm and dropping into the next gear around 2,000 rpm normal? bad? situational? Because this is normal for me. 2. How much does having a worn out engine affect down shifting? Not so much the downshifting with half gears. I just don't see it being practical using the half gear to stop in a reasonable time. I practiced like crazy with them before I was told that it isn't necessary, so if I wanted to I could downshift with the 1/2's without issue but...it still takes to long IMO. Was more curious on that, and maybe I'm still wrong, who knows.
I drive a 99 T-800 with the same C-12, only my tranny is a 10 speed, with 10th gear a .74 overdrive. Usually I figure on going down a steep hill in the same gear it would take to climb the hill. This will help your jakes work better. Like Eric, I can only think of two or three times I have ever used the jakes in any position other than full on. I can relate that at 1700 the jakes are really screaming, but that is when they are working at their maximum rate. You CAN split your downshifts and use the jake to slow down. A 13 speed would really be nice when going down a long grade--you could select the perfect gear that maximize the effectiveness of the jakes and maintains a safe vehicle speed. In your example 87,000 is a LOT of weight and it takes a lot of energy to pull or stop this weight. The heavier the load the slower you will be safely able to accelerate or stop. You have to look down the road a lot further and anticipate situations which might cause you to slow down or stop.
Just a little input for you on the 13 speed/holding back issue,440chevy. First of all, a diesel won't hold back like a gas engine will when you let off on the throttle. Secondly, those older Cat's, especially a smaller bore like a C-12 doesn't have quite the amount of retarding efficiency as a newer style bigger bore C-15 does. The 90's era specifically didn't have a lot of jaking power at all. Next, the best rule of thumb you could keep in the back of your head if you'd like to make your transmission last a while and keep costly repairs to a minimum is this..."The LESS you play with that splitter button, the better off you'll be..." I say that because the back half (or rear section of a 13 or 18 speed,) of your transmission is where the countershafts and synchros and countershaft bearings are located. The main box is the same as a 9 speed Fuller basically. The constant function of splitting up & down and preselecting direct and OD shifts really prematurely wears things out back there. So to try and prolong it's service life, it's strongly recommended that drivers shift the main transmission as much as possible as long as the engine will "take it",(meaning accept the RPM differentials without splitting,) and only split the top gear once you're ready to cruise. When the "death howl" starts underneath the floorboard one day and it suddenly jumps out of OD going down the road, or worse... lose it completely, then this post will probably come to mind that moment. The good news is, normally when the OD section or "backhalf" goes, it's a snychro, a counterdhaft bearing, or something else inside that at least allows you to keep driving it without OD to get it back to the shop. I've had several failures over the span of my career with backhalfs, and drove one of my trucks (an '86 Western Star,) for 2-3 months in direct until I mustered up enough cash and a dry spot to work on it. Deerhauler is right in the fact that using the jake in the full (3rd stage/6 cylinders) mode is the best policy, as it's where you get max efficiency. Old school thinkers always worried by using an uneven amount of jake power, it puts too much stress on the crankshaft. Don't ever worry about using the jake brake too long or too much either. That's what they're there for..to use. Just try and keep your high RPM's slightly lower than 2000 when you're grabbing a lower gear, maybe down around 1900, and that will prolong the life of that little Cat as well.:drinkup Lastly, Cummins always had (and alway will probably,) the most retarding power of any diesel engine. Big difference between a Cat and a Cummins in the holding power.
splitin Just curious as how to split a 15sp like a 13 or 18sp? Just never to old to learn I guess By the way I am still trying to see the difference is in a regular stantard shift transmission comparred to a tranney Maybe it is something they started puting on the new computer controled trucks unlike mine/ Anyway Thanks for your Time and the education for myself! Thanks Divedigger
A 15 spd. doesn't work like a 13&18 Divedigger, in that they have no splitter. They are shifted the same as any normal 8, 9 or 10 speed with the exception of the double OD series that has a backwards U-pattern...high gear is towards the dashboard. That one takes a little getting used to for anybody.
Basically once an engine has some wear and lower compression as a result it will effect compression braking performance. Is the engine a bit smoky? That's a sign that you are not having complete combustion due to worn rings. I am no truck driving man but was taught that you start engine braking at max revs and then drop down to revs that will allow you to skip shift down so that the engine is back up to max rpm. For instance if you are cruising at 1500rpm in 13th, you drop down to 12 which will bring the revs to 2000 and then retard the engine till it gets to 1100 and then skip shift into 10th which should bring the revs back to 2100. Alternatively retard the revs in 13th gear until they go to 1100 and then skip shift into 11th. As others have said, using the split is not that good of an idea because you add wear and tear to the split mechanism.
Yup, that's a fun one, eh, LowBoy... rrrrum, grrrrr, rrrrum, grrrrr, rrrrum, grrrrr............ grrrrrrrrrrr... lol You have heard the term... "get'n lost"... :lmao Our water tender has one... our transport has a 13 OD. Jump back and forth... or is that... forth and back, between the two. lol You do get used to it in a while... kinda... Take care ol' buddy, OCR...
I agree wholeheartedly OCR. You do get used to it..." kinda". I found no matter if I'm fresh from the start or exhausted, I never seemed to remember about the backwards pattern on those 15's...:Banghead I really didn't ever care for the big spread between gears either. Great O T R transmission, but not the best for anything else like short hauling, off-road, (although the deep-reduction gives a false sense of security in terms of low ratios,) or construction applications. To each his own I reckon though...:drinkup
The engine doesn't smoke at all and seems to run strong. I'd like to do an in-frame this winter to learn a few things, that or I might swap in a different engine if that's feasible. I really like this truck, but I didn't know jack about trucks when I bought it. Didn't get ripped off or anything, but I'd like to do some heavy haul in the winters and this truck isn't ideal. Even if I dropped in a bigger engine and maybe an 18 spd :drinkup It's still only 180" wheelbase which just seems a little short for that set up. Anyways, I hauled a few loads with it today and the downshifting went very smooth. I think just the confidence that I wasn't doing anything wrong helped a ton. That and you could hear me a mile away with the jake blaring. Sounds cool but I still wish it wasn't so loud. Also, I forgot to ask about the jump from 4th to 5th (lo to hi range). Every other gear shifts great and I can keep it right in the power band except the range shift. Is this just the way it is? I have tried revving it out to about 1800 but it always seems to drop in below 1500 and lugs on hills. I even tried going back into lo (while in hi range still) but that "gear" seems like it's to close to 4th to help any. While I'm on the topic of up-shifting, I'm curious as to when you guys split the gear. I like to bring it up to 1750 rpm or so then split and resume acceleration around 1500. I don't like to bring it out to neutral and then split and come back into gear unless I'm downshifting. Just seems like I lose to many rpm's while up-shifting that way.
I'm a little curious, are you double clutching your shifts or floating? Double clutching will generally take a little more time. When you get decent at floating the gears then you can keep from dropping too much speed and too many rpms between gears.
Yeah I float gears. Like I said though, with 4th and 5th it just seems like no matter what I do it just drops.
Anyone remember the ole mystery gear in the 13 speed boxes ? Go back into the Granny gear position in the top box instead of dropping the button . Ive spoken to many gearbox guys about it , they said it should not be there but it is and it does'nt seem to hurt them . I use to love my 15OD , when i bought it the guy who owned it showed me how to change out of deep reduction into the middle box on the run . Most guys used to do the first 5 and then try and do the second 5 going back to the the first gear position......gggrrrriiinnnd . The trick is to do 1,2,3,4,5 ,10 .
Yeah like I said I even tried that, but it isn't very smooth to go from 4th to that. However if 5th drops to far and I HAVE to downshift, I use that gear instead of dropping back into lo range. Works great. I was just told not to over do it with that gear.
Sorry , i missed where you said that .
Heh, I didn't really do a good job explaining it. It's a good trick though. Great for when a light turns green.
Hey Iron Horse, I don't mean to muddy the water here, but I've got one I've never figured out. I used to drive a Bucyrus 45C II hydo crane with a 13. You could shift it 3-5-5, i.e., 3 low range, 5 mid range, and 5 high range. Or you could shift it 5-5-3. I'm still, after all these years, scratching my head over that one! Is this anything like your "mystery gear" setup? :beatsme
No , that's a new one on me . It didn't have an air shift Joey box or a 2 speed transfer case did it ?
Darn it! I guess I'll never figure that one out! :Banghead
Hi to you, 440chevy... I'm probably not nearly as masterful with the mixer stick as LowBoy, and some of the other people on the forum... but I have acquired some muscle memory in my right arm... lol Range shifts are a little harder to make... you might need to bump your top RPMs up a little. ( I want the experts to chime in any time... I noticed I'd left the "f" out of shifts, on the first read )...lol And, I'm going to stop now any way... about five posts made since I started... LOL OCR P.S. Maybe some more from me latter... I think we're getting our transmissions mixed up... LOL
That's a favorite trick of mine too Iron Horse, with those 15's. Come out of deep reduction by going through the bottom 5, flip the reduction switch and drop back to 4th without skipping a beat nor grinding (if I said that right...don't usually think about how it's done much.)It's always a nice thing when you've once mastered the "art" of shifting and being smooth and gentle. As for the Mystery Gears in the 13 & 18's, I've been using it since the 70's when I watched my older brother who taught me how to grab gears do it. Not that it's all that progressive due to the closeness of ratios, but it comes in handy a lot of times for sure. :drinkup Especially when you've come to a rolling stop at a light, and don't want to drop to the low side.
Mystery Gears is an interesting topic. I remember an old hand showing me a ghost gear in a 9spd. Pulling a long hard grade was ready to go to the low side and start rowing there. He looks over and says "leave it in the high side and shift to one". Worked great. If you went to that hole you did not have to shift down anymore. It would just keep on pulling steady. I guess that is - six to high one. Must be hiding with high reverse.
Range and main shifts together take a little more time. This is where a quick double clutch helps with timing. It gives the range time to shift before the main shift. Example: set the range - clutch to neutral - clutch to gear.
hopefully no ghosts wow, if my driver's spent as much effort perfecting the Art of the Shift as you guys, I'd see alot less of this.
and that is not damaged, just in the middle of installation.
Well right now I always set the range while in 4th just before I go to shift if that's what your saying. Otherwise I haven't tried a double clutch with the range shift ever. I was thinking about it today though and my range shift makes a very noticeable clunk. I don't know if there could be something worn out which is making this harder then it should be. All I really know about the truck is that it left the factory with a 8LL and now has a 13 spd, so no idea what kind of mileage this thing has on the trans.
Ever consider a few Allison automatics?:falldownlaugh
overdrive? I have another question about the 13 speed. I have a 14613 in a 359, is this just a standerd 13 ? So how can you tell the difference between a single O and a double O ? Thanks
If the tag is still on the PTO side (passenger side) of the transmission divedigger, it should say RTO, RTLO or RTX 14613. RTO is single over, the L-O and T-X are double overs. That's jogging my memory now, back into the 80's vintage era.
double o means that you go up againist the dash in 8th direct and still have the over drive split left twhen you do this you have a double o or if you have the right engine and rearend cobo it is a left lane truck just do not get caught if you tack it out in double o it is a triple didget truck for sure .
When your in 4th going to 5th as you come out of 4th let off throttle quick and let jake come on to drop rpm's quicker when you slide it into 5th your speed should be up a little more cause you didn't have to wait so long for your rpm's to drop to 1500, thus you didn't loose as much wheel speed so that when you go to 5th you won't be lugging as much. Hope that is not so confusing. It takes me longer to explain the 1/2 second move than it does to actually do it.
By strange coincidence I'm tearing into an RTLO 18918 18 speed tomorrow! I'll post some pics if you want to see the guts!
That is strange...:idea Be sure to show the shrapnel in the bottom of the case too, would ya'?
you don't split a 15 speed like you do a 13 or an 18. 15 speeds are just 10 speeds with a deep reduction aux bolted on the back...they serve their purpose for only a few selected applications..usually getting a BIG heavy load started... as for Jakes on Cat's..you will find..that they hold back best between 2000 and 2100 rpms..try it.. you'll see..but the older model cats,prior to 2003 just didnt make the brake HP of the new model C-14, C-15's
To shift out of deep reduction in a 15spd 'box on the run you shift to the lever position below the one you're in ie: 3rd deep reduction - move button - shift into 2nd (which with the button up is 7th), this gives the same ratio as 4th deep reduction. Or, 5th deep reduction into 9th. In a 15spd, 6th to 15th are sequential while 1st to 5th overlap 6th to 10th.