I recently bought a '98 Mack RD690P Dump w/ Marmon Herrington AWD w/ only 74k original miles. I am pricking up on everything else very quickly, but can not downshift without coming to a complete stop, I haven't even got lucky one time, just can't get it sorted out. Fortunately it has great breaks, but I am yet to haul anything, and don't plan to until I can p[roperly downshit without stopping. I have made almost every possible adjustments on the clutch and linkage to spec, hoping that was the issue. Although it has made improvements in all other shifting applications and bottom end torque, but I still can't downshift without stopping. SO I am at the point of bringing it in to TEC- Mack dealer or driving back to dealer where I bought it (9hrs away unfortunately). *****I will gladly trade (or pay cash$$ if preferred) construction services 4:1 , spend 2hours with me and I'll knock out an 8hr day of work at the location of your choice. I do anything but paint.( electrical, plumbing, carpentry, concrete, landscaping, foundation, plus land maint./site work, excavator work)...and I am damn good at what I do!! Please reply if you know someone in my area (Reno/Sparks, NV, Lake Tahoe) that is willing to help a self-taught equipment operator learn how to properly downshift an 8LL Eaton. Thanks! Andy Wilson TCB Reno, NV 89509 (775) 432-5296
I assume you're learning shifting a manual transmission in an HD truck. If yes, those transmissions are not syncromesh, meaning, you have to match up input rpm to output rpm or the gears will not mesh. There is no such thing as getting lucky, one either crams it in gear or one does it proper and has things in place to mesh gears. This is a skill that takes time to learn. First thing you need to establish is the rpm spread of the gears, second is the happy rpm range of the engine. As you drive and rev out a gear, when you shift to the next gear what was the rpm spread? 400 rpm? 500? You need to establish what that rpm spread is between gears. Second, what's the governor speed of the engine. 1500, 1800, 2000 rpm? Those two rpm numbers, rpm spread between gears and max governor rpm of engine are critical to know in order to operate the transmission properly.
If you can upshift it, you can downshift it. Find a level parking lot. Ignore the deep reduction, just drive like a 8 speed. Start out slow L,1,2,3,4 rolling, upshifting in the low side, and then shift back down the lowside. When you come out of 4th to get 3rd, pull it out of 4, increase the throttle until it matches with 3rd, and slide it in. Let it slow down (groundspeed) and do the same from 3 to 2, pull it out of 3 increase rpms and let the ground speed slow until it slides in 2. etc. Get it right in the low side, and then go to using the high side. If you still can't get it, find a local dump truck outfit and their oldest driver to get you sorted. If it has a marmon, does it have a low range in the trans? I wouldn't try to get sorted in the low range with awd in, do it in the high side of the drop box without awd.
Stop using the clutch
Got it, thanks for the info, o have heard so molar but mnothi g this thorough, thank you! I have been upshofting mostly by ear, but was told 1600, but like your saying I think it’s different in certain ranges/groupings of gears, I’ll pay absolute attention to RPms and take notes of the spreads in each hear. I will make a note of the rpm at governed top speed of 65, I think that’s what you mean,my guess by ear is 1600, nowhere close to 2k. Thanks for the info, I’ll put it to task tomorrow.
I apologize for the spelling errors, I will not reply from my phone again. I will collect the rpm spreads between gears and the Gov speed rpm tomorrow, and spend more time starring at the tach in general, and paying attention to rpms, focus on the spread between rpms before/during and after the shift and what works between each two gears. The serious issue I have (I hope is operator error, not a bent fork or similar mechanical failure within the gear box): I cannot downshift from/to any gear two gears at any rpm not even 8-7 which I would assume is the most forgiving downshift, not at any spread. Although I havent been consistently looking at rpms, I can discern the difference between a 100 or 600 spread etc.I have tried many combinations at mostly lower rpms, the gears start to grind, I try to fearther the cluth, wiggle the shifter, tap the throttle, slightly raise or lower rpms, upshift and gently try again, still starts to grind immediatly like its not even close to mathcing, unless the truck comes to a complete stop the it slips right in to the lower gear, with the slightest touch. But, now I have a whole lot to work on tommorrow hopefully its just me, thanks again for advice. This forum is awesome, its actually the first post I have ever made on any forum because you are all total badasses that really know your trades. Thanks
Awesome, thank you! Yes, it does have low range in the transfer case as well as transmission, obviously ha. I'll try it out in Low range first sure, thanks. I would have never thought to try to learn in low, all that tourque doesn't make it more difficult? or is that the point? I'll do it, thanks.
I can try that, cant wait! I would not have thought to try it downshifting but I will, I can do the 7 and 8 without the clutch now, is it the same? Just kinda gently tap/bump it in until it matches up and goes? I assume the truck should be slowing down as well as dropping rpms? If it tries to start making that high pitch grinding noise I'm gonna abort. But I'll try a few different gears and rpms. Thanks cfherman!
Pay attention to the engine pitch by ear or rpm when you're upshifting, you'll notice both drop when you hit the next gear. The recverse will happen when downshifting. When you're driving and have hit the lower limits of a gear and need a lower gear the engine rpm will be low. Slide the shift lever into nuetral and blip the throttle enough to bring the engine up to the upper end of the rpm range and then you should be able to slide the stick into the next lower gear. With practice you can do this without the clutch.
Get proficient on flat ground first. The amount of speed the truck gains/loses during the neutral time of the shift going uphill/downhill really affects the RPM you will be aiming for, and if you can make your shift or not, working on hills. You have to be real aggressive with the throttle when downshifting, if you have not figured that out already. The engine and trans need to be brought up to whatever speed they will be when you grab the lower gear.
That makes sense, I will be definately be trying it today. thanks for the info.
Got it, thanks a lot. You have all given me more useful info in 12hrs than 2 weeks of Youtube. I can't thank yall enough, seriously! I've got the perfectly flat dirt road by my property out in the desert to get to work on all your advice. Headed there now!
No, I have been as gentle as i could be with the throttle. I wouldnt have never thought to be aggressive, but not abusive, I get what you mean. Thank you!
Sounds like you are on the right track. If you still feel like a lesson is in order I can message a friend and see. I don't know how far away he is. He drove tankers out west and knows the ropes.
No need to know top governed highway speed, just need to know what's the governed engine rpm. Stick it in any low gear, pull out, and mash the throttle, what rpm does it peg out? That's your top governed engine rpm. That's your max, you operate below that max number, but you have to find out what that number is in order to find your operating window. Otherwise your just guessing at it.
A lot of replies here, and all have merit depending on the skill level of the driver. But I go back to my original post to your thread, that is, I assume you're learning shifting a manual transmission in a HD truck, which you've yet to confirm or deny. But assuming that's correct, you can't shift by ear, you don't have the experience for that yet. Likewise, don't get aggressive, you're learning to drive the truck, not drag race it. Clutch/no clutch. All this will come in time, but if you're just learning a manual tranny, now is not the time for any of the above. You've got to master the fundamentals, you've got to learn to dance. Driving a manual HD tranny, left foot does this, right foot does this, right hand works the stick to lead your partner, and your brain makes decisions on how all this goes, just like dance. And if you don't do it right you'll trip over your own feet. If you're just learning shifting a manual, we've got to teach you how to dance, the rest of it will come in time when you have gained experience.
Willie is giving great advise the only thing I will add when I started out I found it easier to not use the exhaust brake, it slowed the engine too fast and made it hard to match engine speed with transmission speed
Yea, my post was made under the assumption that you already know how to drive a standard transmission in a car, I come from an era where they were more common than automatics. Also, do your practicing unloaded and work on doing things as smoothly as possible. Once you add the weight of a load any abrupt driveline forces can result in breakage. Ususally driveshaft, pinion or axle. Expensive learning experience.
Don't be too gentle..........like a woman........she needs to be manhandled. Don't tell my wife I said that though
Next thing you need to do when you hop in the truck after it's been running and built air up is just full throttle the engine and let it sit there for like 5 minutes, it can do it all day. Once your not scared of that anymore it should be easier
Pick a shift RPM for every upshift that works on your truck. For my 10 speed, 1500 is a nice comfortable spot to upshift. Now, when downshifting, I know that I need to get the RPM above 1500 to downshift. That's the way I teach new drivers too and they get it figured out real quick. The ones that have trouble try to make some half-hearted, tiny stab at the accelerator and never get the RPM high enough. Practice
All the the advise is good only thing I can think of is not to push the clutch down too far and double clutch. Let of gas, clutch a bit, shift to neutral, clutch a bit again, shift up. Downshifting let go of gas, clutch a bit, put your foot into into it (have to know RPMs to ground speed) and put the shifter at the gate, when the RPM's are right it'll slide right in, don't bounce the throttle keep in it. In my truck 5th is 15 MPH every time.
There are some good shifting videos on the net. That's how I got an idea how to drive my new to me dump truck with a 9 speed home from the auction. It was really strange at first and my biggest problem was over revving when shifting up. I found low range shifted best around 1200 RPM without using the clutch. Once in high range you have a lot more flexibility to let it shift and it shifted best around 1600 RPM. Going from the bull low gear to 1st rarely works. I found it's easier to wait till you get on firmer ground and start off in 1st gear. Downshifting make sure your slowing down to the speed of the lower gear and give the throttle a generous push and as it's coming down should slide right in. I think what helped me a lot was not using the clutch like you would in a syncromesh transmission. I'm not very good at shifting but practicing does help a lot. It's the same as I tell kids learning how to use a clutch on a dirt bike: Spend 10 or 15 minutes starting and going 20ft. and stopping until you get it mastered. Unfortunately most kids just want to ride so it takes them a lot longer to figure out the clutch.