Engine/Transmission (1998.5 - 2002) will not back up under load

[gskaggs]

I have a 99 3500 2wd w/6spd w/large input shaft and a 425hp clutch. I have a 36ft 5th wheel tavel trailer 14800lbs dry weight,my truck starts jumping when I try to back up. I talked to a lot of driveline shops no answer I,ve got 302000 miles ,Its been a good truck hauled lots of heavy loads. I,ve got 3,54 gears in a dana 80 rear end. I would like to know if anyone has had this problem, and what the solution may be.

 

[steved]

I have a 99 3500 2wd w/6spd w/large input shaft and a 425hp clutch. I have a 36ft 5th wheel tavel trailer 14800lbs dry weight,my truck starts jumping when I try to back up. I talked to a lot of driveline shops no answer I,ve got 302000 miles ,Its been a good truck hauled lots of heavy loads. I,ve got 3,54 gears in a dana 80 rear end. I would like to know if anyone has had this problem, and what the solution may be.

Sounds like clutch chatter to me... could be as simple as the clutch itself or a leaking rear main seal.



steved

 

[PC12Driver]

High HP capacity clutches = grabby clutches. Nature of the beast. Traction bars could help with some of the spring wrap that amplifies the hop, but I don't think that would be a 100% cure. Keeping the rpms up (1200 ish) doesn't let the clutch grab as much, but that's not always practical or good for the clutch. I needed to put a 2-low kit in mine to stop the hop, which is unfortunately not an option for the 2wd crowd.

 

[EGaskamp]

Thats right gskaggs, just normal clutch chatter. I've had this with every high performance clutch I've had. I takes some getting used to, but I've learned to do it to where its not so bad with my OFE.

 

[BILLVO]

When you added this clutch did you put in a new flywheel or if the original was used was it cut. I worked at a driveline shop for a few years and have seen this all too often. When a shop puts in a new clutch they do not cut or grind the flywheel surface to a smooth surface and when new clutch is installed it is grabby or jumpy due to not being smooth. A rag type clutch or common fiber is more forgiving than the higher HP ceramic or button type clutches which grab more aggresively. If the flywheel is in good condition there should never be any grabbing or jumping. If there is tell the shop to reface the flywheel. Grinding it will give abetter finish than shops that cut them. I would check into this. Any gear shop should have known this,they were blowin smoke up yours if they said they havn't seen this.

 

[PC12Driver]

If the flywheel is in good condition there should never be any grabbing or jumping.

Not neccesarily the case with metal-to-metal clutches. Mine was ground flat after it was turned down enough to get through the heat-hardened spots, so the flywheel is certainly not the cause in my case. Everyone that runs a metal-to-metal clutch in these trucks ends up with some level of grabbiness.

 

[BILLVO]

Not neccesarily the case with metal-to-metal clutches. Mine was ground flat after it was turned down enough to get through the heat-hardened spots, so the flywheel is certainly not the cause in my case. Everyone that runs a metal-to-metal clutch in these trucks ends up with some level of grabbiness.

NOT TRUE!!!!!!!!



If the flywheel is ground correctly there WILL BE NO GRABBING no matter what the clutch material unless it has been overheated or slipped excessively. I have ground hundreds of flywheels and have never had a problem. If it is grabby it was not done properly. Many shops that do flywheels do not do the correct maintenance on the grinding machine to keep it true. This is what I have found with flywheels that have had problems they are not true.

 

[EricBu12]

I was in the same boat as you... . I have a heavy 5th as well...



i did the 2WD Low kit.



When you put the truck into 4wd Low, there is a valve you push that keeps the front axle dis-engaged so you are in 2wd low. This has helped enormously!!



I can't remember the name of the member that sells it... . someone might chime in here... Kit was not very expensive, and it works like a charm!



Found it..... Guys name on the TDR is BobV ... -- email address removed --



Here is another thread on the 2wd low kits



https://www.turbodieselregister.com/forums/showthread.php?t=141981&highlight=2wd+Low+kit



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[Tcolesanti]

Holy crap, this dude has a 2wd!!!!!

 

[BILLVO]

Only trouble with it is it will not work for the 02. 5 and newer without the Interaxle lock. It is for the crowd with interaxle lock which is most of you.

 

[PC12Driver]

NOT TRUE!!!!!!!!



If the flywheel is ground correctly there WILL BE NO GRABBING no matter what the clutch material unless it has been overheated or slipped excessively. I have ground hundreds of flywheels and have never had a problem. If it is grabby it was not done properly. Many shops that do flywheels do not do the correct maintenance on the grinding machine to keep it true. This is what I have found with flywheels that have had problems they are not true.

Mine was done on a pair of our high $ machines by one of our high $ machinists. I watched the setup, the grinding, the pre-measuring and post-measuring. It was absolutely flat and had zero hot spots. The clutch has been grabby since I installed it (not terrible, but more so than stock), and I'm the only one who drives it so I know it hasn't been smoked. Everyone that I have talked to about it (except you) has said that is just how metal-to-metal clutches are.



To get a clutch to hold more HP you need to increase spring pressure, increase surface area, and/or make it out of more "sticky" material (as is the case for the metal-to-metal clutches). The metal-to-metal will grab harder (since that's why it's there), and combined with the dynamics of our trucks that will amplify the grabby-ness (a lot of weight, good traction, leaf springs and long lift blocks), you will end up with some level of hop under some conditions. Which typically will be while trying to spot a trailer at low speeds.



Everyone who uses these types of clutches in our trucks experiences this. I really doubt that everyone's flywheels were ground improperly.

 

[BILLVO]

Mine was done on a pair of our high $ machines by one of our high $ machinists. I watched the setup, the grinding, the pre-measuring and post-measuring.

As I have stated many times before $ does not replace knowledge or Quality of work. Did you happen to see how hot the flywheel got while he was gringing it? it has to be done slowly and in stages to prevent it from getting to hot which takes the hardness out of the surface. Most grinding machines cool by running a coolant over the surface while being ground but it can still get too hot. What type of stone did it have,What condition was it in. How hot had the flywheel gotten in the past how many times had it been ground before. How and where did he take the measurements,ect.

Another question is was it (GROUND) or(CUT) If it was cut on a lathe type machine it will be grabby.



As you stated the ceramic button type clutch will be more (GRABBY) but if it is (JUMPY) or (BUCKING) that is not normal.



Sorry I'm off my soap box now.

 

[PC12Driver]

Sorry, I must have missed the "many times" before that you have stated that. So to give you a background on the caliber of work that went into my flywheel:



We turned it down first so we could easily hear and see when we were through the burnt spots from the previously slipping clutch. Then it was on to the grinder to knock off the ridges left by the lathe. Not much grinding, and nobody got burnt when they were handling it, so I doubt the composition of the metal was altered from heat from the machines. As far as "knowledge or quality of work", the guy who did the cutting is the lead machinist in the toolroom of our multi-million dollar manufacturing company. Making something flat hardly taps into his abilities. To measure his work, we (the machinist, one of our gearhead engineers, and myself) ran a dial indicator around the outer, middle, and inner radius of the flywheel to measure the runout.



It was flat. This isn't rocket science.



Our trucks have long leaf springs and lift blocks, both of which will aggravate axle wrap. When the high HP clutch grabs (which we both agree they do) while spotting a trailer, the tires can't slip and the truck/trailer combo won't accelerate quickly because of inertia. The energy has to go somewhere, and that's into the leaf springs. They wrap up and unload, which starts the hop. The truck bounces, which bounces the driver, which in turn bounces the clutch pedal. The bouncing clutch pedal starts the cycle all over again (and add some lopey injectors to heighten the effect). This is where traction bars can really come in handy (and have worked for other members to help with the hop caused by high HP clutches).



Anyone who has maneuvered a trailer (as in 8+k lbs) with a high HP Cummins with an upgraded clutch has experienced the hop. Especially if there's an incline involved. That's just what happens when you put a stickier clutch in our trucks.



Bill, since your truck is an auto, I'm guessing you've never experienced what we're talking about. You really need to see what's going on in this scenario before you start bringing folks "knowledge or quality of work" in to play.





I don't need a soap box...