F350 Crew Cab Long Bed shudder hypothesis
Feb 19, 2016 11:32:08 GMT -9
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Rocky Fanning likes this
Post by 907jack on Feb 19, 2016 11:32:08 GMT -9
Some of you may experience this problem and some won't but I hope that this is helpful even though it's a work in progress.
When first accelerating I noticed that I had a shake in the drivetrain at low throttle. It only happens at 5-7mph and once past that speed it goes away. At first I thought I had a rear driveshaft problem, like a U-joint or slip yoke maybe even a carrier bearing. Indeed, after inspection I did have pretty worn splines on the slip joint. After replacing that I still had the little shake/shutter at low speed on initial take off. It was better after the driveshaft replacement but not completely resolved. My next thought was the amount of lift with blocks on the rear axle and it was axle wrap. It may still attribute to it but I was talking this over with Rocky one day and he said he had the same problem before his Cummins swap.
He had found what was happening after he placed a gopro under the truck and ran video of the pinion and then back at the t-case. Turns out the t-case moves in a clockwise fashion and creates this shutter. He hasn't had the reoccurance in his truck after he clocked his t-case down for the amount of lift he is running. I am only running 6" of lift and don't think its the answer for me. However, after brainstorming with him I got around to trying out an idea. I drilled the skid plate at the rear edge at a place in between the front and rear output and then placed a ratchet strap over the top of the t-case hooking the front between the skid plate and crossmember and the rear in the hole I drilled. I just tightened it enough to flex the skid plate edge up a little, triple checked that the strap cleared the front output shaft and test drove.
The difference was immediately better. Not completely gone but much less. My next plan is to reinforce the rear edge of the skid plate with some 1x2 square tube and see if it reduces even more. I think its still able to flex the skid plate.
Overall this of course is really only a partial fix for the issue. After comparing the trans/t-case mount to the one I have for my 8.1L Vortec/Allison combo it looks way to small to control the torque it is experiencing. Eventually the mount needs to be redesigned and beefed up quite a bit and then I think I can be rid of the annoying shudder.
BTW, close inspection of the mount did not reveal any ripped inserts, loose bolts, cracked metal or other damage. Since building a new mount and installing it really won't be too terrible I will problably skip the obvious and not just replace the mount with an OEM unless I get a lot of real world feedback from users who absolutely cured the problem with a mount replacement.
Hope ya'll find this helpful. I'll report back as I test new ideas for this and I will try to get some pics up of how I have it rigged.
After this I will be moving on to the 42mph crew cab long bed bounce issue. Some think its a frame flex/oscillation thing. We'll see. And yes, I have double checked the tire balance ;D
Jack
When first accelerating I noticed that I had a shake in the drivetrain at low throttle. It only happens at 5-7mph and once past that speed it goes away. At first I thought I had a rear driveshaft problem, like a U-joint or slip yoke maybe even a carrier bearing. Indeed, after inspection I did have pretty worn splines on the slip joint. After replacing that I still had the little shake/shutter at low speed on initial take off. It was better after the driveshaft replacement but not completely resolved. My next thought was the amount of lift with blocks on the rear axle and it was axle wrap. It may still attribute to it but I was talking this over with Rocky one day and he said he had the same problem before his Cummins swap.
He had found what was happening after he placed a gopro under the truck and ran video of the pinion and then back at the t-case. Turns out the t-case moves in a clockwise fashion and creates this shutter. He hasn't had the reoccurance in his truck after he clocked his t-case down for the amount of lift he is running. I am only running 6" of lift and don't think its the answer for me. However, after brainstorming with him I got around to trying out an idea. I drilled the skid plate at the rear edge at a place in between the front and rear output and then placed a ratchet strap over the top of the t-case hooking the front between the skid plate and crossmember and the rear in the hole I drilled. I just tightened it enough to flex the skid plate edge up a little, triple checked that the strap cleared the front output shaft and test drove.
The difference was immediately better. Not completely gone but much less. My next plan is to reinforce the rear edge of the skid plate with some 1x2 square tube and see if it reduces even more. I think its still able to flex the skid plate.
Overall this of course is really only a partial fix for the issue. After comparing the trans/t-case mount to the one I have for my 8.1L Vortec/Allison combo it looks way to small to control the torque it is experiencing. Eventually the mount needs to be redesigned and beefed up quite a bit and then I think I can be rid of the annoying shudder.
BTW, close inspection of the mount did not reveal any ripped inserts, loose bolts, cracked metal or other damage. Since building a new mount and installing it really won't be too terrible I will problably skip the obvious and not just replace the mount with an OEM unless I get a lot of real world feedback from users who absolutely cured the problem with a mount replacement.
Hope ya'll find this helpful. I'll report back as I test new ideas for this and I will try to get some pics up of how I have it rigged.
After this I will be moving on to the 42mph crew cab long bed bounce issue. Some think its a frame flex/oscillation thing. We'll see. And yes, I have double checked the tire balance ;D
Jack
