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Engine & DrivetrainDiscussions about the engine and drivetrain of your vehicle.
This is a discussion thread titled "transmission down shifting", within the Engine & Drivetrain forum, part of the Technical & Vehicle Assistance Forums category.
I have a 2001 Tundra 4X4 Limited with the 4.7 liter V-8. Often, but not always, when I stop at a light or stop sign it feels like someone just rear-ended me. The truck sort of lurches forward. I think it's the transmission shifting down after it sits for a few seconds but the Toyota dealer insists it's the front shocks "unloading." The only problem with that theory is that if I coast to a gradual stop so there is no dipping in the front end - in other words no loading on the shocks - it still happens. Has anyone else out there experienced this problem? I think Toyota is blowing smoke up my you know what.
It isn't your shocks unloading it is more that likely your drivetrain unloading. Perform a search here for the words "Driveshaft" , "splines", "grease" or something of that nature. You will find this topic has been discussed before. Have you had the driveshaft greased? There are eight fittings (i think?) on the 4x4. Pay close attention to the fitting that greases the rear splines. That should take care of it.
I had the same thing with my '97 Taco but not with my '97 4-runner. It did it when I came to a fast stop. I also asked the dealer. The 4-runner did not have leaf springs.
I have a 2002 2WD and the same problem.
It doesn't do it regularly. Only intermittently. You never know when to expect it. But... it is definitely something in the drivetrain !!!
It's from the driveshaft spline binding up while you brake.
When you stop, it unbinds and you get a "thunk."
All the trucks I've owned and driven have done this at one time or another, you can grease it up (not the most fun thing to do) or live with it.
No it's not from braking. It happens while I have been stopped for a while at a light or something. All of a sudden you feel a bump like someone rear ended you. Only thing is no one is around you!!
I think someone described it BC as "being rearended by the invisible man." I still have the same problem with mine, but the Hellwig lessened it to a certain extent.
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Originally posted by biggary I have a 2001 Tundra 4X4 Limited with the 4.7 liter V-8. Often, but not always, when I stop at a light or stop sign it feels like someone just rear-ended me. The truck sort of lurches forward. I think it's the transmission shifting down after it sits for a few seconds but the Toyota dealer insists it's the front shocks "unloading." The only problem with that theory is that if I coast to a gradual stop so there is no dipping in the front end - in other words no loading on the shocks - it still happens. Has anyone else out there experienced this problem? I think Toyota is blowing smoke up my you know what.
I'm the one that wrote the original solution to the "thump in the rear" (at one time is was called the arkie6 fix) which was caused by binding in the driveshaft slip yoke being relieved when the transmission downshifted immediately after a stop which allowed the driveshaft to compress and the rear springs to un-wrap. The fix involved liberal application of grease to the driveshaft splines. What you have described here sounds like something different. If you get the bump feeling when you ease into a stop, this likely isn't the result of driveshaft slip yoke binding. What you have described sounds like the air conditioning compressor kicking in which also raises engine speed 200-300 RPMs to compensate for the increased engine load. When this happens at a stop light, the increased RPMs will result in increased torque on the torque converter output shaft and it will cause you to creep/lurch forward if you don't have the brake depressed firmly and aren't anticipating it. Next time it happens, look at your tachometer and see if it jumps up a couple hundred RPM at the same time. If this is what is causing the lurch forward, I don't know of any "fix" for this.
I will decelerate at any speed to a stoplight. Come to a complete stop. Be sitting for 5 - 15 seconds and thump. The a/c is not on by the way. I have only had this happen when the a/c is on once. All other times about 8 total the a/c was off. there was no rpm jump and there was no one that rearended me. I was just in the dealership and watched the service tech grease all the joints in the front and rear drive shafts, I watched him do this. I still have the bump/thump/lurch, whatever you want to call it.
Mine did the same thing when new. Drove me crazy. I just followed Arkies advice and lubed the splines on the drive shaft. Also worked in the suspension hauling a load around in the back and towing a trailer. Now mine is perfect and never does it anymore.
Originally posted by Imdone I will decelerate at any speed to a stoplight. Come to a complete stop. Be sitting for 5 - 15 seconds and thump. The a/c is not on by the way. I have only had this happen when the a/c is on once. All other times about 8 total the a/c was off. there was no rpm jump and there was no one that rearended me.
What about the defrost setting? Are you aware that putting the Heat/AC selector in either of the far right defrost positions will cycle the AC compressor on and off regardless of the position of the AC button?
Quote:
I was just in the dealership and watched the service tech grease all the joints in the front and rear drive shafts, I watched him do this. I still have the bump/thump/lurch, whatever you want to call it.
Is there something else that would cause this?
Have you tried braking to a stop moderately hard with the transmission in neutral? If you get the bump when you do this in gear, but don't get it when in neutral, then it is very likely that the driveshaft slip yoke is binding. The only cure that I have found for this is to THOROUGHLY grease the slip yoke - 5 or 6 shots of grease in the slip joint zerk fitting with a grease gun will do nothing to improve this condition because of the large void under the zerk fitting. You will either have to put like 20-40 shots of grease in the zerk fitting (at least until you see the joint begin expanding from the grease and then a few extra for good measure) and drive it through a half dozen or so abrupt stops (or just bounce on the rear bumper real good a few times) and then remove the zerk fitting to relieve any excess grease (you don't want the slip joint completely full of grease or it will restrict compression of the joint). Don't forget to put the zerk fitting back in when you are done.
An alternative is to drop the driveshaft at the rear end and pull the slip yoke apart (match mark both halves of the slip yoke and where the driveshaft bolts to the pinion flange for reassembly). You can then thoroughly hand lubricate the slip yoke splines. I recommend a good quality moly fortified chassis grease for this application (Toyota only recommends the moly grease in the double cardan joint).
Part of the problem with these binding slip yokes is inadequate lubrication from the factory. Another factor, at least on my truck, is the poor machining of the slip yoke splines. I pulled mine apart and believe that I could have done a better job of machining the splines with a Dremel tool - the splines were wavy and irregular, and this was not from wear or galling, this was the way they were manufactured. Fortunately, with the thorough hand lubrication of the slip yoke with moly grease I haven't had any more "bumps" or "thumps" in the rear end in I don't know how long.
transmission down shifting
