The mysterious Bump - Jolt - late downshift - etc.

Just bought a 2003 tacoma pre-runner 3.4 v6 auto (119k). I wish I would have noticed the bump before I purchased. You know the one - coming to a stop then *bump*...Letting off the break, then *bump*.

After reading probably every thread available related to this mysterious issue, I've formed an opinion on the bump, and I do believe it is a transmission issue, although I don't think it's a serious transmission issue - though certainly a design flaw.

I just drove over to the toyota dealership and spoke with the senior technician who giggled to himself when I told him the issue. He said, and I quote, "your transmission is doing what it was meant to do - relieving built up pressure." He says the tacomas and tundra's have been doing it for years. He also joked that the problem would only last for 500,000 miles - funny guy, but it did make me feel better.

It just seems so wrong. BTW, many of you think this issue is axel wrap and I'm not sure you're wrong, but in my case, I don't think its axel wrap as the vehicle doesn't jolt when I put the car in neutral and come to a stop.

No real question here, but if anyone cares to add their two cents, please chime.

 

In the process of a scheduled drain and refill, once every two weeks for the next two months. I've already drained and refilled once. The old fluid wasn't that bad, but it did need to be changed.

 

Most that I have read said it is jsut a hard shift down to first gear. One thing I noticed is if you put the truck in "1", take off, then slam on the brakes. No thump. Put it in "D", take off and let it get out of 1st gear, then slam on the brakes. Thump. Def shifting back down to 1st gear

As for the axke wrap, even if it was, it would not do it in neutral because the drivetrain is not "pushing" the vehicle as you try to stop. That is what loads the spring causing axle wrap.

 

If those are the original springs, at 120K they are done. Regardless of the doublsspeak from the toyota rep, the tranny is not the cause of the thumps.

 

No offense digi, but you dont know what ur talking about. My springs are most definitely original and without question in perfect working order. Probably best not spout pure speculation when people need to learn about their vehicle. Ive been around trucks all my life and it does this site a disservice to imply knowlege when it isnt there.

 

well maybe you should just get some new ones anyways! get in on the wheelers group buy! haha

weird problem man, hope you figure it out...unless it is suppose to do that?

 

My Taco does this and I have noticed it is not present when I come to slower or easy stop. And, I believe my 4Runner did it as well but I can't be sure. Regardless, it's not a big issue to me. If it is springs, I'll post it in a year when I replace my springs and shocks.

 

No offense taken Lost.

If your springs are originals, at 120,000 miles +, they very much past their prime and can be the root cause of a lot of what you have complained about.

Not to imply that your experience isn't of value, but if your truck experience lies elsewhere, in other makes and models, it is deceiving you when dealing with stock tacoma leaf springs.

If you are willing to invest a little time, do some searches for some of the terms you used to describe the issues. There have been hundreds of similar examples documented on this site.

 

Yes, I think that is sound advice. Thank you.

 

It's not a problem caused by worn out stock springs. I have OME springs that are less than a year old and I have the same issue with my truck. Could be a transmission issue but I'm still suspicious that it might be some axle wrap not caused by worn soft springs, but by frame flex. I am planning on adding some rear frame plates soon to see if it improves the problem. The rear plates should take care of any of the frame flex that might be happening.

 

Whatever became of your issue Matthew?
I have this going on like many others. Definitely does not happen if I stop slowly. It seems to me that the trans doesnt downshift to 1st until you let off the brake and begin to move again. It doesn't seem healthy but I suppose I can ignore it after a while.

 

Wouldn't Axle Wrap only occur under acceleration? The way i understand the phenomenon, i don't see how it could occur under braking.

 

i think axle wrap term is a bit misleading for this issue. i'd describe it more as driveline binding or something.. i think thats why many say greasing their zerks solved the problem. I'm just hoping its definitely something like this and not a trans issue, but the fact that it doesnt downshift doesn't seem right.


I took this from another thread, its a good description of the issue
http://www.tacomaworld.com/forum/2n...akes-disengaging-after-fronts-jolt-lunge.html

 

i am quite surprised toyota hasnt resolved the issue yet...

 

GM had a similar issue as well. Put gear in Drive, drive vehicle, decelerate to stop, "bump". Release brake pedal and accelerate, "bump". The problem in that case, which may be the same here, is that when you are coming to a stop, using the brake pedal, the axle will "wrap" for lack of a better term, as the rotational force is transferred into heat (from braking) and longitudinal force. (when the momentum of the truck wants to continue, but the brakes are saying 'no')


What this does is causes the leaf springs to wrap up, and alters the angle of the pinion. When the pinion angle is altered, it slightly pushes/pulls on the carrier bearing. When this happens, the slip yoke going into the back of the transmission can bind if it lacks lubrication.
The way we would fix this, which lasted anywhere from 30k miles to 100k depending on the truck, was to remove the driveshaft, then apply a generous amount of silicon sealer (RTV Silicon) around the "teeth" of the slip yoke (not the transmission side, but the driveshaft itself) then reinstall the driveshaft, and allow about 2 hours to cure.
What this does is it fills in the minute amount of "free play" between the yoke of the driveshaft, and the output shaft of the transmission.
Now this of course assumes that your "bump" is the same feeling.

I know there is a lot of belief that the transmission is at fault, but I have years of experience in transmissions from all manufacturers, and I have never seen this bump condition be the fault of the transmission. I seriously doubt that is your condition, but again, without actually looking at your truck, I wouldn't swear to it.
That being said, I would be willing to bet that you will fix this problem with my above suggestion.

 

Axle wrap/spring wrap primarily occurs during braking. The weak stock springs actually allow the axle to rotate a few degrees. The thump happens when the brakes are released, as this releases the stored energy in the wrapped spring.



edit: Ha, beat me to it Bama.

 

my truck does the same thing 03 3.4 v6 prerunner with 94000 mi.

 

okay well i have this same problem with my truck (03 4x4 trd 120xxx miles stock leafs) the only thing i have not yet heard that i may think could be the issue for me is the trans fluid used.... i really dont know anything about transmissions so feel free to call me out but in the winter when my truck is cooler i have no problems at all. But in the summer and the truck is hot it is unavoidable. Is there grades of fluid like engine oil?

just my 2 cents.

edit: fluid levels check out in the correct range too. thought i was just low at first.

 

I need to put the square u-bolt on to clamp the rear springs in hopes of fixing this issue.

Does anyone know where i can find 2.5" square u-bolt with the plate? Ace had 2 and 3 inch but i'd like to go with 2.5'' for a nicer fit. i checked 5 autoparts stores today and home depot and none had it!

I will probably end up fabricating my own just using two long bolts and two metal plates if i cant find any.

EDIT: gonna pick this up today,. it is 2.5"
http://www.autozone.com/autozone/ac...ries-and-Parts/Leaf-Spring-Clamp-Kit/_/N-25fq