tranny thunk
Technical Article Contributor
Joined: Nov 2002
Posts: 2,804
Likes: 9
From: Wisconsin
There is a normal thunk the tranny does when the coast clutch kicks in. The coast clutch disengages when you coast. This is a feature designed into an electronic transmission that allows the truck to coast farther by desengaging the engine from the trasns.
Some cars with this trans seem like they will coast for ever. Three of the four vechicles I own have this. It is most noticable when the trans rpm is low, at 20-40 mph.
If you coast through an intersecion at 25 then punch it the engine will rev faster than the clutch can engange, so you get the thunk when it does engage. I figure this is not good for it, so I'll give it a little gas, then punch it.
It's common for people when they drive an electronic transmission the first time to be concerned about the way it feels.
I don't know a lot about the 4r70w trans, but I have noticed that the coast clutch only disengages in 2nd and 3rd, but not in 1st or OD. There is also a funny feeling you get when you are coasting in 2nd and punch it. First the coast clutch engages, then it downshifts to 1st. All in all, there is a lot of delay going on there.
Some cars with this trans seem like they will coast for ever. Three of the four vechicles I own have this. It is most noticable when the trans rpm is low, at 20-40 mph.
If you coast through an intersecion at 25 then punch it the engine will rev faster than the clutch can engange, so you get the thunk when it does engage. I figure this is not good for it, so I'll give it a little gas, then punch it.
It's common for people when they drive an electronic transmission the first time to be concerned about the way it feels.
I don't know a lot about the 4r70w trans, but I have noticed that the coast clutch only disengages in 2nd and 3rd, but not in 1st or OD. There is also a funny feeling you get when you are coasting in 2nd and punch it. First the coast clutch engages, then it downshifts to 1st. All in all, there is a lot of delay going on there.
Senior Member
Joined: Dec 2001
Posts: 599
Likes: 0
From: N.C.
Originally posted by mxracer514
The driveline clunk is normal but for those that continue to complain lube the slip yoke with a teflon grease if it goes away put a new driveshaft in it and it will usually solve the problem for awhile untill the splines in the driveshaft get some wear and then it comes back.
Most of the time this clunk is felt right has you come to a stop or just has you take off. I tell most of my customers its normal because the noise will come back. Its usually seems to be more of a problem on the 2 wheel drive.
The driveline clunk is normal but for those that continue to complain lube the slip yoke with a teflon grease if it goes away put a new driveshaft in it and it will usually solve the problem for awhile untill the splines in the driveshaft get some wear and then it comes back.
Most of the time this clunk is felt right has you come to a stop or just has you take off. I tell most of my customers its normal because the noise will come back. Its usually seems to be more of a problem on the 2 wheel drive.
It is pretty embarrasing when someone is riding with me, mine really does not sound like a normal thing. I do not feel like it is hurting anything but I would like for it to go away. BTW, my truck is a FX4.
Senior Member
Joined: Mar 2002
Posts: 175
Likes: 0
From: Needville Texas
Greencrew that's very good info however its not the cause of the clunk right before you stop or takeoff. The situation you describe would occur during tip in.
2020is your problem might be the locking differential clutches chattering. This problem can somtimes be fixed by adding friction modifier to the rear axle.
2020is your problem might be the locking differential clutches chattering. This problem can somtimes be fixed by adding friction modifier to the rear axle.
Technical Article Contributor
Joined: Nov 2002
Posts: 2,804
Likes: 9
From: Wisconsin
Originally posted by mxracer514
Greencrew that's very good info however its not the cause of the clunk right before you stop or takeoff. The situation you describe would occur during tip in.
Greencrew that's very good info however its not the cause of the clunk right before you stop or takeoff. The situation you describe would occur during tip in.
Senior Member
Joined: Mar 2002
Posts: 175
Likes: 0
From: Needville Texas
My understanding of the coast clutch is it doesn't engage on a e4od unless the od button has been pushed. My auto trans skills are not real strong. The clunk that I was refering to happens about 5 mph right before you stop. Have a great Memorial weekend.