I think my transmission is klunky

Jeffrey · 02-06-2008, 05:43 PM

For two months, my van has klunked when slowing to a stop and taking off, but only when it is moving very slowly. I brought my SMB to the local Ford dealer (my first ever service visit) to look into the klunking sound and thud felt when stopping and starting. I had thought it was the brakes, but they were fine. They thought it was a loose bushing, as they will say with all modified vehicles that they don't want responsibility for.. Then the service advisor started telling me about the transmission and the torque converter and how it may build up pressure as it shifts into low gear. Well, that sounded real to me, because the klunk is when I am VERY slowly rolling to a stop and taking off, and then it feels like I have a loose bowling ball underneath banging against a wall, but it would not make that much impact at that slow speed if it were actually there. The sensation is clearly from underneath and now I believe it is the tranny. Have you heard of this? Do torque converters cause this? Do trannies having a hard time going into and out of low create this thunk? Fortunately, when driving at speed, all is well.

The dealer said that if the tranny or TC were not right, I would get a check engine light that I can identify with my scanguage. But no lights or codes. Any experts out there?

Ford_6L_E350 · 02-06-2008, 07:29 PM

What you are hearing may be normal.

When you slow down, the wheels are pushing the engine. All the drivetrain slack is on the coast side of parts. As you get near a complete stop, the engine will get to a point where it is turning faster than the drivetrain and all the slack will transfer to the drive side of all the parts (trans, driveshaft, rear end, etc.) and KLUNK!

I swear sometimes it does it when I take off, sometimes as I slow down. Some vehicles are louder than others, but all automatics do it to some degree. Our vans have bigger, noiser parts than cars have.

Mike

saline · 02-06-2008, 08:00 PM

A worn U joint can also make this noise and vibration. Might check that.

**daveb** · 02-06-2008, 09:28 PM

My van doesn't make much of a noise but my pickup did from day 1. I was told that the "slop" was from behind the spline on the rear drive shaft. Have you tried to put your van in front 2 wheel drive only? See if it still makes the noise in that mode.
Dave.

**BroncoHauler** · 02-06-2008, 09:49 PM

Quote:

Originally Posted by saline

A worn U joint can also make this noise and vibration. Might check that.

That's exactly what I was thinking. Jeffrey, does your SMB have the full floater rear end? If so, unlock the rear hubs, lock the front hubs and engage 4wd. Then you'll be in front wheel drive only, and see if the condition still exists. Or just use the Atlas to go into front wheel drive.

Herb

John Kalmbach · 02-06-2008, 11:32 PM

Hello Jeffrey,

SMB had a number of transfer case rear driveshaft output yokes that didn't have the correct machining on the splines, and over time would exhibit the same type of klunking noise you've described. Check with Heber, the 4x4 supervisor, to see if your unit might have been built about the time this problem surfaced. You'll find Heber to be extremely knowledgeable and very helpful.

Good luck!
John K.

Jeffrey · 02-06-2008, 11:56 PM

Thanks, everyone, for the advice of all kinds. I did a short test today (before reading the replies) by shifting to neutral as I was approaching a stop, and just before the time when the klunk would typically be heard. It no longer happened, substantiating my belief that it is the tranny or rear drive train. I will do a short run of front drive only (on straight pavement) tomorrow to further test the problem. If it should prove to be the transmission, should I press Ford for repair even though the service advisor says this is normal, as do some of you? It is not just a little sound. I feel it strongly in my seat. I doubt the U-joints are bad after only 6.5K miles of careful driving. I'm not counting anything out.

Thanks, John, for your participation on the forum and with this issue in particular. I'll give Heber a call.

VANZILLA · 02-14-2008, 12:51 PM

Jeffery -

IF...it is the tranny and Ford refuses service because it is "normal". My first suggestion would be to switch oil to synthetic. If your van requires SP, then AMSoil is pretty much your only option.

https://www.amsoil.com/storefront/atf.aspx

I immediately noticed a lower oil temperature and smoother shifting after switching.

Jeffrey · 02-14-2008, 02:09 PM

Thanks, Don. I already have the engine Amsoil system. I don't mind doing the tranny, too, but I don't think that should be the solution. Only if Ford does nothing!

DUKCSUN · 02-19-2008, 10:16 AM

Jeffery,

I had a similar situation with mine. Perhaps not quite as bad but noticable especially when creeping through low speed, stop and go, LA traffic on the way out of town on weekends.

I recently changed my transmission fluid (complete swap and flush) with AMSoil recommended trans fluid.

While I also changed both the engine oil, front/rear diff fluid and transfer case oil at the same time, I can report that the "klunk" appears to be gone or now barely noticable.

While its hard to determine what exactly made the problem go away, my bet would be on the better tranny fluid or diff.

Not sure if it helps but just thought I would share my experience.