Rear end slip

[Riggs]

Upon moderate to hard acceleration, my 98 XLT 4x4 60k feels like it slips/clunks (more like a quick "shlunk" ... a bit gravel-like) repeatedly in the rear. It feels like I'm doing fast and hard shifting with a manual trans. It doesn't seem to repeat the problem when accelerating onto the expressway, only from a stop. Is this a function of the limited slip diff, or is it a problem? It drives great in 2wd in the snow. It's very hard to get the rear to slide, so I would think the limited slip is working. I live in the Chicago area and all our residential streets are pothole ridden and bumpy from salt, snow and cold. Could it be that under medium to hard acceleration the slip kicks in when bouncing over a bump? I briefly mentioned the issue at the dealer once and they gave me the usual "they all do that" answer. It's something I could live with if it's normal ... I just want to be sure it is.

 

[COMMOCOZY]

Riggs-

No sure about your question, but check out the IL guys at NOIEC.com. WE are having a meeting in April if you want to join us.

 

[briantf]

GEM module needs new software

My stupid ass lame wad dealer (Razzarri Ford in Visalia) is such a bunch of morons it's pathetic, but eventually I'm going to force them to download the "BIOS update" for the GEMS unit. You're experiencing a well known phenomenon caused by one of two things:

1) the sensor ring is dirty and is detecting excessive slip in the rear axle as compared to the front, causing the computer to fire up the magnetic clutch in your transfer case. This makes it feel like you are driving over bumpy roads, and only happens accelerating from a standstill.

2) the GEMS unit needs to have its software updated; the firmware revision you are running tries to recalibrate to zero too often/too aggressively, causing minute amounts of slip under initial acceleration to be translated into transfer case lockup. This makes it feel like you are driving over bumpy roads, and only happens accelerating from a standstill.

The aforementioned dingdongs gave me a huge song and dance about how downloading from Ford over their satellite takes hours and hours; they would call when the CD-ROM came in. The dealer we purchased from (not the in-town dingdongs) identified the problem, having attempted to clean the sensor ring to no avail.

I would have your service people check it out; it's a huge PITA, I realize, but you should get it sorted out.

Regards,
Brian in CA

 

[jimbo74]

just a thought could it be an unbalanced driveshaft? that would cause a thunk from a stop but not if it was already moving because it did it at the begining of go

 

[Riggs]

Thaks for all the info!

After searching around the site a bit more there seems to be considerable dicussion of the transfer case slip yoke situation. I guess it needs to be lubed and locktited. Maybe this is the answer. I'll probably wait until I get the funky moaning throttle body replaced (recall) though. I'll be able to hear the transfer case better.

Perhaps it would be better to rephrase my condition as a crunchy:

...slip....slip..slip.......slip...slip................

It's not really dramatic but the rpms do jump slightly with the slippage. Again, it's worse on bumpy pavement.

peter

 

[96Saleen]

i have a 96 with a limited slip rear end and just had it rebuilt by a guy that specializes in rebuilding rear ends on fords. basically, the problem amounted to that fact that it was the bearings and races in the rear end, cost me $400. just one question though, if you answer yes to this, then i know it is your rear end. does it grind worse when you take off from a stop sign and are turning instead of going straight? if yes, then it is time to have it rebuilt.

 

[Riggs]

Actually ... it only slips/grinds/scrunches when I'm accelerating STRAIGHT from a stop ... or at least that's when I notice it, I'll pay attention tomorrow.

peter