Shuddering at 4700 rpm

[kvn113]

Hello all my name is: Kevin
I have a: '95 STEALTH TT
It has the following issue: Shudders between 4300 and 4700 rpm at max boost

I first noticed the problem a couple of weeks ago. While I was overtaking going up a steep hill, the car started to shudder and the acceleration rate dropped. Gauges all held steady and once I got past 4700 RPM, it smoothed out and jumped ahead.

Since then the issue has been completely reproducible. When accelerating under a load and RPMs get between 4300 and 4700 RPM while under boost, the car shudders at about 2 Hz.

Shudder might not be completely accurate, but it really felt like the clutch was slipping, so I replaced it. No joy. No change in symptoms.

While it was in the shop for the clutch, it was suggested that the carrier bearings might be worn, but that was only suggested after the clutch did not fix the problem, so I’m a little suspect. There is definitely some play in the rear one and possibly a little in the forward one. U-joints don’t seem too bad.

It dawned on me (much too late) that it might be engine rather than driveline. Maybe timing or fuel delivery issue or a leak in a turbo line … but it otherwise runs smoothly.

Clearly, I need some direction here. Help, please?

[Enda]

I’m no expert but I’d check the Drive shafts and prop shaft. How much play are you getting at the carrier bearing?
Enda

[lovbyts]

Get underneath and push up, pull down on the drive shaft. Mine didnt really have a vibration or I just didnt notice but when I was having something else repaired they showed me how much play it had due to bad bearings.

[91GTOtt]

Check your compression. Air filter. Fuel filter. How many miles on your car? Turbos could be warn. It’s also possible the intercoolers could be developing a clog in the lines that connect to the radiator not allowing the air to cool sufficiently; the more boost your giving it, the warmer the air passing through them.

[kvn113]

Thanks for the responses!

Enda and Paul:
There is definitely play in the carrier bearings. I was at a bad angle on the floor just now, but even without the leverage, I could move them what I thought was a fair distance (cm+). What looked concerning to me was how off-center they appeared to be. There was roughly 3x the space above the shaft as below. I’m not sure if that is reasonable.

Aft Bearing

Forward bearing

If you zoom in, you can probably see that the condition of the rubber boots is less than great.

I also noted a suspicious “clean” area on the aft shaft.

Any thoughts?

Walter:
My apologies… I was not complete in providing history despite the clear instructions - my bad.

I have no real history of the first 7,500 miles other than it was purchased new in Cleveland in mid 1996 and reportedly driven as a daily driver. My father purchased it from a dealership in June of 1997. Since then the car has seen rain exactly three times. It required no repairs and received regular oil changes.

In July of this year, Dad decided that he’d rather not drive it anymore, and I took custody. When I took possession everything was still original including the tires. It had just over 22k miles on it.

Since I took over, I replaced the timing belt, water pump, and flushed the coolant (Thanks, Joe!). I installed a new speed sensor (Thanks again, Joe) and changed the fuel filter, oil filter, and air filter. I also replaced the O-ring at the rear turbo. I did not do the same for the front turbo as I did not disturb that during the timing belt change. Oh, and yes: new tires.

Between bringing it to Pennsylvania and weekend drives, the odometer now reads 24k. So it’s seen more miles in the last 4 months than it has seen in any year out of the last 24.

I really hope you are wrong about the intercooler, but it sounds more than plausible.

I very much appreciate any and all thoughts. Thank you for the help.

[lovbyts]

One step at a time. Easy enough decision to replace the drive line bearings and go form there seeing if its still having the same problem. Pretty clear they need replaced either way.