Aurora 4.0l / Izuzu 5 speed swap into 88 coupe (Page 102/102)
cptsnoopy JUN 05, 11:52 PM
The project Fiero still lives. I had to add a little Freon after 4 years but other than that it’s doing well.
Rickady88GT NOV 05, 07:35 PM
Cool car. I love those engines
cptsnoopy NOV 05, 09:50 PM
Thanks!
Great to get out and drive a couple of times a month
cptsnoopy JAN 14, 10:43 PM
I’ve mentioned this before but the Fiero has always had a high frequency vibration starting at roughly 75-80 mph. I don’t usually drive those speeds so I never really pursued finding the cause of the vibration. As Californians started moving into AZ the speeds on the freeways and highways have increased. If you are driving 75, you are in the way. So a couple of days ago I tried a few things like getting aluminum hub centric rings and having the wheels balanced again. Neither of those made any difference concerning the vibration at higher speeds. My next thought was the differential carrier bearings being a little worn allowing the tripod joints to cause the vibration. When I went out to put the Fiero on the lift I noticed that some transmission fluid had leaked out onto the floor. First time this car has leaked anything since I started driving it about 13 years ago. I did check for side play at the tripod joints and there is enough to be concerned. The fluid is not leaking from the axle seals though. I’ll probably need to drop the cradle to get a better look at the transmission and likely just install the spare one I have on hand.
One question I have though. If I replace the differential carrier bearings, will that remove a lot of the play or not so much? The transmission I have in the car had about 68,000 miles on it when I started driving it. The replacement transmission has about that same mileage on it as well.
I have read that the axle bearing stabilizer/seal is not a good idea. Any other suggestions?

[This message has been edited by cptsnoopy (edited 01-14-2025).]

fieroguru JAN 15, 08:41 AM
If you replace the differential bearings AND properly set the preload, then the play will be largely removed. This is the right way to address this.

It will also make the transmission last longer.

Differential bearing wear changes the gear mesh between the output pinion and ring gear, increasing the stress and load at that point, and leads to transmission failure breaking the case in high power swaps.
cptsnoopy JAN 15, 10:22 AM
Makes sense. I’ll look into that when I get back to working on it. Thank you Fieroguru!
Will JAN 15, 10:29 AM

quote
Originally posted by cptsnoopy:

One question I have though. If I replace the differential carrier bearings, will that remove a lot of the play or not so much? The transmission I have in the car had about 68,000 miles on it when I started driving it. The replacement transmission has about that same mileage on it as well.
I have read that the axle bearing stabilizer/seal is not a good idea. Any other suggestions?




Correct. The stabilizer bearings are not a good idea. My experience is that they gall the surface of the CV joint on which they ride. This happens because that surface is not intended to be a bearing race and is therefore not very hard.

There are two potential sources of play. The first is the differential bearings and their preload. If this is your problem, then the two inner CV joint cups will rock back and forth as a unit in their lateral play. Put a hand on each CV joint (yes, it's awkward) and feel if they move together. Normal driving will eventually cause this wear, although 60,000 miles is low mileage to see it.

The other possibility is that there is wear in the differential itself in the interfaces between the side gears, the side gear thrust washers, and the diff carrier OR the shanks of the inner CV joints and the diff carrier. This is not normal wear. A history of one-wheel-wonder burnouts will do this to a transmission, though. If the inner CV joints rock back and forth independently in their lateral play, this is your problem.

By "high speed vibration" do you mean a high frequency vibration or a wheel frequency vibration that only becomes apparent at high speeds?