95SASMudRunner

I have a SAS 93 4Runner, when the front hubs are locked i get a horrible vibration (i cant go above 10mph!!!) I had the driveshaft balanced-no help, however the truck can be in 4wd with the hubs unlocked and no problem, moreover in 2wd with locked hubs and have a problem! thus the driveshaft is out of the question. I have check the front diff oil, it is ful and clean... A little piece of history, i had a probelm with one of the hubs engaging... this was thought to be fixed, could that play a role in this? Ideas on fixing it? Also the front has a detriot locker in it aswell...

Thanks,
Andrew

L33T35T 4Runner

well if you're in 2wd with your hubs locked, your half-shafts are still spinning your differential, which is spinning your axle. your transfercase and front axle arent connected, but it's still spinning, so it may be an unbalanced axle

marko3xl3

Did you try locking each hub seperatly to eliminate which side the vibration is occuring?

Bobakazi

Sounds like the hubs are having issues. Have you tried rebuilding them? It is not very difficult. First try driving a little with just one hub locked. Then the other. Does it vibrate with only one and not the other?
Also, (I doubt this part) but maybe your Detroit is starting to fail. Does the vibration change at all when cornering?

Elvota

Whenever hubs are locked... the driveshaft spins, just no load if in 2WD.

Maybe remove front driveshaft completly, would eliminate a possible cause.

Did you have a custom DS made for the SAS? Vibrate from day one of install or after some use?

95SASMudRunner

Works fine with drive shaft spinning but hubs unlocked so not thinking the driveshaft is an issue moreover a shop balanced it professionaly giving me zero improvement

wrenchmonster

From your concern on the original post I'd definately take the hubs apart and check to make sure they are okay.

I'd also check the oil in the front diff. What kind of locker in the front? Some are very oil sensative and getting the incorrect type can really wreak havoc.

Are you running different brand or different tread tires front and rear?

95SASMudRunner

Yes I have checked the oil it is full and looks clean, the locker is a Detroit True Track, the tires are the same front and rear however that brings up a good point the front tires a much more worn than the almost new rear ones, they are 35x15.50 tsl/sx's the hubs appeared fine last tear down with no 4wheeling since....

95SASMudRunner

Well heres the deal the hubs worked fine one at a time, then worked fine together, the hubs unlocked n truck in 4wd worked fine too, however its when they are both on at the same time i get the problem, locked hubs + 4wd = vibration, one with out the other = smooth

shiftless89

maybe you got a bad install on the gears? sounds like its binding?

95SASMudRunner

wouldnt think so because they turn fine when in 2wd right?

^VooDoo^

Just an Idea to check.
I have a simular problem right now and I can tell what it is on mine, Yours may be even more serious.
Happens when the hubs locked only no 4x4 but not when unlocked in 4x4.
The shaft and axel need grease, On mine its a High pitch squeal as the axel is viberating in the shaft, Yours may be really dry and chunky from weathering.
Would have been nice if the axel had zerqs in them just for that.
Im going to fix mine as soon as I can find that stupid 2-1/8th socket.

Thats the cause or your locker is binding/fighting between the wheels.

wrenchmonster

I think the Detroit requires LSD fluid. The vibration you are describing when it's in 4wd and underload is text book wrong fluid. I've seen a lot of this on GM product on rear limited slips where owners or the lube shops don't put in an LSD additive like BG.

For the cost of new fluid, it's worth a shot to change the fluid out and add a LSD additive and keep your finger crossed. Unfortunately, the damage may already be done. Even changing out the fluid may not help. The only way you can tell would be to take the 3rd member out and inspect clutches and clearances.

95SASMudRunner

Any other ideas?

Bobakazi

Is this something recent that started happening for no apparent reason and your Truetrac worked fine before, or was there some work done on it and you have the problem since?

95SASMudRunner

Well spoke with Detroit and this is what they said:

"The 90wt oil is a good choice for a Truetrac, friction additive is not required and should not be used."

He seems to think it is due to the differances in tire wear... i measured from ground to top and only get about 1/2 -3/4 inch differance, he thinks its enough any one else have experiance in this area?

wrenchmonster

Well, at least you got the fluid concern checked off your list. Yes, tire wear is an issue for 4wd systems. If you really want, you can mark your tire and run a string around the tread and compare the front to rear circumference of the tires. Tread pattern can make a difference, but circumference would be more critical factoring in gear ratios. I think it would be worth a shot and either get 2 new tires, or maybe borrow a whole set from a buddy. Good luck and keep posting once you figure out what happened.

yota_krazy

you could try rotating your rear tires to the front for diagnostic purposes to see if that changes.

Elvota

If you find a tire size difference... just drop the air pressure in the larger diameter set. Presto, instantly smaller diameter. Might help you troubleshoot at least.

Bobakazi

I'm not preaching, just blabbing. The Truetrac is a LSD, not a lunchbox or spool. I can't imagine it would make you vibrate that much with only 1/2" tire difference. I do try and keep my tires rotated, but I know I have had that much of a difference in the past and had no issues. I suppose if you had access to 4 more rims and tires that could be easily swapped for a hot minute, and see if it still occurs, that is what I would do. Or, you could just disconnect your rear drive and drive for a bit in 4wd. (essentially front wheel drive only) Any comment on my last post?