50mph Screach

1966 CJ5A V6 tux park.
At about 45-50 I start to get a loud screach/whine when I'm light on the throttle.

However, If I stick my foot in it, the sound becomes a very dull, almost inaudible. if I let off the throttle, it goes away completely.

I'm just looking for some direction before I fire the "parts cannon".

 

Sounds like "U" joint to me.

 

Looked under the hood? Check the fan belt tension?

 

Turn up the radio...
Echoing belts, water pump etc.

 

Back in the day when people complained about how loud our Holley Redline fuel pumps were. The guys were quick to say…if you can hear your fuel pump, you have the wrong exhaust. Lol

 

Another vote to check the front engine accessories; water pump, alternator, fan rubbing shroud?
Also, check both your driveshafts for rub marks. Its possible for the whole engine/transmission/ transfer case to shift around under load due to mushy mounts.
You’ve got to at least narrow down what area of the Jeep to noise is coming from.
-Donny

 

Checked for bobcats?

 

So, after having my local mechanic take a spin, and talking to Herm, we determined that the sound is 3rd gear. Dying T86aa sounds I guess. It's running fine now, but I think I'm gonna ship it to herm for theb"t90 in a t86 box" rebuild. Anyone here done that one?

 

I’d try the same rpm in the same gear in low range before you take another step. That will verify if it’s in the trans or in your rear. It sounds like it could also be a pinion bearing. If it’s not there in low range, investigate the rear.

 

No but if that's the ultimate diagnosis rather than ship it across the continent Sal Walter does top notch work just a few hrs from you. https://vintagejeeper.com/

 

And what does a "dying T86" mean? The gears (the hard to source parts) could be fine. I would look further before sending to Herm. And I was having this conversation with Partsdude4x4 Sam the other day...why does everyone want T90 gears in a T86? Why not just put in a T90 and get a lower 1st? I guess because you don't have one would be one answer.

 

The T86AA and the T90A and T90J all share a 2.79:1 first gear so no advantage there. If BW had ever made a long input shaft version of the T90C, yes that would be beneficial but that never happened and you do need the long input for any of the common conversions. I'm still a bit skeptical that the T86 is the actual problem here. Third gear should not be moving in relationship to the mainshaft when engaged so how would that be making noise?

 

Maybe input or output bearing in the trans?

 

Just some scattered elderly thoughts. I don't believe I have ever had a transfercase or transmission gear screech. Growl, yes. If the input bearing or mainshaft needles are at fault, pretty much constant and varies with engine speed. I have never had a transmission output bearing fail except on the 2 wd version of the SM465. In my experience, failing pinion bearing do not screech either. Again more growling and vibration, especially on deceleration which forces the pinion back in relation to the ring gear.

Maybe the easiest thing to do with this is drain the transmission, transfercase, and rear differential (separately) and carefully examine the gear lube. If any has a lot of metal flake, you likely narrowed the search considerably.

 

My '55 has always done this, and still does this. Goes away under load or coasting, worst when cruising at minimal throttle. In my circumstance, it's the D18 intermediate shaft. I have the Novak hardened intermediate shaft and roller bearing kit waiting to be installed, but have just dealt with the noise in the meantime.

 

Yes, I meant the T90C for the lower gear, (3.34) ran that in my CJ5, and my dad's tux, both with long shaft and V6. Not sure what the application for that shaft is, but in my mind it was pretty common back then. I think it went in the 6-226 pickups.

 

The pickups and wagons used the long shaft T90J with a 2.79 1st gear.

 

Alright, well I'll have to drag that old 3 speed out to see what it is.

 

I think Kaiser only used the T90C to coax a little more "usability" out of the F head. The 226 and 230 didn't really need that coaxing and hence, the T90J was never changed. It always used the 18 tooth input.