'97 Taco V6 4X4 5 speed R150F whining noise in 5th gear

Hey guys,
I have a '97 Taco V6 4X4 5 speed with only 135K on it. The R150F transmission is making a whining noise in 5th gear. 1st thru 4th gear is fine. So I run it on the highway in 4th gear to get to where I am hunting then lock the Aisin hubs for the mud. The Taco has been used primarily as a hunting vehicle here in MS in deep mud/water. I am of the opinion that 5th gear/bearings are worn and it is just time to send the transmission to Marlin for rebuild. Any one had the same problem? Thoughts? TIA!

 

These transmission go 500k plus,
Put redline in

 

Putting Redline MT-90 in the transmission is worth a try. The Amsoil

$30 75W-90 Synthetic Gear Lube - 1 Quart (Pack of 2)

75W-90 I used for many years was WAY better than Mobil 1 gear oil in the R150F 5 speed manual transmission. So I am firmly of the opinion that the type of gear oil used can show a big difference in manual transmission function. Will change the Amsoil 75W-90 gear oil in the transmission out to Redline MT-90 and report if it made any difference.

 

I keep a few used Amsoil oil bags on hand,
I fill the empty Amsoil oil bag up with the redline oil and it makes it a breeze to fill the transmission and Tcase, NO oil pump needed, FYI

 

OK,
I ordered the Redline MT-90 online since I could not find it locally. It arrived and was put in today. I test drove the Tacoma on the Interstate with the Amsoil

$30 75W-90 Synthetic Gear Lube - 1 Quart (Pack of 2)

75W-90 GL-4 Gear lube in it, changed the transmission lube to the Redline MT-90, then test drove the Tacoma over the same course at the same speeds. The Amsoil in the R150F had been in there for 3 years with probably 6-7K severe OFF-ROAD miles on it. 5th gear is noticeably quieter especially under full throttle with the Redline MT-90 and the synchros are working noticeably better thru all the gears. I am sure some of this is simply due to having fresh high quality GL-4 gear lube in the transmission. But I have to give the Redline MT-90 a thumbs-up. It made a noticeable difference in the overall function of my 24 year old gear box. Will take the Taco OFF-ROAD this coming week then make a final decision as to whether to pull the R150F, separate the transmission from the transfer case, then ship the transmission to Marlin for rebuild this summer or let it go a bit further.

 

Looks like some crush washers there. Where can I look up the parts I'll need to do the trans, diffs, and transfer case oil changes? I didn't see anything about it in the owner's manual. Also what diameter tube will I need to pump for the brake flush?

 

I use clear vinyl 3/8" tubing.

$7 Rexka 12pcs Transfer & Differential Service Gasket Kit Compatible with Toyota Lexus 4Runner Land Cruiser Tundra Tacoma FJ Cruiser Highlander RAV4 Sequoia Sienna 1215710010 9043024003 90430A0003

https://www.amazon.com/dp/B07CJHTDVV

Replace the rear differential breather while you're down there. 13mm box/open wrench

$10 Dorman 924-262 Differential Vent Valve Compatible with Select Lexus / Toyota Models

https://www.amazon.com/dp/B00NF1SLT8
@TheloniusDrunk

 

I got the washers from the dealership.
I had the dealership flush the brake system when I had stainless steel lines installed front and rear

 

I did not have a good experience with Red Line MT-90. Within 250-500 miles, I started hearing a whine that sounded like a WWII dive bomber coming in hot.....it got worse and worse until I drained it out and refilled with Royal Purple 75-90 again. I would not use GL4 even though it says it can take it.

 

I have 665,000 miles most of those miles with redline and Supercharged that adds another 100 hp to the transmission, zero issues

 

Yeah...I have read that others have not had any issues with the MT90. I can say that this manual is a transplant from some other Tacoma into my 04 DBL Cab...not sure what year though. Im assuming its an R150F. I was stoked about the MT90 at first but after about 500 miles had a significant whining noise...no...it wasnt the kids....so I went back to the RP 75-90. I say if it works for ya then do it.

 

Ok, so this is not your original transmission and you probably have no history on the maintenance?

I change my running fluids every 75-100k like clock works

 

Yeah....no history. So...other than an R150F...what would it be that its not compatible with the GL4? . The RP works well. No issues AT ALL after swtiching back so.....????

 

No idea but the input shaft bearing is one of the bearings that does go out.

This transmission IF it’s had regular oil changes will last a longggggg time.

If it’s making noise there might be a problem coming your way sooner than later

 

I change my fluids religiously.....and thats whats weird....it didnt start making the whining until I put the MT90 in....so...been running the RP 75-90 with absolutely no issues since. And yeah since then...Ive hauled 3000lbs of concrete, 15 6x12x16 Doug Fir beams and trailers full of crap all over and moved cross country from Washington to the east coast with all our crap...no problems at all. Love it....like a huntin dog man...it just for whatever reason, DID NOT like that GL4 and nothing against them at all I know Redline's reputation is stellar.