Shift pattern 1981 8LL? transmission

[Truck Shop]

Twisted main shaft is not that uncommon. That's why I was betting on a bad main shaft. The torque rating for gear boxes years ago was to low for a range of engines.
Those came from factory behind 3408's, 8V92's and KTA's. The guy I work with had a COE Pete with a 3408 and he would only get about 150 to 200K out of one. He
twisted the main shaft out of three that I recall. And you don't know where that trans came from really.

Truck Shop

 

[92U 3406]

https://www.google.ca/search?dcr=0&...31k1j0i10k1j0i13i30k1j30i10k1.299.5BAWa3610m0

2nd or 3rd link on this list might help you out. I'm no transmission guru but I believe the RTO and RTX are the same transmission but with a different shift bar housing. I can't copy the link to it directly since my tablet just downloads the PDF when I click on it.

 

[coastlogger]

While I hear you all about going thru the whole trans and replacing stuff thats not where Im likely going to go. This trans likely wont see 10000 miles in its expected life,the range synchros etc work fine as is,trans runs quiet etc,Im just interested in solving the two gear issues which I blv the mainshaft will fix. I have the Eaton rebuild manual and will set up clearances as per. OR I might buy the reman,still thinking about it. Anyone have thoughts on the centerpunching of bores in case? Is it common to be able to push a bearing out of its bore? Im thinking theres less than 1 thou of clearance on each bore.Thx for replies theyre extremely helpful.

 

[DMiller]

Never saw need to tighten the bores, always came out fairly easy with a drift and two pound to get it to move on the shaft.

 

[coastlogger]

What Im saying is that the 2 bores are a bit looser than that. I can pretty much push bearing by hand. Theyre not sloppy loose just not tight.
Did the axial clearance thing with old parts just for practice really. I ended up with gaps between gears of around 40 thou where spec is 5 to 12. I think the grooves in mainshaft have worn wider thus increasing this gap. Sound right?
Also my spacers are not in the parts listing for my RTO12515. Mine are 182 thou and part# 14749. The Eaton parts book calls for 14711 thru 14716 part #s, .249 to .274 thickness.My gears are the same part#s as in book .The shaft I have(twisted) is 318729. Book calls for s1341. I did find one for sale on ebay that said it was good for both,they sure look alike.Hopefully theyre same. Anyone have answers?

 

[coastlogger]

Woops the 14749 part is the externally toothed part the spacers are internally toothed(and are without numbers)All makes sense now. The spacers measure in the correct range. Also found an Eaton reference to the s1341 replacing318729 mainshaft so good there too I think.

 

[Truck Shop]

I wouldn't worry to much about the case bores and don't steak them. If the back section is range shifting ok then don't worry about that either. The old Garlock lining
used on the rear synchronizer hub in the back section was better material anyways than the new style replacement. Make sure and refill with 50wt motor oil and not
80-90.

Truck Shop

 

[Tenwheeler]

I wouldn't worry to much about the case bores and don't steak them. If the back section is range shifting ok then don't worry about that either. The old Garlock lining
used on the rear synchronizer hub in the back section was better material anyways than the new style replacement. Make sure and refill with 50wt motor oil and not
80-90.

Truck Shop

Oil question? I have seen transmissions ran with mineral oil, mostly older owner operators, 50W gear oil and then 50W synthetic. One large company, about 15,000 trucks, ran 85-140 in everything. They did not seem to have any more Fuller transmission problems than anyone else. Now you say motor oil? I thought the gear oil had some other additives or properties to protect gear tooth wear.

 

[Birken Vogt]

The manual states 50 motor oil or equivalent weight mineral oil. The modern ones use synthetic 50 Fuller transmission oil that hardly ever needs to be changed. I think smelly gear oil interferes with synchros but probably not too much judging by how many are running it. Still I would stick with what they say. Another reason would be that it seems anything that has an oil pump has to use motor oil type oil. Such as ones with an external cooler. I used to know more about this but I have forgotten.

 

[Tenwheeler]

Thanks for the reply: The 85W-140 folks were not running pumps or coolers. For anyone that does not know do not mix mineral and other oil. It makes jello.

 

[Truck Shop]

Main reason is cold weather the 80 wt is to thick and unnecessary anyway, more drag. The 50wt synthetic is a standard in gear boxes these days and all Eaton transmissions are basically
high torque with a pump plus use the halo top tube for pressure fed spray to help oil the main shaft plus auxiliary drive gear. The Detroit DT12 automatic uses 75X90 synthetic 15 quarts.
Now that said do not use synthetic in transmissions with brass parts it will very slowly deteriorate the brass. Such as an old pickup 4spd transmission-it will shift real good for a while.

Let the clutch out on a cold 10* below zero start in neutral with 80-90 or 85-140 and it will damn near kill the engine.

Truck Shop

 

[Tenwheeler]

Main reason is cold weather the 80 wt is to thick and unnecessary anyway, more drag. The 50wt synthetic is a standard in gear boxes these days and all Eaton transmissions are basically
high torque with a pump plus use the halo top tube for pressure fed spray to help oil the main shaft plus auxiliary drive gear. The Detroit DT12 automatic uses 75X90 synthetic 15 quarts.
Now that said do not use synthetic in transmissions with brass parts it will very slowly deteriorate the brass. Such as an old pickup 4spd transmission-it will shift real good for a while.

Let the clutch out on a cold 10* below zero start in neutral with 80-90 or 85-140 and it will damn near kill the engine.

Truck Shop

That is interesting. A company here has off road equipment with reduction gears in the axle hubs. They run synthetic gear oil and change it every 2,000 hours. Oil out of those hubs looks like gold.

 

[Birken Vogt]

Gear oil and engine oil are on different scales. As far as I know engine oil stops at 60 and gear oil starts at 70. 80W gear oil is like 20 motor oil, 85W is not much different, 50 motor oil would be like 100 gear oil if there was such a thing, and 60 motor oil is like 140. We have an old tractor that takes straight 140 in one of the boxes, that stuff is like molasses even on a hot day.

 

[DMiller]

We always ran mineral based in fullers in the 70's early 80's, when the aerodynes first hit the market can remember all the overheat failed boxes when the manufacturers went to 50wt. Fuller, Spicer even the generic GM and Ford Euro trannies went that way. Only oddball retarded leftover from the dark ages was Jeep. They used a 'Special' available only from Chrysler oil which originated with the older series boxes, Whale Oil but not labeled as such. Use anything else in those Chrysler/Jeep trannies and they would self destruct from lack of lube. Smelled like a trash dump.

 

[coastlogger]

Ordering parts today. A couple of questions arise. The Eaton parts book, on the mainshaft page,where it lists the key,says "must be used with matching washers". I wonder what that means?
I was unable to find the 6504 roll pin that goes in mainshaft anywhere. Hoping the shaft Im getting (used) comes with one or maybe I can extract the one from my twisted shaft and reuse.
Im not ordering any washers yet as the choices are many. Hoping the old ones get me close or I guess Ill measure the axial clearances and order the ones I need. Seeing as how the trans was working,with much higher clearances than spec, Im thinking a few thou above spec might be alright anyway?

 

[Truck Shop]

Ordering parts today. A couple of questions arise. The Eaton parts book, on the mainshaft page,where it lists the key,says "must be used with matching washers". I wonder what that means?
I was unable to find the 6504 roll pin that goes in mainshaft anywhere. Hoping the shaft Im getting (used) comes with one or maybe I can extract the one from my twisted shaft and reuse.
Im not ordering any washers yet as the choices are many. Hoping the old ones get me close or I guess Ill measure the axial clearances and order the ones I need. Seeing as how the trans was working,with much higher clearances than spec, Im thinking a few thou above spec might be alright anyway?

The early key is triangular the later key is ob-long, more than likely the roll pin is in the used shaft if not get one from hardware store and cut to length. And again a slightly loose gear
train on main shaft is better than a tight setup .

Truck Shop

 

[coastlogger]

You were right t.s. the pin was in the shaft. Got the mainshaft assembled and my spacers were right! Got axial clearances in the 8 thou range.
Moving on I'm now installing the ( new)15.5 inch eaton clutch. Using input shaft as alignment bar.got it in and torqued down then noticed the two friction plates or whatever they're called are not exactly in sync ie the fat parts with lining on them are not lined up they're maybe one tooth on the shaft different in orientation. I wonder if this is important?

 

[DMiller]

Ceramic Button clutches need to have the buttons as close to parallel as possible, do not have to be exactly on top of one another but the closer the better, if seriously off center will chatter like all get out and possibly slip having the load off center to each other.

 

[Truck Shop]

Glad to hear it's going together. The drive discs never match up perfectly to each other. Don't worry about it. I always install the clutch loaded in the transmission on 15.5 clutches.
The only thing to line up doing it that way is the pilot, just bar the engine over and start the bolts through the inspection opening in the bell housing and torque to 55lbft.

Truck Shop

 

[DMiller]

Used to do it that way, as I accessed worn out input shafts I began installing the clutch first, just had to remember to rotate the worn out shafts to the clean/smooth side so could get them back out! Still have a few sitting in the drawer!