5 Ton transmission 3rd gear problem

[msisco]

So my transmission is not shifting in or out of 3rd gear so well. When the truck is cold it will not shift into 3rd at all and once warmed up 20+ minutes it will shift into 3rd and I can down shift into 3rd but it will often grind. To make matters complicated the transmission shift patern does not match the dash plate shift pattern. 4th and 5th gear are reversed, meaning my 4th gear is down to the right and 5th is up to the right when the dash plate shows the opposite. The truck also seems to bog down when shifted into 3rd or forth like the gearing is too tall. The truck seems to pull strong in 1st and 2nd but 3rd and 4th seem like it is lacking power. It will cruise 60 mph in 5th at approx 2200 rpm.

I am thinking I may be in for a pandoras box rebuild or I might just replace this trans. Has any out there done a swap? How hard was it? Can an average mechanic do this or is this a major project? Any one have ideas on this?

1954 M54
465-LDT engine dated 1989

Thank You!
Mike

 

[Josh]

You have the newer OD tranny, They turned the old 4th gear into a new 5th OD gear, They just left the old 5th the same and turned it into 4th.


The dash plate is probably for the old direct drive tranny. Also can you float it into 3rd or double clutch it? Sound like the syncros might just be going out, I dont have a ton of knowledge of the 5ton tranny. Hopefully someone who knows more about it can chime in.

 

[M813A1]

Sounds like you have the newer 5 Sp. O/D trans and the 4th and 5th gear positions are reversed to get more speed out of the tranny !! thosea are the same transmission in the M809 and M939 series of truck !! As for your hard shifting Josh is right in that your syncros may be going out on you !! So it may be time to rebuild or replace your trans !!

 

[Ord22]

check your clutch play. ensure you have enough free travel.

 

[Rgdl]

Third gear is supposed to have synchros on these trucks?? Mine only has it in forth and fifth.

 

[jwaller]

have you tried putting in the correct 40wt motor oil? NOT 80-90.

 

[msisco]

[QUOTE=jwaller;688808]have you tried putting in the correct 40wt motor oil? NOT 80-90.[/QUOTE]


Yikes! I thought I saw that it was suposed to have 80-90 wt gear oil in the manual trans? Can you guys confirm? I guess I always have the issue in the back of my head that the trans has been changed already so I don't know what it came from and what Lubrication Order to work from.

I am going to double check but I thought it took gear oil in the manual trans??

Thank You Guys for any direction here! Anyone ever done syncro rebuilds in these trans? Can a mere mortal do this?

 

[msisco]

I will double check the free play in the clutch but it seems ok.

 

[73m819]

have you tried putting in the correct 40wt motor oil? NOT 80-90.

the LUBE TM-12 on page 2, CALLS for 80/90 gear oil for the TRANS, ECT.

 

[jwaller]

the LUBE TM-12 on page 2, CALLS for 80/90 gear oil for the TRANS, ECT.

ya ron thats what the Lube order calls for just like the deuce, BUT if you ask spicer, it's 40wt motor oil that your supposed to use with it, thats why it's hard to shift them when they are cold, the oil is so thick the synchros's have to work overtime and wear very fast when doing so.

 

[73m819]

I don't have a problem , even cold, shifting, of ALL the BIG trucks that I have had or worked on, NON used 40wt, it seems that 40wt would not have the squish for the loading of the gears, nor would it have the additives that gear oil would have

If you let the truck warm up to op. temp. this should also warm up the trans also, I have seen trans. and axle heaters on real cold wreather trucks

 

[Hammer]

API viscosity ratings for gear oils are not directly comparable with those for motor oil, and they are thinner than the figures suggest. For example, many modern gearboxes use a 75W90 gear oil, which is actually of equivalent viscosity to a 10W40 motor oil.

 

[Hammer]

I took the above statement from a wiki article.

So, I guess it would be ok to just use some Delo 15w40 for the transmission huh?

 

[BIG_RED]

I'm not an expert, just a backyard/oddjobs mechanic. The way I understand it is that engine oil has different additives than gear oil. Piston engine oil has to deal with carbon and junk slipping past the rings so it has additives to keep this in suspension to get it to a filter, where it will be removed from the system. Compressor oil (non industrial compressors), gear oil, electric motor oil, etc. does not expect there to be a filter, so it generally has less detergents (or none) so that it doesn't set free big chunks of sludge that are stuck to the inside of gear cases from previously overheated/overused oil. I have been involved in cases where engine oil set free chunks of stuff when it as used in old transmissions that were long overdue for oil changes. I don't think engine oil would be a bad idea, but I would suggest you check the oil often after it's changed to make sure it isn't setting free all kinds of sludge and garbage. Actually I recommend that on all old transmissions that just had the oil changed, regardless of what new oil is put in. I once revived an engine that sat for 20 years. Had to change the oil and filter 4 times in 2 weeks because of how much sludge was being set free by fresh oil. If I didn't check, the sludge could've plugged up the passages and starved the bearings. I go by the general rule of thumb that if I change something on an old machine (oil, belt, rings, coolant, anything), I check it often for the first little while to make sure nothing bad happens. Just my $0.02

 

[Autocar]

Motor oil and gear oil are different animals. Due to the high contact loading of gear teeth, gear oil has special high pressure additives in it.

 

[Hammer]

Newer gear oils have a lot of additives, GL1 and stuff like that have almost nothing as far as additives go.
Personally, I would swear that the delo 15w40 is thinner then 75w90 gear oil. But what do I know.

 

[OPCOM]

The rating for gearbox lube without the destructive additives is MT-1. Do not use anything that says EP extreme pressure additive. Use a lube with MT-1 on the can, or, go with what Spicer said. Or the TM. gee whiz it is confusing. I put 80-90 MT-1 in my deuce, no issues for 17K miles and then I sold it to a friend. He is still a friend. I spoke with the chemist for the company supplying the lube, he told me that lube designated MT-1 was designed not to harm the yelow metals.

 

[msisco]

Well... I guess I can try some of the 30wt then. Maybe that will help that third gear syncro get in and out of gear. Since it seems to have a problem this will either speed up my repair or delay it. Sounds like a 50/50 to me.

Any of you guys ever rebuilt the syncros or trans? Is it better to swap in a used trans or get into a rebuild?

Thank you guys!

 

[gimpyrobb]

Just saw a syncro on ebay for 160ish, I just sold a 5ton trans for not much more. I'd find a good take out if I were you.

 

[msisco]

Just saw a syncro on ebay for 160ish, I just sold a 5ton trans for not much more. I'd find a good take out if I were you.

That's not to bad. I think I would prefer to buy a used known working trans then. If you know of one please let me know.

Thanks!