tranny leak

[wc63]

my 3 speed 66 gmc is leaking tranny oil from the front and rear seals. i friend suggested i go with thicker gear oil for a quick fix. can this affect the tranny negatively? would it hurt much to try? any help is appreciated.

[Oklahoma]

I would just replace the seals, it would be cheaper than the oil. It would not take much time either.

[1Bad62Pro/Street]

Has the trans sat for along time?
I would also replace the seals.
Go to Asvance Auto Parts or Autozone.
I just bought a rear seal for my THM350 yesterday.

THM350 - Turbo 350 Blow Up

[markeb01]

If the trans is old enough for the seals to be worn out, thicker oil probably won't hurt anything and may slow the leaks a bit. Heavier oil will make the transmission harder to shift especially when cold. You're probably already running 90 wt, so the next step up is 140 or whatever the current markings are, which is quite a bit heavier.

In comparison, when I pulled my Turbo 350 and went back to a manual 4 speed (Richmond Super T10) about 5 years ago, the local manual transmission expert recommended running straight 50 weight Valvoline (not multi-weight) motor oil. I thought he was nuts, but did some Google searching and found many other recommendations saying the same thing, while also realizing many late model manual transmissions actually run automatic transmission fluid for lubricant. I've been running it since the transmission was new. Theoretically it lubricates better since it flows easier into tiny recesses. Shifting is very smooth and much easier than with thicker lube, especially when cold.

I get it at the local Napa store. They don't have it out front, but they do have it in back if you ask for it. 50 wt motor oil won't work in a rear axle, as those must have the thicker hypoid gear lube which also has much different chemical properties.

I mention this to indicate what the transmission requires for lubrication compared to heavy goo that might help plug up a leaking seal. All this of course assumes you are running a stick shift.

[wc63]

the truck has sat for a while. the lady i got it from never used it. it was her late husband's. upon getting it running, it ran nice. just changed the points and it idles and shifts nice. the leak is the main concern (among other things). is there a thread on how to do this? i dont think ill have a problem taking the tranny out, but i wouldnt know where to begin to dismantle it and im not sure if i got the necessary tools. i got regular stuff, but something out of the ordinary or specific to trannies i dont think ill have.

[1Bad62Pro/Street]

Originally Posted by wc63

the truck has sat for a while. the lady i got it from never used it. it was her late husband's. upon getting it running, it ran nice. just changed the points and it idles and shifts nice. the leak is the main concern (among other things). is there a thread on how to do this? i dont think ill have a problem taking the tranny out, but i wouldnt know where to begin to dismantle it and im not sure if i got the necessary tools. i got regular stuff, but something out of the ordinary or specific to trannies i dont think ill have.

Here is one!
TH350 Rebuild Tech:
http://www.hotrodders.com/forum/th35...ch-145361.html

[wc63]

thanks for the quick response mamma jamma, but my truck is a 3 on the tree. its way different than the 350. that tutorial looks too complicated ill probably just save up and hope someone gives me a reasonable quote on a rebuild. i dont think i need it but since the truck will be off and dismantled i might as well.

[1Bad62Pro/Street]

Ooooops....
Sorry, I missed that!
My fault!


Hmmmm...
Maybe I can still help you!
A long ways off from Oxnard,Ca. though.
1960-1964 rebuilt 1/2 ton 3 speed transmission
http://67-72chevytrucks.com/vboard/s...d.php?t=349416

[1Bad62Pro/Street]

Well you have a 66....
Oh well...
Sorry

[raycow]

Thick oil won't really hurt anything other than making the tranny hard to shift when it is cold. However, any oil that is thin enough to pour will still find any leaks that you have.

The tranny doesn't have a front seal, just a slinger. Most leaks are between the bearing retainer and the case, where there should be a paper gasket. One in a thousand will leak where the cluster shaft goes through the case. Front end leaks should be fixed as soon as possible because there is a slight risk that the oil will creep along the shaft and get to the clutch disc.

Ray