'66 1500 slipping out of second gear

[George Bongert]

Originally Posted by Harleyq

I'm rather new to the forum but have spent a lot of time reading posts on here and totally impressed with the level of knowledge here, for most things either so.eone has been through it or knows someone. Not sure on exact numbers on tyranny although it is a 4 speed, or 3 discounting 2nd. It goes I to gear just fine, tends to pop out under load. I agree with the worn gear and changing the synchros while there...thanks for enlightening.

Dave
Medford, Or.

Greetings Dave!

Since it is a 4 SPEED, (shifter on floor) it would be the SM420.

[Harleyq]

Hi, sorry for any confusion, it is indeed a 4 sp out of the floor. I will have the exact nomenclature off the trans tomorrow. I may just be suffering from cranial rectimitus, but it seems there shouldn't be that much difference between a 3 and 4 sp as there is only one more gear added, however, as I stated earlier, I haven't had the pleasure of rebuilding a transmission yet. And not really lookin forward to it either. Thank you for your time and advice, I greatly appreciate it.

[Harleyq]

Thanks George from all that I have found that would be my guess as well. That's a good starting point..
Dave

[George Bongert]

Originally Posted by Harleyq

Hi, sorry for any confusion, it is indeed a 4 sp out of the floor. I will have the exact nomenclature off the trans tomorrow. I may just be suffering from cranial rectimitus, but it seems there shouldn't be that much difference between a 3 and 4 sp as there is only one more gear added, however, as I stated earlier, I haven't had the pleasure of rebuilding a transmission yet. And not really lookin forward to it either. Thank you for your time and advice, I greatly appreciate it.

Greetings Dave!

There is a big difference between the 3 and 4 speed transmissions. For the 3 speed, the transmission can be removed from the truck from underneath the truck without disturbing anything in the cab. Removal of the 4 speed will require the removal of the floor tunnel from the inside of the cab, as well as either removing the shift lever, or the entire top cover/shift fork assembly so that the transmission can be removed from underneath the truck using a transmission jack. The 4 speed is much bulkier and heavier than the 3 speed which can be removed with or without a transmission jack. I have personally removed the SM318 3 speed laying on my back underneath the vehicle more than once. I had a 1963 Chevy Biscayne (car) with the SM318 that jumped out of 3rd (high) gear, so I know that tranny can be removed and reinstalled without using a transmission jack. The SM420 truck 4 speed is an entirely different animal, and will require the use of a transmission jack, unless you are built like Hulk Hogan.

[Harleyq]

Merry Christmas folks, thank you for the I formation, I even know what a sm318 is now lol. I do believe it is a worn gear. It goes into gear just fine with no grinding, and if I baby it, it may stay in second but will feel the spot that is worn. Under load it has no chance of staying in gear. Brings me to my next question...where might I find a second gear for a sm420 4 sp, and any idea what it will set me back? So far I've been blessed and very fortunate in costs for parts. While not original the 350 v8 previous owner put in is in great shape. The only issue needing immediate attention other than tyranny is the heater fan screams like a banshee when first turned on. Took it out cleaned and oiled/wd40'ed and put back in...maybe time for a new one... thanks again for I fo and help.
Dave

[George Bongert]

Originally Posted by Harleyq

Merry Christmas folks, thank you for the I formation, I even know what a sm318 is now lol. I do believe it is a worn gear. It goes into gear just fine with no grinding, and if I baby it, it may stay in second but will feel the spot that is worn. Under load it has no chance of staying in gear. Brings me to my next question...where might I find a second gear for a sm420 4 sp, and any idea what it will set me back? So far I've been blessed and very fortunate in costs for parts. While not original the 350 v8 previous owner put in is in great shape. The only issue needing immediate attention other than tyranny is the heater fan screams like a banshee when first turned on. Took it out cleaned and oiled/wd40'ed and put back in...maybe time for a new one... thanks again for I fo and help.
Dave

Greetings, Dave!

You may very well be able to obtain the part(s) that you need from The Filling Station, LLC
E-mail: fssales@fillingstation.com They specialize in many older model GM Parts. Their phone numbers are;

800-841-6622 (direct line)
and
541-258-2114 (tech line)

Give them a call, and keep us posted. Don't forget to tell them that you need parts for a SM420 transmission!!

[Harleyq]

[Due to holidays and other pressing matters it's been a minute since I've been able to get back to my 1500. I'm having trouble finding a 2nd gear for the sm420 that is in it. Anyone have any suggestions? I guess I made the mistake of starting a new thread to ask the ? since the thread was deleted...oops! Thanks for the help I have recieved here. There is an unlimited amount of knowledge here.

[Harleyq]

Well I guess it would help if I checked up on posts huh? Thanks George for the info I'm on it and will let ya know...

[Harleyq]

Good morning, I think, folks. The filling station was no help on this one George, however, they can help on other needs. Having searched searched far and wide and the internet too, I have learned a couple of things. 1 they no longer make parts for the sm420, I know big surprise there and 2 if ya see the part ya better get it quick. I ha e found a couple of used 2nd gears which I was trying to stay away from but have no choice but to get one. My question is this, there is some wear on some of the teeth is it possible to do so e tack welding and grind back to shape? Without causing any weakness at this spots? I've got the skills to do it just can't remember if it will cause a weak spot if I do that. Anybody else try this?

[kknotts]

Could u have one cut at a machine shop?