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SM465 shifting rough

yakmastermax

yakmastermax

1/2 ton status
Joined
Feb 4, 2012
Posts
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Location
Albuquerqu NM/ Austin TX
Hey all, I think my synchros are going out or maybe it is a clutch problem not sure.

I'm having a hell of a time getting the transmission in gear; it slips right in when it rev matches are certain RPMS and speeds but for normal driving it is proving a bear to get the shifter to cooperate. At times I'm afraid I'm gonna break the stick or the forks cause I'm yanking so hard on it. From a standstill, in order to get into first I generally have to shut the engine off, shift in, then turn it on. To make the drive smoother I've been sitting at red lights with the clutch in but that's getting old and probably not great for the throw out bearing.

Sounds like synchros?
clutch adjustment?
Start looking for a new sm465?

thanks!
 
Mechanical or hydro cluch? If mechanical, have you tried adjusting it?
 
My master cylinder on my hydro clutch went out and it was an easy fix and made a difference but i think my sycnros are going bad too
 
yakmastermax said:
mechanical, don't exactly know what goes into a clutch adjustment:D
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Get under the truck and find where the linkage hits the clutch fork on the driver side of the bellhousing. The short horizontal piece that touches the fork is threaded and has a nut for adjustment.
 
black dawg said:
when you slowly let out the clutch with the truck in gear, how far do you let the peddle out befor you start to move?
Click to expand...

maybe 20% of the way, tops. once I'm in gear i can get the tires to chirp just fine. it starts to engage pretty quickly.

what is most interesting to me is how easily it slips into gear when it rev matches. I'll speed up to 4k rpms in 1st, then depress the clutch and push the shifter against 2nd as the truck rolls. it won't go into second until right around 1.5k it just slips right in every time.

thanks again for all the feedback guys. asap i'll get under there and adjust it i'm assuming so that clutch disengages even earlier? (engages around 50% travel?)
 
You don't even need to use the clutch pedal if you are rev matching it.

Martin
 
You should feel about 1" of free play in the clutch pedal before much resistance is felt as you push it in...anything more it might not release enough to allow easy shifting and it'll wipe the synchro's out in short order...not enough free play,and it'll slip,and burn up in a short time...........................................................................................................My guess is if the free play is correct,that your pressure plate isn't releasing fully,it might have a 3 finger style pressure plate that has one finger not releasing that portion of the pressure plate--diagphram pressure plates can "drag" too,but its less likely...the failure of the disc to fully release is what causes the hard shifting......I got pretty good at upshifting my SM465 when I had 2 of the Borg & Beck 3 fingered pressure plates fail in my 72 K5,it would not release at all !..had to shut it off at red lights and put it in granny low ,and start it in gear,then upshift it without using the clutch....my synchro in second gear was never the same after I got another clutch installed,from me trying to jam it into gear when the clutch wasn't releasing..
 
diesel4me said:
You should feel about 1" of free play in the clutch pedal before much resistance is felt as you push it in...anything more it might not release enough to allow easy shifting and it'll wipe the synchro's out in short order...not enough free play,and it'll slip,and burn up in a short time...........................................................................................................My guess is if the free play is correct,that your pressure plate isn't releasing fully,it might have a 3 finger style pressure plate that has one finger not releasing that portion of the pressure plate--diagphram pressure plates can "drag" too,but its less likely...the failure of the disc to fully release is what causes the hard shifting......I got pretty good at upshifting my SM465 when I had 2 of the Borg & Beck 3 fingered pressure plates fail in my 72 K5,it would not release at all !..had to shut it off at red lights and put it in granny low ,and start it in gear,then upshift it without using the clutch....my synchro in second gear was never the same after I got another clutch installed,from me trying to jam it into gear when the clutch wasn't releasing..
Click to expand...

yup i got the three finger style pressure plate.

i've been doing a similar method shutting it off at red lights. I think i'm gonna stop driving till i can change the clutch.
 
how much free play does it have (from where you start to push in the clutch till the feel changes)?
If you do replace the clutch, check the pilot bearing/or bushing very closely, because it can cause this issue.
 
Why would you replace the clutch? Just try adjusting the linkage first.

Martin
 
Mine did the same thing till the slave started leaking a new one fixed everything. That was 6 months ago and clutch is still good. I think you just need to adjust it.
 
thanks guys for the useful tips and pointers; i backed out the nut on the linkage so that the clutch begins to disengage earlier and the shifting problems went away. I hope that i didn't damage the transmission or clutch with all those times i forced it into gear! she's shifting much smoother (as smooth as an sm465) can get :thumb:

thanks again:D
 
I'm sure you put some wear on the synchros. But they are designed to wear a long time.
You might change the fluid, or just suck out a sample and look for brass. I think they are brass in that transmission. Not sure.

All they are designed to do is to spin up or slow down the weight of a gear set as you shift.
Here they are having to try to slip the clutch also since it was still driving the gears.
 
Just be sure there is still some free play at the pedal,if you adjusted it so there is none so it'll release fully,it'll never fully engauge either,and it'll slip and roast the disc in short order....should be about 1" of free play before you feel any real resistance....the 3 finger pressure plates are notorious for having one of the 3 levers break or bend,and that will let the pressure plate get cocked sideways some and make the clutch drag and fail to release fully,adjusting it sometimes "cures" it temporarily,but it'll soon give you more grief down the road most likely...I prefer diaphram style pressure plates after having several 3 finger style ones fail on me in only a few months time under normal daily driving,no abuse whatsoever!..
 
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