4 spd shifting issues - HELP!

[HanSoloWS6]

A problem I have been having since I got my truck was after driving for a while, about 20-45 minutes, I couldn't shift into 3rd or 4th, or some times out of 2nd. It's a 4spd manual behind a 6.2 diesel.

It doesn't feel like a clutch problem. It feels more like either shift linkage or something internal. But I was hoping someone may have had the same problem and had a fix. I might try getting a new shifter before tearing into the tranny. And BTW, the fluid level is up, in case that was anyones first thought lol.

Thanks for any help.

[Robert1970C20rstbukt]

Was it grinding any when you tried to shift?

[James McClure]

Han: Cast Iron HD 4 spd? try shifting without the clutch. Clutches are for starting out or stopping. I never use it on the road once I'm rolling. Drove 18 wheeler for 6 or 7 years and never used it. I just went thru this with my 84. Clutch felt fine but would drag just enough to make shifting difficult. Does it grind going into low or reverse? If it does swap out the clutch, especially if it's high mileage or you don't know the trucks history, jim.

[HanSoloWS6]

Originally Posted by Robert1970C20rstbukt

Was it grinding any when you tried to shift?

Nope, no grinding.

One thing I didn't mention was it would feel as if it would get stuck between a forward gear and reverse and not move at all. This it where I would assume it has to be in the linkage or internal. I've been trying to get it started over the last few days so I could get it in my barn to work on it, but now it wont fire. The fuel or filters are probably bad since it sat for a long time. But that's another issue all together lol.

[HanSoloWS6]

Originally Posted by James McClure

Han: Cast Iron HD 4 spd? try shifting without the clutch. Clutches are for starting out or stopping. I never use it on the road once I'm rolling. Drove 18 wheeler for 6 or 7 years and never used it. I just went thru this with my 84. Clutch felt fine but would drag just enough to make shifting difficult. Does it grind going into low or reverse? If it does swap out the clutch, especially if it's high mileage or you don't know the trucks history, jim.

Jim,
I tried float shifting when I dove it daily, but it worked until it got warm/about 20 minutes. The clutch was replaced about 6 months before I got it, but my wifes ex was trying to learn how to drive a manual and failed miserably. Practically got thrown out of the truck by my father-in-law lol. But he didn't drive long enough to put much of a hurt on the clutch. It probably has about 500-1000 miles on the clutch.

After it would get stuck, I could usually pull over and climb under the truck and free things up, but at the same time I couldn't tell if I loosened up the shift linkage or something internal, just from the angle I was at.

[chev74]

well if it started after you clutch was replaced, i think its your clutch adjustment

i dont think you pushing the pedal in is releasing the clutch far enough to totally disengage. there is a threaded rod that sits just about inder the gas pedal that can be adjusted by the nut on it, making it shorter or longer. Thats my best guess

[HanSoloWS6]

Actually, it started doing this about a month or 2 after I got the truck. The clutch works properly as far as I have seen.

[bigtruck81]

Originally Posted by HanSoloWS6

Jim,
I tried float shifting when I dove it daily, but it worked until it got warm/about 20 minutes. The clutch was replaced about 6 months before I got it, but my wifes ex was trying to learn how to drive a manual and failed miserably. Practically got thrown out of the truck by my father-in-law lol. But he didn't drive long enough to put much of a hurt on the clutch. It probably has about 500-1000 miles on the clutch.

After it would get stuck, I could usually pull over and climb under the truck and free things up, but at the same time I couldn't tell if I loosened up the shift linkage or something internal, just from the angle I was at.

i'm confused. a 4 speed in an 84 should be an SM465. it has no external shifter, the shifter rod drops right through the top of the trans into the shift forks insdide the trans. if you're freeing anything up under there, and it will start working again, 100% positive its clutch related. mine was hard to get into 3rd and 4th (or 2 and 3 if you go by factory markings of L-1-2-3)

[HanSoloWS6]

Originally Posted by bigtruck81

i'm confused. a 4 speed in an 84 should be an SM465. it has no external shifter, the shifter rod drops right through the top of the trans into the shift forks insdide the trans. if you're freeing anything up under there, and it will start working again, 100% positive its clutch related. mine was hard to get into 3rd and 4th (or 2 and 3 if you go by factory markings of L-1-2-3)

Actually, it's an '82. I probably didn't mention that in the beginning. It's external linkage. Compared to a 3 speed that I had in my first truck and one in my dad's truck, the rods look somewhat bent more than normal. But it's hard to tell since I can't find a good picture of "new" shift rods.

[Robert1970C20rstbukt]

Does the shift knob have L-1-2-3 on it? If so that's a SM465 transmission. A 3 speed transmission will have externally mounted shift rods, one for reverse and 1st, and one for 2nd and 3rd. This truck is floor shift right?

[HanSoloWS6]

The shift knob is bare. Everything was worn off years ago. It's a floor shift. The linkage and levers are external like a 3 speed Saginaw, IIRC. And I definitely know its a external lever 4 speed since I drove it for about a year before I parked it and had to crawl under it plenty of times lol.

Now when I got the truck and it started having these issues, I thought it could have been an SM465 until I pulled the shifter boot off and saw it was external. I'm not "in the know" too much when it comes to what transmissions came in the truck, so I can only describe what I have.

[HanSoloWS6]

Maybe the shift pattern will help. Probably not much lol.

R 1 3
---2 4

[Robert1970C20rstbukt]

OK now I see. If your truck originally had a manual transmission it was a SM465, somewhere down the line it was changed to your current one. Anyway it sounds like the linkage is the problem. Try lubricating the shift rods with some engine oil if everything looks dry. If that doesn't help they might be out of adjustment. Other than that I don't know too much about those types of transmissions.

[HanSoloWS6]

Well, it is possible that it has been swapped out. My father-in-laws company, that I work for, does some work with a company that rebuilds GM diesels for military and service vehicles. We have another truck, a '92 4x4, with a 6.5 turbo diesel, and it had been replaced by them. I think my truck was bought from them and may have had the trans and engine replaced. I'll have to ask to make sure.

Thanks for the help/suggestions.

[bigtruck81]

yeah, that trans is definitely not stock for the truck.

there was a 3 speed manual available in column shift, and the SM465, nothing else in the way of manual transmisions.

[James McClure]

Morning guys. I worked for GM for 33 years and never saw a 4 speed trans with external linkage unless it was in a car, never a truck. Military or civilian trucks (4 speeds) were all internal linkage. I would be very interested to see a photo (s) of this gear box and related linkage.
The only vehicles I have ever seen with an external type shift linkage were larger trucks where the drivers position was well in front of the shift tower on the transmission, similar to a cab-over design. These were a nighmare to drive and almost impossible to fix as they wore out. You had to syncronize the "slots" in the control head (shifter handle) with the gates in the transmission!! Everything had to be perfect, even the body mounts were an issue because the relationship between the frame and body had to be right.
If you have any photos please send them to "jmcclur2@nycap.rr.com"jim

[HanSoloWS6]

After looking in my Chilton's manual, according to them, it's a 4 speed overdrive, available for 82 and up trucks. I can't remember if it was a Saginaw, Muncie or Borg Warner though. I'll have to get the book and look again.

I'll try to get pictures tomorrow, or maybe tonight when I get back home. I finally got it in my barn, so it'll be easier to work on.

[69cruiser]

Just a thought, I worked at a transmission shop for a couple years, and there were a couple instances where people had the same problem you are talking about. They had replaced their clutches recently as well. the cause of the problem with each of these instances was an un-machined Flywheel.

Replacing a clutch and not machining the flywheel can cause this as the wear pattern from the old cutch may be enough to cause the new clutch to stick ever so slightly causing shifting problems....

My advice would be to take the flywheel in to your local machine shop and get it machined flat..... if you have already done this then just ignore this, but I have seen this problem before and everytime it was an unmachined flywheel.

Cory

[HanSoloWS6]

I have no clue if it was machined or not, so I'll definitely look into that if the cheap/free fixes don't give me any results.

Thanks!

[James McClure]

Morning guys. I stand corrected. Just because I never saw a trans in our trucks with external shift linkage doesn't mean it was never offered as an RPO.
There were 3 manual transmissions available from what I see in the 84 shop manual. One is a 3 speed for 3 on the tree shift, one is a 4 speed with external shift linkage and in the book is called an overdrive, but in reality isn't. The power flow chart shows 4th gear to be directly connected to the input shaft. Ratio is 1 to 1.
Book doesen't give numbers we are used to, or the manufactures name, but lists transmissions by length or RPO. 3 speed is 76MM probably cast iron and made by Saginaw. 4 speed is called an 89MM. It looks like a Muncie but I wouldn't swear to that. Last trans, what we call a 465, is a 117MM in GM talk.
The 465 was also called an "OD" transmission in certain applications\years, when in reality never was an "OD" transmission. The shift knobs were different!! Early 465's had a 1-2-3-4 knob, next came the 1-2-3-OD knob then came the L-1-2-3 knob.
GM shop manuals are real good at telling you how to fix an assembly, but suck at the identity part, mostly to confuse the public I think.
I hope this helps somehow, I'm confused, LOL. jim

[jokersbowtie]

It not much of a pic but the ground is wet!
its from the factory 1984. i was told it was a Borg Warner

[Robert1970C20rstbukt]

I looked in an original '85 Chevrolet 10 thru 30 series repair manual and there sure is a 4 speed external linkage transmission like James described and what Joker has shown above. Soooooooooo, it's factory alright! Ya learn something every day.

[James McClure]

Looking at the pic I see a potential problem. The 3-4 shift lever has "rust trace" showing at the linkage\lever interface (adjustment block). Seems minor but one never knows. I don't know what shifter is in it though. The factory shifter will have a 1/4" hole in it someplace on the shifter body. Loosen all the adjustment blocks and make sure the linkage slides thru them easily. Take a piece of 1/4" rod (drill bit base end works) and insert it into the hole and make sure it bottoms out against the back side of the shifter or trans case (someplace around 2") I know your going to have to jiggle the linkage to get it thru. Once bottomed out finger tighten adjustment nuts against blocks and tighten both nuts on each block equally. (2 9/16 wrenches turned in opposite directions the same ammount) OH, trans MUST BE IN NEUTRAL to make the adjustments. This will eliminate the shifter as a problem. Common sence will tell you if the shifter is damaged. If it's loose with the drill in it, replace the shifter. If it's real rusty, replace it. Hurst makes a lot of shifters, buy a good one. One they make is called a "vertigate". Had one in my 69 Chevelle SS street rod. Great for really fast shifts but not something you would like to drive every day. Upshifts were a snap, getting it back into first was a ***** and backing up required the use of a second shift lever after you got the main lever in neutral. Let us know how you do, call me if you have any problems. I'll walk you thru it. jim

[HanSoloWS6]

I read the adjustment process in the Chilton manual, that's just as Jim posted. I plan to try that as soon as I can work on the truck. It's free and just might work. I haven't been out in the barn though since I moved the truck in.

If it doesn't do the trick, then I'll look for a good replacement shifter. If the shifter doesn't work, then I'll tear down the tranny and replace the clutch. If that doesn't work, I'll swap it all out for a Duramax and Allison tranny lol.

[HanSoloWS6]

I got out to the barn today and got some pic's. Not the greatest and it looks like the same trans as what jokersbowtie posted. Sorry the pic's aren't the best, I didn't have the camera set right lol.