trans trouble: unable to downshift

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Joined
Jul 19, 2006
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Location
victoria, bc
hi,

just installed a rebuilt h41 trans into my 76 and everything works well except i can't downshift into second or first until i am rolling at about five m.p.h. there is no grinding at all. it just won't go into gear.

the trans cover and tower were not rebuilt, just the main box, shafts, gears, bearings, etc. top end was simply transplanted from my old one. but i did not have this problem with the old transmission.

i can come up with two possibilities:

1. detent spring/ball issue
2. clutch not engaging fully

any experienced advice greatly appreciated.

thanks.
 
Make sure the clutch is releasing fully first.

It could also be a balky synchro assembly. Try shifting more slowly. The 1-2 synchro is ginormous so it may take some time to spool up the input gear speed so the clutch sleeve will mesh.

If that doesn't help, try double clutching it to match the gear speed.

I doubt it is a top cover problem if it shifts fine when stopped.
 
it could be the clutch. i did have to realign the p/p and cover when installing the rebuilt. but i did not thing to the clutch slave/fork adjustment. also, the t/o bearing is not rubbing when clutch pedal is out.

it is a bit sticky when i am just going thru the gears with the engine off, sitting still. especially 2nd. doesn't want to go all the way into gear. then i clutch a few times, jimmy the stick a bit and then it goes in. but when i'm driving, no way.

i hope this isn't something to do with the rebuild job. man, would i hate to rip this thing down again.
 
took the truck out for another test drive tonight to get more acquainted with the problem. started off shifting like yesterday: not downshifting at all until complete stop, even when double clutching. then, after a bit of low speed around the neighborhood (no insurance) it started to stick in first and second. then it would reluctantly come out of gear after clutching in and out a few times. then it stuck into reverse. additionally, it became nearly impossible to get it into gear from neutral.

more of the story: when i was swapping the top cover and shift tower from the old trans i discovered that there were two missing detent springs. the one from first/second and the other from reverse. this helped to explain why the shifter would just fall out of first gear unless i held it there until the trans engaged. second, it explained why the transmission would slip into reverse while the truck was sloped downward without me actually shifting into reverse. so......... what i did was put in some generic springs which resemble the originals in diameter, gauge, and tension and bolted it onto the new trans.

could this be part of the problem? would the po for some reason have taken out the springs in the first place in order to alleviate the problems i am currently dealing with?

i need someone who knows what they are talking about here. :confused:
 
Your current description sounds more like a clutch hydraulic problem. Could also be that the pushrod is too loose. How much freeplay is there between the throwout bearing and the pressure plate?

would the po for some reason have taken out the springs in the first place in order to alleviate the problems i am currently dealing with?

As far as this goes, it's more likely that the springs were stuck in the tower when it was removed, the po didn't even notice they were there, set the tower down on a grassy knoll in TX, and the rest is history.;p

Best

Mark A.
 
i'll start troubleshooting the clutch. i did just replace it last spring, adjusted pedal height, etc. the t/o bearing is as close as it could be to the p/p without touching. but i'll double check everything and rebleed.

then i'll look into the trans cover. pull out the generic springs i put in, see how that affects it, etc.

but does this sound like it could be a problem in the gearbox itself?
 
tonight i took another look at the situation. one thing that struck me as odd is that when i rolled the truck back and forth with the transmission in neutral the flywheel was turning. this obviously means that the transmission is not actually in neutral. correct??

however, when i put the transmission and t-case in neutral the flywheel stopped turning when i rolled back and forth.

anybody with ideas on this??

thanks
 
yes, detent balls are there.

how could it be in a gear when the shift forks/gates are aligned in the middle like this: - - - ??

is there any way i could have put the top cover on with the gates aligned but with the tranny part way into a gear? could everything be just slightly misaligned? it certainly seems like this may be the problem.

and why does it roll freely when both the transfer and tranny are in neutral but not when transfer is in gear? what would explain that?
 
From all you've said, I'm picking you've got a problem with one of the needle bearings on the main shaft in the gearbox and it's seriously binding...

When you have it in 'neutral' and the flywheel is turning as described, jump in, put foot on brake and try to start it - I'm picking it will start without driving away on you, but will creep if you let the brake off...

if so, it's pull out the gearbox time :(
 
i had another idea flash thru my brain: i may have munched the pilot bearing as i was fighting the last half inch with all i had when installing the thing. could be binding.

yeah, this trans is coming back out :crybaby:
 
A bad pilot bearing doesn't account for why the flywheel turns when you push it with the tranny in neutral. Don't bother with yanking the tranny yet.

The reason the flywheel doesn't turn with the transfer in neutral is because the transfer really is in N.

Yes, the top cover could be installed improperly, but you would expect that it would be unable to shift in one or more gears when standing still.

I would pull the top cover and shift it to watch the fork operation. If the forks move positively and stop in their detents without wobbling I would start to suspect other problems. The cover is hard to get installed properly with the reverse shift fork because the gear slides easily on its shaft.
Stick it in place with a dab of grease while you install the cover.
 
you're right. better to check out the top cover first before yanking the thing.

it shifts like a stubborn mule while sitting with the engine off in the driveway. i don't think i've been able to get it fully into 4th yet. second is a serious problem as well. i had my wife trying to shift with the clutch in and out, in 2h, 4h, 4l, everything while i checked it out from below. when she was unable to get it into a gear, the flywheel was moving slightly, like things weren't lined up, even with the damn clutch pedal down.

the fact that second and fourth are the most difficult could mean something. i don't know....

off with the top cover.

sure LOOKS perty though, don't she?
h41rbld.jpg
 
so, in the end the problem was related to the 4th gear synchro. it was stuck directly against the straight cut gear that is under the sleeve between 3rd and 4th gears and could not be moved. i tried to pry it and it was stuck SOLID. it was causing the whole tranny to malfunction. so i pulled and separated the trans/txfer. then the syncro became unstuck easily and everything looked like it was rolling as it should. anyway, those who rebuilt it are replacing it with another rebuilt.

thanks to all those who gave me feedback along the way.

anybody hazard a guess about what happened? this is obviously way out of my league.

here's a pic.
stuck synchro.jpg
 
I was wondering what this was.

In the picture the 3-4 synchro is in 3rd gear. The "clutch sleeve" slides on the synchro "hub". The hub has 3 "keys" that act as a detent to hold the sleeve in N that are retained by 2 circular springs. The ends of the keys engage slots in the bronze syncro rings. My guess is that the synchro assembly wasn't assembled correctly. Just because it slides now doesn't mean that it is assembled correctly. Make sure that the keys all fit in the slots of the synchro rings. Take a look at the FSM for proper assembly. It is always a good idea to check that everything slides properly after a rebuild.
 

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