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trans popping out of 4th gear

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M

mudd

Senior Member
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hello all,

just had the overdrive rebuilt, due too the pin on 2nd gear shaft came out and got stuck. so, had the shop fix that and rebuild the OD that was trashed. od drive works great, but now, when letting off the gas, trans wants to pop out of 4th gear.

is their an adjustment someplace for this, or does the trans have to come out AGAIN :-(
 
Unusual for fourth (4th) gear to disengage, as it's usually the indirect gears that are most susceptible, but I guess you can prove it happens.

The first place I'd be lookin , is that NEW detent springs were installed in the two (2) synchromesh hubs (3 + 3 = 6 total) and three (3) NEW detent springs installed for the selector rods.

The springs for the selector rods can be replaced with the trans in situ, but the whole thing needs to be torn down to access the synchro hubs.

A shop that doesn't replace these known (and clearly inexpensive) parts shouldn't be taking on work that's this labor intensive in the first place. I'd try to get them to comp the labor for R&R the xmsn, plus the basic tear-down and reassembly. On the other hand, if they only worked to the level of satisfaction you have now, when they were being paid for it, what kind of work will they do for free...?

Synchrmesh hub for 3rd/4th gear:

IMG_7289.jpg


IMG_7294.jpg


Shift selector rods (side-shift xmsn, but typical for both):

IMG_7358.jpg


IMG_7384.jpg


IMG_7385.jpg


Edit: here's the link to the entire album for the assembly of that particular trans. Note that nearly every part received some type of polymer coating; either a dry-film lubricant or a thermal dispersant or thermal barrier.

https://www.spcarsplus.com/gallery3/index...assembly?page=3
 
In my experience, limited mostly to older 3 speed US cars and some 4 speeds, coming out of high gear is often attributed to the input shaft either whipping or simply worn items. Randy is right in trying the easy fix first, check and/or replace the shift rod detent springs and ball bearings. After that, I fear that the trans will need come be back out.

Did the trans pop out of 4th before the work?? if not, then you may take it back and tell them it didn't do it before they worked on it, and they will probably check it out and tell you what is wrong. It may be their fault as Randy says about the syncro detent springs, or it may be wear.

Coming out of high gear may be due to a worn pilot bearing on the input shaft which will cause the shaft to whip and work its way out of gear. Or it may be a worn input shaft ball bearing also causing the shaft to whip. And the final, worst case, is a worn syncro hub, input shaft, and syncro drum. That would be fairly expensive, and the parts may be hard to find.

I don't know if this helped, but I love Randy's pictures...8^)
 
FWIW, my BJ8's gearbox would pop out of 4th coasting down steep downhill grades after we rebuilt it (we didn't replace any detent springs). After a couple thousand miles it quit doing that and has been fine for about 90K since.
 
Are the dowel bolts fitted correctly to the bellhousing? This could give the same conditions mentioned above where the input shaft is not on the same line as the mainshaft.

Andy.
 
(Are the dowel bolts fitted correctly to the bellhousing? This could give the same conditions mentioned above where the input shaft is not on the same line as the mainshaft.)

it slid right in and bolted up easily.



nope, didnt pop out of 4th gear before. just the trans got stuck in 2nd because the pin fell out of the 2nd gear shifting arm. while fixing that, decided to rebuild the overdrive. got it back, put it in and pop, as soon as i let off the gas in 4th, it popped out. terry at toy shop thought it might be the shifter was hitting and wasnt going all the way back, but we took the spring and clip out, wasnt in the way and still popped out, so i removed the redline gear oil and put in 20/50 castrol, no difference, stil popps.so now, he gets to remove the trans and interior, i did my part,already took it out once and put it back in, and it didnt pop out until he fixed the arm and over drive. so will keep you posted.

thanks for all the info though
 
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