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OD Oil for A type, Revisited

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hondo402000

hondo402000

Darth Vader
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ok here we go again, My transmission and A type OD were rebuilt last summer, the transmssion is coming out of 2 and 3rd on deceleration. My rebuilder said everything was replaced excpet the shift forks, I have ordered new shif forks, all the springs and balls to replace when I pull the top cover off again, I tightened up the selector rod springs and still does the same. Now my rebuilder specified for me to put Chevy Corvet transmission fluid in my transmission and it is synthetic, I have read all sorts of ideas for oil, 30 weight non det, 80/90 gl4, ATF fluid, I just wonder if the synthetic oil is too slippery, but I cannot figure out what to use instead of the current oil. I read quantum mechanics site that suggest 30 weight oil and why, so I dont know what to use.

only one not suggested is hydrolic oil. Haha

Hondo
 
I just rebuilt my top cover on my 4A. Haven't tested it yet, but I did use a scale to measure the force to move those shifters. I was surprised that 1st/2nd required so much more force than 3rd/4th and Reverse.

I'm curious whether you used a scale as well. The specs are in the book, so I won't try to guess/recall right here.

I'd be surprised if synthetic lube is the culprit, but I learn something quite frequently around here. As for the forks, I'm not sure.

What did surprise me was that one of the cover springs was shown as N/A by MOSS. They must feel it's too easy to find or cut your own. Another surprise was that one of the springs I bought, I think for 3rd/4rth, was too stiff and took almost 30lbs to move the shifter. I doubt that setup would have slipped out of gear--but I just used my old spring and tightened it down a bit more.

By the way, how did you fare getting those taper bolts out of the shifter forks? I broke one and lost 3 weeks of fun.

Good luck.
 
well I have not removed the transmission yet, so dont know about the tapered shifter bolts, I am not sure it was dismanteled so I might have issues, I have a used non OD tranmission that was pulled and is a spare and I might practice on it taking it apart first, I could rebuild its top cover but I would have to drill out the bosses where the switches for the OD go and I here its not as easy as it appears to be.

Hondo
 
When and if you remove the tapered bolts or "setscrews" as they are sometimes called, remember this tip: Use an eight point socket and an impact driver. The impact driver somehow works on the fit to allow the screws to loosen with each blow. Using a straight socket wrench, and even a T-Bar like what I used, can easily result in the setscrew or bolt sheering off at the base, and that is a machine shop mess.

Good luck.

PS By the way, are the forks really a source of the issue of popping out of gear?
 
Is there any chance they replaced or mixed up any of the gears when they rebuilt the tranny? A friend of mine had problems with a "rebuilt" gearbox jumping out of gear on deceleration, which was eventually traced to the rebuilder having used mixed components. TRF has a diagram at

https://trf.zeni.net/TR6bluebook/index.php?page=85

that shows what to look for.

Another possibility is that the big circlip that holds the gears on the mainshaft has jumped out of it's slot. But if that were the case, you'd be noticing other problems IMO, like hard to get into gear.

Did you install the proper locating hardware for the gearbox to engine (plate) joint? The TR6 used special "dowel bolts" originally, which don't seem to be available from the usual LBC suppliers (some of whom are selling ordinary bolts instead). If the gearbox is far enough out of line with the crankshaft, it can cause problems with jumping out of gear (although again it will also make it hard to get into gear).

If the problem is persistant, then IMO it isn't likely to be the shift detents. They are mostly to hold the shift linkage in place, so the fork doesn't press against the shift ring; not to keep the shift ring from moving.

PS, I also doubt that your choice of oil has anything to do with jumping out of gear. The box should work well enough (no jumping out of gear) with just about any kind of oil; the differences between oils are things like minimum wear, best synchro action, easiest shifting, long seal life, etc. My personal favorite is Redline MT-90 (Manual Transmission 90 weight); but it won't make up for an existing mechanical problem.
 
I can only believe that the guy got all the components in the correct places and used the correct parts, in his latestest email he said he thinks its 75 percent possibility that its in the top cover, and could be the shifting forks are worn and not moving the hub all the way in, He is confident its not associated with syncros, gears, clearances etc. so once I get the new shift forks its off with the transmission tunnel (again) and rebuild the top cover with new shift forks and all new springs. If I have to send the transmission out again it will go to someone else to evaluate. He say he only trust a guy in florida that rebuilds transmission properly

Hondo
 
Sounds like I have similar issues, I was popping out of 2nd on deceleration. I was convinced it was a broken 2nd gear bushing but after tearing it down the bushing was fine. The top cover springs were a little weak on mine, they've since been tightened up. I'm running a backup gearbox so can't test if that fixed it.

I'm interested in your theory of worn shift forks - I did see some wear on the forks. I agree though- I don't think oil will fix it, I've used regualr gear oil, VR1, MT90, etc and the symptom stayed the same.
 
I was instructed to increase the spring tension in the top cover which I did by turning the screws in one complete turn but that didnt solve the issue for me

Hondo
 
KVH said:
...I'd be surprised if synthetic lube is the culprit, but I learn something quite frequently around here...
Click to expand...

Hmmm... I also spend time on the Porsche boards because of my 911 RSA.

I can tell you over there this is a <span style="font-weight: bold">huge</span> issue. The theory is today's synthetics are far too slippery for the syncros - this is a real serious issue for "915 style" Porsche (early 80's and older) transmissions. For these transmissions the P-car guys swear by what they call "Dino (as in dinosaur) oil" - hydrocarbon based oil, definitely <span style="font-style: italic"><span style="font-weight: bold">not</span></span> a synthetic. But, I agree with Randall. I'm not sayin' it's why a TR3 trans would pop out of gear - that's a different question. Anyway, take it for what it's worth.
 
I see no where in the bentley book the original thickness of the shift forks or the allowable wear but I measured the spare gear box and it appears the original thickness is 0.275 inch and I measured the worn areas and on 1/2 gear fork and its down to 0.260 and 3/4 gear fork its down to 0.270

and just so happen my transmission builder said they should be between
.260 and .272

Hondo
 
hondo402000 said:
I can only believe that the guy got all the components in the correct places and used the correct parts,
Click to expand...

I'm not saying he didn't. But my friend's rebuild was done by a well known (and BMH approved) LBC supplier in Europe. Even after paying to ship the thing across the Atlantic 5 times, they couldn't find the problem. Herman van den Akker is the one who figured it out.

So, when all else fails (yes, I know it's a pain), check those gears & hubs.
 
luke44 said:
The theory is today's synthetics are far too slippery for the syncros
Click to expand...

I'll agree with that, if you add the proviso <span style="font-weight: bold">some</span> synthetics are too "slippery". But Redline MT-90, which is a synthetic, is actually less "slippery" than dinosaur juice (even motor oil), by design.

Redline also offers some gear oils that are less "slippery", but I've not had occasion to try them.
 
I'd probably re-focus on the ball, spring, shaft and pull resistance.

I'm trying to imagine slipping out of gear in an old British gearbox just because of the oil. I'm not sure I recall anything about a Triumph being that sensitive.

Anyway, gut only.
 
I'm not clear what forces even cause it to pop out of gear - but in my case when I was trying to engine brake a bit on a downgrade twisty road, the gearbox made it very clear it did not want to be in 2nd. Keeping my hand on the gearshift was not going to solve the issue.
 
And you can easily apply a lot more force with your hand than those detents are supposed to hold.
 
I notice from the Moss drawing that the two transmission hub assemblies have a ball and spring to snap in place, somewhat like the shift detents. Are those a possible source of the problem as well?

When mine was fixed after popping out of third, usually during deceleration, the shop said they fixed a broken spring in the shift mechanism--I assumed that meant the detents but I suppose they could have meant elsewhere.
 
The detents in the hub assemblies are only for neutral. They force the synchro rings against the cones on the gears while you are shifting (by transmitting force from the shift ring to the hub itself). But they don't have notches to hold things in gear.

If you look at the TRF drawing I linked to above, in the inset labeled "synchronizer sleeves", you can see a notch that runs through the center of the teeth. That notch is what the 3 balls in the hub engage when the ring is (near) neutral.

It's actually kind of tricky to move the ring on the hub with your fingers, without letting it go too far and launching the balls in 3 different directions.
 
I was told the springs and balls were replaced in the hubs, it didnt look like the springs and balls in the top cover were replaced but I was told the force was set to spec, alos I pulled the top cover off and increased the force by turning the screws one complete turn, I dont have a scale so I dont know what the force is now, but when I replace the shift forks and put new spring in I will purchase a scale and set them correctly
 
I bought a scale from Ace Hardware. Overkill. It will measure the weight of a 50 lb black bass, if there's one out there (still).

I was rather surprised by the force suggested in those specs. But a full extra turn does sound suspicious.

REMEMBER, depending upon your model transmission, the slot for third and fourth gear takes one extra part: a spacer. So there are three things for that shifter fork, not two. They are: spring, ball and spacer.

So, to elaborate, it's possible someone lost or forgot the spacer, or used the newer setup with the plunger and assumed the old spring would work with the newer plunger set, which would not be the case. The required spring for the plunger setup is a different part. I'd check if you had a plunger in that slot, and, if so, whether you have the correct spring. If no plunger, then do you have the ball, spacer and correct spring?
 
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