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Old 07-08-2013, 04:05 PM
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Synchro break in?

I rebuilt my BW Super T-10, but it seems a little hard to shift. I am expecting it to shift like a hot knife through butter. Maybe my expectations are too high? Maybe the synchros need to break in...what is a normal break in time? I am using straight dino blend 90w gear oil.

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Old 07-08-2013, 04:19 PM
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Oil Viscosity & Speed Synchros

If you rebuilt the trany did you use synchros that have a slot cut across the synchro grooves. These synchros allow the oil to squeeze out of the synchro quicker as they press into the gears tappered surface. This will improve the shifting speed and engagement. Secondly, you should be using a 75W90 gear lube, I prefer synthetic, but thats a personal decision. 90W straight is heavy and will cause the synchro to engage slower that normal and the feel will be a stiff pull on the shifter until the box warms up quite a bit.
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Old 07-08-2013, 05:36 PM
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Also be sure you use gear oil for yellow metals. The regular gear oils presently marketed are not safe for synchro mesh trannys.
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Old 07-08-2013, 06:17 PM
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Quote:
Originally Posted by BOBCRMAN@aol.com View Post
Also be sure you use gear oil for yellow metals. The regular gear oils presently marketed are not safe for synchro mesh trannys.
Thanks for posting this - I learner something today. I knew some lubes are labeled 'for syncromesh transmissions', but I didn't remember that, or know what the difference was until your post (which caused me to look it up).
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Old 07-08-2013, 07:49 PM
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Quote:
Originally Posted by zooma View Post
If you rebuilt the trany did you use synchros that have a slot cut across the synchro grooves. These synchros allow the oil to squeeze out of the synchro quicker as they press into the gears tappered surface. This will improve the shifting speed and engagement. Secondly, you should be using a 75W90 gear lube, I prefer synthetic, but thats a personal decision. 90W straight is heavy and will cause the synchro to engage slower that normal and the feel will be a stiff pull on the shifter until the box warms up quite a bit.
I rebuilt the trans in 2005 and it sat unused until a couple of months ago when I got the truck all back together. I don't remember this far back as far as slots on the synchros...but I would say there were not any.
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Old 07-08-2013, 07:55 PM
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Quote:
Originally Posted by BOBCRMAN@aol.com View Post
Also be sure you use gear oil for yellow metals. The regular gear oils presently marketed are not safe for synchro mesh trannys.
I called Richmond Gear a while back about what oils they recommend even though mine is an OEM trans from 1979, before Richmond was in the picture, and I can't remember what brand of rebuild kit I used...but I figure they had the best insight as to the correct oil. They suggested 75w-90 (synthetic) hypoid oil. But they said to stay away from anything that was for limited slip diffs because of the additives and yellow metals. I couldn't find anything at the local stores that fit the bill, so that is why I used low tech 90weight gear oil.

I do have a bunch of quart bottles of synchromesh I must have purchased some time ago. But that stuff is THIN! I mean its like 20 weight oil. Is that supposed to be used straight up in the trans...or is it supposed to be an additive?

Also is synchromesh a generic term for a manual GM transmission with synchros? Or a GM brand/label?
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Old 07-08-2013, 08:19 PM
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Synchromesh is a term used for most old standard transmissions, Ones that used some kind of synchronizer system to allow smooth gear changes while on the move.
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Old 07-08-2013, 08:24 PM
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Quote:
Originally Posted by BOBCRMAN@aol.com View Post
Synchromesh is a term used for most old standard transmissions, Ones that used some kind of synchronizer system to allow smooth gear changes while on the move.
Thanks!

Any idea on why the Pennzoil Synchromesh I have is so thin? Are there different grades/weights? I am concerned about running this water like oil in there. There is nothing on the label as to what weight it is...I think it says something like "good for all GM manual transmissions"
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Old 07-08-2013, 11:26 PM
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Is your pennzoil this:

Synchromesh manual transmission fluid

Here is the product data:

http://www.pennzoil.com/wp-content/u...rans-Fluid.pdf

it is not suitable for your T-10, it`s for tko:s and such trannys:
PENNZOILŪ SYNCHROMESH FLUID is specifically formulated for synchromesh transmissions used by General Motors
requiring General Motors Part No. 12345349

AutoGear will tell you what oil to use.
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Old 07-09-2013, 08:16 AM
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I can solve this right away. But, I have a couple questions.

When you replaced the synchros, did you replace the synchronizer assembly (hub, sliding clutch/slider, springs and dogs/struts) or did you just replace the brass colored Synchronizer Rings?

Did you inspect the engagement teeth on the mainshaft gears that the slider mates with? Were they in good shape?

Did your hubs and sliders have excessive axial rock?

Is your linkage adjusted properly?

How much oil is in the gearbox?

============
Now that short answer; go to your local Napa and ask for Sta-Lube GL4 75w90. Napa PN is SL24229. This is old school dino-oil with the proper GL4 rating.

You can use a GL5; if, and only if it says GL5/MT-1. The MT1 sub-spec means that it is 'safe' for yellow metals.
If the kid at Napa tries to sell you a different part number, tell him no. You need 'SL24229' and he probably has it at the warehouse. Buy a few quarts if you have to; because after the first 200 miles with lots of shifting you'll want to drain out the lube and refill anyways.
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Old 07-09-2013, 08:27 AM
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Technically 2.5pints to have the proper amount of fluid; however you won't get all of the residual lube out, so just dump 1qt (2pints) of the new stuff in and call it good
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Old 07-09-2013, 08:50 AM
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Quote:
Originally Posted by AutoGear View Post
I can solve this right away. But, I have a couple questions.

When you replaced the synchros, did you replace the synchronizer assembly (hub, sliding clutch/slider, springs and dogs/struts) or did you just replace the brass colored Synchronizer Rings?

Did you inspect the engagement teeth on the mainshaft gears that the slider mates with? Were they in good shape?

Did your hubs and sliders have excessive axial rock?

Is your linkage adjusted properly?

How much oil is in the gearbox?

============
Now that short answer; go to your local Napa and ask for Sta-Lube GL4 75w90. Napa PN is SL24229. This is old school dino-oil with the proper GL4 rating.

You can use a GL5; if, and only if it says GL5/MT-1. The MT1 sub-spec means that it is 'safe' for yellow metals.
If the kid at Napa tries to sell you a different part number, tell him no. You need 'SL24229' and he probably has it at the warehouse. Buy a few quarts if you have to; because after the first 200 miles with lots of shifting you'll want to drain out the lube and refill anyways.
What a great answer! Thanks!

You know the very first thing I did when I began hotrodding was rebuild the trans (guess that makes me a gear head, eh?). I have always worked on stuff, but I was comfortable doing the work. Everything looked good, but I certainly had no experience, let alone knowing if there was excessive axial rock.

I used the old synchro hubs. From memory there were some brass things (looked like DC motor brushes) and springs in the kit...not sure what else was in the synchro pack.

I also haven't found anything on how to adjust the linkage. I had both the Hurst Competition Plus shifter disassembled and the linkage apart. I spent quite a bit of time getting them back together and working smoothly on the workbench before the trans was stabbed back on.

The trans is full...I think it took 2 quarts...maybe it was pints...? Anyway it has 300 miles on it, I will drain and refill with the Napa oil you suggest!
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Old 07-09-2013, 01:30 PM
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Good luck. If the engagement teeth are worn, hub/slider are a sloppy fit, it will degrade the gearboxes performance. the C shaped spring and sort of I beam shaped strut help the transmission shift at low RPMs. Putting the proper amount of lube in the gearbox will help some to cure your condition. Back the shift stops off a little and make sure you don't have carpet or floormats getting in the way of your shifter. Even a really stiff rubber boot can cause frustration. NOW try to dial in your shifter. Put it in neutral, use a pin through the hole in the bottom of the 3 levers to center the assembly and then adjust the shift linkages (1-2, 3-4 and R). Now drive the car. DO NOT lean your hand against the shifter handle while driving. It kills engagement teeth.
Go home and then adjust the shifter stops.

Put trans in 1st, adjust bolt till it makes light contact with shifter handle, back it off slightly and tighten the jam nut. Check this adjustment in 3rd gear. Now put the trans in 2nd and adjust the stop until it makes contact, back it off slightly and retighten the jam nut. Check adjustment in 4th. Run trans through the gears. If you dont hit the stops shifting normally, we're good. Go drive car, smile. Come home; drink beer, smile.
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