Manual Transmission Grind

Yes, after you rebuild/repair the first 100 transmissions you get to know them pretty well. I'm an old fart I worked on vehicles for 41 years many of them in the largest transmission shop in the state then got a clean job working for the PD for another 15.

 

I too am older but not as old as you. I also worked as a mechanic for a number of years, put myself through college, and am now a Mechanical Engineer. Although not on transmissions, I rebuilt engines. Doesn't frictional characteristics of the lubricant cause the synchros to operate properly, or if the wrong lube - improperly? Isn't it all about the right amount of friction between the synchros and the cones to get the gear at the right speed to allow engagement? I'm sure if the wrong lube were put in, it would cause all sorts of noise and difficulty shifting. If that's so, then why wouldn't a lube with a bit different frictional characteristics help alleviate the bump grind that a number of 6sp owners complain about. I know redline improved mine. No disrespect, but everyone on the Internet is an expert - You and I included. All sarcasm aside - If lubricant doesn't affect shift quality, then why not use whatever is on sale? Help me understand why it wouldn't potentially improve the grinding?

BTW - Thanks for your service as a PD. You guys don't hear enough of it these days.

 

You guys are having a weird conversation about synchros.... I think you're both coming into it from the same perspective, but you sound somehow like you're arguing over how synchros operate???

Anyhow, yeah. Synchros are VERY sensitive to their lube. But it isn't in my experience so much as having the "right" oil, as it is in having oil that isn't "too viscous" or "too low friction". To seriously oversimplify in layman's terms, the thicker the oil, the worse it works... since it pads the contact between the ring and the cone rather than allowing them to grab hold of each other and pull the gear into synchronization with the shaft before locking it in place. Even a very light weight oil should work well for the synchros, like this stuff; http://www.amsoil.com/shop/by-produ...omesh-transmission-fluid-5w-30/?code=MTFQT-EA ---- however, that light of oil probably wouldn't be the best choice for the gears in the transmission.

I think that for some of the extra notchy transmissions (i.e. the 6-speed), maybe a MIX of 5w30 and 75w90 mt synchromesh fluids could yield an improvement. Perhaps 3 parts 75w90 + 1 part of 5w30? That might pull it down to around a 60w75 or so.

 

I kinda had the opposite happen on my old 2000, when the temperature was really cold it was difficult to shift into 2nd gear until the truck warmed up a little. I tried Amsoil and then it basically refused to go into 2nd when it was cold, I think the stuff was just too slick, I left it in the front and rear diffs and the transfer case but had to switch back to regular for the trans.

 

A synchro will work dry but granted not for very long it is a friction device that brings the freewheeling gear on the main shaft up to the same speed as the fixed hub that way the shift hub can slide over the synchro on to the gear at the same speed. One of the biggest causes of a “grind” is incomplete clutch disengagement or someone shifting fasted than the synchro can bring the gear up to speed. Over the years anything from ATF to heavy gear oil has been uses in transmissions the gear compounds have not changed and synchro alloys have changed back and forth with different mixes. Oil will not “fix” a problem it may improve it but that’s up for conjecture, driving habits have a greater effect. Toyota addressed the issue I have no idea if it made a difference or what they changed. I have no issues with my 6 speed but I can say it was a learning curve.

 

Synchronnized or synchromesh means all the gears are turning all the time. The gears don't move when you shift. When you shift you move clutch collars that lock the output gear for one speed to the shaft. There is one speed where the input and output shafts are connected and the ratio is 1:1, usually 4th gear on a 5 speed transmission. 5th gear would be less than 1:1, called an overdrive gear.

Synchronizers are brass rings that push against a cone on the gear when you move the collar to make it easier to engage a gear.

All modern transmissions are synchronized but not all have the brass rings because they take up space and make the transmission weaker. Heavy duty truck transmission and some race cars don't have them.

As the brass rings are depending on friction to work the lubricant could affect their operation.

More info https://en.wikipedia.org/wiki/Transmission_(mechanics). In the picture at the top right you can see the clutches, the toothy rings between the gears and the brass rings.

I like transmission they are fun, lots of interesting parts to put back in the right place.

 

Thanks for your input, maineah. I'm aware that changing lubricants will not "fix" a mechanical problem. The Toyota 6 spd problem is more a nuance thing. If a different fluid helps the synchro speed slightly, then it will be a operative "fix" to me. I'm getting used to the 6spd. But getting used to it doesn't make it a good, just something that you've adapted to.

Paul

 

Like I said they do have a learning curve it took me couple thousand miles to master the damn thing and I have only owned two automatic vehicles but now I have absolutely no issues with it. The first change of oil got syn gear oil because I bought it for the diffs. No difference. It now has EP oil no change but with time I have come to enjoy my 6 speed and have no shifting issues. Does it have problems? Yes I believe it does and there are many people that have complained about it and it should not be some thing that requires one to learn how to use it. I have not looked but I would bet there are plenty of people with GM's that have complaints also.

 

Since no one has brought it up...........URD short shifter kit. My 5 speed was notchy too. It is also grind sensitive to clutch not being all the way to floor and unattentive shift timing with pedal action. I installed the URD ss kit and shifting is much improved. It's not lube and it's not magic but it sure eliminated the notchy feel and that notchy hesitation is what gets your shift and clutch action out of sync.

On sale at near GB pricing. I paid $99 in a GB..................

http://urdusa.com/store/Short-Throw...-Shifter-05&#39+-Tacoma-4.0/product_info.html

 

What about bleeding the clutch fluid? It uses brake fluid right? As I understand, some models share a reservoir between the clutch master cylinder and brakes. I know it's not a high pressure system like the brakes, but would an occasional purge and fresh fluid have any effect on clutch performance and possibly synchro timing? I know the issues exist right off the assembly line, but does clutch performance degrade as the fluid degrades? I might be over thinking this.

 

Okay, I'm the original poster of this thread. I followed through and bought the Ford Synthetic Manual Transmission Fluid (

$33 Ford XT-M5-QS Full Synthetic Manual Transmission Fluid - 1 Quart, Black

Ford XT-M5-QS) and put it in my truck. I was hoping for just a little improvement, but was already getting used to the "notchiness" of the second to third gear shift.

Well, the fluid change exceeded my expectations by a lot. The transmission shifts noticeably smoother. I was not anticipating such a clear improvement even though friends of mine who have used it in Miatas have all said the same thing. Miatas, by the way, are a little "crunchy" going into 2nd gear when they are cold.

I spent $26 for the two quarts needed and the fluid change took about 1/2 hr for this 68 year old guy to do without a lift. I highly recommend this fluid to anyone who is unhappy with the way their 6 spd. Shifts. Thanks to the other member who dug up the Ford Lube info for me. His post is on the previous page and I don't think that I can get to it without screwing up what I'm typing here. You know who you are! Thanks man. Happy shifting!

Paul

 

Glad to hear it worked out for you!