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Transmission grinding!

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John_Progess

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A friend has a tri carb that he says has a faint grind whenever he shifts gears like the synchro's aren't working. When down shifting he says he has to double clutch. I am going to check out his slave cylinder for proper length of travel (approx 3/8" to 1/2" ?) but I suspect he has a clutch problem. He had the tranny rebuilt with new synchro's by a very knowledgeable Healey owner here in town. Any suggestions of things to check? Thanks and have a good day!

John
 
One of the other threads discussed possible problems with synthetic gear oil being a cause for good syncros not doing their job. Just a thought.
 
I agree. The lower the coefficient of drag, the harder it is for synchros to do their job. I now use GM Synchromesh Modified in my transmission. It was designed by GM to address the problem you describe. My gear box shifts great (but I only have 100 miles on the car, so this is in the FWIW category at best.)
 
Me too!!!- :iagree: with all the comments above.--Keoke
 
My gut feel is a problem with the clutch hydraulics.

FWIW, my Mustang GT with 5-speed didn't shift as smoothly as I expected when I first got it. On the recommendation of a Mustang racer I replaced the factory fluid with Royal Purple Synchromax. It seemed to help, but I also got better at timing my shifts. The RP is supposed to improve shifting over time; it must condition the synchros somehow.

I use MT90 in my BJ8 and have never had a problem with the synchros (didn't with engine oil, either).
 
BJ8 Synchros different than those used in the earlier cars BOb.--Keoke
 
The synchro rings sold by Denis Welch are the best available , the standard offering from others will cause this problem where going to heavier oil won't fix. Had the same problem in my tri carb. Now it won't grind even on the hardest down shift into second. Check the parts receipt. Worse case scenario , they aren't hard to change. Coupla hours or so...
 
Heavier or lighter oil is not the issue. Coefficient of drag is the issue. Think slippery here. The synthetics offer long engine life at low viscosity due to how slippery they are. That is good for engines, but bad for synchros which actually work on friction and drag. How can the synchro start spinning the next gear if the oil is so slippery that it won't allow the two surfaces (synchro and gear) to generate drag. This is why different companies offer oils specifically for transmissions. The oil has some type of additive that increases the coefficient of drag so the synchro can drag the next gear into motion and spin it up to speed before it is selected.

I'm no expert in this field, but I got the information from a tribiologist (look it up) unaffiliated with any lubricant producer.

As for oil that somehow treats the surface of the synchro, I never heard of that, but the synchros are brass so perhaps it is possible.
 
Yep. Redline, for one, is pretty specific about synchronizer properties and coefficient of friction:

https://www.redlineoil.com/product.aspx?pid=46&pcid=7

NFW, etc.--I've just been generally happy with Redline products.

The racer said my Mustang's gearbox would shift better with Synchromax over time. I took that to mean the oil would somehow condition the gears and/or synchros but I don't know exactly how. The shifting did improve (but I was hitting my shift points better, too). Note that Synchromax is for gearboxes that specify ATF or similar fluids, which I believe have ingredients to enhance friction since the clutch bands in ATs require some friction to operate.
 
The tranny has heavy gears with lots of enertia. I'm not sure the grinding problem can be easily overcome. I think the reason the transmission synchros were changed for later models may have been because of problems with synchros overcoming enertia. I have the Welsh synchros and still have to shift slowly to avoid a grind between 2nd & 3rd. It's worse at high rpm. Perhaps someone knows why the synchros were changed??
 
Redline MT90 worked wonders for my trans...Had it filled with Castrol GTX 20w50 for a few days and it was notchy into 3rd and 4th...drain and refill with MT90....Problem solved! Avoid oils with friction modifiers...and use a GL-4 lube.
 
Why are you telling people to avoid oils with friction modifiers? I would bet good money that the oil you are recommending is friction modified.
 
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