View Full Version : Info about brass OR lined synchros.

05-06-2005, 12:27 AM
In my search for decent replacement synchros for the M5R2, I talked with Michael Weinberg from Rockland Standard Gear www.rsgear.com

They sell a rebuild kit as well as BRASS synchros for our transmissions. As far as I have been able to find out, there is only ONE kit available. It comes in a flat cardboard box and has a sticker on the side that says, "BK248B" or "BK248BWS". The second one means that it includes the synchros. The kits come with all the large bearings that are in our transmission. However, none of the needle bearings are included. However, I'm told that they don't tend to get worn out. Also included in the kit are 2 o-rings, 2 plastic pieces that are part of the shifter rebuild, the plastic oil-scoop/pickup, the front seals, and the tail-housing seal. I have not ordered the kit from Rockland Standard Gear, but the two other companies kits I have seen, are pretty much the same.

Here's what Mike had to say about using brass synchros in the rebuild.

Hi Mike,

I have read your thoughts on the lined/brass ring situation. However, I am very concerned with your statement that brass rings need a heavier fluid. If you don't mind I would like to explain some of the problems and technology involved in synchronizer design and transmission durability. Gear oils were used forever in manual transmissions. This prompted many complaints from owners regarding the difficulty of shifting when in cold weather. This prompted almost every manufacturer to begin to use ATF (automatic transmission fluid) in gear boxes.

The synchronizer designs are made to work with a specific fluid. Brass and lined rings will work correctly with ATF. A synchronizer ring is a wet clutch. As you begin to select a gear, the shift fork moves the synchro slider toward the cone of the speed gear to be selected, and as the slider moves forward it moves the synchro keys with it and that applies the ring to the cone of the speed gear. Before the ring can engage the cone properly to either speed it up or slow it down to match the output shaft speed, because during the shift the rear wheels are driving the output shaft, the ring must first exhaust the fluid between it and the cone in order to apply friction. The heavier the lube, the longer it takes for the fluid to exhaust and the slower the shift.

Now we need to look at the design of the M5R1 and M5R2 transmission itself. The input shaft bearing is a tapered roller bearing. It is set very deep into the case and necessitated the use of an oil slinger on the front of the input to actually pump lube through the bearing. These transmissions are splash lubricated, which means they depend on the rotating gear mass to throw lube around inside the case to circulate lube to all parts needing same. The most difficult parts to lubricate in the transmission are the front input bearing and the pocket bearing inside the rear of the input that supports the nose of the mainshaft. The oil slinger design on these transmissions helps to force oil into those critical areas, and MUST only be used with ATF. The M5 series of transmissions was only designed to use ATF regardless of the kind of rings used. We build about 50 of these a week for sale to professional repair and transmission shops. Over the years we have seen many complaints caused by the use of heavier weight oils than ATF. If you put a 90 weight gear oil into one of these transmissions you will get an actual moaning noise from the front of the trans as the oil slinger cavitates in the thick oil. We have successfully used GM synchromesh fluid in these units, which is a 30 weight motor oil based fluid, but is really uneccessary due to the added expense. Stick with ATF, and if you wish to raise the coefficient of friction for better performance, you can add a bottle of Lubegard Red Friction modifier. This will work with both brass and lined rings.

Lined rings have become the current fashion in many stick gear boxes. Carbon fiber, sintered metal, and paper compounds are being used with great success by many manufacturers. Some transmissions went to lined rings and then went back to brass (Mitsubishi, Nissan, Toyota) due to inconsistent manufacturing quality. It is much easier to machine a brass or bronze ring to exact specs than to get carbon fiber or paper to hold an exact tolerance. We use brass rings in all of our remanufactured units because of the price difference and have no problems with shift complaints providing the customer uses ATF.

As a side note, we remanufacture the T Bird M5R2 unit. Our part # is M5R2-10, and sell that unit for $995.00US with a refundable $300.00 core exchange deposit. This might be some help to your club members who cannot rebuild one of these units themselves. I will get you the Ford parts numbers for the lined rings and email them to you.

I hope this helps you understand some of the engineering involved in synchronization and lubricants.

Best regards,


05-06-2005, 01:08 AM
Excellent information Mike, thanks. :)

Ira R.
05-06-2005, 02:06 PM
Yes. This is good information to have. Thanks.


Andy 94SC
05-06-2005, 02:56 PM
That is realy a good explaination on the operation of the synchronizers, but DAMN $1k for a rebuild using the cheap all brass rings? Thats twice what Liberty charged me....

05-07-2005, 12:11 AM
I'm in the middle of my rebuild right now, just waiting for the right synchro's from southern gear. But, if I had a BIG hydraulic press, then it would have been totally do-able in the garage. However, I had to go and get some of the bearings pressed in at the local machine shop. So far so good, I guess, when I get really good at it, I could knock it out in about 3 hours or so? maybe? but I'm one of those guys who has to spit-polish every part before it goes back into the car...

Anyone have some advice on an easy way to remember how the synchro-assemblies line up properly? The shop manual mentions the little dot on the one side, and the thicker/thinner side, but, it's slow going for me.