4 speed 833 question

I’ve got a question about the synchros between 69 down and the 70 up. They changed in 70 for a “ better” design. Is it that much better? I’ve built all years but only owned and driven 70 up style for many years. Is it worth upgrading from the 69 style on this next rebuild? Brewers has a complete assembly for pretty a reasonable price. I’m try to advice a couple of customers on the upgrade. P

I heard yes they are better. Ultimately if you need a new hub and slider the 70 up is more prevalent and less expensive I believe. If the slider and hub are in excellent shape I would stay with the original type. Lot of extra money to get the new hub and slider.

Absolutely not. If you want to “upgrade” it, you need the later hubs and struts. Everything else is the same. I have both, use both and there is ZERO difference in shifting or anything else.

If the early struts you have are worn out they are easily replaced. Upgrading is a waste of time and money IMO.

Mopar had NP make three different synchro assembly in their trannies, 1964 to maybe mid 1966 or mid 1967, and then upgraded them some.
The 1970 and later, wider synchro types work okay as far as I'm concern, no better than the second generations synchros as long as you have the clutch pedal linkage adjusted properly

Just to be clear, the syncro, hub, slider, strut and spring are different. Swapped as a set. If you look closely there is a difference in the strut height, and therefor the slider is different too. Internal cut.

They changed the slip rings so as not to have that "sharp" notch in them.
Were prone to breaking during "hard" shifts, or maybe over a period of time.
Probably to accommodate the racing that was dominant during that era.

Thanks. I’ve got both styles and have three 4 speed to build. I have enough but I thought about upgrading on one to the 70 stuff Brewers has the assembly pretty cheap. It cost about 250 more than just buying syncros.

The later synchros are substantially better. There is a reason that the company spent all the money to redesign and supercede the parts.
It's not a question of how well they work or shift, it's a durability issue.

I have personally had two cases of early brass synchro ring failure over the years in my cars. The notch that locates the ring in the synchronizer hub and keeps it from rotating is square and has sharp corners, ideal for stress concentration and cracking. The crack starts at the bottom of the notch and cracks through the entire ring, making a gap that lets the ring open up and provide zero clamping force against the gear clutch cone. The later synchro rings have a notch that has a large radius curve to significantly reduce the stress in the brass ring.

Either type of shychro will shift the same way, when they are working. Once the earlier style cracks, it will stop shychronizing and you will grind gears unless you learn to match speeds when shifting.

I would personally not consider using the pre-1970 shychronizers.

Robert

Thanks Robert. That’s kinds of the answer I was looking for. I’ve rebuilt both and the 70 up sure looked like a better design to me. I did talk to Wayne Brewer and his opinion was if all the parts of the 69 were in good condition, they would be just fine. I tend to agree if all they parts are in good condition. However, both of these customers are good friends and want really good transmissions and cost the additional cost is not a factor. One is going behind a 650 hp hemi. Both are going to use the gear vendor overdrives.