M66 Rebuild Parts and Suppliers | SwedeSpeed

To answer my own question – yes, the M66 is rebuildable.
Assuming that you need a rebuild and only require the wear items, I’ve listed suppliers and part numbers below. For AWD cars, you will of course need additional seals for the angle/bevel gear along with bearings if you plan to rebuild the angle gear, as well. A rebuild that includes the key wear items would replace the seals, the bearings, and the synchros.

The below lists contain the parts you need for M66* equipped Volvos, Fords, and Land Rovers.
Unfortunately, I do not have the bearing preload specs since Volvo/Getrag did not publish that info. I also do not know the bolt torque specs for the shaft assemblies.
The bolt torque specs for the casting, shifter assembly, and ring gear are out there so I need to dig those up.
*The Volvo M66C(AWD) may be unique in that it uses a a bearing with a larger OD on the 3-4 output shaft. I believe that it is Koyo 30306JR but need to confirm. For now, the safest bet is to measure your bearings before ordering your parts/kit if you have an M66C.

OE Synchros:
ACL and Ganzeboom normally supply shops and commercial customers so I imagine that their customer service/sales teams are staffed accordingly. I’ve been in contact with a couple of people from each of those companies and they’ve been very helpful. I kindly ask that you contact them only when you’re ready to buy. That way they aren’t carrying on correspondence and generating an inordinate number of quotes, as measured against the actual number of orders placed. If that happens, we become a nuisance. Worst case, they would stop responding to individual buyers of M66 parts.

Carbon Synchros
For those of us who plan to push their builds well beyond factory output levels and would be willing to pay more for “better than stock” synchros, you may wish to go with Synchrotech and order the part numbers listed below. I bought new OE M66 3rd gear and 4/5/6/R gear synchros then shipped them to Synchrotech for profiling. They did some comparisons and found synchros in their offering that appear to match all of the M66 friction rings. I ordered the synchros that they called out and they look good. 1/2, as well as 4/5/6/R have identical dimensions to the OEM rings. The only difference is with the 3rd gear friction ring. I do not think that the difference represents a problem and will expand on that in this thread. Once one of us installs a set and runs them, we can ask them if they can create an M66 kit like their kit for the MMT6. That would save future buyers a little money. I am not sure when I will be able to install them on an actual gear/shaft assembly so if anyone gets to it before then, please report back.
I should also say that the factory/OE synchros are more than adequate for most builds.

If you are going all out on a big power build, maybe you’ll also want to consider cryo treating 2nd gear for added insurance. I personally know of two instances of people wrecking their 2nd gear. Unfortunately, my search did not turn up any 2nd gear replacement options. For the vast majority of us, I don’t think it’s necessary.

Diagram of the M66’s internals from the Automatic Choice’s catalog.

M66 OE Rebuild (Automatic Choice)

*Prices are rounded up to the next dollar(USD) and do not include applicable taxes and shipping. Accurate as of July, 2022.
**This is a gear 1 & 2 synchronizer hub assembly kit for the MMT6 gearbox. It includes both synchro ring sets, the shift sleeve, and the hub’s retaining bits. It also includes the MMT6’s 1-2-5-6 output shaft shift fork but I don’t know whether that fork can be used in the M66. I imagine that it would require modification.

M66 OE Rebuild (Ganzeboom)

*Prices are rounded up to the next dollar(USD) and do not include applicable taxes and shipping. Accurate as of July, 2022.

M66 OE Rebuild (Transmission Products NL)

*Prices are rounded up to the next dollar(USD) and do not include applicable taxes and shipping. Accurate as of September 2022.

M66 Upgraded Rebuild (Synchrotech)

*Prices are rounded up to the next dollar(USD) and do not include applicable taxes and shipping. Accurate as of July, 2022.
**These are friction rings only. It is unlikely that your blocker ring needs to be replaced. However, if you are concerned that your blocker ring is damaged, you can order a synchro ring set or complete hub assembly from one of the other vendors that I’ve listed.
***I’ve seen only one negative review of these carbon rings on YouTube. When a commenter asked what gear oil the poster used, the poster stated that he used OEM fluid. That was his mistake. It is critical that you use appropriate gear oil. It must not only be yellow metal safe but it also must be correct for a gearbox that uses carbon fiber as friction material.

Additional Sources

*Prices are rounded up to the next dollar(USD) and do not include applicable taxes and shipping. Accurate as of February, 2024.

It’s expensive but shops like Mountune can perform the actual rebuild for you if you do not want to DIY. Pricing should be close to what they charge for the same service on the MMT6. I call them out specifically because they have experience with this gearbox being that they developed the sequential M66.