Unlicensed mechanics did an astonishingly bad job and left me with an inoperable vehicle. I cannot…read morerecommend SF Differential for any work, and would strongly discourage Yelpers from working with either Curtis Williams or George Cook on any vehicle repairs.
As a car guy with lots of experience, I was able to get out relatively unscathed. If you're just a driver and not a mechanic, you're especially vulnerable to these incompetent mechanics.
So first thing: SF Differential is not a licensed repair business with the California Bureau of Automotive Repair. I didn't know this when I started working with them, but I now know that I should have checked.
Also, Bryant Transmission Center, operated by George Cook out of the same location, license number 223373 - https://search.dca.ca.gov/details/1310/ARD/223373/322605e30ebc15ba43b29993eda5ca3d - and who in fact appears to operates SF Differential for Curtis - had their license canceled in 2019 and has not had that license restored.
I own a vintage car with an older Dana differential. While I am set up to do most restoration work, differentials need precise setup and require a lot of knowledge and specialized tooling to get right, so I looked very carefully for an expert to help me switch out the crown and pinion in my Dana Spicer M27. Referred by several local vintage mechanics, I connected with SF Differential - originally based in San Francisco, then South San Francisco, and now San Leandro.
Owner Curtis Williams, who told me he worked for prior owner John David for many years and purchased SF Differential from his estate in 2016 when John passed away, is a kind and friendly guy, and he initially impressed me with his confidence regarding Dana final drives. I met Curtis in person and talked about the work, then coordinated through George Cook - whose role was not explained but who appeared to be the business manager for SF Differential and who provided verbal pricing quotes ($900 for the work, exclusive of parts).
N.B: George provided no written quotes or documentation, something I should have taken note of at the time, but passed off as "old car guy" quirks. This proved to be a mistake!
As the owner of a vintage car, I wasn't too surprised when I had to supply things like factory service manuals, hard-to-find parts, and guidance - and I did so, spending weeks sourcing parts in response to texts and phone calls from George, supplying bearings, seals, shim kits, and extensive service information. I was, however, surprised that I had to learn a lot about differentials as well! Do you know what a "fully loaded carrier" is? I do, now.
Several weeks later, my car was ready for a test-drive - and it noisily failed. On inspection, the gearset was trashed - galled teeth caused by a pinion depth set at random - Curtis told me he didn't use measurement tools for setting up backlash and preload, relying on "feel and experience", and had simply guessed at pinion depth.
Having learned a lot about differentials while sourcing and supplying parts, I was shocked to find that Curtis doesn't appear to own a depth micrometer, a dial indicator, a test indicator, or an inch-lb torque wrench. As I had learned, those are minimum-viable tools for this kind of work - and Curtis' work on my differential proved to be far below standard.
George eventually offered a 3rd party mechanic who thought he could take a swing at the project, but only if new gears were supplied. You won't be surprised to hear that I declined, and got my car out of their hands ASAP.
I had trouble getting Curtis and George to make this right - while they eventually paid for a replacement gearset and half of the towing costs to get the car out of his shop, I am still out hundreds of dollars in seals and bearings and incidentals and a couple hundred more in towing costs - and i'm now doing the work elsewhere to make sure it's done right.
I'm posting this review approximately two months after this failed service. That is because I wanted to make sure the replacement gearset ordered by George was actually delivered to me before I shared my feedback - and it arrived today.
tl; dr - SF Differential destroyed a brand-new Dana Spicer M27 gearset through a deep lack of knowledge and a reliance on "feel" setting up a differential, and cost me both hours of negotiation and hundreds of dollars in towing and trashed parts while nominally making it "right". If you have a Jeep CJ or a 60's era classic car, or frankly a car at all, I cannot recommend this unlicensed business for any work.
