MTFCA Forum

Hello,
I am in the process of rebuilding my rear differential which I decided to move to a 3to1 gear ratio. I placed one half of the differential case, plus two thick washers and 1 modern bearing on the drivers side and turned it to see how it did without ring gear shims. It is rubbing. Not by much... but it is still rubbing.

I need to buy "ring gear" shim/shims. However, before I just buy a bunch of ring gear shims I wanted to know what did everyone , who has used the 3 to 1 ring gear, ended up with in order to get an idea of what I need to buy as a starting point.

There are two sizes .010 and .015 shims.

Did you only need 1 ? , if so... what size? Did you need two? If so, what sizes?

If you've done it before , please let me know what your experience was that way I can narrow it down before I start. I'm only interested in what you
ended up with as a starting point for what I will use. No ruxstell , normal install.

Thanks for your assistance,
Michael

Ring gear shims should be avoided. They create a more likely area that will slip & shear the ring gear bolts.
The best way to fit is to narrow the thick bronze thrust washer. Going away from the way Henry designed it is a recipe for failure down the road.
The obvious problem is your new fangled, modern bearing isnt compatible with the 3-1 gear set.

Hi Michael,
Probably me but I'm thinking that because of the back set of the ring gear it is rubbing on the housing? Model T rear ends can be a complicated
dance of assemble, measure, disassemble, measure, reassemble, measure again. Have you tried assembling the whole housing & checking the
thrust bushings? you may need shims there. To figure out what you will need to order try using cereal boxes, junk mail flyers & paper to make
shims to figure out what you will need. Otherwise you end up with a envelope full of shims you will never need.
Craig.

Do not use the modern bearing. Go with the bronze and fit accordingly.

Michaelb ..... What is the present gear ratio that's in the car that you're accustomed to?. If it is standard gear ratio 3.63 to one, and you change to 3-1, you will be unpleasantly surprised when you step on the brake pedal as usual , and find that you'll need a heck of a lot more pressure to stop the car.

After reading how people replied to my post I went and measured the new bearings that they suggest from the parts dealers. What I found was actually shocking. Both measured 0.124 I guess I'm the sucker for buying the new stuff? The extra 0.08 would definitely let it clear the housing and keep it centered. And, having only 1 piece and not many rotating pieces is a big plus! auto zone vs. oem.

I won't shim it! But, the ring bolts are now way way too long! like 1/4'' too long. I asked the vendor if they sell 1/2'' bolts but they don't... I asked what they did and they said they cut them off 1/4''....

What do you say? cut/grind flush? (dremel) Anything sticking out is extra sh.. imo.

I dont put 3-1 gear sets in non rux diffs.
But the bolts can slightly touch the pinion gear & need a bit of clearance. With the correct pinion/ring gear mesh, the pinion should not hit much.
Test the full revolution & clearance the few as needed with your dremel grinder.

Putting a 3-1 gear set in a non rux isnt normally done or advised.
Before doing this thing, find another guy that has this ratio in a rux & try driving it in direct only.
As noted, braking effectiveness is less. Just pulling away from a stop or going up driveways is a real noticeable lack of power.
Its not a pleasant overall drive. Better to stay with stock gears & get your motor to wind up a bit more.
I have been in unrestored , T's that will run the freeway @ 55 with stock gearing.

I expect you will be learning this the hard way.

I have a 22 Runabout with 3:1 and a Ruckstell. We have some grades up to about 6 % around her. When I get it going about 35 up a grade it will pull in High High, but any slower and I need Ruckstell. When on tours, most of the cars have standard gears and go up the grade about 25 MPH, so I usually end up using Ruckstell on tours. It is sometimes necessary in starting out on hills to use Ruckstell and low together to get going So unless it is very level around where you live I would recommend either the Ford gear ratio even with Ruckstell. On one of our tours some cars came from the flat country to the hotel which was up a hill and had a hard time making the grade with higher gear ratios. They finally parked the cars and rode with others for the remaining days of the tour. But, it's your car and I would recommend that you keep the stock gears just in case you decide to change back.
Norm

Michael

I do not know what kind of car you are improving or how heavy your car is. I have 3:1 and the car runs fine. Mine is a speedster. The car may be a bit slow to get going, but it is faster than any other cars I have toured with. I tend to take the caboose position so I can zip up to the engine to tell him to stop in case one of the middle cars break down. 3:1 works fine in a car that is not too heavy and no I do not have a Ruckstell

Dave, I'm going to give it awhirl... with an I-timer.

Norm, I'm keeping them... just in case!

Which modern bearing are you using the axle or thrust?
Craig.

Michael

You are going to love that I timer!!!

As advised, shims should not be used between the ring gear and the carrier. It is better to use a shim behind one of the side thrust plates to shift the diff centre within the housing.
As advised, a 3:1 gearset will severely effect the braking and accelerating ability of all but the lightest of vehicles. A compromise option is the 39 tooth ring gear and a 12 tooth pinion, for 3.25:1 ratio.
By all means have a go, but be prepared to retrace your steps.

Allan from down under.