Notes on Differential Thrust Plate Washers
The recent discussion on this forum about what material and when was it used on the rear axle thrust washers made me wonder what the Ford engineers had to say about them. The Differential Thrust Plate Washer was assigned the Factory (Symbol) Number T-30. The information below is from Accession 1701, Model T Releases, Box 1, at the Benson Ford Research Center, a part of The Henry Ford. Although they are referred to as “Releases” at the BFRC, the Ford engineers referred to them as “Record of Change” cards. For the most part, they recorded the change that was made in a Model T part, when the change was ordered by the engineers, and which engineer authorized the change.
The ROC cards are organized by the factory symbol number of the part. In order to find the ROC for a part, you must know the factory symbol number of the particular part you are interested in. Model T parts catalogs are organized by catalog numbers, and the catalog numbers themselves have little relationship to the factory symbol numbers. However, the factory symbol numbers can often be found in the entry for a parts catalog number, as part of the information for that particular part.
The first ROC card for part number T-30 begins on April 6, 1910. There is no information on this part prior to this date. Interestingly enough, under the typed name of this part, DIFFERENTIAL THRUST PLATE WASHER (capital letters were used in the name of the part on the ROC card) in parentheses is the word “Regular”. I do not know why it was called this, but it does raise the question in my mind whether they also had an ‘Irregular”. The number required per car was 2.
OK, so here we go:
4-6-10 Changed thickness from .198 -.200. Howard
10-13-10 Changed thickness from 1.98-.200” to .196 -.198.” Howard
10-9-14 Changed material from babbitt to bronze. Galamb
10-24-14 Changed name from Differential Thrust Plate Washer.
Also called for two ¼” holes located 1-1/2” from center
of washer. Changed thickness from .196-.198” to
.183-.185”. Changed material from bronze to semi
steel. Changed number required from 2 to 4. Galamb
10-27-14 Changed thickness from .183-185” to .196-.198”, the
material from semi steel and the number required
from 4 to 2. Galamb
3-2-15 Specified that this washer to be made of X bronze. Wills
4-28-15 Changed thickness from .196-.198” to .200-202”, I.D.
from 2-9/32” to 2.254-2.257”. Also specified inside of
washer to be finished. Have also brought drawing up
to date with washers as they are being made, by
specifying the sides to be disc ground. The above
changes to take immediate effect, all washers on hand
to be used up. Galamb
10-8-15 Specified oil grooves to be straight instead of spiral,
located 1-7/16” from center of washer, 2 on each side,
the center line of grooves to be at right angles with
each other. This change is to take immediate effect.
All washers on hand to be used up. Galamb
1-14-16 Brought drawing up to date by specifying number
req. on 1916 cars. Howard
3-11-16 Changed material from X bronze to steel and babbitt,
i.e., the plate will be made by taking the rough side of
T-31 and babbitting the sides and edges. This changes
the O.D. from 3-3/4 to 3-3/16”. Howard
6-9-16 Brought drawing up to date with washers as they are
being made as follows: Changed outside diam. From
3-3/16” to 3-3/4”. Changed material from steel coated
with babbitt, to composition having 25 Brinell hardness.
Removed note specifying oil grooves inside to come
even with top of plate and added dimension specifying
them to be 1/32” deep. Mosher
6-16-16 Specified the weight of 1 washer to be 8-1/2 oz. This
weight was added for the convenience of the purchasing
dept. in buying stock. Wilson
12-20-16 Specified this part to be used on 1917 cars. Howard
8-30-17 Specified for use on 1918 cars. Galamb
10-8-20 For 1921.
11-3-21 Changed material from “Metal Composition” to “Alloy
Bearing Metal (Approved)”. Howard
3-13-1923 For 1923.
12-12-23 Specified for use in 1924. Howard
3-24-24 Specified edge to be beveled. Galamb
11-1-24 Specified for 1925.
8-1-24 Change thickness from .200-.202” to .198-.200”. Galamb
1-3-26 Specified for 1926. Howard
9-14-26 Specified for 1927. Howard.
The purpose of this document is simply to inform the reader of the many, many changes in the design and material used in the manufacture of the Differential Thrust Plate Washer. It should not be used as a guide of what to use when restoring a Model T rear axle.
For 5-1/2 years, from March 11, 1916 until November 3, 1921, the washers were made from a “Metal Composition” having a Brinell hardness of 25. I do not know what metals were used in this composition, and have not found it referenced elsewhere in the engineering document collection at the BFRC.
Interesting - has someone found any of the odd ones when opening up an axle, like the babbitt coated steel thrusts from the spring of 1916?
Thank you for your time and dedication to the hobby. Certainly the time and effort you and several others offer for the advancement of the knowledge of the Ts contribute greatly to the fact that so many of the early machines are still in existence and roadworthy!
Kudos to all you researchers.
All this effort for such a small part. The amount of detail!!! I wonder why they kept changing the thickness by 0.002" and material. I suppose it was caused by a dimension change on another part.
Thanks to Trent for the research.
Do you suppose they were changing the dimensions so often to find the optimum thickness in order to set the pinion backlash without having to continually adjust it?
Thanks Trent for all your work..
Michael, that's what I was thinking too. They might have been trying get to come up with the perfect average size and a material that would wear in easily to keep that assembly line humming. It looks like a lot of the changes happened in 1914 when the assembly line started.
Thanks, Trent, for all you do for our Model T hobby.
Let me also add my "Thank You!" to Trent B.
Thank you for all your research and efforts to better our knowledge of the wonderful model T!
Drive carefully, and enjoy, W2
Thanks Trent, as was said, Kudos! Although all of this doesn't answer some questions, it does bring up some. For a long time, I have wondered if the "babbitt" thrust washers were made of similar material as the main and rod bearings. There have been many opinions, mostly that the "babbitt" thrust washers were made from similar material, but were compromised by time, water, and "acids" from "condensation" in the rear end housing. Myself, I don't buy that. I think the "babbitt " thrust washers were made from something much different than the engine babbitt. Then there have been posts that NOS, or nearly, NOS washers crumbled rather easily when dropped or crushed, they almost looked like die cast material. To me, the term "Metal Composition" suggests something other than babbitt, at least the babbitt that was used in the engine, was used for the thrust washers. On 11-3-21, material was changed to Alloy Bearing Material. That to me says that the earlier washers were not made from the same babbitt as the engine babbitt. All of this is JMHO. Dave
Thank you so much for all you do for our hobby and clubs.
Hap l9l5 cut off
I realize this is hearsay, but an old timer from Ford told me years ago that the composition was non-ferrous chips from the various lathes pressed into shape and the babbitt was cast around these turnings.
That would have been typical for Ford to use waste material to reduce the needed amount of babbitt
Maybe oil or dirt in the chips made the composition material unstable with varying quality that corrodes and cracks easier than pure babbitt?
Do the original washers found in 1916-1921 axles differ in brittleness from those seen in 1922-27 axles or are they about the same now after 88+ years?