Author Topic: Peerless MST 200-Series Transaxles -- Heavy-Duty vs. Standard, Gears, Axles  (Read 930 times)

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Offline RoMow

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   The information in this post is applicable to all Peerless aluminum-case manual-shift gear-drive transaxles that have 3/4"-diameter axles and Model Numbers that start with MST-20x, such as MST 206-545C, a popular Sears/Craftsman/Husqvarna/Poulan 6-speed transaxle.

Standard-duty vs. Heavy-duty

   If you are wondering how to tell a "heavy-duty" MST 205 or 206 Peerless transaxle from a "standard-duty" one, the following should help:
 
   The "duty" differences are determined by whether a letter, if any, follows the 202, 204, 205 or 206 Spec Number.  The Spec Number is the 3-digit number following the 20x-.  For example, if it's a plain MST 205-510, with no letter suffix following the "510," then it is not as heavy-duty a transaxle as, say, an MST 205-510D.  (The 3rd digit of the 20x number tells how many speeds the transaxle originally is -- a 204 is a 4-speed, a 205 is a 5-speed, etc.)  "Duty" differences are: 
   A. The suffix-free MSTs originally had 5/8"-diameter output shafts for the gears between the brake shaft and the differential.  The MSTs with letter suffixes were improved with 3/4"-diameter output shafts and larger shaft-end bushings. 
   B. The suffixed models also had improved final-drive gears. 
   C. The really heavy-duty MSTs also have case-hardened cut-steel 16-tooth differential spider gears, whereas the standard spider gears are 13-tooth powdered metal. (Some of the non-suffix MSTs do have the 16-tooth spiders.) 
   D. Some MSTs also have hardened-steel cluster gears instead of the standard powdered metal gears.
 

   'A'-Input transaxles are mounted with the input pulley, shifter and brake Ahead of the axle ("Axle-Rearward"), while 'B'-Input transaxles mount with the input pulley, shifter and brake Behind the axle ("Axle-Forward").  Mounting them incorrectly will give you multiple Reverse speeds and only one Forward speed. 

   AXLE BEARINGS:  Most standard MST transaxles have the axles riding in the aluminum-alloy case material, which is dimensioned to act as a "bushing."  The aluminum-alloy case material has a small amount of silicon in it which aids in its bushing capability.  However, for heavy-duty service, you can also add needle bearings or ball bearings inside the case recesses to better support the axles and provide for increased durability and longevity, as well as reduced friction.  These bearings are available from Peerless - P/N 786218 for the Needle Bearing/Sleeve Assembly and 780119 for the Ball Bearing.  I would recommend the needle bearings, as they provide more bearing-area support for the axle. 

   So...if you are looking for an MST 205 or 206 for racing, you would probably want to avoid the ones without the Spec Number suffix letters, find out what ratios and gears are in it, and, ideally, add the axle bearings.   
 

Gear Ratios

   The following list gives all possible gear ratios available on the MST-Series transaxles.  The first column will be the Number of Teeth on the cluster gear pairs; the second column will be the actual Ratios themselves; and the third column shows the Part Numbers for the respective Forward gears.  The first number in the Number of Teeth column will be the number of teeth on the "drive" gear on the countershaft, the shaft with the large bevel gear on it -- and the second number in that column will be the number of teeth of the "driven" gear on the shift-key/brake shaft.

Input Pinion Bevel Gear Ratio - 2.31:1 (13T:30T - 778309p:778334p)
Final Drive Ratio - 9.89:1
   [Output Ratio - 3.45:1 (11T:38T - 778330s:778331p) x  Differential-Gear Ratio -  2.87:1  (15T:43T - 778332s, 778365s or 778369s:778327p or 778370p)]
These "fixed" ratios for all shift speeds compute to 22.87:1.  To determine the "overall" ratio in any gear, simply multiply your Cluster Ratio x 22.87 and this will give you the overall ratio for whatever speed you are in. 

All Possible Low-to-High Ratios:
4.00:1  (10T:40T - 776400 ['A'-Input] or 776404 ['B'-input]z:778357s)
  NOTE: The 10-tooth drive gear for the lowest ratio is made onto the countershaft; this heat-treated gear is not available separately.  All other gears are individual gears.
3.00:1  (10T:30T - 778335p:778336p)
2.64:1  (11T:29T - 778355s:778356s)
2.07:1  (13T:27T - 778337p:778338p)
1.50:1  (16T:24T - 778339p:778340p)
1.30:1  (17T:23T - 778353s:778354s)
1.225:1  (18T:22T - 778341p:778342p)
1.00:1  (20T:20T - 778343p:778344p)
0.90:1  (21T:19T - 778351s:778346p or 778351s:778352s)
0.67:1  (24T:16T - 778349p:778350s)
0.60:1  (25T:15T - 778345p:778346s)

Reverse (also fixed for all MSTs) - 2.08:1  (13:27 - 778333p:778338p ['A'-Input] or 778363p:778338p ['B'-Input])

NOTES:
1.  With the exception of the "granny-low" 1st gear ratio of 4.00:1, the number of teeth on both the driver and driven gear always totals 40 for these MST 200 transaxles.
2.  Powdered Metal gears will be noted by a 'p' suffix following the gear part number; Heat-treated Steel gears will have an 's' suffix.  The suffixes ARE NOT part of the Part Number.
* 3. Three different 15T Differential Drive Gears are used, depending on transaxle model - 778332, 778365 or 778369.  All three 15T gears are Steel.
z 4.  The 10T Countershaft gear for the 4.00:1 "granny-low" ratio is steel and is made as part of the countershaft.  The 'A'-Input Countershaft w/Gear is P/N 776400; the 'B'-Input Countershaft w/Gear is P/N 776404.
5.  The Reverse-drive spur gear includes (is made a part of) the Reverse-drive bevel gear, with the bevel gear having the same 30T as the Forward-drive bevel gear.

 
Axles

Left Side                                                         Right Side
Length - Part Number                                   Length - Part Number


  9-15/32" (9.464" / 24.0 cm) - 775042            14-3/64" (14.046" / 35.7 cm) - 775041
10-17/32" (10.531" / 26.8 cm) - 774981          15-5/32" (15.156" / 38.5 cm) - 774982
11.0" (27.9 cm) - 774888                                15-9/16" (15.562" / 39.5 cm) - 774909
11-1/16" (11.062" / 28.1 cm) - 774999             15-5/8" (15.625" / 39.7 cm) - 774689
11-1/4" (11.25" / 28.6 cm) - 775047               15-13/16" (15.812" / 40.2 cm) - 775048
11-5/16" (11.312" / 28.7 cm) - 774686           15-7/8?"(15.875" / 40.3 cm) - 774687
11-3/8" (11.375" / 28.9 cm) - 775000             16-5/32" (16.156" / 41.0 cm) - 775054
11-5/8" (11.625" / 29.5 cm) - 774688             16-1/4" (16.25" / 41.3 cm) - 774747
11-3/4" (11.75" / 29.8 cm) - 774974               16-5/16" (16.31" / 41.4 cm) - 774926
11-13/16" (11.812" / 30.0 cm) - 774697          16-7/16" (16.437" / 41.7 cm) - 774738
11-63/64" (11.984" / 30.4 cm) - 775028          16-1/2" (16.5" / 41.9 cm) - 774691
12-7/32" (12.218" / 31.0 cm) - 774942            16-9/16" (16.562" / 42.1 cm) - 775027
12-3/8" (12.375" / 31.4 cm) - 774638              16-3/4" (16.75" / 42.5 cm) - 774930
12-7/16" (12.437" / 31.6 cm) - 774943            16-13/16" (16.812" / 42.7 cm) - 774869
12-1/2" (12.5" / 31.8 cm) - 775006                  17.0" (43.2 cm) - 774837
13.0" (33.0 cm) - 774772                                17-1/32" (17.031" / 43.3 cm) - 774944
13-13/16" (13.812" / 35.1 cm) - 775102          17-5/8" (17.625" / 44.8 cm) - 775001
14-3/8" (14.375" / 36.5 cm) - 774891              18-1/8" (18.125" / 46.0 cm) - 775007
16-7/16" (16.437" / 41.7 cm) - 774738            18-3/8" (18.375" / 46.7 cm) - 775101

NOTE: 
1. These axles are the ones with 3/16" straight keyways and snap-ring grooves that hold the wheels on.  There are a few other axles that have pinned or threaded ends; they are not included in this list.
2. Axles are interchangeable left-to-right, provided they extend far enough past the housing to be useful. 
  a. The transaxle housing covers 7-1/4" of the left axle and 11-3/4" of the right axle. 
  b. Using the first (shortest) axle in each column as an example, the 775042 left axle will have 2-7/32" of axle exposed; the 775041 right axle will have 2-19/64" exposed. 
  c. Likewise, using the last (longest) axles, the 774738 left axle will have 9-3/16" exposed; the 775101 right axle will have 6-5/8" exposed. 
3.  Special axle-spider gears are available that will lock the differential without damaging or welding the original spider gears.  Check my internet store. 



Respectfully,
Rodney Rom 
. . Peerless Gear Master Technician
Rom's Reworks
Butler, MO 
https://ROMs-Peerless-Transaxle-Supply.eCrater.com
"No matter how many material possessions or awards you may acquire in your lifetime, the only thing you will ever truly own is your reputation." (Age 73)

Offline Negrey

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Re: Peerless MST 200-Series Transaxles -- Heavy-Duty vs. Standard
« Reply #1 on: October 04, 2020, 12:23:13 am »
Thanks for sharing, neat information!
Evan