6/8 speed question

[1mor Project 98]

I have a 1976 B-100(61-10K801) with a broken rod. I am in the process of repowering with a 16 HP Kohler. In researching the transmission on Lowel's site I find it has a 5091 transmission with a 103907 optional. Same transmission options up to C-160 that year. My question is does only one of the transmissions have the 7235 spring for poor man's posi, or is there some other difference? My other question is, what is the difference between the B and C series in 1976. Looks like only decals and headlights/tail lights.

Thanks in advance.

[gwest_ca-(File Mod) 11,942]

The 5091 and 103907 don't have the 7235 spring.

 

[1mor Project 98]

Thank You. I see the difference is mine has 4 pinion gears and the other is 8 pinion. 

Nothing wrong with mine right now, just a little seepage. I was just curious. I wonder if the 7235 can be retrofitted at rebuild.

[ri702bill 11,046]

All will physically bolt up to your frame. BUT, there are differences between the 6 and 8 speed versions. Your 1976 tractor is a long frame style, uses two pedals - a clutch and a brake?

If so, you should be looking for an 8 speed - the brake works the same. Earlier 6 speeds are different, similar to early 3 speeds.

You will need to deal with the HI-LO shifter - a hole would need to be added to the sheet metal. Same for the Dipstick / tube.

Look for an 8 speed from an early C series, like a C81. That has the 8 pinions and 1-1/8" axles. The later 300 series use the 1" axles.

[ebinmaine 76,835]

7 hours ago, 1mor Project said:

. Same transmission options up to C-160 that year.

 

Correct. 

 

4 hours ago, 1mor Project said:

Thank You. I see the difference is mine has 4 pinion gears and the other is 8 pinion.

 

NOT Correct.... for 1976/77 the transmissions are the same. 

The B and C series both used the heavy duty 8 speed 8 pinion transmission. 

 

The 4 pinion transmission in the 1970s was only in the 1974/75 B series which was a 4 speed. Not 8. 

 

 

7 hours ago, 1mor Project said:

My question is does only one of the transmissions have the 7235 spring for poor man's posi, or is there some other difference?

4 hours ago, 1mor Project said:

I wonder if the 7235 can be retrofitted at rebuild

 

 

Unfortunately,  no. 

At the base it's a geometry issue...

Circles & squares. 

 

The Wheelhorse Limited Slip Differential was a 10 pinion design that arranged the gears in a circle. The spring is placed under tension between what is effectively two circles of 5 gears each. 

There are both 6 and 8 speed versions of that and it ended in 1972. 

 

 

The 8 speed 8 pinion Open Differential started in 1973. All 1 1/8" axle transmissions from then up used 8 gears arranged in a square. 

 

The 8 pinion design is quite a lot more robust than the 10 pinion. @Handy Don could explain the difference better than I. 

 

 

7 hours ago, 1mor Project said:

My other question is, what is the difference between the B and C series in 1976. Looks like only decals and headlights/tail lights.

Thanks in advance.

 

Perhaps @Racinbob can confirm.  I believe it was basically headlamps being optional vs standard,  steering wheel, and seat differences.  

 

The B series had the 8 to 10 HP engines where the C series was 10 to 16.  

 

B60 and B80 were all manual transmission. The rest could be hydros.  

 

 

 

[Racinbob 12,547]

 The 5091 and 103907 are the same transmission. Both 8-speeds, both with 1.125" axles and neither have the 7235 spring. You are right is saying your B-100 is essentially the same as the C-series. In 1976 and 1977 ONLY the difference between the B's and C's are as follows: B's had low back seats, C's high back. B's had 22-7.50 rears, C's 23-8.50 but if you went for the optional cleats both were the larger. Headlights optional on B's, standard on C's. Of course the horsepower. A few other minor things. Don't let the 74 and 75's confuse things. Those B's were medium frame and 4-speeds. Starting in 1978 the B's became lawn tractors. Keep in mind that it was very common for owners to swap things out over the 50 years. I can attest to that as I purchased a 1976 B-80 brand new and still have it. The mods over the years that I did have been countless. 

 Eric posted while I was typing. All good stuff. 

[Racinbob 12,547]

5 hours ago, 1mor Project said:

Thank You. I see the difference is mine has 4 pinion gears and the other is 8 pinion. 

Nothing wrong with mine right now, just a little seepage. I was just curious. I wonder if the 7235 can be retrofitted at rebuild.

 

If yours is a 4 pinion it's not original to a 1976 B. 

[Achto 30,648]

Go with an 8 speed open diff. This is what can happen to the 6 speed 10 pinion with limited slip if you push it too far.

 

 

The 10 pinion lasted 3/4 of a pulling season. I replaced it with an 8 pinion open diff from a 520H, this diff will be starting it's 3rd season this year.

Edited 3 hours ago by Achto