matching diffs

[Vic Eaton]

HELLO ALL
Help needed to determine ratio of back axle can it be done by counting revolutions of propshaft to revolutions of wheel i have always thought it could for some reason but on trying it on our c 30 rear axle it doesnt to work out as the book states . thr front axle has had the diff removed and i want to replace it knowing it has to match the rear axle. and dont want to fit the wrong parts
thanks vic eaton .l

[Alex Blair (RIP)]

Hi Vic
From C-30 up used 6-43 axles..C-30,C-60S,C-60L,CGT)
C-15A....6-37....
C-8A.....7-38.....

[Bruce Parker (RIP)]

Factory differentials were often changed by post war users. For example, 15 cwt diffs were put in 60 cwts to increase speed, and C8A's have two different ratios depending on date of manufacture. In most cases, diffs with different ratios plug right in so it's hard to know what you have.

Of coures front and back have to match, but I'd suggest taking things apart and counting gears to be sure.

[chris vickery]

Vic, if you devide the number of teeth on the ring by the number on the pinion, you will get the ratio. A bit of a pain but the only true way to tell. Sometimes the ratio is marked on the ring and/ or pinion.
Just helped out on a 1/2 ton Dodge that had questionable diffs using this formula.

[Bob Carriere]

I was under the impression that the gear ratio was always stamped on the gear cluster casing..... numbers are about 1/2 inch high ans some times stamped

6

39

.....not always in line..... all my old axles C15A and C60 are stamped...... sometimes hard to read..... once cleaned with a wire brush and a spray of WD 40.... shinning a light off the side will allow to read the numbers.

The two C15 axles I have opened have parts numbers but no ratio stamped on them like what I have seen on Dodge rear ends.

Bob C.

[Tony Smith]

Originally posted by victor eaton
HELLO ALL
Help needed to determine ratio of back axle can it be done by counting revolutions of propshaft to revolutions of wheel? I have always thought it could for some reason but on trying it on our c 30 rear axle it doesnt to work out as the book states.

Yes it can be done. Firstly, you need to understand how a differential works and secondly, you need the diff ratios in a numeric form.
The spider gears in a diff mean that if one axle does not turn (ie that wheel remains on the ground) the other will turn at double speed when the pinion gear is turned.
The numeric ratios for large CMP diffs (C8A won't fit) are either 6.66:1 for C15, 6.5:1 for C15A and 7.16:1 for C30/C60.
Now, (with the vehicle chocked/secured etc) jack up one rear wheel. Put a chalk mark somewhere on the tyre to note it's position, and another on the pinion flange to help count rotations. You now count how many turns of the pinion flange are required until the tyre chalk mark returns to the start position, either 13.3 turns of the pinion for a C15 diff, 13 turns for a C15A diff or 14.3 turns for a C30/C60 (double the numeric ratio). You can either turn the pinion from the the vehicle or slowly turn the tyre while you count the pinion rotations. Don't lose count! You will see that the the number of rotations for the C15 and C30/60 diffs could be confused if you lose count.

[Bob Carriere]

I filled in the stamped ratio on my C15A cab 11 axles......

First the front axle....

[Bob Carriere]

Now a picture of the rear axle ratio.....

[Vic Eaton]

THANKS
For all this info on the diff problems i have printed it all off ready for the start of dismantling . had some trouble loggig on so sorry to be slow in replying to you all .
again many thanks vic eaton. uk .

[Vic Eaton]

HI ALL OUT THERE
Can any one advise me on the following i have just dismantled two axles to extract the diffs i need one for the radio truck you have given me advice befor on matching diffs well all the years i have had these trucks i have never seen inside a diff as chris vickery told me , divide the teeth on the pinion gear by the teeth on the ring . fine . but all i can see is the ring gear what else do i need to dismantle to see this pinion gear .
regards vic uk.

[Keith Webb]

Count the teeth on the crownwheel (ring gear) 43 teeth is the low- speed one for 20" wheels (6 on the pinion and 43 on the crownwheel) - this is the 7.2:1 ratio and 39 teeth for the 6.5:1 ratio (for 16" wheels).

[Alex Blair (RIP)]

Originally posted by Vic Eaton
HI ALL OUT THERE
Can any one advise me on the following i have just dismantled two axles to extract the diffs i need one for the radio truck you have given me advice befor on matching diffs well all the years i have had these trucks i have never seen inside a diff as chris vickery told me , divide the teeth on the pinion gear by the teeth on the ring . fine . but all i can see is the ring gear what else do i need to dismantle to see this pinion gear .
regards vic uk.

Hi Vic..

. Remove the old gear set and thoroughly clean both the ring gear carrier and rear end housing with solvent. After cleaning, air dry all parts.

2. Always verify that you have the correct gear ratio that you have purchased. This can be checked by dividing ring gear tooth count by the pinion tooth count. e.g. (Ring gear tooth count 35 T, pinion gear Tooth count 10 T, 35 divided by 10 = 3.50:1.

3. Many differential cases have many thousands of miles of service. Check all threads in the case for ware. It may be necessary to chase the treads to clean and align threads.

4. Check side bearing adjusters as they are often warped and out of shape making ring and pinion settings difficult. Replace as necessary.

5. Check ring gear back face for flatness. Generally after heat treating there may be a degree of taper. This may be rectified by lapping gear on sand paper on a glass flat plate. This will give you more even and uniform pattern when setting up you new gear set.

6. Careful attention should be give to blueprinting your rear end. Accurate clearancing will lead to a longer life for your unit.

7. All new parts should be thoroughly cleaned before assembly and checked for damage.

8. Examine the ring gear mounting surface for nicks or burrs which might prevent a flush mounting of the newly installed ring gear. Ring/Pinion tooth depth variations can result from a ring gear that is "cocked" on its mounting surface. If a ring gear spacer is to be used, also check it for surface imperfections. Nicks or burrs can be removed by using block-backed grit paper ora small file. Following material removal rewash in solvent and air dry. Mounting ring gear. Loctite ring gear bolts and torque to factory specifications.

9. All Motive Gear and Motive Gear Performance ring gear and pinions have been "Lapped" in sets and should never be mixed with another ring gear or pinion. Check to see serial numbers are the same on the ring gear and pinion.

10. Each motive gear and Motive Gear Performance ring gear and pinion is prerun and marked on the pinion face with its proper depth setting called the "Checking Distance". This dimension is from the face of the pinion to the axle center-line. A setting tool must be used to measure the checking distance. Pinion depth is adjustable by adding or subtracting shim thickness. Stay +/-.002 of the pinion dimension, (see Figure 'A' and 'B').

11. Once pinion depth is achieved using a new crush collar or preload shim pack set pinion bearing preload to 15 inch-pounds rotating torque with used bearings, and 25 inch pounds with new bearings. Once preload is set install the seal and loctite pinion nut.

12. Once the pinion gear is installed, position ring gear and carrier into housing to check backlash. Motive Gear and Motive Gear Performance ring gear and pinions are developed to be run at .008" to .012" back-lash for street gear sets.


13. Adjustments for backlash is done by spanner rings in the housing or shim packs behind the carrier bearing cups (GM) or cones (Dana). Always be sure carrier bearings are preloaded. The carrier should not fall out of the housing, but should have to be "tapped" in during final installation. Replace bearing caps and torque to factory specifications.

14. You are now ready to verify the tooth contact pattern. A gear marking compound should be used. Paint gear teeth with compound in several spots and rotate ring gear several revolutions. A tooth contact pattern will appear and should be similar to the pattern shown in illustration 'C'. If the pattern is not in the approximate position shown, reset pinion depth and backlash to correct pattern. Pinion shims usually must be moved in .003 of an inch increments to notice a pattern change. If a pattern is heavy toe subtract shims, (see Figure 'D') If a pattern is heavy heel add shims, (see Figure 'E').

NOTE: Reverse the procedure for 8" and 9" Ford

15. Fill the case with required amount of GL6 Torco 85W-140W with additive gear lube, and maintain the proper level at all times. Proper maintenance is a must to protect your safety and the working life of you gear set.

Go Here for the torque specs and other info..
Enjoy...
http://www.drivetrain.com/ringpinioninstal.html

Keith will have you fixing his Pentax...

[Vic Eaton]

HELLO KIETH AND ALEX
Thanks for the reply im just wondering how much i have to dismantle to be able to see the pinion gear as i have to count teeth on the one on the truck rear axle to see if it matches either of the two i have on the bench will i have to remove the whole diff from the truck or can it be done on there .
many thanks vic uk .

[Keith Webb]

As long as you can count the teeth on the ring gear you'll know - it's either 39 or 43 teeth. Often it's stamped somewhere on the diff housing exterior too.

[Vic Eaton]

HELLO KEITH
Thanks once again for your help i couldnt find any stampings on the diff casing on the truck but will look at the ones on the bench and do some teeth counting
regards vic uk .
PS weather here cold dry and cloudy hard frost overnight.
makes it difficult to start the old truck 6 volt doesnt seen enough cant imagine how they got on in places like NORWAY.

[Bob Carriere]

Photo by Rob Clarke....... dusk Dodge trucks in barn area...... very white and cold......

Bob

[Vic Eaton]

HELLO BOB
Blimey im glad i dont have to fit a diff in that weather not seen that much snow since barry sent me some pictures of his place also in ontario. i hope you have anti freeze in them there trucks regards vic . i enjoy seeing what its like in other countrys as i think others do on here as well. vic uk.

[Vic Eaton]

HELLO KIETH
At last had the excitment of seeing a diff they are well made thats for sure and very heavy the one on the truck matches the two we have on the bench 43 teeth so thats fortunate . on the radio truck someone in the past had cut off the half shafts and removed the diff lucky we have all the parts to replace it all
once again thanks to all for advice we can now get on with the job at hand regards vic uk.

[Bob Carriere]

Hi Vic

Actually this has been the mildest Winter on records so far.....and very little snow..... usually we have snow up to the engine bonnet of the Dodges by this time of the year.

....did go down to minus 21 Celsius this morning.....but then our new prime minister made a speech and by 5 PM it was and even
O Celsius........ all that warm air.....

Doing a 1500 km round trip recovery tomorrow forecast is for a Summer like + 5 Celsius....... with Sunny periods.... it helps when pulling a trailer at 120kmh.....

Hope you are not to close to all them bush fires we have seen in your country....

Bob C.

[Vic Eaton]

HI THERE BOB
GOOD JOB YOUR NOT LOOKING FOR ME .Im in the uk the bush fires are in AUSTRAILIA . i think and thank god for that they must be very scary indeed especialy if your truck is close by
regards vic uk.

[Alex Blair (RIP)]

Originally posted by Vic Eaton
HI THERE BOB
GOOD JOB YOUR NOT LOOKING FOR ME .Im in the uk the bush fires are in AUSTRAILIA . i think and thank god for that they must be very scary indeed especialy if your truck is close by
regards vic uk.

Hi Vic..
Bob get mixed up once in a while..The missus sent him out for some "tuk",and he thought she said "Truck" so he's off to get some more iron...it looks like.We'll hear the details when he gets back from where ever Rob and he have gone..He can't find his a$$ with both hands but he sure can come up with some great iron...

[Brian Gough]

Hi Alex

I can confirm there was a sighting of Bob and Rob out CMP hunting in the Oshawa area this morning. Apparently that was not their final destination but they did stop long enough that we got some work out of them..... and that is most appreciated.

I am sure something close to the truth will come out in time.

Brian

[Alex Blair (RIP)]

Originally posted by Brian Gough
Hi Alex

I can confirm there was a sighting of Bob and Rob out CMP hunting in the Oshawa area this morning. Apparently that was not their final destination but they did stop long enough that we got some work out of them..... and that is most appreciated.

I am sure something close to the truth will come out in time.

Brian

Thanks Brian...
And for our friends abroad that don't know where we are talking about,Brian is 400 KM south West of where Bob,Rob and I are in Ottawa...So Bob and Rob are off somewhere collecting iron ...fodder for our get togethers at Gracies bar and grill,beer and ROT tales...