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Hi,
I have a 1968 Olds 442 with a rear differential with the code BU, CFD7, 394139 and 132.
I know it’s not Posi but I’m trying to figure the gear ratios. I tried the roll the axle and count but that didn’t seem to work. Wasn’t consistent which seems their maybe a problem, that’s for a different thread.
I can’t find anything on the differential code BU, CFD7, 394139 and 132.
Those are cast numbers. Look on the passenger side axle tube for two letters about 1/4 inch high, stamped into the tube. Could be upside down also. RA, S4, TA, T2 etc.
As stated above, the numbers you referenced are basic housing casting numbers and you will need to look for the two letter code that is stamped on the passengers side axle tube. Below is a picture of the code on my 1968 O-Type (3.42:1 open).
Kenneth,
Thanks for the reply.
The builder of this car removed a 350 ci and th350 trans. So I’m thinking the axle was also replaced. Will this axle code honestly reflect the differential gearing?
The code represents the gearing the axle had when it left the factory. After nearly 50 years the gears could have been replaced. You can pull the cover off and either look for the numbers stamped into the edge of the ring gear or count the teeth on the gears to determine the ratio. If you have never opened the diff, it may be due for an oil change anyway.
Last edited by Fun71; February 11th, 2018 at 11:55 AM.
Only true way is to always open the diff to see what ratio it is...
TL is 3.42 open
ALL the olds axle tube codes we run into with 12 bolt cover and 10 bolt ring are upside down like yours is.... Back side of the passenger axle tube.
WHY? I do not know
Chevy was always front of passenger axle tube
Pontiac was back of driver side axle tube
and
Buick was always facing the ground on the driver side axle tube.
1) Hold one wheel so that it cannot turn.
2) Count the number of times you have to turn the pinion flange to get the other wheel to turn exactly ten times.
3) Divide the pinion turns by five. This is the ratio.
Holding one wheel ensures that the turns all take place on the one wheel you are looking at. FYI, the reason you divide by five is that on an open rear, the differential gears add a 1:2 multiplier to the count. You could also divide by ten and then multiply by two.
Also, the reason I use ten turns of the wheel instead of one is because it is much easier to tell the difference between 34.2 and 32.3 turns of the pinion rather than 3.42 or 3.23 turns.
I still do not get why people have such a hard time pulling the cover...??? Your going to have to evaluate the condition whether you keep it or sell it...???
So just pull the darn cover. Take some pictures of the condition and find the stamping on the edge of the ring - This can never be wrong.
Inside the diff is the only part of a car I've never done. Painting with engineers blue, setting up the backlash, shimming, pulling it apart again and again to get it right and such just seems like black magic to me.
Fear of the unknown is all - and getting it wrong.
BTW my diff housing has some strange numbers and letters front side of the pass tube. 'KA B283 1'. I've posted here before and no positive id on what the numbers actually are, although Kennybill had a stab.
Apologies to Frisbee_k9 for the hijack.
Last edited by 73aussie455; February 13th, 2018 at 09:08 PM.
Reason: shorten post
Inside the diff is the only part of a car I've never done. Painting with engineers blue, setting up the backlash, shimming, pulling it apart again and again to get it right and such just seems like black magic to me.
Fear of the unknown is all - and getting it wrong.
BTW my diff housing has some strange numbers and letters front side of the pass tube. 'KA B283 1'. I've posted here before and no positive id on what the numbers actually are, although Kennybill had a stab.
Apologies to Frisbee_k9 for the hijack.
KA is the ratio B2831 Is the plant date and shift of day that worked on the rear.
KA is the most important digits... Find a GM manual for your year car it will be in there some where. Do not expect any great gearing for that tank...
Is that KEENY BELL? or BILL
Eassiest way AGIN...is to just open the rear inspection cover and read the stamped ring gear edge for gear ratio...it will be in tooth count number form.
IE 15 41 = 2.73
16 41 2.56 ratio
divide the small (pinion tooth count) into the big tooth count (ring) raund to the second decimal
You have your ratio.
Blueing does not work as good as the yellow or white grease type marking compound for seeing the pattern...
February 10th, 2018 | 07:51 PM
