Getting Shafted

Getting “Shafted”

Having taken my Mopar 8 ¾” differential to DTS in Grand Rapids, Michigan for service, I wanted the driveshaft and U-joints changed to handle the horsepower I would be putting through it, and I was given a serious lesson in driveline engineering by the crew at DTS.

I was instructed by Jay, a very knowledgeable individual on axles, ratios, and driveshafts (and not a bad salesman either) to measure the length, center to center for the new driveshaft I needed using the following procedure:

Support the weight of the vehicle at the wheels while taking this measurement
Slide the bare driveshaft yoke into the transmission all the way to bottom and then pull it out ¾”.
Measure center to center from the yoke at trans to the yoke at the rear axle.

Sounds simple, eh? Anything but --- and the measurement itself is critical for proper operation of the vehicle.

Now having been a Michigan certified Master Mechanic for 20+ years and now an Engineer on computer systems, I fancy myself as someone who knows something about automobiles of the era I am working on. Mainly Mopar Muscle Cars. I raced Chevelle’s and Malibu’s on the old dirt tracks of Northern Michigan in the 70’s and did my fair share of winning. I worked as a Mechanic, Service Manager, and Automotive technology instructor Para-pro at a local high school for some years. Now I’m an ENGINEER and DTS can’t just build me a damn driveshaft for a 1971 B-Body with a 360 engine, A-833 4-speed and 8 ¾” rear axle without having a stupid measurement with all the weight on the axle? Anyone knows a B-Body with a 727 auto or 4-speed uses the same shaft – right?

So now, OK. I take the measurement center to center from the shaft that came out of a running 1971 B-Body Satellite with the same trans and rear end (literally, I drove the car and it appeared fine). The measurement is 51 7/8”.

Then I go through the pain of shoving an old 741 differential in the housing, mounting my trans up in there, going to some pains making sure it is square and where it’s supposed to be, follow the proper procedure --- and get 51” dead on. STOP. RED FLAG. Why is the measurement on the car SHORTER than the original shaft? It should be LONGER as the factory used 1-1.5 inches when they did this. For God’s sake. The factory only made two driveshafts for these cars, I’VE SWAPPED THEM A HUNDRED TIMES AND GOTTEN AWAY WITH IT IN MY YOUNGER DAYS, RIGHT?

So, the next day I call my friend Jay at DTS and explain the situation to him. I tell him what I’ve run into and he asks all the qualifying questions:

A. Is the car all together or is it a shell? --- it is a shell with the interior and gas tank out of it.

B. Did you have the weight on the wheels when you took the measurement? YES

Jay explains to me it may be better to wait until the car is done to get them this measurement properly as gasoline weighs x amount of lbs. Per gallon (I believe around 6.xlbs, haven’t done the research on that one yet….) I don’t want to wait. I want my damn driveshaft before wife and daughter spend the money on useless stuff (food, clothing, bills, etc) AND BESIDES, THERE ARE ONLY TWO DRIVESHAFTS MADE FOR THE DANG CAR, ONE FOR 904 AUTO’S AND ONE FOR 727 AUTO’S AND 4-SPEEDS, RIGHT? A B-BODY IS A B-BODY, RIGHT?

My friends, arrogance is an awful thing that has bitten me in the buttocks more than once over the years. At 43 years of age, I have finally learned to cool my jets when someone tells me something I believe to be ridiculous. If I have a theory, I must prove it and by God Jay was just being a pain in my butt, RIGHT?

Can you see the crow I am beginning to eat here yet?

I get out my trusty 1971 Chassis Service manual one Friday night and start looking through it, researching how propeller shaft and u-joint angularity are measured from the people who made the car. Page 16-3 of the manual comes up and the second paragraph reads:

“All joint angle measurements on the vehicle should be made with the car supported by the tires if possible; such as, on an alignment pit or a platform hoist. A two-post hoist may be used where other means are not available. The vehicle should be approximately level when taking angle measurements with any heavy items removed from luggage compartment or passenger compartment. The fuel tank should be full or the equivalent weight simulated. When using a twin post hoist, the vehicle must be supported by the lower control arms and rear axle housing. DO NOT USE A FRAME CONTACT HOIST WHEN MEASURING PROPELLER SHAFT ANGULARITY (sic)”

Fine. Still doesn’t explain why when I measure the damn thing using the DTS method and I get a shorter number than the actual center to center length I get in the car --- AND THE TRANS AND DRIVESHAFT WERE IN A B-BODY OF THE SAME STYLE AND RUNNING OK, RIGHT?

Page 16-9 of the manual. I’m going to have to learn to like crow. In a big sort of way. As I look down the page for the Dodge Dart, I count, not two --- BUT FOUR DIFFERENT DRIVESHAFT LENGTHS FROM THE FACTORY. On to the Charger page, hell I know there’s only got to be two there, Darts were stupid anyway, RIGHT?

Page 16-11 --- LOVE THAT CROW! With the Charger for 1971 there are not four --- BUT TWELVE, COUNT’EM, 12 DIFFERENT LENGTH SHAFTS FOR DIFFERENT MODEL ENGINE/TRANS/REAR_AXLE/BODY COMBOS. And guess what? 51.875 (51 7/8” the measurement I got from the shaft that came out of the car) isn’t listed and isn’t even close to anything that is. But you know what it? The driveshaft for a Dart with a 4-speed with 8 ¾” rear and small block is 50.96 inches – close enough for me to buy. And the shaft that is supposed to go into My Charger with the combination I have is --- you guessed it, 50.68 inches in length --- SHORTER THAN THE 51” MEASUREMENT I GOT USING DTS’S METHOD, AS IT SHOULD BE. I now understand the discrepancy and why it was the way it was.

The bottom line here, is don’t get arrogant. Listen to the people at DTS. They REALLY did me a favor by forcing me to research this issue. They could have been like so many other outfits and just said “it’s good enough” and then charged me again for either cutting the shaft down when the car is finished because it’s too long or by having to re-tube the shaft again because it’s too short. They did not do this to me so I can pretty much guarantee they won’t do it to you. Did they lose business by doing this? No way. EVERYTHING I have driveline wise from this day forth is going to DTS. With that kind of honesty, I can’t lose. The end result is I’m going to run my loud and sometimes arrogant mouth to everyone I know about DTS and the services they perform and have written this to thank them for their help and honesty.

As for the Charger, well, I think I’ll just wait until everything is mounted and the gas tank is full and then take that measurement again --- and get it done correctly ONCE. Thanks Jay. Thanks DTS.