Maybe that's where "Aggressive" came from....................
Ted.
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| 8 3/4 rearend question https://slantsix.org/forum/viewtopic.php?t=53348 |
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| Author: | '67 Dart 270 [ Wed Sep 18, 2013 2:43 pm ] |
| Post subject: | thanks for the info, keep it coming... |
Wow, I wasn't aware that the 7 1/4 was that weak, but I'm glad I got the larger unit - my work is 50 miles from home.... I don't think my drive shaft has rubber, I've been under there a few times, but don't recall seeing any rubber...I'll have to climb under there this weekend to be sure. Slantzilla, I think you mean measure twice before cutting, isn't that the rule...for me it's like 6 times...unless I write it down... |
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| Author: | Romeo Furio [ Wed Sep 18, 2013 4:24 pm ] |
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Maybe that's where "Aggressive" came from.................... Ted.
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| Author: | Aggressive Ted [ Wed Sep 18, 2013 5:09 pm ] |
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Good one!  you got it.....You wouldn't think that a potent SL6 could tear up a 7.25" rear but I went through the stock 2.76 a 2.94 a 3.23 and a 3.5. I guess driving on the twisty foothill mountain roads is too hard on the rear. I had Randy's Ring and Pinion build the 742 case around the 2002 time frame and the gears are just starting to whine this year. |
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| Author: | '67 Dart 270 [ Wed Sep 18, 2013 7:45 pm ] |
| Post subject: | whine.... |
come to think of it, I had my 7 1/4 ring and pinion replaced less than two years ago, and it's whining a little bit already...the slant does have some torque, mine would chirp the tire when my A-904 hit second pretty regularly. |
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| Author: | '67 Dart 270 [ Thu Sep 19, 2013 9:01 pm ] |
| Post subject: | drive shaft with rubber... |
Ugh, I crawled under there and indeed my drive shaft has the rubber between the yolk and the shaft.... So, what is the most expeditious route to procuring a shorter drive shaft that fits the 8 3/4 rearend and A-904 3 speed automatic (1967 dart 270)? should I just start with a new tube? What tube should I use? Do I take a drive shaft from another car that had 8 3/4 with A-904 and call it a day (will that already be the right length)? Are these easy to come by or hard? thanks all, Brian |
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| Author: | Charrlie_S [ Fri Sep 20, 2013 4:10 am ] |
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I was lucky when I replaced the 7 1/4 rear in my 66 Valiant with the 8 3/4. We have a old Mopar only salvage yard not too far from me. Went there and got a shaft from a later 340 powered "A" with an 8 3/4 for around $100 Finding one depends on your area, but it might be easier/best to have a shop make a new one. As I posted earlier, it is usually easier/cheaper, to have the shop use a new tube. Take your old shaft, put the front yoke into the trans, all the way. Then pull the yoke back out about 1 inch, and measure from the center of the front u-joint to the center of the rear u-joint seat in the 8 3/4 yoke. That is the length the new shaft needs to be. Have the weight of the vehicle on the suspension when taking the measurement. |
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| Author: | Sam Powell [ Fri Sep 20, 2013 5:01 am ] |
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Find a local large truck service place. They will have a drive shaft servicing depatment that will consider this a piece of cake. I watched mine being made and he did everything to the shaft in the lathe. That included cutting, welding, cleaning with a rotary sander while spinning, balancing, and then painting. It took maybe 20 minutes, and cost maybe $150 which included a new front yoke. A new tube would not have added much to the cost. While you are at this you might consider asking about aluminum tubing. It will save a bit of weight. I had an amateur shorten a drive shaft for my old Pontiac back in 1964, and it always vibrated. This really is not a DYI project. Sam |
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| Author: | slantzilla [ Fri Sep 20, 2013 6:58 am ] |
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A buddy and I shortened a couple shafts in his garage years ago. They both turned out fine, but I have to believe it was luck. For the pain in the azz it was, taking it to a shop would have been cheaper. |
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| Author: | '67 Dart 270 [ Fri Sep 20, 2013 10:47 am ] |
| Post subject: | thanks! |
Thanks everyone, especially Charlie for the measurement method, very helpful. So, is the front yolk that slips onto the splined shaft of the tranny the same for A-904 and 727 or are they different? That is, if I get a shaft from a car that had a different tranny but an 8 3/4 rearend, do I need to switch the front yolk to my current one? Do all 8 3/4 rearends have the same rear yolk, or do I need to find one specifically with the same case 741 or 742? Brian |
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| Author: | '67 Dart 270 [ Fri Sep 20, 2013 10:58 am ] |
| Post subject: | front yolk... |
is the A-904 a 25 spline yolk or a 29 spline yolk... |
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| Author: | Sam Powell [ Sat Sep 21, 2013 9:04 am ] |
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On my '69 904 the front yoke was smaller than the 727 behind my 360 Dart. However, the 833 manual tranny I later installed used the same yoke as the 727. Current yoke is a Ford piece. The car shown below has had a stock 904, an 833 OD, and now a t-5 five speed. I have had three different rears and 4 different drive shafts in it, three of them made custom. Don't be afraid of the custom drive shaft thing. Sam |
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| Author: | '67 Dart 270 [ Sat Sep 21, 2013 8:13 pm ] |
| Post subject: | maybe I'm in good shape... |
So, the guy that sold me the totally rebuilt 8 3/4 rearend had a bunch of A-body driveshafts laying around and he gave me one. I hadn't taken any measurements of mine yet, but I knew I needed one about 1.75-2.25 inches shorter than mine... When I got home, I measured my driveshaft from universal joint center to universal joint center and it was exactly 2 inches longer than the one he gave me. What are the odds? I think the one he gave me will exactly fit when I put the 8 3/4 rearend in...NOTE: the one he gave me was from a Demon or Duster of '73-74 vintage. I may not have to get it shortened. I'll certainly try it and see. Anyhow, I found a local shop that specializes in custom drive shaft work so, no matter, I'm in good shape. thanks everyone. BG |
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| Author: | '67 Dart 270 [ Sat Sep 21, 2013 8:21 pm ] |
| Post subject: | many tranny's... |
Sam, Special note to you regarding your feedback...I have all the carpet and most of the interior torn out for eventual replacement. I have to say, when I saw that circular flat area on the sheet metal over the transmission...I had this fantasy of putting a four speed in my Dart.. Maybe after I've put in the new rearend and driven it for a bit to see how I like it. I really like my automatic, but I'm intrigued to see how a slant six responds in first gear with a four speed...I've only ever driven a three on the tree with a slant before... My new rearend has 3.55 gears in it; does anyone know if there are limits to how fast I can drive on the highway with these gears and an A-904? Is it OK to drive 65-75 mph over long distances with these gears? BG |
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| Author: | wjajr [ Sun Sep 22, 2013 5:42 am ] |
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I have 3.55 rear with 205/70 R 14 tires and 904. One point to keep in mind is unless you have an overdrive transmission or aftermarket overdrive device all transmissions will have 1:1 top gear. In third my car turns 2000 rpm @40 mph, 3000 rpm @ 60 mph, and 4000 rpm @ 80 mph which happens to be the rpm that a stock 904 would up shift when in drive at WOT. 3000 rpm is rather busy to one’s ear particularly after jumping into one of these old cars from a modern low revving at cruise speed drivetrain. Will a slant run all day at 3000 rpm, yup, 3750 rpm (75mph) probably, will you have a good dose of road buzz after a few hours of driving at those engine speeds, you bet. Do I like that gear, not particularly it is a trade-off between performance, and highway cruising performing neither task very well in my book. I would go to a taller gear, except the cam currently installed is torque-less under 2500 rpm, engine is high revving liking 4000 rpm and up which as you can see 3.55 is always off the sweet-spot at highway speed. I generally cruise at 3000 to 3250 rpm. Taller rear tires will knock down the rpm a bit, but there is not much room under a 67 Dart for that to make a big difference. If you want to run at 75 mph all day long, I would be looking for a taller rear gear in high 2.xx:1 range as long as your engine has a torque curve that would be compatible, or cruise at a lower speed. |
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| Author: | Sam Powell [ Sun Sep 22, 2013 5:56 am ] |
| Post subject: | Re: many tranny's... |
Quote: Sam,
To put a four speed in you will need the hump for that tranny. These are now being produced new. Good news on the drive shaft. I do think 355 gears are going to be a little high reving for the highway. You might consider an overdrive auto from Mopar such as Lou Dart270 has done. I think they called that a 518. I also recall it needed a special adapter for a slant/v8 bellhousing. You need to shift in and out of lockup manually but aside from that I think Lou has been happy with it. Some guys are working on getting a newer GM tranny behind a slant, but this takes an expensive adapter. I actually think the GM idea is a winner. It is widly supported and efficient. The cost might be worth it in the end.Special note to you regarding your feedback...I have all the carpet and most of the interior torn out for eventual replacement. I have to say, when I saw that circular flat area on the sheet metal over the transmission...I had this fantasy of putting a four speed in my Dart.. Maybe after I've put in the new rearend and driven it for a bit to see how I like it. I really like my automatic, but I'm intrigued to see how a slant six responds in first gear with a four speed...I've only ever driven a three on the tree with a slant before... My new rearend has 3.55 gears in it; does anyone know if there are limits to how fast I can drive on the highway with these gears and an A-904? Is it OK to drive 65-75 mph over long distances with these gears? BG Good luck on your project. Can you show us some photos? Sam |
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