ChrisM Posted March 6, 2018 Share Posted March 6, 2018 Hey everyone, I was trying to get my drive shaft in today, first thing I noticed is it was a really tight fit between the transmission and rear diff. Next, the rear u-joint is to big to fit into the axle yoke. It's a 12 bolt out of a 70 monte, I am a 402 big block with a th350 (I know it's a small trans) The drive shaft is out of my probably monte I had far as ago, that was a 10 bolt open axle. Any info would be great! Thanks. Quote Link to comment Share on other sites More sharing options...
MC1of80 Posted March 6, 2018 Share Posted March 6, 2018 Hi Chris. What you can do is get what used to be called a "conversion" u-joint. Lakewood used to sell them. I think zoom also. It's to convert the bigger 10 bolt yolk to the smaller 12 bolt yolk. The driveshaft fitting tight is most likely how you have the rear "hanging". Example- jackstands under the frame not the rear itself. If you jack up the rear t believe the driveshaft should fit with no problem. Hope this helped and good luck. Quote Link to comment Share on other sites More sharing options...
cny first gen 71 Posted March 6, 2018 Share Posted March 6, 2018 Were the th350 and th400 the same drive shafts? For some reason I am thinking one is longer than the other. Quote Link to comment Share on other sites More sharing options...
ChrisM Posted March 7, 2018 Author Share Posted March 7, 2018 Ok so that's one option, getting a conversion u-joint. Now, the rear of the car is on the ground, the front of the car was lifted so the rear axle was sitting completely where it needs to be. So in terms of length, the shaft is almost completely bottomed out in the transmission. I am not used to That, usually there is room for you to push the shaft into the trans to aid in removing from the rear axle. Can anyone tell me if the drive shafts for a 10 bolt are longer then for a 12 bolt? Quote Link to comment Share on other sites More sharing options...
Paul Bell Posted March 7, 2018 Share Posted March 7, 2018 I'll say it's the wrong drive shaft. Quote Link to comment Share on other sites More sharing options...
ChrisM Posted March 7, 2018 Author Share Posted March 7, 2018 Here's another question, why is it on the 10 bolt I took out of the car this driveshaft u-joint doesn't work in it either? My issue is the cup size, they over hang on the yoke of the diff by maybe a 1/4 inch each side, could be less and that's the same for the 12 bolt and 10 bolt I have at the side of my house. This driveshaft is out of my origanl monte carlo 70 350/350 10 bolt. If it's the wrong shaft, I am not sure how or what shaft to use. Quote Link to comment Share on other sites More sharing options...
Paul Bell Posted March 7, 2018 Share Posted March 7, 2018 I "think" the 12 bolt yoke sits a little further out from the differential housing. IOW, i't closer to the transmission-which caused the driveshaft to need to be shorter. Can anybody here confirm? But I do know the 12 bolt rear needs strap type U-joint retainers. Quote Link to comment Share on other sites More sharing options...
MC1of80 Posted March 7, 2018 Share Posted March 7, 2018 There are different length shafts for a th350 trans and a Th400. I don't remember correctly but I think the th400 shaft is 3/4-1" shorter. You want about 5/8-3/4" play in the yolk going into the trans. As for the u-joint , again if I remember correctly the 10 bolts had 2 different yolks. Some used the strap and bolt and the other used the u bolt type with nuts both had big caps on the u-joint as compared to the small 12 bolt caps. You may want to have the shaft you have now shortened and the trick joint installed. You should be good to go then. Or if you have a "friend" or scrapyard with allot of shafts you may get lucky and find the right length. Quote Link to comment Share on other sites More sharing options...
ChrisM Posted March 7, 2018 Author Share Posted March 7, 2018 Paul bell, not sure what you mean by strap type, I have a set of u bolt style that seem to at least fit the holes on the diff yoke. Mc1of80, so really if I could find a drive shaft from a th400 I should be ok, is that what you mean? I can't seem to find anywhere around me that shortens drive shafts Quote Link to comment Share on other sites More sharing options...
Paul Bell Posted March 7, 2018 Share Posted March 7, 2018 U-bolts on top, straps on bottom. Quote Link to comment Share on other sites More sharing options...
ChrisM Posted March 7, 2018 Author Share Posted March 7, 2018 Ohhhh ok I get what you mean, Ok, so I have to take a measurement of how much of the front yoke at the trans, should have 5/8 to 3/4 of an inch out from the seal, once I do have the correct u-joint, now is there a way to figure out whether it's a strap or u bolt style? Or it going to be try what works, thank you for all the help and advice everyone Quote Link to comment Share on other sites More sharing options...
Paul Bell Posted March 7, 2018 Share Posted March 7, 2018 ....now is there a way to figure out whether it's a strap or u bolt style? If it's a 12 bolt, its strap style. 10 bolt rears got the U-bolt. On the 12 bolt yoke, the strap bolts THREAD INTO the yoke-no nuts needed. On the 10 bolt yoke, the bolt PASSES THROUGH the yoke and and nuts spin on from the backside. Quote Link to comment Share on other sites More sharing options...
ChrisM Posted March 7, 2018 Author Share Posted March 7, 2018 Ok perfect thanks Paul! Ian going to try and find the correct u-joint, and find some strap style hold downs Quote Link to comment Share on other sites More sharing options...
John S Posted March 7, 2018 Share Posted March 7, 2018 I believe the u-joint you are looking for is a Moog 449 Summit racing Part # MOG 449. That is on my 1970 with 12 bolt. John S Quote Link to comment Share on other sites More sharing options...
ChrisM Posted March 8, 2018 Author Share Posted March 8, 2018 Thanks everyone for the info, I have found a drive shaft shop, they know exactly what I need, I'll be dropping the shaft off, they are going to shorten it and put a new u-joint after cutting the old yoke and replacing with a newer style 1 Quote Link to comment Share on other sites More sharing options...
Paul Bell Posted March 9, 2018 Share Posted March 9, 2018 Just for information and searchable posterity, the 12 bolt yoke and U-joints were different for the 454 cars vs. the 350/402 cars. They were even coded differently despite having the same ratios. When servicing the U-joints on an unknown sourced 12 bolt rear, it's best to take measurements and purchase to match. All 12 bolt rears have the same strap & bolt setup. I created a sample of 1971 rear end codes: Quote Link to comment Share on other sites More sharing options...
ChrisM Posted March 20, 2018 Author Share Posted March 20, 2018 That's awesome, thank you Quote Link to comment Share on other sites More sharing options...
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