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Discussion Starter #1
Hello all, I have not posted in some time nor assisted others so I am not expecting much help. I am having a weird issue with my 72 and I could use some suggestions. It is a 72 coupe 350 with a Saginaw 4 speed and 10 bolt posi. I had the trans rebuilt last summer by a shop that a bunch of car guys use and recommended. It shifts smooth and no noise. I had the flywheel resurfaced and put a Rock Auto stock clutch in. The rear is stock except for fresh fluid/posi additive a while ago. I don't drive it hard. The issue is the car shudders and seems to not want to roll when I try to take off. It is like the brakes are hanging up or bad clutch chatter. It does not happen every time, but often enough that something is up. I heard rear brake hoses can collapse, so I removed it and ran a wire thru. It seemed clear, but I replaced it anyway and bled the brakes same issue. It has disc brakes up front. I have never disturbed the proportioning valve in the 30 years I have owned. I did front brake hoses and rear wheel cylinders years ago. It happens in forward or reverse and seems to happen after the car has been parked for a few hours. I pump the brakes and go in and out on the clutch and it "frees". Any suggestions would be great.

I have recently taken 4 or 5 100 mile highway trips and I don't think you could with a blown rear. I don't think its that or the trans. Regards
 

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Could be limited slip additive is causing issue, or a wheel bearing in the rear is failing.
I would suggest park on a flat surface and put car in neutral, engine off and manually push car forward and backward, maybe a couple times to determine if it requires the same Force both directions. Then jack rear off the ground, put on jack stands, and try spinning both tires By hand, both directions also, and pay attention to any difference in force as well. With car still on jack stands, rear tires off the ground, start engine and put transmission in gear and release clutch, do this in each gear and note if it still has the problem. If the problem persists, pull driveshaft and lower car on ground and once again push it forward and backward, and note if the problem persists. If final answer is yes, problem is in rear end or mismatch tires in the rear.
If car pushes much easier with driveshaft removed, problem is in clutch or transmission
 

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I had that happen on my 69 and it ended up being the driveshaft U joints were bad. It would cause a shutter but not sure about the bind. That is usually the posi plates sticking. Even though I used Valvoline gear lube designed for posi I had to add the additive to stop the brake feeling especially in reverse
 

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Discussion Starter #6
Thanks much for the replies. I ruled out the oil leak. The bellhousing and back of the block is dry, but that is a good suggestion. It seems none of the replies are centered around brakes hanging up which is where I was going. I like the possibility of u-joints or maybe the posi clutches. I will run some of the tests suggested by Kirk and follow up. Thanks for the time.
 

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Discussion Starter #7
Hello, I thought that I would provide a quick follow up. I tried several of the tests suggested. The car rolled forward/backward about the same. U-joints look ok. I pulled the diff cover. The oil looked pretty dark and thin. The teeth on the ring gear and pinion look real good. No chunks or even small bits of metal. I am thinking(hoping) that the gear oil and posi additive maxed out their life span. I will put fresh stuff in and see what happens. The preventative maintenance guys will curse me, but the stuff has been in there about 22=25 years, so its time. Regards.
 

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Discussion Starter #8
Hello, I thought I would follow up on this. I replaced the gear oil with fresh Lucas stuff. I also went to a GM dealer for the additive. Same issue, no improvement however the fluid needed to be changed anyway, so there is a fringe benefit. I noticed that the trans has what I consider more than normal movement at the mount. I placed a screwdriver in between the tail of the trans and the cross member and there was quite a bit of movement. The mount is not broken but seems like the rubber is soft. Any suggestions on how stiff a stock (and probably 20+ years old) mount should be? Should I go stock or performance for a new one? Thanks!
 
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