700r4 shake?

[Bloodhound1981]

So I disconnected the driveshaft from the pinion. I checked for play in the yoke at the transmission. Of course I have no reference for what is normal, but it definitely seemed like more play side to side than I would expect. Also, I learned that the Corvette 700R4 has an output shaft that is about 5/8" shorter than a regular one. With the truck tailshaft I swapped onto this vette 700R4 so it would mount to the crossmember, the output shaft does not extend out past the rear seal at all. @NickTransmissions On a regular 700R4 do the splines normally stick out of the tail shaft? Sorry if this is boring everyone, just determined to figure this out.

 

[Bloodhound1981]

I continue down the rabbit hole. I pulled the tailshaft housing off. I would love to know if this amount of play in the output shaft could be the source of my problem? I assume this may have been caused by the too short length of the Corvette transmission running a regular length tail housing.

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[xm20k]

I continue down the rabbit hole. I pulled the tailshaft housing off. I would love to know if this amount of play in the output shaft could be the source of my problem? I assume this may have been caused by the too short length of the Corvette transmission running a regular length tail housing.

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I'm pretty sure that output shaft should protrude out beyond the tail housing seal 3/4 give or take a hair.

A quick Google search and the vette output and tail housing are both shorter.

 

[Bloodhound1981]

I'm pretty sure that output shaft should protrude out beyond the tail housing seal 3/4 give or take a hair.

A quick Google search and the vette output and tail housing are both shorter.

Correct. Well, replaced the tail shaft bushing and seal. No difference, still a shake from 67mph to around 74mph. I think a 4l60E is in the cards for next spring.

 

[NickTransmissions]

Correct. Well, replaced the tail shaft bushing and seal. No difference, still a shake from 67mph to around 74mph. I think a 4l60E is in the cards for next spring.

Are you sure one of your wheels isnt simply out of balance?

The output shaft will always have movement/play as that allows for driveshaft articulation. The ext housing bushing simply stablizes the slip yoke while the rear case bushing stablizes the transmission's rear reaction shaft. Both would have to be worn by 90%+ or missing to cause the vibrations as mentioned and they would be present at all road speeds, increasing in severity proportionally to output shaft speed.

 

[Ricko1966]

Move the front tires to the rear and vice versa maybe you have a bad tire.

 

[xm20k]

Move the front tires to the rear and vice versa maybe you have a bad tire.

Oof didn't even think of that, but yah you could have a busted/slipped belt swap ends and see if it goes to the steering you'll see/feel it in the wheel if so.

 

[Bloodhound1981]

Move the front tires to the rear and vice versa maybe you have a bad tire.

I really hope that's it, I'll feel like a dope if it is but be relieved. I had all four tires re-balanced on a new machine that was literally 1 day old a few months ago. But it wasn't a road force balancer, and I'm now realizing they could still be balanced but causing the shake. Tonight I shall find out!

 

[Bloodhound1981]

So the very TLDR is that a slightly out of balance brake drum can cause a really annoying highway speed shake. That was the problem all along.


The long version...with pictures haha...I had put the rear wheels/tires onto the front as suggested. No change in the shake. So I was really out of ideas. However, I decided to throw my brake drums onto the wheel balancer at work to see what I could see. The passenger side was pretty good. The driver side on the other hand had a very obvious runout. I never felt this in the pedal. Less than 3k miles on them, and it is clearly a manufacturer defect.

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I ordered up two new drums (11x2in size), and for good measure threw those on the balancer. They were perfect. I then cleaned and painted them black. I noticed that they had no weights on them like the old ones and they seemed lighter, but I didn't think too much of it. Obviously if I had looked closely I would have noticed a problem. When they dried, I excitedly went to put them on the truck, and low and behold, I have the 11x2 3/4 HD brakes on my normal C10. Why? I have no idea. So now I have these painted drums that don't fit.

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I order another set of the correct drums and put them on for a test ride. Well, the shake now changed. It felt different and started out at 62mph instead of 67mph. I put the new drums on the balancer, one of the two is clearly out of round, in addition to a little out of balance.

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I then take the original passenger side drum that had balanced ok, and put that one back on, along with the new good driver side one. Voila! No more shake. At least none that I find unacceptable in 52 year old technology.

The good news is Advance Auto is letting me return the drums I painted, and now I have to just do an exchange on the out of round new one for hopefully a good one. Of course there's none in a hundred miles from me, but that's ok, I can wait. Thanks for all the suggestions!

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[HotRodPC]

So I guess we're waiting for new drums to see if this corrects the problem? Not to be that guy, but I'll be totally shocked if this is it. I can't imagine drums could cause this much problem. This will be interesting. Please do post up and let us know for sure.

I was going to suggest, just cuz the rear end is all new, doesn't mean that's not it. Not everyone can set up a rear axle properly. However, if there's no whine, chances are it's good, and that slack you're talking about sounds about normal or good. They do have some. If you had a Detroit Locker in it, it has even a bunch more than that. I've seen Detroit Lockers have close to a 1/4 turn before. Also part of the reason, they're so noisy on turns or even worse backing up.

 

[Ricko1966]

So I guess we're waiting for new drums to see if this corrects the problem? Not to be that guy, but I'll be totally shocked if this is it. I can't imagine drums could cause this much problem. This will be interesting. Please do post up and let us know for sure.

I was going to suggest, just cuz the rear end is all new, doesn't mean that's not it. Not everyone can set up a rear axle properly. However, if there's no whine, chances are it's good, and that slack you're talking about sounds about normal or good. They do have some. If you had a Detroit Locker in it, it has even a bunch more than that. I've seen Detroit Lockers have close to a 1/4 turn before. Also part of the reason, they're so noisy on turns or even worse backing up.

He ran it with two good drums1 new 1 used and that cured it ,he's waiting on another new good drum.

 

[HotRodPC]

He ran it with two good drums1 new 1 used and that cured it ,he's waiting on another new good drum.

OK, so I musta skimmed again. Well great news, but Wow. I really never heard of brake drums doing this before. Of course if I had a good running rig, changed my brakes and drums THEN the problem exists, I for sure would have to suspect the new parts, but NOPE, never heard of drums causing a vibration. it does make sense though, and obviously true if he's fixed with a drum swap.

 

[Ricko1966]

OK, so I musta skimmed again. Well great news, but Wow. I really never heard of brake drums doing this before. Of course if I had a good running rig, changed my brakes and drums THEN the problem exists, I for sure would have to suspect the new parts, but NOPE, never heard of drums causing a vibration. it does make sense though, and obviously true if he's fixed with a drum swap.

New parts quality these days isn't like it used to be. He said 1 drum was out of round and out of balance.

 

[xm20k]

Not surprised one of my front wheels was outta round it looked fine till they spun it on the balancer, and it moved side to side about, and inch and quarter. Summit sent me a new one in 2 days and a UPS label via email.

Hopefully the replacement drum they send you is good to go.

 

[idahovette]

@xm20k was the replacement wheel straight?