Weird issue
Thread Starter
Joined: Jun 2014
Posts: 1,241
Likes: 47
From: Noblesville, IN
Weird issue So I know at this point I'm grasping at straws... but I'm honestly out of ideas.
I have an issue in my Z28 where, when coasting in 5th and 6th, i'm getting a thumping noise, and the car is jerking slightly, as if I'm tapping on the brakes. I've had the trans apart about four times now, and I'm seeing absolutely NOTHING wrong internally. The only other thing I changed was I bought a UMI adjustable long torque arm and a new trans mount to relocate the arm off of the tailshaft housing.
Hence why I'm posting about this here... I'm wondering if it's possible, someway, somehow, that this issue is suspension/rear end related? I set my pinion angle to -2 degrees (differential is at 0, and driveshaft is pointing downhill at 2 degrees towards the rear) and the torque arm is on the 2nd set of bolt holes on the trans mount (which according to the instructions I got, are supposed to be the same angle as the factory settings). Everything is torqued to spec as well.
The only issue I saw so far with the new torque arm is the bracket running into the drivers rear seat bucket, but I hammered that out and am fairly sure that it's no longer making contact.
Any thoughts? Anyone?
I have an issue in my Z28 where, when coasting in 5th and 6th, i'm getting a thumping noise, and the car is jerking slightly, as if I'm tapping on the brakes. I've had the trans apart about four times now, and I'm seeing absolutely NOTHING wrong internally. The only other thing I changed was I bought a UMI adjustable long torque arm and a new trans mount to relocate the arm off of the tailshaft housing.
Hence why I'm posting about this here... I'm wondering if it's possible, someway, somehow, that this issue is suspension/rear end related? I set my pinion angle to -2 degrees (differential is at 0, and driveshaft is pointing downhill at 2 degrees towards the rear) and the torque arm is on the 2nd set of bolt holes on the trans mount (which according to the instructions I got, are supposed to be the same angle as the factory settings). Everything is torqued to spec as well.
The only issue I saw so far with the new torque arm is the bracket running into the drivers rear seat bucket, but I hammered that out and am fairly sure that it's no longer making contact.
Any thoughts? Anyone?
Thread Starter
Joined: Jun 2014
Posts: 1,241
Likes: 47
From: Noblesville, IN
Well I threw the stock tq arm back on and the issue seems to be a lot better. It's now gone from all the time, to seemingly only below 1500rpm in 5th and 6th, and doesn't happen NEAR as much.
Was talking to RPM transmission about it, and they think that the pinion could be loose. So I'm gonna pull the cover off the diff and see what that looks like.
Was talking to RPM transmission about it, and they think that the pinion could be loose. So I'm gonna pull the cover off the diff and see what that looks like.
Thumping noise Ive done some reading on this do a google search : tunnel mount torque arm thumping noise site:ls1tech.com that should give you quite a bit of reading material most fix it with the bfh mod
Do you have a misfire? That wouldn't explain the thumping noise, but at cruise speeds in 5th and 6th, the ignition system is under heavy load and is more likely to misfire if there's a problem.
Thread Starter
Joined: Jun 2014
Posts: 1,241
Likes: 47
From: Noblesville, IN
I would be amazed if it was a misfire. Haven't seen anything on any data logs.
500, you might be correct. I was doing reading and it seems similar. Years ago when the car was still stock I lowered it and put on a cheap adjustable PHB. WHen I did I didn't loctite the adjuster nut so it back off and I was getting a really annoying rattle from the rear. This rattle sounds very similar, so I'm wondering if the heim joint bolts aren't tight enough, though I did torque them to the spec UMI gave me (something like 125 ft lbs)
Still have the stock torque arm on for now. Weather has been inconsistent recently so waiting for a couple of nice days to do some back-to-back testing.
500, you might be correct. I was doing reading and it seems similar. Years ago when the car was still stock I lowered it and put on a cheap adjustable PHB. WHen I did I didn't loctite the adjuster nut so it back off and I was getting a really annoying rattle from the rear. This rattle sounds very similar, so I'm wondering if the heim joint bolts aren't tight enough, though I did torque them to the spec UMI gave me (something like 125 ft lbs)
Still have the stock torque arm on for now. Weather has been inconsistent recently so waiting for a couple of nice days to do some back-to-back testing.
