81 auto shifting hard

[mikejpss]

Lil Red is an automatic, with 75k miles on her. When going into reverse, she has a solid "thump" as it goes into gear. When shifting into Drive from "N", it feels and sounds normal. Anybody got an idea what's going on with the "N" to Reverse thing?
THANKS, Mike J.

 

[Scott81]

Check your rear pinion bushing, a common problem when it's worn out is the dreaded "thump." Does the rear also drop when shifting from P/N to Reverse or Drive?

 

[mikejpss]

Scott- yes, it does "drop" as you mentioned. What next? Where do i go from here?
Mike J.

 

[Scott81]

Mike,

I would check out the rear pinion bushing then, it's not an expensive part it's just a small pain to replace. Here's all you ever wanted to know about the rear suspension; http://www.c3sharktank.com/tech2/rearsusp/rear1.html to replace the bushing you'll most likely have to pull the driveshaft, unless you have fingers the size of a 6 year old and can contort your body like gumby. It's not hard, just a dirty job that takes patience.

One other thing to check is to drive a normal speed then get off the gas and back on the gas, if the rear end sways noticably then check the trailing arm bushings. Those ARE a pain to change.

 

[mikejpss]

Scott81- I can not thank you enough for the info. Kind regards to you, and hope I can repay you sometime.

If anyone else can add info/suggestions, I would very much appreciate hearing from you too.
Mike J.

:Twist

 

[Pir8football]

Scott,

I'd like to say thanks for all the info and pics on the site. We sent each other an e-mail or two in the past. I am modeling a lot of my 81' after yours. A few weeks ago I dropped the 289 gears for some new 3.55 GM's. My project for this winter is my suspension and nitro. The Corvette group here in Columbia has been a huge help. We are close to replacing the front end with a C4 suspension. What are your thoughts? The rear I am planning to resemble yours.

 

[Scott81]

Mike- you're welcome, glad to help out. Just post pictures when you are done, and we'll call it even.

Mitch- you're welcome as well. I remember, sounds like you're making good progress. I wouldn't be able to tell you a thing about the C4 suspension. I sometimes get a lot of pretty technical questions and each time I have to say I don't really know. When I rebuilt my rear suspension that was my first time doing anything like that, I just started taking things apart and took lots of pictures so I would know how it went back together. The places I found most helpful were Van Steel and Guldstrand as well as people on the forum that had done this before. As for me finished rear suspension, a lot of people said the 7-leaf would be too stiff, it wasn't at all. Just after that job I drove to the museum with Brutus, took us 13 hours and it was no worse than the fiberglass spring. One thing I have read though it that the selection of the right shocks is very important. I go by the old saying that you get what you pay for.

One thing I do suggest is the suspension video from Van Steel, it's not a Hollywood production but it shows you all the neat tricks to save time and hassles, and for 20 bucks you can't go wrong.

 

[mikejpss]

After much studying of the website sent by Scott81, I can not tell where the "rear pinion bushing" is located , knowing (obviously) only that it is in the rear chunk. Can I safely assume that it is the pinion shaft "bushing" , and not the bearing?
Again, another assumption is that the "bushing" is located at the front of the pinion shaft behind the u-joint coupling?
Can someone add a little to the previous postings on this- to get an old beer drinking 81 owner pointed in the right direction?
Dont wanna tear down no more than whats needed!
Thanks in advance- Mike J.
:confused

 

[Scott81]

Mike,

Don't panic. The rear pinion bushing is located where the rear diff mounts to the frame at the forward most point, right under where the driveshaft hooks to the rear diff. There's a rubber bushing and large bolt, ya can't miss it unless it's missing...and then you would have had bigger problems already.

See this picture; http://www.c3sharktank.com/tech2/rearsusp/rear20.jpg where the arrows are pointing. The bolt and bushing are missing in that pic but you can see where it's located.

Here is a cleaner picture looking at it from the back of the car; http://www.c3sharktank.com/tech2/rearsusp/frontmount.jpg

 

[mikejpss]

Scott81- now i got it ! Thanks for clearing this up for me, you've saved me MUCH time and trouble- didn't want to get into the rear chunk unless I had to.

By the way- if the pics on the website you sent earlier are pics of your car, then MAN, do you have a clean lil ride ! I envy your ride, hope to "one day" do mine like that. Looks super sharp!
Again, thanks for the info. Mike J.

 

[Scott81]

Mike- thanks, yes that's my car. Getting it clean just takes a little elbow grease and some time. Of course it helps that I took everything apart but you could do a good cleaning by just dropping the spare tire and carrier. I used an industrial grade cleaner, similar to that purple stuff, be sure to wear eye protection, good rubber gloves and clothes you plan on throwing away. A pressure washer helps too.

I did that project over a period of 4-5 months or so, a couple hours each day while going to school full time and working 12 hour shifts, I was glad it was finished.

 

[mikejpss]

I am having a difficult time finding this "rear pinion bushing" locally. Does anyone know where/whom I may order it from?
Thanks, Mike J.
:confused

 

[Scott81]

Mike,

I bought all my suspension stuff through Van Steel because they are honest and take care of problems with customers but all the Corvette vendors probably carry it. I also got a solid mount from Guldstrand, also a good vendor. You can get either rubber or poly bushings, I went poly because of their ability to withstand the elements and any leaking fluids better than rubber. Here's a link to the part on the Van Steel site; http://www.vansteel.com/index.cfm?fuseaction=ProductList&SubGroup=1004 for rubber it's part #FC-09, for poly it's part #FC-09P, both are $25 If you call them to order you'll probably talk to Art or Danny, tell them Scott sent you.

 

[mikejpss]

Scott81- I feel like you have held my hand thruout this problem completely- except for actually installing the bad part. Can't thank you enough, unless of course, you want to come over and install it !:L
I will call these guys today and place the order. Again, THANK YOU.
Mike J.
:BOW

 

[Scott81]

Mike,

No problem at all, unless you tell people we were holding hands :L If you pay for my plane ticket i'll install it