NASA DE, 72T corner balance #'s, blown wheel bearing, and upgrades?

[arrivederci]

I ran in a DE with NASA at Summit Point this weekend. It was generally a good time, but overcrowded. On the second day, first session, a spec racer decided it was OK to pass me in the carousel without a point by. I was kinda pissed at first, but got really angry when he did it a second time in the same session! Of course I brought it up in the classroom session. The chief instructor wasn't happy...I didn't see him on the track any more that day.

I had a chance to put my car on a set of scales to get the corner weights. With me in it, here's what I had:

Total weight: 2418 with driver and 1/2 tank of gas

LF = 476
RF = 476
LR = 780
RR = 686

Not too bad...it weighed a little more (25 lbs) before I stripped out the interior and put in a roll cage.

Next topic -- in my last session, I heard some clunking on right hand turns and the car felt a little squirrely. It was almost as if might left rear tire was low on air. Once I had the car on the trailer, I could see grease all over the left rear hub. Bingo. Wheel bearing blown...wheel was loose.

My car still has steel banana arms and non-adjustable spring plates. Do the AL banana arms require a different bearing? If I have to replace the bearing on the left side, why not do both and upgrade to AL banana arms and adjustable spring plates? This is something I've wanted to do for a while...anything tricky about this mod?

[Chuck Moreland]

Just did this to my '73, AL trailing arms and adjustable spring plates.

The AL trailing arms do use a different bearing. Swapping out the bearings is probably the hardest part of the job, but doable. There is a factory tool to do this, but it can be done without. Do a search, there are several threads on the process.

Unless you use 74 trailing arms, you'll need to swap in your old 4 bolt stub axles.

This is the time to upgrade the trailing arm inner bushing and spring plate bushings too.

[Jim Richards]

I replaced bearings and bushings on my steel banana arms while the engine was out of the car. It doesn't look like you can swap banana arms, or even replace bushings with the engine/transaxle in the car. Is my perception correct?

[911pcars]

Jim,
I think the deciding factor is the orientation of the control arm pivot bolt. In most early 911s, the bolt is installed from the inside and its removal is blocked by the gearbox.

If you could devise a method of cutting off the bolt head and shortening it, you might be able to free the arm with the engine/gearbox installed. During installation, reinstall the bolt from the outside like later models. However, you should weigh any alternate removal methods with the time it takes to simply R&R the drivetrain.

Sherwood Lee
http://members.rennlist.org/911pcars

[arrivederci]

Good points. I probably won't do this work myself, but I want to educate myself before I get an estimate from a mechanic.

I could probably do the banana and spring arms, but the desire to deal with heating/cooling bearings/races, presses, etc. What would take a good mechanic a day would end up taking me weeks...

My mechanic is pretty conservative and he knows early cars very well. He recently did an RS conversion on his '72. I'm pretty sure he did the alum. banana arm swap on it.

[Jim Richards]

and he knows early cars very well

Josh, every now and then I may need a good wrench for our 73E, especially until I learn how to set up the MFI myself. I work in McLean, so I'm wondering, who's your mechanic?

[911pcars]

As an option, you could let your repair tech prep the arm with new bearings, control arm mods, etc., then simply gather up all the required pieces and do the R&R yourself.

BTW, I wrote an article in Excellence many years ago that attempted to describe the modifications required (4/96). I guess it was a starting point at that time, so there might be some info of value there. The major points were repeated in an Excellence article last year (Mitch Rossi) I believe.

Sherwood