I stripped the trans mount bolt. Help!

[911Etarga]

I was installing a rear sway bar and thought I would tighten the two big transmission mount bolts. The ones that hold the trans to the car. The driver's side one got tight, then loose, then really loose.....****!! I thought of using a little J&B weld, but then I might not be able to get it off again.
Anyone had a similar problem?
It was the female side that stripped, not the actual bolt.

[sc_rufctr]

Let me start by saying you're a "Dill" ....

I'm also a "Dill" because I bought a 911 with a slightly larger "Imperial" bolt in place of the original Metric M12. (no PPI = Dill)

Now that we have the niceties out of the way...

The "Imperial" bolt was barely in there and I'm guessing this was done to "repair" the same issue in your post.

I fixed mine using an M12 thread saver kit (HELICOIL type). It cost me about $70 for this kit but I figured I didn't have an option.

The instructions in the kit tell you what size drill you need to prepare the hole for the repair tap. It's bigger than M12 because once tapped you insert a stainless steel spring to replace the stripped thread... Use plenty of WD40 or similar to lubricate the drill as you go. Wear safety glasses and make sure the the drill is as straight as possible when drilling.

It's not that hard to do but don't use a creeper while drilling, instead lie on the floor so that you have less chance of moving while drilling

Once done what you'll have is an M12 thread but it won't have the same fine thread of the original so then you'll need to buy an M12 bolt to match the new thread.

Just fix the one that is stripped.... Don't be tempted to do both as drilling and repairing threads like this is somewhat risky.
You don't want to double your chances of stuffing up.

I'll take some pics of the repaired hole, the custom M12 bolt and the kit and post them here later tonight... (I'm at work)

(...I made some assumptions in my original post: You have to get the trans mount out of the way to get to the hole. So you have to support the engine/gearbox to do this. Go slow on the drilling...)

[SteveinTO]

I've never played with those bolts before, but I can tell you JB Weld is not the answer. Nor is duct tape. Nor anything that's cheap and easy.

Whatever it threads into, if you can't replace it, you may have to drill it out and tap in new threads or helicoil back to the original thread.

You might first try a thread chasing tool (not a tap) and install a new bolt. If you go that route and the thing torques up, then keep an eye on it for a few hundred miles.

Good luck!

[aigel]

Thread repair kit is your only solution. This is a common thread to go, as shops put the BF air hammer on it. You may have to mail order it in metric. Imperial is readily available locally and ok in a pinch, as you - the one who put it in there - will remember it is there. Of course the new owner won't be happy when they switch the bolts around and use air to put the bolts back.

Peter: I would be surprised to hear about any PPI that uncovered imperial bolts in the transmission mount. That's not going to be easy to see. PPI is good for bigger issues.

Cheers,

George

[rcecale]

Originally Posted by SteveinTO

You might first try a thread chasing tool (not a tap) and install a new bolt. If you go that route and the thing torques up, then keep an eye on it for a few hundred miles.

Good luck!

This worked for me a few years ago on my 86. Picked up a thread chasing kit at Sears for around $50.00 or so...

Randy

[sc_rufctr]

Originally Posted by aigel

Peter: I would be surprised to hear about any PPI that uncovered imperial bolts in the transmission mount. That's not going to be easy to see. PPI is good for bigger issues.

Cheers,

George

George

If I was doing the PPI for someone else I would looks for stuff like this but that's only because of how my 911 was when it came to me.

I had issues with cut oil lines that had been repaired with a small sections of hose and clamps.
Also the nuts and studs holding the the rocker covers on had been replaced with bolts. WTF??? on this one!
More recently I discovered the bolts on my differential had been tightened with an impact gun and had failed.
See my thread here... 915 Shift fork check with an unexpected outcome

All of these thing point to a poorly maintained car that I should not have bought but at the time I didn't know a lot about the 911 and it did look good in its Fern Green bodywork.

I can not tell you how much time and money it has cost me to get my car as close to OEM as possible in the last 9 years.

I hope anybody reading this post learns from my experience.

A professional PPI is not an option.... An absolute must do.

Wayne had an extensive one done before he bought his 959 and it picked up some very minor things... You should check it out at the site he's built for this car.

http://www.959registry.org/

[Porsche_monkey]

I up-sized to the next imperial bolt, fine thread, IIRC.

I know, it's wrong. But it worked. Then I sold the car, out of shame.

[sc_rufctr]

Originally Posted by Porsche_monkey

I up-sized to the next imperial bolt, fine thread, IIRC.

I know, it's wrong. But it worked. Then I sold the car, out of shame.

haha... lol... At least you're honest...

[dtw]

Both of the female trans mount threads got stripped on my '72 (no, I'm not telling the story). I was able to repair them and still use the correct/original fasteners by using timeserts. I wouldn't want to use anything but the original bolts - they have a nice tapered tip that makes 'finding' the hole a lot easier. Any good automotive supply house can sell you the correct size timeserts, though you'll probably have to buy the install kit too. Still, all told should be under USD 100.

If I recall correctly, I had to trim the timeserts down a bit with a cutoff wheel, but still had 8-10 threads of engagement, which was more than enough.

Since your drivetrain is in the car, I suggest that you first put a jack under the transmission so as to take the weight off the trans mount. Then, inspect the remaining mounting bolt to see if it is also damaged.

To do the repair, I'd keep the jack on the transmission. Remove the remaining mounting bolt. Then remove the four M8 nuts that secure the trans mount to the trans. Drop the mount so you now have room to perform the timesert installation. Install a jackstand under the transmission and keep the jack there as a backup. Ensure that the drive train is not, at any time, resting on the shift shaft.

Install the timesert per the instructions. You only get one shot at drilling out the hole nice & straight, so make it count. It is not as hard as it sounds, the existing hole will help guide the drill bit. Make sure to thoroughly degrease the hole before installation, and I'd recommend red Loctite for the install. Let the Loctite cure before reinstalling the transmission mount.

While you're in there, it is a great time to inspect your shift shaft boots, shift coupler bushings, ground strap, trailing arm bushings, CV boots, throttle bellcrank bushings, brake lines, etc.

[Gunter]

Originally Posted by Porsche_monkey

I up-sized to the next imperial bolt, fine thread, IIRC.

I know, it's wrong. But it worked. Then I sold the car, out of shame.

+1 using next size Imperial NF instead of drilling larger to fit an insert; nothing shameful.

Both fixes (Insert or Imperial) mean that the original M10 is no longer in there, so what?

The main concern is to have a solid mount for the transmission.

[911Etarga]

Thanks for the replies guys. I am going to take care of this today. I will let you know how it works out.

[Porsche_monkey]

Bad Karma is generated from an Imperial bolt on a Porsche. Bad Karma on the windshield fluid pump is on thing. But bad Karma that close to the engine and tranny is not good.

[Mahler9th]

I had this problem on one side on my race car. When I bought the car, the threads were already weak, and after a couple of cycles of engine/tranny service, despite caution, they were too weak to feel comfortable.

Don't know about using a different type of bolt.

Helicoil or Timsert can work, I chose Helicoil. Bought the insert kit and a very expensive drill bit. You have to drill very carefully, as stated above. I drilled carefully, just a little bit too fast at first (rpms). The metal hardened and it was all over!

In my case, I had two further choices: next size larger Heli, requiring another expensive drill bit and another insert kit, or a custom mount. I chose the latter approach.

I ended up buying a piece of steel rod with about a 2 inch diameter and a thickness that would be appropriate based on the dimensions of a standard tranny mount. I drilled three holes around the perimeter for bolts so I could attach it to the car. And I drilled and tapped a hole in the center for the large bolt to hold the tranny support. This all took some time and care, but it worked.

Of course this was for a race car with solid mounts.

In any case, the key is to drill very carefully and keep the rpms down very low. If you succeed with an insert kit, I might still suggest an inspection paint dot on the bolt head after installation, and a schedule of inspections to make sure everything is okay for a period after that.

In my car, I have both of those bolts paint dotted, and the bolt heads (socket heads in my case) are drilled so I can safety wire the bolts.

Good luck.

[JFairman]

Time serts are the best.
The kit for that size may be around $100 or more depending where you buy it.

Recently I've been seeing really inexpensive helicoil kits in a variety of metric sizes at advance auto part stores and harbor freight that look like they would work ok.
You could possibly go this way for around $20.

[David E. Clark]

Time serts are the best

+1

The kit for that size may be around $100 or more depending where you buy it. ...

-1

Time serts are great but I was able to get an entire kit, 6mm, 8mm, 10mm and 12mm with bits, insertion tools, loads of inserts, oil, thread-locker and a metal case on eBay for $90.00 from a Chrysler dealer that was going under. They are sold under the name "Kent-Moore metric thread repair kit" but are real time serts. You might try this approach.

[JFairman]

Sounds like you got lucky on that one...
I just tried an ebay search for "metric thread repair kit" and here's the result..

http://shop.ebay.com/items/?_nkw=metric+thread+repair+kit&_sacat=0&_trksid=p3286.m270.l1313&_odkw=metric+thread+repair+kit&_osacat=0

[David E. Clark]

You need to add "Kent Moore" to your search but I didn't find anything in metric with my quick search. The deals are out there however, here is a two box set (I'm guessing SAE the ad doesn't say) for $149.00. Mine are all in one box and are barely used like these. Just keep looking, unfortunately car dealerships are going out of business every day.

[Gunter]

Originally Posted by Porsche_monkey

Bad Karma is generated from an Imperial bolt on a Porsche. Bad Karma on the windshield fluid pump is on thing. But bad Karma that close to the engine and tranny is not good.

So, drilling for Timeserts would have to be done with metric drills?

And never use a 13/16" socket on the spark plugs?

Or use a 3/4" wrench or socket instead of a 19 mm?

And 15" or 16" Fuchs wheels are bad Karma? Hm.............

As an old ME, I can tell you that the next size Imperial Fine thread to replace a 10 mm Metric has the same integrity.
It also has the advantage of not having to drill any bigger than necessary like for a Timesert insert.

Timeserts or CaseSavers are very good for certain application and I would make a decision on what is best meaning: The least invasive repair getting satisfactory results without weakening the area any further.

[Kemo]

I am resurecting this thread because I recently replaced my transmission mounts with Sport Mounts and noticed that the passenger sided mount bolt was "a little bit different". So I ordered the correct bolt and now it wont fit at all...it started tightening then it went slack and thats when I knew I was hosed.

In any event, I need to repair the area. I have been finding Helicoil kits on line for about 40 bucks but I was wondering if anyone knew the correct size to order.

Also, if I decide to upsize to the nearest Imperial bolt, what would that size be? I am assuming I would need to run a tap/die thingy for the imperial size up there to "waller" out the stripped threads.

[Gunter]

I think the stock Metric bolt is M12?

If you replace it with SAE, make sure it's NF (National Fine) not NC (Course)

Take a vernier caliper to a hardware store, measure the M12 and use the next SAE - NF size, maybe 9/16"? or 5/8"?

9/16" is an odd size, harder to find but 5/8"NF should be fairly easy.

Then get the appropriate taps to re-thread the hole. Use light oil and keep the tap straight.

I see nothing wrong with SAE bolts to avoid going even bigger with Helicoil inserts.