need help, CV Joint Failure '77' Carrera

[UH1Charlie]

I just got my car back from the shop after a transmission rebuild less than 200 miles ago. This afternoon I took the car out and got about three miles from my house traveling at about 30 mph when I heard a big thunk, pulled over immediately. Looking around on the road to see what I hit. I spotted a few scattered parts on the road, which included a snapped CV joint bolt and what looked like an bent accelerator linkage plate and bolt. Looking underneath the car I could see the inner halfshaft dangling, the CV looked fine boot fine full of grease, it appears the bolts had sheared at the transmission. Never any hint of a rumble or noise. What would cause the bolts to shear after only 200 miles ?

I'm lucky this happened at 30 MPH rather than 90MPH. So now I'm looking at replacing both half shafts with new units, ouch. Can anyone tell me what the correct half shafts I need for a 'Euro' Carrera, and the difference quality wise between OEM Porsche and Lobro units.
Thanks,
Bob

[Jim Sims]

What would cause the bolts to shear after only 200 miles ?

Failure to properly tighten the CV joint bolts; grease on the flanges. This is all too common. Do a search on this topic; you'll find plenty to read. Sounds like your failure could be due to poor installation practices at the shop when the transmission was put back in.

I believe Lobro was the OEM manufacturer for Porsche so they should be equivalent.

[Motorhead-45]

I can't answer your questions but just wanted to chime in and say that the flanges on the new Lobro CV axles are thinner. They require a shorter bolt, 45mm for the new Lobro vs 50mm for the original Porsche flange. If you attempt to use 50mm on the outboard side with the Lobro CV axle the bolts will bottom out.

Everything I've read on this board says you should recheck CV bolt torque within a short distance after re-installing axles. Sounds like yours may have loosened and backed out. Given the mess these things make when they come loose it's also probably a good idea to use new bolts of the correct grade and new Schnorr washers every time you take that CV axle loose.

[UH1Charlie]

BTW I have the stock magnesium 915 trans with a LSD

[UH1Charlie]

Originally posted by Jim Sims
What would cause the bolts to shear after only 200 miles ?

Failure to properly tighten the CV joint bolts; grease on the flanges. This is all too common. Do a search on this topic; you'll find plenty to read. Sounds like your failure could be due to poor installation practices at the shop when the transmission was put back in.

I believe Lobro was the OEM manufacturer for Porsche so they should be equivalent.

I rather suspected this might be related to the transmission rebuild, as the half shafts looked like they had been replaced not too long ago, as they still had a new finish patina and no rust. Ouch, Ouch.

Thanks,
Bob

[Hugh R]

If you had trannie work, I'd go back to the shop for damages. Grady Clay on the board says retorque after about 250 miles and again at 500 and annually thereafter. I had several bots loose at 250.

At high rpm, I've heard they will absolutely destroy your cases when they come loose at the trannie.

[Jim Sims]

I checked the CV joints (six 8 mm x 50 mm long screw version) in my '76 a few weeks ago; not a sign of loosening after four years and 20,000 miles since reinstallation. All I did was keep the flanges, tapped holes and screws clean of grease, use new Schnorr lock washers (no moon plates) and the correct tightening torque.

[Motorhead-45]

Jim,

I think you nailed the issue. Any grease between the two mating surfaces will lead to a false torque reading on initial install. Once that grease has a chance to work it's way out after a few miles of driving you are left with a loose fit between the two sides which translates into broken bolts and flailing CV axles.

This post reminded me that I haven't rechecked mine since installing new axles almost 600 miles ago. Headed for the garage now!

[Nine9six]

Of course the faces of the flanges MUST be free of grease, thats just common sense. More importantly, is to clean the internal and external thds when reinstalling. Those threads must be free of grease and oil, and torqued to their propper settings with schnorr washers installed.

[randywebb]

the thread with recale on it summarizes a ton of CV stuff - required reading

sorry to hear of the mishap - could have been worse.

[Grady Clay]

Here is Pelican rcecale Randy’s classic thread:
”Reconstructing Constant Velocity (CV) Joints”

Best,
Grady

[UH1Charlie]

This is the 4th time the transmission has been out of the car in less than 1500 miles for repair. Each time it's had to go back because the tranny was not fixed properly. After picking it up this last time it was still sticking in third gear on coming to a stop. After picking up the car we both took it out for test drive, 3rd was still the sticking. When we got back to the shop I was at my wits end. I was promised that he would do it over again no charge. So the attachment bolts could/must have been reused and retorqued 4 times in 1500 miles. Replacing the attachment bolts with new one's seem to me a to be a no brainer, cheap insurance. but I didn't ask because that was his specialty. I was never told to recheck them to torque specs. If this was neglience, I imagine it might be prudent to ask for the failed parts and if push comes to shove do a failure analysis; if that is it what its going to take to make my case with him. I hope it dosn't come to that, but I suspect I'm going to get nailed, I hate this. If anyone has any ideas how I should proceed, I sure would appriciate it. Thanks for all your great and timley input on Pelican!
Bob

[Jim Sims]

If the wrenching features are in good condition and the bolts are not corroded they can be reused almost indefinitely. Schnorr lock washers should be replaced every time; in bulk they're 11 cents a piece. I will conjecture the problem was the joint wasn't properly prepared nor correctly tightened the last time around.

[greg bradbury]

Just wondering. What do you guys think of using loctite on the bolts. The red stuff works really well. I have heard that it will affect the torque when the bolt is tightened. Also on the subject of checking the tightness of a torqued bolt. When a bolt is torqued the only way of re torquing is to loosen the bolt and start over again as a substanially higher torque is required to move the bolt. So I guess you are just checking for any looseness, what I call nipping up the bolt.

[Grady Clay]

Bob,

Here is your other thread of 03/10/06:
”need 915 tranny advice”


After you gather together all your info you should go discuss all this with the shop. At 250 miles it is unreasonable to have an axle come loose. I would expect him to stand behind his work and cover all the parts and labor.

You also might consider finding someone better to do the work – you don’t want a 5-peat.

Best,
Grady

[Jim Sims]

"The red stuff works really well."

Sometimes too well; to get it to release one often has to heat it to melt it. This could be awkward; I can envision melted rubber CV joint boots and bolts with ruined heat treatment.

[randywebb]

Red is way too strong -- Loctite also will not stick to oily fasteners. They have a new Green level product out that they say will do so. You could try that, or clean them dry and use Loctite Purple (lowest strength).

I just torque them with new washers.

[jdowty3]

Schnorr washer go along way to keeping them tight and a retorque after several hundred miles is required. No way should all the bolts have loosened up and allowed the CV to shear them off. I hesitate telling you to back to the same shop given the previous tranny rebuild experience. Any chance they would cover the repair expense of another shop?

[UH1Charlie]

Originally posted by Grady Clay
Bob,

Here is your other thread of 03/10/06:
”need 915 tranny advice”


After you gather together all your info you should go discuss all this with the shop. At 250 miles it is unreasonable to have an axle come loose. I would expect him to stand behind his work and cover all the parts and labor.

You also might consider finding someone better to do the work – you don’t want a 5-peat.

Best,
Grady

Grady,
I just spent the last two hours reading the classic Constant Velocity (CV) Joint Replacement post. The mother of all CV Joint threads, what a great read! I had no idea of the complexity of the problem, nor the danger of failing to pay heed to the issue of proper CV care. My problem is that the car is at the shop and I was told he was going to address the third gear problem along with the CV joint replacement on Tuesday. Since it was agreed third gear had still not been fixed after three attempts, he would fix it on his dime. After reading the monster thread I realize this should never have happened. Right after this happened today, I began to suspect that the CV failure was not a random event but a failure on his part to use proper care and/or the use of improper parts and proceedures. But how can I prove it ? If I take it to another shop them I pay $1500-2000 for the transmission repair, then get wacked for X dollars for the damage caused by the CV failure and replacement costs and labor ffor two new half shafts. After his first two failures to fix the tranny my wife flat out told my to take it to another shop and pay to get done right. I actually did that but I went back to him to tell him that I was taking it to another shop he begged me to 'let him do the right thing'; well I relented and the rest is history. He is a one man operation who is 911 only shop. Major race creds. but I think he is having cash flow problems, so I doubt if I'm going prevail, at this point....Gotta run dinner on. I'll check back in a few.
Thanks,
Bob