What is the deal with all "Stretch" Bolts?

biopete

Veteran Member
Joined
Apr 4, 2005
Location
Nashville, TN
TDI
A3 Jetta 1998, A4 Jetta 2001
Man, what a pain to work on your car on the weekend and then never be able to put anything back together because you do not have brand new "always replace" bolts. They are also known as "stretch bolts", or "torque to yield". Since the A4s VW uses them everywhere it seems :

Engine mounts,
Flywheel,
CV Axle to tranny,
Rod bearing cap,
Main bearing cap,

...
...

It is such a long list. There are major problems with this engineering decision for the home mechanic.

1) Only dealers carry them and they are never convenient to get to or available when you need them, like on saturday afternoon or sunday.
2) They are expensive, often 4.00 or 5.00 a bolt. An engine swap costs 50.00 just in bolts.
3) They are a waste of metal

What is the purpose of this engineering trend? Older VWs did not have these. Or if they did they were not written about in The Idiots Guide to Volkswagens. I don't remember them on my 1991 Jetta Diesel when doing a timing belt.

Having not researched it at all, i would venture the main motive is quick assembly on the line. You do not need locktite and that slows the worker down. Just push the button on the torque gun three times for initial tighten, the torque, and then the extra quarter turn or "torque to yield".

Anyone know anything thing about these torque to yield bolts used in way too many places on these cars? Do you resuse yours? In protest I'm thinking of just using locktite and torquing a little less than spec and seeing how it goes.

Has anyone ever reused one and it broke? Where?
 

jcrews

Top Post Dawg
Joined
Jul 28, 2007
Location
Round Rock, TX - VCDS
TDI
All gone
The bolts deform permanently when tightened. The rationale is simple:

-More consistent clamping force
-A given amount of clamping force can be achieved with fewer fasteners.

Don't reuse the deformed bolts. They're weakened and will break sooner or later. A lot of the one time use screws can be bought with better pricing as sets for a given application from the specialty parts dealers as opposed to the VW dealership, which can have pretty horrible pricing.

One of the most common things (you can search for) that happens is the occasional engine that falls down due to someone somewhere not replacing the engine bracket to mount bolts when changing timing belts. A lot of the other single use screws don't get taken apart as much.
 

biopete

Veteran Member
Joined
Apr 4, 2005
Location
Nashville, TN
TDI
A3 Jetta 1998, A4 Jetta 2001
Interesting. Fewer fasteners. Hadn't thought of that. Just googled a bit and read about the bolt science.

Unfortuneately specialty parts dealers are not available on Sunday usually either. It is such a one sided rationale. I guess i wont be reusing any TTY bolts on important things.

But can you tell a difference between tty bolts and non tty , like if someone replaced them with not tty? My flywheel bolts have blue locktite and look like just regular steel black allens. I'm wondering if someone did a clutch job and replaced the tty ones.


I suppose i could just get a matching bolt that is not TTY and lock tite it?
Can you replace these bolts with not tty bolts?
 

eddif

Veteran Member
Joined
Dec 17, 2006
Location
MS
TDI
2004 Jetta PD Automatic
Opinions are cheap but I will give my opinion as to why the tty bolts got into use. Long long ago when you put on a head gasket things tended to settle in and you needed to have your head bolts re-tightened in 50 (?) miles. The head gasket itself compressed and the bolts stretched a little more, leaving the head not pulled down enough and risking a blown head gasket. The industry worked on the head gaskets, and that helped. Finally, they found a way to help stop the head bolt stretch. Now you buy a car and within reason the head gasket just goes forever and ever without blowing. This all might allow the use of fewer bolts, but over the years they have found that the number of bolts you use is more stable with tty bolts.

I wrote a little on tty bolts here yesterday.
http://forums.tdiclub.com/showthread.php?t=241279&page=42

There is a little difference of opinion on why, but that is why we come here to discuss at times. There are some non tty bolts you can get to allow multiple removals of parts. When you get into standard stretch bolts you have to watch thread lubrication, and there is always a limit to the number of times aluminum will allow bolts to be retightened in it. You have to go back to re-tighten some areas as mentioned before. Tty bolts might be a way to keep folks from stripping out bolts threaded into aluminum. They just do not work on things at the house as much. Heli-coils will fix that, but it might cost the company a USD to do 3 bolts with coils, and they want to save that money.

Progress, got to love it.

eddif
 

owr084

Top Post Dawg
Joined
Oct 20, 2004
Location
Northern Virginia (NoVA)
TDI
Passat GLS, 2005, Stonehenge Gray
biopete said:
It is such a long list. There are major problems with this engineering decision for the home mechanic.

1) Only dealers carry them and they are never convenient to get to or available when you need them, like on saturday afternoon or sunday.
I would add that many times, the dealer does not have them in stock at all, even though they are REQUIRED for many common repairs. Makes you wonder if their own mechanics are following the procedures for replacing tty bolts.:mad:

Last week, I needed 4 tty bolts to attach the rear caliper carrier frames to the car. Impex was only able to find 2 for me and I had to order 2 more from the dealer. I wonder how the dealer is able to replace rear rotors in a day when they do not stock key parts:rolleyes::eek:
 

PDJetta

Top Post Dawg
Joined
Nov 6, 2003
Location
Northern Virginia
TDI
'04 Jetta GLS TDI Pumpe Duce Platinum Grey w/ Leather
"Man, what a pain to work on your car on the weekend and then never be able to put anything back together because you do not have brand new "always replace" bolts. They are also known as "stretch bolts", or "torque to yield". Since the A4s VW uses them everywhere it seems :

Engine mounts,
Flywheel,
CV Axle to tranny,
Rod bearing cap,
Main bearing cap,"

Don't forget the cylinder head, shock and strut mounting, subframe, tranny dogbone mount, and ball joint bolts. Give me a few minutes and I will think of a bunch more!

Yea, they are used in many places on VWs. I looked at the Honda service manual for my son's car and you see no mention of stretch bolts. I wonder if this is an European tradition. It is a pain.

--Nate
 

scubagli

Veteran Member
Joined
May 7, 2009
Location
leeds ny
TDI
1986 audi 4000Q ALH SWAP in progress...
you have to know. Yea they're a pain, planning... I have had the same issues. Comes with the territory.
 

Lee_Taylor

Veteran Member
Joined
Sep 26, 2004
Location
Kent, England
TDI
Audi A3 1.4 COD
PDJetta said:
Yea, they are used in many places on VWs. I looked at the Honda service manual for my son's car and you see no mention of stretch bolts. I wonder if this is an European tradition. It is a pain.

--Nate
It would be interesting to know how many other car manufacturers use TTY bolts. Personally I don't like them and consider it poor engineering. No doubt some bolt meister will come along to teach me the error of my ways but as far as I am concerned it's a racket.
 

Fix_Until_Broke

Top Post Dawg
Joined
Aug 8, 2004
Location
Menomonee Falls, Wisconsin, USA
TDI
03 Jetta, 03 TT TDI
My opinion is that not all "Torque+Angle" fasteners need to be replaced. Torque+Angle does not always mean "Torque to Yield" and without dong the calculations you don't know which is which. I think that Bentley/VW lean to the conservative side on telling you which ones to replace (all of them).

I have re-used many "Always Replace" bolts on my car and have not had any issues. (motor mount, dogbone mount, Axle flange, Flywheel) Many of the times I've done this I was in a similar situation that the OP describes where a new replacement was not available and the car had to go back together. Many of them I have since replaced, however, I ran my flywheel bolts 20+k miles on a 2nd use. Do this at your own risk - I am not recommending it - Just sharing my experiences.

Here's another "fix" I did on my left side motor mount

There's a few that I wouldn't risk though - head bolts, rod caps, main caps - basically anything that is a real big PITA to replace in the future and/or could cause significant other damage.

The official stance is to replace what it recommends.
 

Curious Chris

Top Post Dawg
Joined
Jun 11, 2001
Location
Pineview GA
TDI
Jetta Wagon 2003 RIP Rockford IL
IMHO the auto manufacturers are try to save money. You can put in a lower strength bolt, stress it just shy of permanent deformation, and it will hold find for one use. Or maybe it is more noble and the auto manufacturers are trying to lower weight, I doubt it though.

The left side motor mount aka bracket is a classic case of what were those engineers thinking!
 

El Dobro

Top Post Dawg
Joined
Feb 21, 2006
Location
NJ
TDI
2017 Bolt EV Premier, 2023 Bolt EUV Premier
Lee_Taylor said:
It would be interesting to know how many other car manufacturers use TTY bolts. Personally I don't like them and consider it poor engineering. No doubt some bolt meister will come along to teach me the error of my ways but as far as I am concerned it's a racket.
GM and Subaru uses tty head bolts.
 

gonesurfing

Veteran Member
Joined
Jul 5, 2009
Location
Wilmington, NC
TDI
'09 JSW TDI - Sold Back 12/22/16
Doug Huffman said:
Another way to look at it; ferrous alloys don't fatigue if they don't cycle through zero stress, like a spring with plenty of internal stresses or a proper bicycle spoke.
Yes, higher initial tightening force helps keep the fastener or thread below the fatigue limit which can be well above zero. Also, tightening by torque is very dependent upon thread lubrication and fastener coatings. Tightening force can vary outside the safe range very easily, thus permanently deforming the fastener.
 

compu_85

Gadget Guy
Joined
Sep 29, 2003
Location
La Conner, WA
TDI
... None :S
Mercedes specifies a length of their stretch bolts... too stretched and you can't re-use them. I don't know if I entirely trust that...

-Jason
 

lkchris

Veteran Member
Joined
Apr 3, 2008
Location
Albuquerque, NM, USA
TDI
2003 New Beetle
Turbine Suburban said:
Can you identify them by a quick glance? Or do you just "have to know'?
No, you read your official service procedures prior to commencing the operation and determine which parts you need to have on hand before beginning.

Do folks actually attempt DIY without reference to official procedures?
 

je

Veteran Member
Joined
Jun 6, 2000
Location
Chesterton Shores, Ontario
TDI
-
The most accurate way to test clamping force is with an ultrasonic machine that measures bolt length. Look at any text about bolted joints and it comes down to that - the bolt acting as a tension spring.
 

Ian F

Veteran Member
Joined
Sep 26, 2002
Location
Croydon, PA
TDI
Jetta Wagon, 2003, Indigo Blue
Lee_Taylor said:
It would be interesting to know how many other car manufacturers use TTY bolts. Personally I don't like them and consider it poor engineering. No doubt some bolt meister will come along to teach me the error of my ways but as far as I am concerned it's a racket.
The new MINI uses them all over the place, per the manual (Bentley)... mainly in the same places a VW does (motor mounts, suspension, etc)... However, it's general indie-shop & DIY practice to reuse them... doesn't seem to be a problem.
 

jokila

Vendor
Joined
Dec 3, 2004
Location
Houston, Texas
TDI
2003 Jetta GLS, Manual
owr084 said:
I would add that many times, the dealer does not have them in stock at all, even though they are REQUIRED for many common repairs. Makes you wonder if their own mechanics are following the procedures for replacing tty bolts.:mad:

Last week, I needed 4 tty bolts to attach the rear caliper carrier frames to the car. Impex was only able to find 2 for me and I had to order 2 more from the dealer. I wonder how the dealer is able to replace rear rotors in a day when they do not stock key parts:rolleyes::eek:

I agree with your cynicism. But, I also know the dealership can get parts overnighted, at least here in Houston, because the Dallas distribution center for VW is one day away even with regular UPS delivery. This means they end up controlling their inventory better by ordering the batch of bolts they need.
 

jetta 97

Vendor
Joined
Dec 25, 2008
Location
Dallas (McKinney) ,TX ,USA
TDI
2 X Jatta MK5 2006
owr084 said:
I would add that many times, the dealer does not have them in stock at all, even though they are REQUIRED for many common repairs. Makes you wonder if their own mechanics are following the procedures for replacing tty bolts.:mad:

Last week, I needed 4 tty bolts to attach the rear caliper carrier frames to the car. Impex was only able to find 2 for me and I had to order 2 more from the dealer. I wonder how the dealer is able to replace rear rotors in a day when they do not stock key parts:rolleyes::eek:
I newer replace caliper carrier bolts in my 18 years of mechanic job And newer had any problem reuse them over and over. That is big BS .
Also there is so many other bolts you don't have to replace and what says has to be replace.
THE PROBLEM comes when you put bolts back. Lot of people become mechanics over night and had no clue how much bolt can take torque.
I have seen guys used 3 feet 1/2 in pry bar and tight 8mm bolt.(hell NO)
I always say "Being mechanic is like being with women" . You have to have filling for it. You have to know how this thing is breathing.
 

eddif

Veteran Member
Joined
Dec 17, 2006
Location
MS
TDI
2004 Jetta PD Automatic
jetta said:
I newer replace caliper carrier bolts in my 18 years of mechanic job And newer had any problem reuse them over and over. That is big BS .
Also there is so many other bolts you don't have to replace and what says has to be replace.
THE PROBLEM comes when you put bolts back. Lot of people become mechanics over night and had no clue how much bolt can take torque.
I have seen guys used 3 feet 1/2 in pry bar and tight 8mm bolt.(hell NO)
I always say "Being mechanic is like being with women" . You have to have filling for it. You have to know how this thing is breathing.
This is the point that the conversation gets dangerous. You can make some things at home that might explode. When nitro was first manufactured it was a highly dangerous situation and some lost their lives. TTY bolts are like this. I would really refrain from telling anyone how to re-use tty bolts. You are asking for failure by giving out the information, and the person who practices this is risking a broken bolt or stud. They were intended for one time use and you do not get the quality of holding power after they are used. Even experts can have a faillure re-using TTY bolts. You never know when a non expert has been on the scene before you.

Dangerous area of discussion. Beware of the re-use of TTY bolts. There are some cases where even the experts can not re-use tty bolts and expect them to work. There is not enough stretch left in used TTY bolts to hold parts that might wear a little and release the tension.

Dangerous stuff. you can actually risk car crashes. Even loss of power in an engine failure can cause danger.

Dangerous stuff.

eddif
 
Last edited:

Curious Chris

Top Post Dawg
Joined
Jun 11, 2001
Location
Pineview GA
TDI
Jetta Wagon 2003 RIP Rockford IL
compu_85 said:
Mercedes specifies a length of their stretch bolts... too stretched and you can't re-use them. I don't know if I entirely trust that...

-Jason
Yes that is what BBC does with their gas turbine split line bolts. If the length of the bolt does not change, it was stretched within its elastic range. Bolts can be used as long as you have stretched them within their elastic range, once you cross over into permanent deformation the end is near.
 

PDJetta

Top Post Dawg
Joined
Nov 6, 2003
Location
Northern Virginia
TDI
'04 Jetta GLS TDI Pumpe Duce Platinum Grey w/ Leather
I look at it this way: Since I am doing my own repair work, I am saving a lot on labor and a good bit on parts, so why not just spend a few dollars more on fasteners that Bentley says to replace and know it is done correctly!

--Nate
 

eddif

Veteran Member
Joined
Dec 17, 2006
Location
MS
TDI
2004 Jetta PD Automatic
In Defense of TTY Bolts

There is a dummy proof aspect of TTY bolts. The instructions and construction of TTY bolts is such that you do not have to be trained as much to use them. A short paragraph for a certain application, and possibly a special tool, and you are good to go.

Standard stretch bolts require a certain amount of art. Standard stretch bolts may need to be re-tightened. Standard stretch bolts can be over-tightened. Standard stretch bolts depend on a lot of feel / knowledge or complicated tools to get past the human element. Standard stretch bolts do have a service life. Standard stretch bolts may have been tightened wrong the last repair job and need to be measured before or during tightening, to assure correct success.

Trying to explain to a technician:
The feel of bolt stretch
The feel of the bolt head digging into a washer or surface
The feel of dirty threads
The feel of poor lubrication
The feel of a bolt that is over-streatching
How to understand the visual hints a standard torque wrench pointer gives
How to tell if a click torque wrench is working properly
How to not stop on that last final pull so that something does not stick

How to tell the customer:
1... I need to take your car on a 100 mile trip, bring it back to the shop for cool-down, take off half of the minor parts and re-torque half of the bolts.

2... I overtightened the head bolts because you are headed on a trip and can not come back in for a re-torque. Help me remember to replace your head bolts next time.

3... I have to keep your car till I find special washers that will allow that special engine to get correct torque specifications because the bolts gall on a surface.

It just goes on and on.when you use standard fastners.

Of course the TTY bolts have been engineered to handle all this trouble and the cost is passed on to you. At times it can be a toss up as to which is cheaper. With modern sensors and computer control a manufacturer might could assemble a car with standard fastners now, but we have gotten so used to TTY bolts now I do not know if we could go back. We sure do not have trained assembly line workers that know how to tighten standard bolts.

Just a little depressing, but true.

eddif
 
Last edited:

jetta 97

Vendor
Joined
Dec 25, 2008
Location
Dallas (McKinney) ,TX ,USA
TDI
2 X Jatta MK5 2006
lkchris said:
A person with your engineering knowledge should have a better job.
Do you think every shop or dealer for every car has caliper carrier bolts in stock and replace them?
Do you know how many bolts you need to have it ,since there is 1000 different models?
It would take a big tool box to have it these bolt.
Like I said it is not problem in bolts it is how works with it.
But I am not saying every bolt can be put back. There is some bolts you have to replace when you do some job (Like inside engine).
 

Frankendiesel

Veteran Member
Joined
Mar 3, 2008
Location
Cedar Rapids, IA
TDI
2000 Beetle TDI
lkchris said:
No, you read your official service procedures prior to commencing the operation and determine which parts you need to have on hand before beginning.

Do folks actually attempt DIY without reference to official procedures?
LOL! Do folks actually attempt DIY WITH reference to official procedures? :p

Never seen the inside of an "Official Repair Manual" for my '98 TDI. I've used this website for "unofficial" procedures. I think I see what you're saying though. I would say that the trip point of referring to an official procedure is different for varying levels of DIY'ness.
 

streeker02

Veteran Member
Joined
May 12, 2008
Location
Halton Hills
TDI
2003 Golf TDI
jokila said:
I agree with your cynicism. But, I also know the dealership can get parts overnighted, at least here in Houston, because the Dallas distribution center for VW is one day away even with regular UPS delivery. This means they end up controlling their inventory better by ordering the batch of bolts they need.
One example here.

http://forums.tdiclub.com/showthread.php?t=263995&highlight=stealership

It appears that many in our group can't be bothered with stretch bolts either (I'm not one of them, personally).
 

RamMan4x4

Veteran Member
Joined
May 6, 2007
Location
Raleigh, NC
TDI
'03 Jetta TDI
Doug Huffman said:
By definition a permanent change in length indicates plastic deformation and yield strength exceeded.
True but the yield strength is less than the ultimate/tensile strength for ductile materials which means the bolt can continue to be loaded without failure if the proper engineering is applied...i.e. known material limits, known starting length/diameter, current length/diameter.

That said...I'd pay the extra $50 for bolts as cheap insurance. Although I would prefer non-stretch bolts in applications that don't require them.
 
Top