By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by Allendale Jan 24th

Tightening a Threaded Bolt

All Topics | Latest Posts

Search for:  in Thread Title in  
William Harvey 101/09/2021 10:07:06
149 forum posts

Hi,

I am rebuilding a Classic Mini Subframe. To clean the Brake Caliper threads on the Swivel Hubs of paint, I ran through a 3/8" UNF Tap. The Tap went through with minimal effort.

However on fitting the bolt it is rather sloppy, compared to all the others which have not been cleaned out.

The thread was identified the thread as a 3/8 UNF and I had a 3/8 UNF thread, item 10 in the parts catalogue link here.

What would be the best way to 'fix' the slight sloppiness? I was thinking Loctite Blue Thread Lock or a little Epoxy? It will also have a locking washer.

noel shelley01/09/2021 10:24:43
758 forum posts
19 photos

I would torque it up and see if it takes the load - if yes then loctite ! If not then helicoil or similar thread repair. Good Luck. Noel

John Hinkley01/09/2021 11:18:16
avatar
1184 forum posts
391 photos

The last thing you want when you throw out the anchors is the brake caliper flapping about in breeze. If it was my life on the line, I'd be using a helicoil. No question. Better still, buy another hub carrier with decent threads.

John

William Harvey 101/09/2021 11:23:18
149 forum posts

Thanks guys, I'll try the caliper in place and see if it locks up ok and then use some Thread Lock. If not looks like it will have to come off and Helicoil.

not done it yet01/09/2021 11:30:18
6322 forum posts
20 photos

First question: Is the bolt the original or what is its origin - like was it purchased from mini spares on that part number?

Howard Lewis01/09/2021 11:33:14
5298 forum posts
13 photos

The correct torque for a 3/8 - 24 UNF bolt, according to Hobson Engineering website, would be 30 lb ft.

Although this might depend upon the grade of material of the bolt. Presumably this figure is for high tensile bolts.

If you are worried about security, you could always tighten to less, having treated the threads with an anaerobic thread locker.

An anaerobic should function quite well with a gap of 0.003", which is probably less than you have.

Howard

John Haine01/09/2021 11:40:02
4170 forum posts
242 photos

Can you get a nut on the back?

A Smith01/09/2021 12:14:57
55 forum posts
4 photos

It seems that some of those responding assume that the car is not intended to be driven.

Martin Connelly01/09/2021 12:28:09
avatar
1889 forum posts
203 photos

The replacement brake pad kits I have fitted recently came with replacement calliper bolts with pre-applied blue thread locking stuff (for want of a better description) on them. It is obviously felt that the calliper securing bolts are a highly stressed part that should be routinely replaced with new ones when the pads are replaced and that the fit should be such that the thread locking will work. So if you don't have new bolts get some, if the fit is too loose for thread locking liquids to be effective either Helicoil or replace the calliper. It should not something that causes you to worry every time you apply the brakes. Don't forget also that they can get hot in use so a good mechanical fit is essential, not a sloppy one that only just takes the torque. With front wheel drive you are not just stopping the car, you may also be braking the engine so the front brakes do a lot of work, the back ones hardly any.

I had a Fiesta that I commuted to work in in the 1980s. Coming up to a junction as I applied the brake I had a failure that that reduced the braking effect by about 50%, one of the front brake hubs sheared between the disk and the hub due to corrosion and stress. If it had happened in an emergency braking situation I think I would have been unable to avoid a collision. Don't take any chances with the brakes being good enough, they need to be properly maintained with parts that are in good condition.

Martin C

Dave Halford01/09/2021 15:58:09
1726 forum posts
19 photos

Given that the thread in the hub will not have corroded, what was the old bolt fit like?

l'm also assuming that the hub wasn't blast cleaned without bolts protecting the hub threads and cleaning out the threads did not involve metal dust.

New bolts can be a little loose on the clearances

john halfpenny01/09/2021 16:24:55
189 forum posts
27 photos

From memory, shouldn't it be a shouldered bolt, ie plain portion larger od than the threaded portion?

not done it yet01/09/2021 18:24:54
6322 forum posts
20 photos
Posted by john halfpenny on 01/09/2021 16:24:55:

From memory, shouldn't it be a shouldered bolt, ie plain portion larger od than the threaded portion?

That is what is shown on the illustration? I would not expect a high tensile bolt to be threaded right up to the head.

Michael Gilligan01/09/2021 18:39:42
avatar
18925 forum posts
942 photos
Posted by William Harvey 1 on 01/09/2021 10:07:06:

Hi,

I am rebuilding a Classic Mini Subframe. To clean the Brake Caliper threads on the Swivel Hubs of paint, I ran through a 3/8" UNF Tap. The Tap went through with minimal effort.

However on fitting the bolt it is rather sloppy, compared to all the others […]

.

I have to ask : What grade of fit is that Tap … and is as per specification ?

MichaelG.

HOWARDT01/09/2021 19:50:47
778 forum posts
28 photos

Cast iron and steel do form a slightly corrosive interface. To some extent both will deteriorate. If you do fit a helicoil ensure it is correct for a through hole.

William Harvey 101/09/2021 20:19:21
149 forum posts
Posted by not done it yet on 01/09/2021 11:30:18:

First question: Is the bolt the original or what is its origin - like was it purchased from mini spares on that part number?

Yes the bolt was purchased new from MiniSpares.

Michael Gilligan01/09/2021 20:39:43
avatar
18925 forum posts
942 photos

Posted by Michael Gilligan on 01/09/2021 18:39:42:

.

I have to ask : What grade of fit is that Tap … and is as per specification ?

MichaelG.

.

Apologies … wrong terminolgy ^^^
I should have written ‘class of fit’ not ‘grade of fit’ blush

.

Please see Thread Fit, on p2 of this document : **LINK**

https://www.fastenal.com/content/feds/pdf/Article%20-%20Screw%20Threads%20Design.pdf

MichaelG.

Edited By Michael Gilligan on 01/09/2021 20:40:12

Nick Welburn01/09/2021 21:36:49
81 forum posts

I’ve had a couple of these that are less than great. Not sure why they get chewed up. On my last project I just fitted new castings. Not sure if some of the aftermarket callipers are a touch off and make it easy to chew up?

old mart01/09/2021 21:52:28
3345 forum posts
208 photos

I don't understand the op's second paragraph in the original posting.

bernard towers01/09/2021 22:04:09
293 forum posts
84 photos

Howard T , Interesting point you made about thru hole helicoils, I used them several years ago and they were called centre nip but when I rang for some recently I was told they were no longer made and to use standard ones!!

William Harvey 102/09/2021 10:23:47
149 forum posts
Posted by old mart on 01/09/2021 21:52:28:

I don't understand the op's second paragraph in the original posting.

I only cleaned out one of the threads with the 3/8" Tap, The ones I haven't cleaned out are nice and tight, so I have left them.

All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Latest Forum Posts
Support Our Partners
Eccentric July 5 2018
cowells
JD Metals
walker midge
BOLDON
emcomachinetools
Warco
rapid Direct
Eccentric Engineering
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest