Tightening a Threaded Bolt

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.

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

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

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.

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

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

Can you get a nut on the back?

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

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

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

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.

.

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

MichaelG.

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.

Yes the bolt was purchased new from MiniSpares.

.

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

.

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

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?

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

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!!

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.