23 replies to this topic

[BusheyTrader]

I'm having to replace the captive bolts from my pedal box, some sheared off or had to be ground out to release it, the others are mangled or bent. The bolts are approx 30mm long. I'll weld in replacements.



Any idea what pitch / size of bolt they should be? I couldn't find the replacement nuts on the Minispares parts diagrams, otherwise I would got the size from there.

Also, is there any advantage in bolting the box back in at the steering wheel end with shear bolts? I'd prefer to use normal bolts unless there's a safety issue.

Thanks for help.

Edited by BusheyTrader, 11 March 2016 - 12:28 PM.

[nicklouse]

the originals as 5/16"  but you could go metric if you wanted as they don't screw into anything.

 

and as they are not a service part you will never find any listed.

[Cooperman]

Best to stick with UNF/UNC on a classic Mini if only to keep everything the same.

[BritishRacingGreen]

Stick with imperial, 5/16 UNF, otherwise future owners will be cursing your name as they destroy the metric threads with imperial nuts.

Edited by BritishRacingGreen, 11 March 2016 - 01:28 PM.

[Itsaminithing]

If you're going to the trouble of replacing the studs then use STAINLESS bolts.

I removed the existing bolt heads & used 5/16 UNF x 3/4" cap head bolts for the Brake servo bracket (use 1" if  using  non-servo master cyl) & 1" for the clutch master cylinder - this is shorter than the original set up but plenty of room for a flat washer & nyloc nut & a lot easier to bolt/unbolt the clutch cylinder.

You'll need slightly longer bolts if you don't remove the head of the original captive bolt, they're spot welded in 3 places & are a pain to remove so it's easier just to cut the threaded section & then drill & tap the remaining section of bolt.

[Spider]

Edited by Moke Spider, 11 March 2016 - 07:29 PM.

[MRA]

This post shows up the people who know and those who do not..... this is an 1988 (Oct) onwards pedal box with later type servo, therefore as the servo has metric fittings it is acceptable to change the main bolts to metric.

[MRA]

I've repaired a number of these. I used Grade 8 5/16" x 1-1/4" Bolts. I tune the box up-side-down and take my time centre popping the original weld studs bang on centre, then pilot and then final drill them to 5/16".

 

Put the bolts in from the bottom and hold them in place on top with old washers & nuts, check the spacing is correct with a master cylinder and then braze the bolts in place.

 

Sorry Itsaminithing, but I would,t use stainless here, they have no tensile strength and I don't like mixing dissimilar metals.

 

You can get Stainless steels with very high tensile properties they are used in the aircraft industry all the time...... also what is brazing but dissimilar metals ?  lol

[midridge2]

How to make friends and influence people.

[Spider]

This post shows up the people who know and those who do not..... this is an 1988 (Oct) onwards pedal box with later type servo, therefore as the servo has metric fittings it is acceptable to change the main bolts to metric.

 

Sorry.

 

Fixed.

[Itsaminithing]

This post shows up the people who know and those who do not..... this is an 1988 (Oct) onwards pedal box with later type servo, therefore as the servo has metric fittings it is acceptable to change the main bolts to metric.

 

It's not really critical which bolts he uses but the pedal box retained the 5/16 UNF captive bolts right up untill the end of production. Better to keep it the same in case it ends up in a garage having work done on it.

 

Moke Spider: I would agree with you on mixing dissimilar metals esp having had 'fun & frolics' removing stainless bolts from captive nuts before i knew better - DOH! ....but when using stainless bolts with stainless washers/nuts it isn't a problem.

As for the tensile strength issue we're talking about 25Nm torque required for the servo bracket nuts. A2-70 has a tensile strength of 700N/mm2, it's less than 8.8 heat treated bolts but higher than the ordinary low grade steel which these bolts seem to be made from.

Brazing might be Ok for engine breathers etc but not for this application, the bolts were originally welded so welding is required.

[MRA]

 

This post shows up the people who know and those who do not..... this is an 1988 (Oct) onwards pedal box with later type servo, therefore as the servo has metric fittings it is acceptable to change the main bolts to metric.

 

It's not really critical which bolts he uses but the pedal box retained the 5/16 UNF captive bolts right up untill the end of production. Better to keep it the same in case it ends up in a garage having work done on it.

 

Moke Spider: I would agree with you on mixing dissimilar metals esp having had 'fun & frolics' removing stainless bolts from captive nuts before i knew better - DOH! ....but when using stainless bolts with stainless washers/nuts it isn't a problem.

As for the tensile strength issue we're talking about 25Nm torque required for the servo bracket nuts. A2-70 has a tensile strength of 700N/mm2, it's less than 8.8 heat treated bolts but higher than the ordinary low grade steel which these bolts seem to be made from.

Brazing might be Ok for engine breathers etc but not for this application, the bolts were originally welded so welding is required.

 

Yes better to keep the same for same but not necessary, ....  dissimilar metals ? stainless steel will gall when used with the same material that is why stainless fixings used for aircraft are passivated and coated in G2 compound to stop galling.

 

Bolts with rolled threads will stand a better chance than those that are cut at resisting galling issues.

 

A2-70 is not the maximum grade for stainless steel fixings.

 

I think these fixings were made from SAE5 but could have been a lower spec, they wouldn't have been made to ISO8.8 as that is a metric spec.

 

Brazing is or can be stronger than welding as it doesn't have the inherent cracks that welds have.  Some peugot's were brazed during production to allow them to pass the crash tests.

[Itsaminithing]

I bow to your vastly superior knowledge on this topic -i certainly didn't know about the strength of brazing.

Not sure the captive bolts were SAE5 grade, the way they rust/shear i imagined they were made out of some sort of grey cheese.... the point was you can safely replace the standard bolts with standard inexpensive 'off the shelf' stainless fixings that aren't so prone to self destruction.

SAE, ISO -it all gets so confusing.  If you own a MPI you know what i mean.

 

Stainless steel will gall???? it might be a bit cheeky using non standard materials but i wouldn't describe it as insolent or impudent

[dklawson]

I have no dog in this fight but I offer the following statement.

 

It makes no difference at all (in this application) whether the bolts are welded or brazed to the pedal box.  They are not welded/brazed to support a load, they are welded/brazed to secure them in place (literally so they don't fall out) and prevent their rotation when the nuts are tightened.  Either one (brazing or welding) will do this.  The advantage of welding is that you will get in and out quickly with the minimum heat added or time spent.

[Cooperman]

The mixing by Austin-Rover, of Imperial & Metric threads was very bad engineering practice and was done to save money.

It is hard to imagine any other motor manufacturer, or anywhere else in engineering, where such poor practice would be allowed.