Doug_B_928

The bolts for my front calipers thread in, but they won't tighten completely. They are new bolts and washers (M12 x 1.5 x 50mm). The left side is at 50 ftlb, the right maybe at 30. Spec is 62. As far as I can tell, the steering knuckle and calipers are not threaded. Only the protective plate/guard has threads. But I don't understand how the bolts can thread down on those threads all the way to the end, but then not tighten down completely??? What is the solution; get new protective plates?

GlenL

Something is wrong. The threads are on the knuckles. Almost impossible to strip or cross-thread but could happen. I'd remove the bolts and calipers and check how the bolts go into the knuckles and carriers. Maybe you missed the holes entirely.

Doug_B_928

Hmmmm....when I put the bolts through the knuckle holes they would slide right through same for the calipers, then would thread into the protector plate, IIRC.

GlenL

What?

Doug_B_928

The bolts do not have threads at the top. The outer most is the knuckle, so not sure what threads in the knuckle would do without threads on the bolt there. Attached is a pic I took of the caliper yesterday. I can't tell when I zoom in, but I don't see any threads on the caliper either??

Imo000

Are the new bolt the same length as the old ones?

Doug_B_928

Yes, both new and old are 50mm.

SeanR

How do they fit with out the calipers on there?

Doug_B_928

I didn't check without the calipers. I'll take them apart again tomorrow and also check to see what does and doesn't have threads.

Imo000

And the threads are the sale length too?
Are the new bolts the proper grade?

Doug_B_928

New bolts are from Roger. I'll double check that they are the same as original. I know the replacements are M12 x 1.5 with 50mm of threads.

Imo000

Alsmost sounds to me that the threads might be short and you are starting to push the non threaded part into the threaded hole.

Mrmerlin

^^^^^ this

OK so get the vernier caliper and measure the thickness of the caliper mount, ( the unthreaded portion that the bolt passes through).

Then measure the thickness of the threaded portion add these two numbers together,
then add 3 threads thickness thats how long the bolt should be,

NOTE If the caliper mount thickness is less than the unthreaded shank length of your bolt,
then your threading the shank part of the bolt into the threads of the spindle and damaging them.


I think you have the wrong bolts as these are too long ,

also the the unthreaded portion of the new bolts is also too long as its bottoming out into the first threads of the spindle.

The other important thing to remember is that you dont want the bolt passing too far out of the other side of the spindle threads,
as it could hit the studs on the hub flange thus locking the hub,
and or damaging the bearings

Doug_B_928

Good morning gents,

I took it apart again this morning. It is as I remembered. The bolts supplied by Rog are the same as the ones that were there before. There are no threads in the knuckle nor in the caliper. I can't tell if there used to be threads in the caliper. As shown in the pic below, the bolt has threads where the caliper goes. The threads on the nuts that are part of the protective plate are not great but the bolts do thread onto them. I suspect that they are weakened which is why the bolts aren't torquing down anymore. There were shavings of metal in them when I took the bolts out. So, questions:

1. Should there be threads in the caliper?
2. I'm guessing the answer is no because one can't put metal where it isn't, but can a tap be used to chase the threads in the protective plate?

Thanks very much to all of you for helping me get to the bottom of this.

Mrmerlin

OK better pictures and more info..

From the looks of things that last two pictures have the threads stripped out of them.
I have not ever seen this assembly where the bolts thread into the backing plate,
the spindles usually have the threads.

BUT since this is an early car this may be how they were assembled,
you will need new backing plates or remove the stripped nuts and install new nuts.

It looks like there is enough space to slide a wrench holding a nut then screw in the bolt.

Its also possible that you tightened one of the bolts and then tried to tighten the other bolt but it wasnt fully lined up,
thus creating a situation where the threads got damaged,
try screwing both the bolts in by hand till they are snug then tighten with the socket or wrench.

NOTE dont use your torque wrench,
just make the bolts tight,

your T wrench may be off calibration and thus you overtorqued the bolts thus stripping them

NOTE My previous diagnosis in post 13 isnt correct,
as I was thinking that the assembly went together a different way.