Boge Strut - Caliper Clearance

[Hawkeye]

Hello to all I've posted this to our brethren on Pelican:

I believe I have a major interference &/or clearance problem between the rotor and caliper body on my front suspension (1970T). The struts are wedge-pin style Boges: the ident. nos. - as near as I can make out on the strut bodies are (1-0211-32-315-0 & 911-3 080-08 – made in Western Germany). I had exchanged the original Boge “pinch-bolt” style struts (as per the advice of a couple of esteemed members of this board) & 'swap meet' purchased a set of 2nd hand wedge-pin struts with the 3 inch bolt spacing to save on buying new calipers. As my intent was to use the original M style Ates, I therefore had a MPI (magnaflux) inspection on the Boges. All seemed well (no bends or any damage) & proceeded to re-hab & install the replacement Boges & mounted the new rotors.

This work was done about 15 yrs. ago – this has been a long very slow resto project. I have now since progressed to the process of installing the re-built calipers & find what appears to be an unacceptable clearance between the outboard rotor face & the caliper body - .05mm – too damn close (IMHO) considering the gap in the caliper body is 23.5mm & the rotor is 20mm in width.

Here is a photo of the (RHS) rotor/caliper body as it bolted showing the caliper body & its position relative to the outboard face of the rotor.

The gap in the photo is a bit mis-leading as a .05mm feeler gauge just makes it. One can see the difference with the gap on the inboard side of the rotor. This issue is typical for driver side strut as well. I don’t have a clue as to what has gone wrong or any method or process as to how to correct this. Maybe the replacement wedge-pin Boges have a different mounting offset vis-à-vis the ‘pinch-bolt’ style ((??) I sure do need some advice.

I also noted a rotor/caliper (inboard) offset problem with the rears but I believe a 1mm steel spacer/washer was installed (?) between the trailing arm & the caliper bosses to centre the rotor between caliper halves. I hope I am correct in assuming this was the case.

Any advice or suggestions & answers to this situation will be most appreciated.

Cheers
JB

[edmayo]

I assume you have tightened the spindle nut and adjusted to a slight bearing pre-load ?

[Hawkeye]

Hi Ed

Thanks for your input. I shall definitely be re-visiting this issue in a couple of days to see if indeed this is the root of my problem.
Much appreciated.

Cheers
JB

[gled49]

How’s your problem coming along. I posted about checking your seal ring on the spindle, as the SWB and LWB rings are different thickness. If u replaced these, a mistake could have been made.

[Hawkeye]

Hey gled49

Thanks for your input - on both websites. I will be examining all of this in a few days time.

Cheers
JB

[Chris Pomares]

I had a similar challenge. Mine not as severe. When I converted to front Boxster calipers the rotors were offset outboard like yours. I bought brass strips to make spacers about one inch wide and one mm thick to center the rotors. If everything is in spec, you should be able to have a machinist make a spacer, then use slightly longer bolts. Outboard is fixable. Inboard would be a tougher solution.
Or it could just be the bearing ring is the wrong one as gled49 suggested.

[Hawkeye]

Hi Guys

An update of sorts: while I still haven't had a chance to physically examine my current set-up, I do recall using all original components from the old struts & I assume the spacers would be LWB (21mm) as opposed to SWB (17mm). Therefore my reasoning is if I had (or used) the SWB rings - the problem would be opposite to the one I have, given the 4mm difference between these seal ring spacers. I assume I would have an interference with the inboard face of the rotor.

I tried what I believe is Mr. Ed Mayo's advice about tightening the spindle nut to achieve a bearing pre-load & gained about .02mm - a very minimal gain & still leaves things a too 'tight'. Chris's suggestion may be a workable alternative solution. I may be guilty of 'over-thinking' this but I get nervous about shims or washers between the rotor & the hub as I feel this might subject those rotor bolts to shear forces the Porsche engineers never intended.

I could be way out in left field here but as this is a highly critical component area, I want to make sure all is OK before forging ahead to a resolution which is achievable with my existing parts & above all else - is safe.

Thank you Gentlemen for your patience & indulgence in this matter.
Cheers
JB

[Hawkeye]

Hey Guys

Just a quick note to say thanks to all of you for your inputs to this clearance problem. I finally 'rectified' (I think) the situation by using the 3 'precision' tools we all know & love; a chunk of pipe of suitable length & dia (in my case - ABS), a small block of wood, & a BFH. A couple of good solid whacks against the seal ring to seat it at the shoulder of the spindle - seemed to work. I now have just a little over 1mm of clearance. I hope I am correct in assuming this amount of clearance is sufficient & within spec between the rotor & the caliper body.

Thanks again Fellas
Cheers
JB

A special thanks to stephers & LM3929