[Mgs] MGB rear brake questions

David Ambrose stargazer1 at cox.net
Sat Oct 23 12:33:50 MDT 2021 

You have the wrong wheel cylinders. The GTs have a different (larger) 
rear brake cylinder than the roadsters. The roll pins are in different 
locations to prevent them from inadvertently getting swapped. I don't 
think you want to use the GT cylinders on a roadster as it would put too 
much braking in the rear which will make the car very tail happy under 
emergency braking.

Cheers,
Dave

On 10/23/2021 10:44 AM, wkilleffer at epbfi.com wrote:
> Thank you for your reply.
> As far as the type of wheel cylinders, I don't recall that there was a 
> choice as to whether they were for a GT or a roadster. The only choice 
> was either Lockheed brand (maybe) for more $, or an aftermarket for 
> less $. As far as I know, the back plates are original, but I've only 
> owned the car for 20 years. Its engine is not original, so who knows 
> what else could have been swapped.
> Can you shed more light on the whole speed bleeder thing? And how do 
> do pedal pumping bleeding when you're by yourself?
> The fluid is making its way back to the wheel cylinder, so no lines 
> are crimped. But thanks to the poor fitment of the bleeder thing with 
> the tool, I can't tell if the air bubbles are coming through the brake 
> lines or are air being drawn into the bleeder because the fitment 
> isn't good.
> Yes, I did the clutch system a couple or three years ago. It was a bit 
> frustrating, but seems ok now.
>
> Thank you,
> -William
>
> ------------------------------------------------------------------------
> *From: *"Robert's New iPad" <mgbobh at gmail.com>
> *To: *wkilleffer at epbfi.com
> *Cc: *mgs at autox.team.net
> *Sent: *Saturday, October 23, 2021 1:36:03 PM
> *Subject: *Re: [Mgs] MGB rear brake questions
>
> The rear-brake question opens more questions.    MGBs had rear 
> cylinders to fit the Tourers and the GTs, different sizes of cylinders 
> and different back plates.    The roll pins located the cylinders in 
> the correct backing plates.
> Thus the questions arise:  Tourer back plates and new GT cylinders? GT 
> backplates and new Tourer cylinders?  Car modified before you got it? 
>  Wrong cylinders ordered/shipped?
> Having wrestled through this with my GT, it was years back and now I 
> do not recall which cylinders (size and pin location) are Tourer or 
> GT.  Someone will know, though, and that challenge easily mastered.   
> GT cylinders are larger, suited to the additional weight of GTs.  If 
> you have to swap parts, do it the way MG built it—they got it right.
> As you replaced them years ago, my bet is that the vendor shipped 
> wrong cylinders.
> As to the bleeding, my experience has been that ordinary pedal pushing 
> has done fine for me on many cars, though I did install speed bleeders 
> on this GT.  They are an easy exchange and work OK, but the savings of 
> 1/4 cup of brake fluid doing the job are hardly worthwhile.   If the 
> rear brakes are difficult to bleed, have a close look at the metal 
> pipes on the axle.  A car that has been flat-bed carried may have had 
> the straps wrapped around the axle, crushing the tubes.  That’s not an 
> unusual thing to find.
> Since you are changing hoses, have you changed clutch hose?  These 
> break down internally whilst appearing fine externally. As you do the 
> change, do it swiftly, w/o interruption, as introducing a bubble into 
> the line is altogether too easy, and bleeding the clutch line has made 
> many an owner irate.
> Bob
>
>
> On Oct 23, 2021, at 1:04 PM, wkilleffer at epbfi.com wrote:
>
>     Hello everyone,
>
>     The car I'm working on is a 1974 MGB roadster. I decided that I
>     wanted to replace everything relating to the brakes and their
>     hydraulics except for the metal lines. I ordered the parts from
>     Moss but had to sit on them for a couple of years before actually
>     starting the project.
>
>     So, I got the new master cylinder installed, which is probably one
>     of the more challenging things I've ever done on the car. Next
>     step was working on the rear brakes. The rubber hose in the back
>     was pretty simple, but the issue is with the wheel cylinders. I
>     replaced them maybe twenty years ago and didn't have any trouble.
>     But these new ones have a roller pin on them that doesn't line up
>     with the holes on the brake's backing plate. It's been too long to
>     try and swap them with Moss, and I'm not sure that would do any
>     good anyway because I don't recall that there were too many
>     choices for that part. You could get a cheaper aftermarket or a
>     more expensive part that may be made in England. I went with the
>     cheaper one.
>
>     Has this been an issue for anyone else? I could probably drill
>     another hole in the back plate to match the roll pin, but that
>     seems like one of those DPO solutions. Also, I don't feel like I
>     should have to entertain such a notion anyway. The part should fit
>     and function correctly. The current wheel cylinders are probably
>     ok to re-use, but I liked the idea of all new parts. The front
>     brakes are also on the agenda, but we're not there yet.
>
>     The next question has to do with bleeding the rear brakes. I
>     started to bleed the brake furthest from the MC using a vacuum
>     tool I got at a well-known less expensive (think shipping at a
>     port) tool store. It's been a letdown for several reasons, among
>     them that the bleeders on the wheel cylinders seem too small for
>     the bleeder fittings that came with the tool, which causes the
>     tool to draw a great deal of air through its system. I seemed to
>     barely be able to get any fluid through the system. The trouble I
>     have is that I am single and live alone, so I don't have any
>     readily available sources of help. If the brakes are going to be
>     bled, I have to do them by myself. Does anyone have any advice on
>     this topic?
>
>     Thank you,
>     -William
>     1974 MGB
>
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