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MG MGB Technical - Banjo Leak From Fuel Pump

I have recently had to change the Pump Petroflex inlet and outlet hoses on my June 1976 Roadster because of a fuel leak in one of the hoses (suspect Ethanol, or just old age). Having replaced both the hoses to the pump I'm having trouble getting the banjo's to seal. This car uses a fibre washer and an O ring to seal the banjo to the pump.

The pump was replaced a couple of years ago and I had no problem getting a good seal using two fibre washers (one each side). Interestingly, when I took the old Petroflex pipes off, they had a copper washer inserted on the flat side that faces on to the pump and a recess on the side to the banjo bolt. See attached pictures.

So my question is, should I continue to fit the O rings to the flat side of the hose (which look very thin to me), or ditch them in favour of just using two fibre washes?

Thanks in advance.

Andy






Andy Robinson

Are you using the same banjos? I've found some replacements are thinner than the originals and won't seal because the bolt bottoms in the thread. The symptom is that as you tighten the bolt they suddenly stop instead of slowly tightening as the fibre/rubber seals compress. The test for that is to fit the banjo without any seals and if it is still loose when the bolt is tight then you need additional fibre washers.

I see no benefit in using copper washers, and if the pump body has recesses as in the attached then you must use O-rings and not fibre washers that side. If the face is flush with no recess then use fibre.

Soak fibre washers in light oil overnight.

I never use braided hoses now at either end of the system. Modern rubber is rubbish and you can't see what is happening to it under the braiding. I've changed probably original hoses when the braiding crumbled away to dust because I felt I ought to, but cut them open and they were perfect. By contrast hoses that I've replaced on both cars have needed replacing again, second attached is roadster carb hose under perfect braiding.

As long as you stick to E5 fuel you shouldn't get any issues down to that.






paulh4

Thanks Paul for your reply. The Petroflex hose was used according to MGOC spares from 1975 to September 76 (my car is June 76) and it comes with the banjo already fitted. See https://www.mgocspares.co.uk/product/ahh7371/braided-pump-hose-mgb

So you could be right and the banjo on the new hose may be slightly thinner than the old one. I'll check to see if the bolt is bottoming before it's able to fully seal the joint and if so add another fibre washer.

Andy
Andy Robinson

I ordered up two new banjo bolts for the pump and when compared to the original ones they were slightly shorter. I soaked the new fibre washers in some lamp oil as recommended and fitted new O rings. All fixed and no leaks I'm pleased to say.

I can only think that those copper washers that were in the old petroflex pipes took up the slack in the old banjo bolts.

Thanks for your help.

Andy
Andy Robinson

Thanks for the feedback, good to hear
paulh4

I recently went to move my B and noticed a strong smell of petrol, having moved the car there was a trail of petrol. A quick look revealed it was coming from the flexy pipe on the outlet of the pump. Today I took the flexy pipe off and dissembled it, it was one of the braided type. Having removed the outer metal braid it showed a cotton braided pipe marked Cohline 2122. I removed the cotton braid to reveal the rubber pipe, with a little tension on the pipe it looked like it was made of Swiss cheese. I replaced it with some 8mm ID fuel rated rubber hose.

The braided hose was purchased and fitted 11/23 so not yet 3 years old, I avoid E10 where possible so it's clear these braided hoses are not fit for purpose.



R.A Davis

BT, DT, with braided (1st above) and unbraided in recent years.

Never ever fit braided hoses, at least with plain rubber you can keep an eye on them.

Everyone will blame ethanol but it's not, it's just rubbish rubber just like other components which perish with no contact with fuel. Because of problems with hoses I'd replaced (more than once in some cases) I decided to replace the V8 pump hose which was almost certainly original as the braiding was crumbling away when I got the car some 25 years earlier. Probably 40 years old, I cut off a section, slit it lengthwise to open it out, and the rubber was perfect inside and out (2nd pic). Never used E10 although I was using 95 octane in the V8 until that became E10.

I note Cohline 2122 specifies up to 50C, a well-known supplier not a million miles from here shows their braided hose uses Cohline rated at 50C. In hot weather (not as hot as we have had this year) I've measured the roadster engine compartment temp at 50C and the V8 at 58C. I use SAE J30 R6 which has a temp range up to 100C and R9 goes up to 135C.






paulh4

Interestingly (according to MGOC Spares) Petroflex Hoses to and from the fuel pump were fitted to both Chrome Bumper and Rubber bumper cars from 1964 - September 1976. From September 76 onwards, they changed to rubber hoses. Not sure why that was, maybe cost cutting, as I assume a Petroflex hose would offer some sort of protection underneath the car.


Andy
Andy Robinson

A pal's 77 has really skimpy hoses, very thin-walled thinner than anything else I had seen to that point. They cracked.
paulh4

This thread was discussed between 08/08/2026 and 24/08/2026

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