MGB: Pedal box Difference on 75 B's

I've seen a couple references lately about the difference of 75 MGB's, apparently in the pedal box area, that causes unique problems with air filters when converting to dual SU's. Can anyone show or explain what the difference is?

I've had a 74 1/2 and a 76, but I don't remember ever having a 75 so I never notice the difference.

Thanks!

[quote=mayuhm]
I've seen a couple references lately about the difference of 75 MGB's, apparently in the pedal box area, that causes unique problems with air filters when converting to dual SU's. Can anyone show or explain what the difference is?

I've had a 74 1/2 and a 76, but I don't remember ever having a 75 so I never notice the difference.

Thanks![/quote]

X 2

74 1/2 MGBs didn't have a power brake booster.......later models did. Its the booster that gets in the way of running proper air cleaners on the twin SUs.

The 75 is indeed unique, if you look at a late model pedal box you'll see it is offset to one side in relation to its mounting bolts. The 75 is offset TOWARDS the engine, 76 and later is offset AWAY from the engine giving you about 1/4 inch of extra space. It is possible to put a 76 and later pedal box in a 75 but you'll have to drill a couple of holes as not all the mounting bolts line up.

wow WIZ......I didn't know that....wonder why that was..........

Lloyd. I thought you were moving the computer out of the shop!

Dirk. The early brake booster type pedal box as fitted to the '75 model Federal cars puts the brake master and booster slightly closer to the centerline of the car than the 1976 and later pedal box.

I don't have the vin number break points confirmed, but do have solid evidence that the pedal boxes are slightly different.

The change probably coincides with the 1st type of servo mounted brake master, which had the wedge type reservoir and the brake warning light switch with black/white wires. That change point was 368082 - 386600.

We ran into this problem with the Moss supercharger system. The original kit was designed for the 1968-74 application. Modifications were made so that the kit could be installed with adequate clearance on what we believed to be the 1975-80 cars. It was found that on some 1975 cars there was not adequate clearance for the intake extension.

When the pedal box was changed out to the later 1976 type, the clearance issues were resolved.

This issue is going to also be a problem if fitting K&N tapered filters to twin carb conversions.

Kelvin, Are saying the Moss Supercharger will not fit the oddball 75 pedal box?

I don't know about the supercharger, but I converted to HIF's and I have K&N filters. I did have to put on a new driver's side motor mount, but they fit. No clearance issues so far.

WIZ...not feeling well today..............feel even worse after spending the day doing nothin'

Dan. There is less clearance, and in a couple of cases there wasn't enough clearance for the modified angled inlet. True 1975 model cars are rare enough that it's impossible to get a definitive answer.

As Frank points out, it seems to vary from car to car. Variance in the motor mount locations are also an issue, as some cars came with motor mount spacers, others didn't.

It's true to say that 1975 model cars with this brake master frame have less clearance for twin carb air filters, or the supercharger than later cars.

How much less varies.

This is some pretty interesting stuff, and I can just imagine the frustration of the people that learned this the hard way.

Now, what we need is some pictures!

Thanks for the responses.

[quote=mayuhm]
This is some pretty interesting stuff, and I can just imagine the frustration of the people that learned this the hard way.

Now, what we need is some pictures!

Thanks for the responses.[/quote]

Welcome to my nightmare :X

I had no idea that '75s were odd-ball when I bought mine. Of course, having owned other British cars I knew it would have its quirks, but... Dammit. The switch to SUs has been particularly annoying. I mean, they're on there all right, and they work fine - but there was some annoyance getting 'em on there, and I'm still searching for a good air filter solution.

Honestly it's starting to sound like I'm going to have to get a '76 pedal box. Oh joy.

I installed SUs on my 75 about three years ago (took off the Weber downdraft) and did have to machine the black spacers ( I think I took off about 3/4 to 1 inch) to allow the rear K&N tapered filter to clear the pedal box and booster. This was an easy and inexpensive solution that did not require replacement of the pedal box and the work associated with this. It has worked fine for me but in a hotter climate it may pose some problems as the carbs are closer to the manifold.

I did not know about the difference in that item on the 75 B, althogh I could not even fit the flat conical K&N filters after changing to SU's on the 75 RD. Before starting the job, I had seen pics and asked around and everything looked promising.

Finally, I took off the emulsion blocks and the heat shield and had to fabricate a new one and used shorter studs.
Afterwards the SU's looked like seen on most conversion pics but without the plastic pieces on the inlet manifold.
It always made me thinking why it worked on other RB cars but mine, now I know.

Thank's for that information!

I sure do thank everyone for the education! I sit here in awe that 1/4" has caused so much trouble, but I remember times when "Oh, what I would give......" over even less than that.

I would still like to see pictures of this "QIFH" (Quarter Inch From Hell), and thanks again for taking the time to teach me.

[quote=7317]
I installed SUs on my 75 about three years ago (took off the Weber downdraft) and did have to machine the black spacers ( I think I took off about 3/4 to 1 inch) to allow the rear K&N tapered filter to clear the pedal box and booster. This was an easy and inexpensive solution that did not require replacement of the pedal box and the work associated with this. It has worked fine for me but in a hotter climate it may pose some problems as the carbs are closer to the manifold.[/quote]

Considering that I'm north of you, I assume that fix will work. I've been considering it, but haven't bothered to do so yet (I kind of dread taking the whole damn assembly apart again. What are the spacers made of (so I know who to take 'em to)?

That's what she said. Just a 1/4" more.

[quote=Dashface]
[quote=7317]
I installed SUs on my 75 about three years ago (took off the Weber downdraft) and did have to machine the black spacers ( I think I took off about 3/4 to 1 inch) to allow the rear K&N tapered filter to clear the pedal box and booster. This was an easy and inexpensive solution that did not require replacement of the pedal box and the work associated with this. It has worked fine for me but in a hotter climate it may pose some problems as the carbs are closer to the manifold.[/quote]

Considering that I'm north of you, I assume that fix will work. I've been considering it, but haven't bothered to do so yet (I kind of dread taking the whole damn assembly apart again. What are the spacers made of (so I know who to take 'em to)?[/quote]

I just took mine to the machine shop that did my engine work (Autosport in Seattle)