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TR4/4A Dual circuit brakes in TR4

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richie

richie

Senior Member
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So of course we have revvington style kits which exist, but I was wondering if anyone has used factory parts to make this happen.

Would a late TR6 pedal assembly would fit the TR4A which would then allow one to use a factory booster and dual circuit master cylinder from the later TR6 as well?

Of course the appropriate clutch cylinder would have to be swapped along with the brake setup but this whole thing seems like an easy way to bring a safer and stronger brake setup to the 4.

Anyone have any thoughts to add?
 
If TR6 assembly simply swapped over, which it doesn't, it would be a popular conversion. I think a specially engineered kit is the way to go - personally I think the money is well spent to have someone else have done the engineering. Just me.

Why would the clutch need to be changed?
 
I just realized the TR250 shares the same configuration. I think this might work...

As for the clutch, it's simply because the clutch master cylinder is not positioned in the same place
 
Hi Richie,

I plan to do this conversion to my 4A. I purchased a used TR6 pedal cluster, new m/c, rebuilt servo/booster, PDWA (optional), and a new replacement toe-kick (from TRF) that has the cutouts to mount the above. I plan to section the existing toe-kick since the lower section of mine already needs a rust repair, and weld in the section for the new mounting. I could also have cutout the TR4A toe-kick but the raised ribs on the sheetmetal needs to be hammered flat to mount the TR6 bits. Look and you'll see what I mean. All is reversible too, just have to block off the new m/c mounting hole.

Another thing to considfer if you do this is to change the rear hydraulic lines from the single rear feed to a dual flexible feed as in the TR6. Just weld a tab to the frame to mount the new line and add a splitter.

It is very doable.

-Pete
 
I did it with a TR6 system on my 4A. Much like Peter K says above. You'll need to adapt to a vacuum source via the TR4A manifold and replace the original PCV with another in line PCV. I used GoodParts kit. If you want to write to me I'll send you some photos. I might be able to find the part reference that I used to adapt into the TR4A manifold for the vacuum source.

jerryvv@roadrunner.com

JVV
 
Right, you'll need an in-line check valve for the vacuum line between the booster and the manifold vacuum connection. ISTR that I got mine from VickyBrit.

I still haven't finalized the manifold vacuum port for the booster but ISTR on the 4A there's a boss on the manifold that I could tap for a threaded connection. Or just T it into the PCV line (with the check valve in place.)

So Jerry, how is it? Post a shot here on BCF for all to see. BTW, I think that I sent you a tracing of my panel with the proper cutouts when you were doing yours. Mine is still on the shelf.
 
PeterK said:
Right, you'll need an in-line check valve for the vacuum line between the booster and the manifold vacuum connection.
Click to expand...
I'm confused : What happened to the check valve built into the booster vacuum port?
 
Peter, I do not have a second check valve in my lines. The check valve on the booster works just fine. During the restoration I had a TR6 panel welded into the body shell and had the two slots for the TR4A system welded closed. That eliminated the raised boss on the vertical part of the foot well. If someone wants photos of my system I'd be happy to send them to you. I don't want to go thru the process of getting accounts for photo's posting to the web etc so that I can post them here.
 
I went the same way as Jerry. When I did the rebuild, the registration regulations here in Oz required that any car converted from left to right hand drive had to go to dual circuit brakes. That has since changed and you can now register left hand drive cars.

Using TR6 parts seemed like the safest and simplest way to go. The panel mods were done while the body was being repaired. The TR6 pedal box bolted in although changes had to be made to the pedals for the RHD configuration. It looks stock and all the parts are Triumph. I put a T-piece in the PCV valve for the vacuum for the booster. I may have a look at putting another check valve in.

All 4A owners should consider whether they should go to dual circuit brakes if they have not replaced their rear stub axles. If the stub axle breaks, you lose the rear drum and you have NO brakes. Guess it is a question of which is cheaper and easier - new brake system or new axles. Mine now has both as I do not want to rebuild the car again!

Rocky
67 4A
 
I have a friend who tested the dual system on a TR6 when the fronts went away going down a Pittsburgh hill. He said the rears would not stop the car. His may be an isolated case but I hope I never have to find out for myself. I do know that the hand brake on my 4A is abouit useless and I even have the lever extenders from a late TR6 installed for extra leverage.

I can lock them up however but I wonder if I could if the fronts went away? In theory yes but.................!
 
Anyone know a source for the late TR6 lever extenders? I've been looking for a set for a long while for my TR4A. Not at Vicky/Moss/TRF.

Used to have a set that were on a car, and wish I'd had the presence of mind to remove them before the car got sold.....
 
JerryVV said:
I have a friend who tested the dual system on a TR6 when the fronts went away going down a Pittsburgh hill. He said the rears would not stop the car. His may be an isolated case but I hope I never have to find out for myself.
Click to expand...
And that is the dirty little secret of systems that are split front/rear. The front brakes do by far the majority of the braking; the rear brakes border on useless by themselves.

Many years ago I had the front brakes fail on my Audi and made the somewhat foolish (in retrospect) decision to try to limp home on just the rear brakes. Carefully drove well under the speed limit and gave myself lots of stopping room ... until some woman in a station wagon pulled out in front of me. Would have had plenty of room to stop if the front brakes had only worked; but the rear wheels just slid and slid and slid. Fortunately it did slow the car enough that by the time I hit her, it only broke a headlight.

So, if you are going to all the trouble to convert to a dual system, you might want to consider doing a diagonal split.

Or the really killer setup would be to use 4 pot calipers, with each pair of pistons within the caliper on a separate brake circuit. There were some production cars with that setup, but I forget which ones offhand.
 
Wouldn't a diagonal be off balance as the piston/cylinder assembly in the caliper will be much larger in volume vs a drum wheel cylinder? I would imagine it would require 2 priportioning valves?

Additionally this would require that the two circuits on the MC are evenly split in fluid displacement?

Maybe it's it's easier than that?
 
TR3driver said:
Or the really killer setup would be to use 4 pot calipers, with each pair of pistons within the caliper on a separate brake circuit. There were some production cars with that setup, but I forget which ones offhand.
Click to expand...

I know Volvo in the '70s-'80s had them, as when we rebuilt them here at work, you had to be real careful about getting the correct halves together after disassembling and cleaning a batch. Each of the four, four piston calipers had two brake lines feeding them. There may have been others, but those were the most common.

Also, I've had a few early Saabs back in the day, and they had a diagonal brake circuit. I had one circuit fail on a three cylinder 96 once, and it's definitely better to have one front and one rear rather then facing the crap shoot of only having rears which I've also experienced. That said, it's still better to have pedal operated rears only then having to rely on the hand brake.
 
richie said:
Wouldn't a diagonal be off balance as the piston/cylinder assembly in the caliper will be much larger in volume vs a drum wheel cylinder? I would imagine it would require 2 priportioning valves?

Additionally this would require that the two circuits on the MC are evenly split in fluid displacement?

Maybe it's it's easier than that?
Click to expand...
Those are valid concerns. But TR4 brakes are already balanced without the use of a proportioning valve; so to keep that balance you would want to use a straight-bore dual MC (or a pair of equal bore MCs) anyway. And since it is balanced, then you could split diagonally and have the same balance.

Easiest route with the dual circuit calipers would be to balance them by adjusting the rear slave bore; but dual proportioning valves would also be a possibility.
 
I am pretty sure my 1986 Pontiac Sunbird had that split system side to side. It didn't work all that well after a few years and resulted in an odd feeling only at times when appling the brakes. That car was a POS in many ways, established my less than positive thoughts regarding GM products.

As for the lever extenders I got mine from Scott Harper at Team Triumph several years ago. 330-392-7176. May have been the only set he had but try him. Maybe fax him a picture from the TRF parts book. He is one of the good guys and will help if he can.
 
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