TR7 & TR8 Forum

i have rebuilt the master cylinder of my TR8, replacing all the seals and o-rings, as well as the pressure switch. I followed the TR8 shop manual and I have the seals in the right way (or at least they agree with the picture in the manual). In fact, the whole system was dry, as I rebuilt the front calipers, and put new cylinders in the rear. While I had the system open, I blew out the lines and replaced the flexible lines with stainless steel.

I have bench bled the master cylinder. (Not sure if this is normal, but when I did this it seemed that the rear port was moving more fluid than the front.)

I did not rebuild the prop valve, but I did blow air through it when I disassembled it and blocked up the ports until I reconnected them today. Air passes through the prop valve no problem.

When I connected the lines and tried to bleed the brakes, no fluid moved; not to either front caliper, or to the rear. There is no air movement out of the bleeder on the downstroke, and no vacuum on the upstroke.

When I open the rear bleeder on the pedal downstroke, I can hear and feel air moving out through the bleeder. If I close the bleeder for the pedal upstroke, when I open it again in preparation for the next downstroke, there is vacuum and air is drawn back in. No fluid moves.

When I connect vacuum to either of the front calipers and try to draw fluid through the system, nothing moves. It is perfectly sealed.

I removed the master cylinder and disassembled it to check if I had made an error. I couldn't find anything amiss. I put it back together and tried again. No joy. So I took it apart again. And tried again. And you can guess what happened. Bupkis.

To merely say I am frustrated would be a failure of the English language to capture the essence of this experience.

I am fairly new to working on cars, but thought I had understood the basic principles of this procedure. Apparently not.

Any suggestions welcome. In the meantime, I will be out back beating my head against a tree.

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Brent



Edited 1 time(s). Last edit at 2019-05-04 08:23 PM by sheetsofsound.

Brent:

Honestly, it sounds like your proportioning valve is toast.

The valve can be rebuilt, although it uses square seals. That said I have rebuilt them with round seals and they do work just fine.

Alternately, you can replace it. I found that the original unit is hard to find, but the unit from the Discovery 1 is a drop in. I am currently using the Disco 1 replacement with good results. Part number ANR3194.

Rebuilding is a bit of a challenge, since the unit uses a crimped on cap which can be removed with a bit of persuasion. I rebuilt the unit on the TR8, and when I disassembled it it was filled with something that looked like oatmeal. Bizarre. Sadly, when I went to reinstall it the threads pulled out for one of the brake pipes, so it was scrap. Hence the switch to the Disco unit.

Vance

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1980 Platinum Metallic TR8, frame off restoration, complete.
1974 Jensen Healey, now assembled and awaiting startup. =:-)

If it is the prop valve as Vance suggests, Ted at TS imported automotive (web site) rebuilds them and has a modified version to increase rear braking.


Brent:

Honestly, it sounds like your proportioning valve is toast.

The valve can be rebuilt, although it uses square seals. That said I have rebuilt them with round seals and they do work just fine.

Alternately, you can replace it. I found that the original unit is hard to find, but the unit from the Discovery 1 is a drop in. I am currently using the Disco 1 replacement with good results. Part number ANR3194.

Rebuilding is a bit of a challenge, since the unit uses a crimped on cap which can be removed with a bit of persuasion. I rebuilt the unit on the TR8, and when I disassembled it it was filled with something that looked like oatmeal. Bizarre. Sadly, when I went to reinstall it the threads pulled out for one of the brake pipes, so it was scrap. Hence the switch to the Disco unit.

Vance
[/quote]

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Patrick
1980 TR8 DHC TPVDV8AT209637
1959 TR3A TS50063LO
TWOA Secretary
Western Pennsylvania Triumph Association
North Coast Triumph Association
Scions of Britain

If you go that route, I would first confirm with Ted that they do indeed rebuild them. Last I heard, they just do the modification.

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Darrell Walker
66 TR4A IRS-SC CTC67956L
81 TR8 SATPZ458XBA406206
Vancouver, WA, USA

Thanks for the tip. I will start there. I have another valve or two out of a couple of TR7's that I scrapped a few years back, so I just need to find them and I'll swap one in. I am assuming they are the same as the 8's?

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Brent

I thought about doing my master and booster but with british parts they are querky and left it to someone who has done our tr8 and 7 brakes many,many times...they know british brakes-look at website pics and you will see the tr8 booster/master.......also they powder coat to original factory look so he give you OEM part that works...see pics before & after....he has all our internal hard parts/rubber/seals/labels etc..or you send him your parts if you want......prop valve I went with straight thru to get more braking to rear wheels..if you want original part check with ted Schumacher...I have his modified proportional brake valve.....the next change on my car when they go will be to wilwood parts...

Brake materials and parts in fort wayne Indiana

Brakematerialsandparts.com

More

Rebuilding does not save much money. These guys offer the proportioning valve for as little as $55..

I bought the AP valve from them a couple of years ago. It was under $100 shipped. They now offer some less expensive options.

Decisions, decisions.

Vance

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1980 Platinum Metallic TR8, frame off restoration, complete.
1974 Jensen Healey, now assembled and awaiting startup. =:-)

Just had a look through all my spares. I have 3 master cylinders and boosters, TR7 calipers all over the damn place, enough rear drums to start a percussion ensemble.... no prop valve. Weird. I wouldn't have chucked them, and I have a pretty organized system of cataloging my spare parts. I will keep looking. In the meantime, i think I will talk to Ted and see about the modified one that he sells.

Before I had the car up on blocks and took the brake system apart I had taken the car out on a couple of short test drives. It seemed that the rear brakes were always 'on', which I put down to the very stiff and corroded parking brake connections at the rear wheels. It had apparently been enough of a problem for the previous owner that he had smeared the pivot point on the axle with what appeared to be an entire can of lubricant. It looked like a grease blob with cables sticking out. His ministrations solved nothing, surprisingly. I'm now wondering if the stuck brakes were indeed caused by the prop valve.

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Brent

As far as I know the proportioning valve only limits the rear brakes when the pedal is pushed hard enough. It's extremly unlikley for the proportioning valve to get stuck in the "limit-the-rear-brake" position while applying the brakes.

Presumably someone could apply enough pressure to get the proportioning valve to stick in the "shut-off-the-rear-brakes-entirely" position ... but I doubt it.

A different cap makes any proportioning valve into an adjustable one as seen here:

I'm assuming you mean the rear port to be the one at the end furthest from the end the pushrod goes into ... correct ? It should flow more when no ports are connected to anything.

In fact almost nothing should come out of the front port unless you block - or partially block- the rear port. Such as when you run a return line up into the reservoir ... NOT recommended by me by the way. The spring between the front and rear (primary and secondary in Service manual nomenclature) pistons is a little heavier than the rear circuit return spring.





Loosen the lines at each fitting on the Pressure Reducing Valve (correct name) to see if you get flow there when you push the brake pedal down.

One other item might be worth inspecting is to make sure there is freeplay between the booster pushrod and the master piston when your foot is off the pedal. You can put a thick gasket in between master and booster if not.

Correction... i have the wedge shop straight thru prop block on the car now but did have teds modified prop valve on before...wanted a cleaner look and i installed prop valves off master to control braking.....

Brent:

My WAG (Wild Ass Guess) is that you don't have any because a) They drop like flies and b) They are not considered to be rebuildable.

I have had three wedges, and only the most recent acquisition has had a working valve in it. So in my admittedly limited experience, two thirds of them fail at some point.

Vance

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1980 Platinum Metallic TR8, frame off restoration, complete.
1974 Jensen Healey, now assembled and awaiting startup. =:-)

In a former life I was a mechanic and found one of the best ways to get stubborn brakes to bleed i used the Gravity bleed method. It is really very simple but takes some time. All you have to do is open the bleeder valves one at a time until brake fluid starts to drip out. Once you get fluid out of all the bleeders you shouds be good. Just be sure you get no bubbles out of them before you close them and be sure to keep an eye on the reservoir so you don't run out of fluid. YMMV.

Dave Leininger

Thanks for the problem solving ideas. I checked and there is flow at the Pressure Reducing Valve (thanks for the info on the name). As soon as I loosen the hardline and press the pedal, I get fluid. I also opened it at the outflow port and drew vacuum at the caliper just to make sure the line was clear. (It was.) I will check the freeplay at the pushrod tomorrow.

But from your description, Jeff, I think I have made an error of some kind on the reassembly. Most of the fluid movement is coming from the primary port, which according to the TR8 manual is the port closest to the pushrod. The secondary piston is the first one to go back into the bore on reassembly, and the port associated with it is the farthest from the pushrod end according to the manual. It does not flow very much fluid. Did I get this backwards somehow?

Dave: I have tried gravity bleeding the system for the last 5 or 6 days by leaving the left front caliper open with the hose I attached submerged in a bit of brake fluid. Nothing has moved.

Vance: I am late to the car enthusiast hobby, and about 8 years ago or so I got a few wrecked TR7's over the course of a few months. My thinking at the time was to get 1 running and learn about the car by taking apart the others to see how things worked. I remember throwing out one pressure reducing valve as it was clearly buggered (threads had been re-drilled and tapped for an adapter), and one other car was missing the part. But I do remember that I had at least 2 that appeared ok. Where they are now, who knows? I'll find them in 6 months when I clean out the garage maybe. Having very limited storage space has forced me to be fairly efficient about how I catalogue and store parts. It seems funny that I missed them somehow, but I have a vague memory of boxing one up to sell... can't remember.

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Brent