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Anti-Squeal Shim & Other Brake Questions...

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RobT

RobT

Jedi Warrior
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Hello all:

I am in the process of rebuilding the hydraulics on my TR250 including new master cylinders, rear slaves (Morgan oversize), rebuilt clutch slave and front calipers, Hawk pads, stainless flex. hoses & silicon fluid (Dot 5) throughout. I have the anti-squeal shims from TRF, but they did not come with instructions. There is a little arrow stamped in them, and I assume this points in the direction of wheel rotation. Does anyone know if this is correct?

Also I "split" the calipers during the rebuild, although this is generally not recommended. Anyone have problems from doing this? Anyone have any suggestions on the bolt torque to use when reassembling the halves?

As always, many thanks,

Rob.
 
Rob, you got it right on the anti-squel shims. The torque for the bolts on the brake caliper halfs is 35.5 to 37 lb. ft. or 4.9 to 5.1 kg.m. Just make sure that both surfaces are clean and the treaded bolt holes are dry or you will get a bad torque reading. Wayne
 
Hi Rob,

Did you replace the o-ring seals between the brake caliper halves? If so, I was wondering where you got the parts?

Over the weekend I was working on installing the brake system on my TR4 frame-off project. If I may make a few small suggestions, if you are doing any work on the wheel bearings and/or replacing rotors and haven't already done so, carefully check the rotors for runout with a dial gauge. Or just go ahead and have them lightly turned at a local shop before final installation, not much, just enough to true them up.

I found one of the brand new Brembo rotors I'm putting on my car was out by 6 or 7 thousandths, the other 10 to 12 thousandths! I'm not sure if this is typcial. But, allowable runout is only 2 thousandths, according to the service manuals. These rotors would have made the brakes pretty jumpy in my car, if I'd just installed them as is.

Best to trial fit and check the rotors *before* installing the inner felt grease seal, too, in case turning is needed. It's not easy to remove that seal without damaging it.

And, you may already know, most shops need you to leave the rotor mounted on the hub for turning, with the bearing races in place.

Also, speaking of the felt seal, it seems to have grown over the years! The new ones I got from one of the big three U.S. vendors (I forget which) are far too thick and made it absolutely impossible to adjust the wheel bearings correctly. I trimmed away about half the thickness of each seal with a razor blade. I'd actually prefer to use a modern, rubber seal on there, but haven't found one to fit as yet.

Best of luck with your project!

Alan
 
Hi rob,

Just a question, why are you going with the DOT 5 fluid? Is the car going to be sitting for long periods without being run? The reason I ask is that when I rebuilt the brakes in my TR6 I initially went with DOT 5 fluid. Worst thing I've ever done for the car. First off, it took me forever to get the brakes to bleed clean of air. After that, I had problems with a mushy pedal, which got progessively worse as the temperature and the brakes got hotter. Finally, I decided to take an LBC mechanic buddy of mines advise and switched over to the DOT 4 Castrol GT-LMA fluid. What a difference, rock solid pedal feel, no fade that I've detected yet, even in some "fast road" driving. If there's a little more maintenance involved with using this fluid, even a once a year flush, then so be it, the end result is well worth the effort in my opinion. Being that your using some pretty good performance brake hardware, Hawk pads (great pads by the way), braided lines, performance rotors, I don't think you'll see the full benefit off all that gear by using the DOT 5 fluid. Just about everyone I've spoken to has said that, unless the car is going to be rarely driven and you're worried about internal corrosion in the brake system, don't bother with the DOT 5 fluid, espeically if the car is going to be driven hard or possibly at the track. I;m sure others here may have had different experiences with the stuff, but that's what I've seen and experienced in my car.

Good Luck
Scott
 
Good point about DOT 5, I'm not a big fan of it either.

Somewhere I read one of it's major drawbacks is that it's more prone to boiling than one would believe from the specs. It doesn't absorb water like other fluids, but instead water is trapped in larger "globules" for lack of a better term. Apparently those significantly lower the boiling point of "pure" DOT 5, which is strictly theoretical since all brake fluid becomes "impure" as soon as the can is unsealed. The lower "effective" boiling point might explain the softer pedal you noticed when the brakes were warmed up.

Yes, Castrol LMA is good.

Castrol SRF if even better, but it's damned expensive stuff!
 
Alan, even using SRF, Castrol recommends a maximum change interval of 18 months.
I use it on the racer, running a track that uses a lot of brake, and boiling has never been a problem.
Jeff
 
Thanks for all the helpful advice....

Thanks to trrdster200 for replying to my initial question on the shims and on the very helpful info on the torque settings for the calipers.

Alan - I did replace the o-rings between the calipers, Moss sells these. I will check the run-out on the rotors, although to date they have felt pretty good. I was also planning to repack the bearings with grease while I have the calipers off, but the bearings feel nice and smooth so don't anticipate a full rebuild.

As for the question of Dot 5 fluid, I have two reasons for wanting to use this over Dot 4:

1) The car does sit most of the winter unused, and I am hoping the Dot 5 will reduce moisture absorption.

2) It seems to me that the master cylinders always start leaking at some point on LBCs, and the Dot 4 strips the paint (this is what happened this time round - even with a master only 5-years old and an annual flush. I had to respray the damaged area under the bonnet).

I know the Dot 5 will give a bit of a spongy pedal compared with the mineral fluid, but since I do not intend stressing the breaking system, (no racing for me!)this is O.K. I have used Dot 5 before and have been pretty happy with it.

I will let you all know how this works out. BTW has anyone installed the larger bore Morgan rear slave cylinders? Was there any noticable difference?

Thanks again, Rob.
 
Re: Thanks for all the helpful advice....

Hello Rob,

if by Dot 5 you are refering to Silicone brake fluid, then I have used nothing else for twenty years, I do not experience a soft pedal or difficulty in bleeding the brake or clutch.
What is your thinking about using larger bore rear cylinders as that will alter the brake balance to the rear, and may cause rear wheel locking? (OK if you are rallying :smile: )

Alec
 
Re: Thanks for all the helpful advice....

Not wanting to change anyone's mind or turn this into a DOT5 thread, but FWIW...

I suspect (no proof to offer) that some problems encountered with the silcone fluid occur because tiny bubbles are easily introduced when pouring the stuff and stay suspended in it for a very long time.

I was advised to insert a very clean screwdriver into the reservoir and gently pour the fluid down along the blade to eliminate bubbles. Also, I top up the reservoir several days before I do the bleeding. Bottom line: I have used DOT5 for years with no spongey pedals or other problems.
 
Re: Thanks for all the helpful advice....

With the more "grippy" Hawk pads on the front, I am guessing the larger bore Morgan cylinders on the rear should even out the balance. These are a direct replacement and provide appox. 25% increase in breaking to the rear wheels. I think these will be a bit of trial and error to see if these really make much difference, or if the rear wheels start locking-up under heavy breaking.
 
Re: Thanks for all the helpful advice....

I believe you can buy a universal type brake proportioning valve that will enable you to eliminate any added rear brake bias associated with using larger rear wheel cylinders. All you would have to do is remove the hardlines, make the splice where the valve will go, and have a shop put on the proper sized nuts and make the flares to the line. Then make a series of experimental runs until you get the desired rear bias dialed in.

Does anyone know of a rear wheel disk brake conversion kit for these cars? I would be really interested in something like that. Also, I've toyed with the idea of making the Toyota truck 4 pot caliper conversion on my front brakes, that looks like a pretty easy swap. Has anyone tried that?

With regard to the fluid specs, yes, by the numbers the DOT 5 silicon fluid looks to be superior. However, what seems to happen is that since free water isn't absorbed by the fluid, it tends to pool. Then when the brakes get real hot, that pooled water will turn to boil and turn to steam, which will then create more gas in the fluid and make the pedal go very mushy. This is why silicon fluid is not suited to extreme duty or racing. Also, I can understand why people want to use this fluid in cars that sit for long periods, due to the perceived lower maintenance. However, that pooled water that I just mentioned will settle in the low parts of the brake system, and cause very rapid, localized pitting of the brake components. So in the end you might end up doing more damage than good. My next step is to switch to the Ate Super Blue fluid, dry boil of 536, wet boil of 392, as compared to the Castrol GT-LMA 446/311 respectively. I've been using this fluid in my Volvo and it's nice because when it's due for a change it's easy to see, it changes color. It is more expensive than the Castrol LMA though, and not always easy to find.
 
Re: Thanks for all the helpful advice....

Hi all,

Someone please correct me if I'm wrong, don't you want smaller diameter slave cylinders to increase brake pressure?

Yes, a brake proportioning valve might be the easiest way to get everything balanced. But all these operate by reducing pressure to the rear only, to the degree you dial in, up to about 50% reduction. So if the front brakes are out-performing the rear, i.e. the front brakes lock up first, other work needs to be done to increase the rear braking action first. I see J.C. Whitney sells simple, in-line proportioning valves. If you were to set one up right at one of the connections, you might be able to avoid cutting and splicing any of the lines. I'm not familiar enough with the TR6 brake system to know if there is a convenient location to do this. An undercar location would be a pain to adjust and might be too exposed to road debris. Perhaps somewhere in the engine compartment.

Yes, I can understand wanting to use DOT 5/silicone in a car that sits alot and isn't driven hard. I'm replacing a floor that rotted as a result of a DOT 3 or 4 leak from the master cylinders while the car was in storage.

Everyone has to arrive at their own "best" solutions to these sorts of things. My ideal would be to drive the car more often and change the fluid regularly, continue to use DOT 3/4 in the system... but I realize that may not always be possible, for me or anyone else. Long term storage systems might best be drained, although all the rubber parts would probably suffer and there should probably be some sort of flushing done after the fluid is removed. Has anyone ever done that sort of thing?

Just last evening I popped the pistons out of a set of calipers that haven't seen the road since 1986. They had a lot of gross-looking old fluid pooled in them, but no rust or pitting inside. I can't really say if they were leaking... theres a 1/2" of road grime built up on the outside.

My point though is that the piston wells are in really nice shape, after sitting full of DOT 3 or 4 for nearly 20 years. The pistons themselves are not usable and will be tossed, but mostly because of external damage.

The first caliper cleaned up well and the fresh paint is drying. Both will be getting new stainless steel pistons. Now if I can just get them in without twisting or tearing those pesky rubber seals! I'll use Raybestos Hydraulic Assembly lube, helps things go together easy and preserves rubber parts in longer term projects where things might stick or rust if assembled with brake fluid.

I've seen that blue or purple brake fluid at one of my local suppliers and may give it a try. The color change indication would be great! I wish it came in smaller cans, though. It's best to use a freshly opened can of any brake fluid, not something that's been unsealed and then stored on a shelf for a while.

Cheers!

Alan
 
Re: Thanks for all the helpful advice....

Alan - smaller master cylinder or larger slave cylinder will increase breaking pressure. Compare the size of the caliper pistons with those for the rear drums - much larger diameter at the front = much more breaking pressure. Pressure(lb/in2) x Area (in2) => Force(lbs).

I think I will still try the silicone, and I can always convert back to mineral if it dosen't work out (would require another rebuild but is much quicker the second time round, and of course, break rebuilds are such fun!).

Rob.
 
Re: Thanks for all the helpful advice....

[ QUOTE ]
... Now if I can just get them in without twisting or tearing those pesky rubber seals!...

[/ QUOTE ]

Do you run your air compressor hose to a loose fit connection on the bleed screw to pump up the seal so it wants to pop right over the piston?

First one I did like this took about 5 minutes to get the hang of it. By the time I got to number 4 it was a 3-second job. I won't go into any details unless someone really wants to know.
 
Re: Thanks for all the helpful advice....

Hi Geo,

That sounds like a neat trick, I'll try it!

Actually, I've pretty well got the hang of it with a dental tool, a couple careful moves, one or two curse words, and the outer dust seal is properly oriented. I've had several of the inner seals get twisted and damaged when pushing the pistons in place. So I always pop the piston in, then back out to check. Putting it back in the second time is usually easier.

I'm using stainless steel pistons for the first time, perhaps that's why they seem to be fighting me, although I can't imagine why there would be a difference.

I've just recently discovered and started using the hydraulic assembly lube and it's a big help, although it's sort of like handling a greased pig at times.

Sometimes I wish I had the later TR6 calipers, with the different dust seals: easier to install and more positively retained by the wire clip.
 
Re: Thanks for all the helpful advice....

'Greased Pig' is about right... I've called it 'red snot' and other unflattering terms, but couldn't do without it.

For the air trick I had my wife 'man' the air gun connected to a length of 1/4" irrigation hose jammed into the bleed valve opening. The opposite piston is in and held with a c-clamp and the other sits on the boot. The air blast swells the boot then I used a little tool made from a length of 12 ga copper wire rounded on the end (no scratching) to ease the boot around the piston. I also used stainless steel pistons but that shouldn't matter.
 
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