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UKJames
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Hi

Slowly working my way around the JH and have replaced calipers, flexi's, master cylinder and lines, and put in a set of green stuff pads for good measure. Brakes are now useable and progressive, but still do not bite down as much as I would have hoped. Bled the brakes thoroughly. Good pedal pressure.
So looking at my booster I've done a vacuum test, it holds vacuum. I've replaced the non-return valve, the hose to the manifold (and fitted an in-line non return valve as well).
However two things I have noticed that may or may not be related (or maybe my brakes are as good as they are going to get):

1) When I depress the brake pedal, and keep my foot down, there is a constant 'chuff chuff' sound that sound like air leaking somewhere. Diaphragm? but if the diaphragm's gone wouldn't the booster not be able to hold vacuum?

2) Manifold vacuum low- I know that long duration cams can cause this (and I believe the stock JH cams are) but surely this would affect the vacuum to the booster? My readings at idle are around 10in.

Any thoughts on this appreciated

Jim

subwoofer
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Don't know about the sound, but as far as stopping power goes: I think the brakes were described as "adequate" back in the 70's. Ring HiSpec if you need more stopping power.

--
Joachim

Jim Ketcham
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What master cylinder did you use. There is a Landrover master that looks just like the original JH master, but has too big a piston resulting in considerable increased pedal effort.

UKJames
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Yes it is a SWB LR Master Cylinder. When I checked it, it looked like a 3/4" bore. It was certainly comparable to the one that came off. I might double check as I heard some talk that they split the difference between the 3/4" and 1" MC's and started making 7/8" ones.
I am still erring on the booster not boosting as efficiently as it could. Might try capping the hose off and trying unassisted to see if there is any discernible difference

gmgiltd
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I believe that if it was a SWB pre 89 it should be the same as the JH one - Padock Landrover has them.
The more you drive modern cars the more you realise that the brakes on the JH are marginal at best - Joachim and I have both gone for the four wheel disk kits from HiSpec but I imagine that the front kit would make the biggest improvement.
Gordon

UKJames
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Yes Paddock are the people I got it from. The brakes are OK, but my daily driver is a newish BMW so it is probably more 'perception' than anything else. If I stamp on them hard I can just about lock them up. But they are nice and progressive.

The HiSpec kit sounds interesting- I might look into that. It seems a shame that the brakes are not as good as the engine....

gmgiltd
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Take it in context - in the early seventies you had roads infested with Ford Cortinas, Moris Itals, Austin Alegros, Vauxhall Victors all of which gained momentum - they could not be called accelerative nor were the brakes particularly good. Compare that with now with VW/Audi, BMW, Merc or Jaguar. Even Fiat 500s, small Citrons, Pugs and Skodas have four wheel discs with ABS. The Jensen was good in its time but in modern conditions it's scary sometimes.

UKJames
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Nothing like seventies brakes to sharpen the senses when you are in traffic...
But there is an appeal in improving on the original design with more modern brakes. I'll add it to the to-do list..

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I can't say I'm familiar with the "chuff' sound you're experiencing, but I did want to comment on the choice of master cylinder. I was looking to replace mine and didn't want to use the TR6 unit-with the 3/4" bore-as I'm attempting a restoration and it just doesn't look right. I had also heard that the Land Rover dual cylinder for the SWB (pre-June '80) is a good substitute but that suppliers had increased the bore to 7/8" (to split the difference between the SWB and LWB). To make matters worse, not a single supplier I contacted in the US could confirm the actual bore diameter of what they were selling! The most authoritative voice I found on the matter was Paul Hunt at PowerTrack Ltd. in the UK, who specialize in obsolete brake parts. They are well acquainted with the JH master cylinder and confirmed that the original bore size is actually 13/16." Paul warned against fitting LR or other masters as there are internal variables beyond just bore diameter. Not to say that what you've found won't work well, but just a word of caution. PowerTrack has the proper seal kits for the originals and I know Martin Robey also sells a professionally rebuilt original on an exchange basis. Best of Luck

Screenplay
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I forgot to add that I read in an online Land Rover forum that, depending on year and wheelbase, there are master cylinders that look exactly like the ones we are discussing that actually reverse the front/rear reservoirs. Is it possible that a greater proportion of of fluid and effort is going toward the rear brakes? As is said, online chatter so take it with a grain of salt but food for thought. Can anybody comment?

UKJames
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Interesting points as I have my doubts on the master cylinder. To put it into perspective I would say the brakes are 'borderline OK' and maybe a different MC would give it the extra say 10% that would raise the confidence level. The different bore size or setup could easily account for this.
I don't feel there is any problem with brake force distribution though, it seems absolutely fine.
Has anyone any thoughts on low manifold vacuum affecting the boost at all?
 
 
 

gmgiltd
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I had similar feelings when the original fully reconditioned / new braking system. On top of that my servo was on its way out and was replaced by JH one which is smaller than the GT one and this firmed the pedal but not the confidence. The OEM brakes worked - just not powerfully - the HiSpec ones are very progressive and powerful.

Jim Ketcham
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I do not see how the booster can be partially faulty. If it holds vacuum it should be fine. If it is faulty pedal effort is very noticeable.
Low vacuum to the booster means either an external leak or an internal one. External is easy to check. Internal, unfortunately, means worn engine. If engine is running fine that is improbable.
It does not take much difference in master cylinder piston size to make a big difference in pedal effort. If my math is correct, the difference in area between a 3/4" and 7/8" diameter piston is >35%. That would significantly affect pedal effort.
Having tried a pre-89 SWB LR master I noticed increased pedal effort. I was able to correct it somewhat with high performance pads. I eventually pulled the LR master and measured the piston. It was slightly less than 7/8" in diameter. The original JH master measured a hair over 3/4". I switched to a TR6 master and pedal effort was marked improved to the point that I no longer have any concerns about braking.
My bet is if there is no vac leak it's the master cylinder.
Good luck,
Jim

UKJames
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I will pull the master cylinder and verify the size when I get a moment.
The car had a Girling type MC on it unusually with Metric threads. It might have been an old Ford Cortina one.
I had to change the unions to 3/8-20UNF and 7/16-24UNF to fit the Landrover MC.
Can anyone confirm what threads the TR6 master cylinder has? Would be nice if I didn't have to change the pipes...again.

Thanks for all the replies so far

Jim Ketcham
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The fitting sizes and positions are the same. That is 3/8-24 and 7/16-20 as you stated. The TR6 master should drop right in.
Jim

UKJames
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Jim Ketcham wrote: The fitting sizes and positions are the same. That is 3/8-24 and 7/16-20 as you stated. The TR6 master should drop right in.




Jim


Thanks Jim I'll order up a TR6 master and hopefully that will improve the feel a bit.

-Jim

UKJames
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I've got a GMC234 (TR6) Master Cylinder on order. Using the math it looks like:

 

Original stock master cylinder (two possible sizes):

3/4 (19.05)... area 285mm2

13/16 (20.6)... area 333.3mm2   16% greater effort (nominal)

 

TR6 Master cylinder GMC234 (need to clarify if 3/4 or 7/16)

13/16 (20.6)... area 333.3mm2   16% greater effort (nominal)

 

Landrover SWB Pre '80 569671

7/8 (22.2)... area 387.1mm2   35% greater effort (heck of a lot)

 

So I am hoping this will crack it... I will let you all know....

 

Jim

 

Screenplay
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You've certainly done your homework. Please do keep us posted; I'm very interested to hear how this works out. Best of luck with the project.
Clinton

UKJames
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The new 'TR6' master cylinder arrived this afternoon so I have installed it. I can confirm the Land Rover master cylinder I just removed had a circa 22mm bore, the new one is smaller at between 19-20mm.
Will give them a proper test tomorrow but my initial thoughts at low speeds is that it has made a significant difference, possibly even a third less force required for the same level of braking. Much nicer.

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James,
Great to hear; it will be good to read about your thoughts after a little more time with it. Thanks for posting this-I believe it is the first direct comparison I've seen.
Clinton

UKJames
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OK the brakes are now pretty much modern car feel, ok not 4 pot calipers like my BMW but then the JH is a lot lighter so they feel pretty good.
The one issue remaining is the servo/booster. I have attached vacuum gauges to the four Dellorto take-offs in order to balance them, but when I apply the brake, No. 4 vacuum signal drops to zero. This is also the manifold port that the vacuum to the servo/booster is taken from. So although the booster holds a vacuum, there seems to be a leak ONLY when the brake is applied. I am wondering if the rubber around the push rod has failed in some way and I am leaking vacuum at the join with the MC. It can't be the diaphragm internally as the leak would be permanent.
The pushing action of the rod appears to be opening up the leak?

Jim Ketcham
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Interesting. I have never checked vacuum under those conditions.
Does the vacuum eventually recover while your foot is on the brake or does it remain zero until you release the break? Just trying to determine if it's a temporary surge or vac drop with diaphragm volume change or an actual leak being exposed when the pedal is depressed.
If temporary it might be normal. I guess I can try the same test on my car when I return home next week.

UKJames
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The vacuum doesn't recover, drops off sharply for the duration of the full down brake pedal (that's the noise I was hearing). Recovers immediately the brake is released.
I suspect the output seal is partially worn, and only lets go when the push rod is extended. I guess these seals must get a fair bit of wear in normal use, they're not lubricated. Visibly the seal looks in very good condition... I'm not sure if you can replace it easily.

Jim Ketcham
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I noticed a listing on the UK ebay for JH brake servo seals repair kit. In includes an internal schematic of the booster that I can't view well on my mobile device. Might this be of help?

UKJames
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I think that's the seal I need included with this kit. With the MC off I should be able to access well enough to remove the old seal. I'll clean up the push rod while I'm at it and lubricate with some brake lubricant for good measure.

I am quite surprised at how quickly the vacuum is lost though on pedal pressure, I would have expected a faulty seal to 'seep' air not 'dump' it. Maybe the whole seal is lifting of the flange it sits on. I'll have a closer look tonight.

 

UKJames
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Probably wishful thinking on my part but after driving it around a bit it seems the new MC has helped with the feel, but the boost is only there on hard braking.
The vacuum leaks out so quickly, progressive braking (normal driving) is still not good. I thought the servo was only leaking through the front seal but I think it is generally shot, looking inside there is no obvious large ingression of fluid, but it does look 'damp'. My thoughts are that at some point the bad output shaft seal has created a vacuum between the servo and an old MC, and sucked brake fluid into it.
I've now removed the servo and pedal box and will use the opportunity to clean up and paint the box & bulkhead area before I get a new (old but good) servo this Saturday.....

UKJames
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A quick update. Took the servo off and on the bench looked through the valve hole with a torch to see the condition- on one side, the diaphragm was shot. Got a new (old) servo from Rejen on Saturday, replaced the foam filter (perished), cleaned and lubricated the rods, gave the thing a spray over. Installed in this morning and bled the brakes. What a difference. Together with the TR6 master cylinder this thing now has some good stopping power.
Bonus is that now I don't have a vacuum leak every time I touch the brake pedal I was able to balance the carbs and colourtune the mixtures properly as well. Now the engine doesn't rock, and as the 4th cylinder isn't constantly getting leaned out I no longer have any spit back through the Dellorto either.
All in all some good progress...



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