Dead brake boosters on my '74, rebuild?

[BDA]

Thanks for the DIY and the link! That could come in very handy!

[analogmike]

Thanks for posting the 411.
So how do you like stopping with the boosters as compared to without?

Good question!

I have only driven it once so far, I am heading home from work in it soon, midnight Sunday is long enough!

I have CRAPPY KUM-HO tires on it, they can't take much braking before they lock up. The fronts are locking up first, which is correct and I think I can hear the rears kicking in too if I keep pressing after the fronts lock.

In normal driving, they start out without a lot of force, then when you press a little more the boosters kick in and you get a NICE amount of boost - not as bad as my Audi S3 which is overboosted. I squealed the tires a few times just feeling them out without trying to brake hard. I think with some practice I will really like them, glad I got them working instead of bypassing them as most do.


update: driving home I tried some hard braking at higher speeds like 40mph, and the fronts are locking up too soon, they are too sensitive. I will have to check the rear booster. I previously adjusted the rear drums as tight as they could go before dragging and bled them well so they should be good. These boosters are not the stock ones, the ratios may not be quite right.

[analogmike]

I did some brake testing in my parking lot, and sure enough the rear brakes are not working much. I even plugged the front booster's vacuum line, and the fronts are still locking up a bit before the rears. The rear booster is getting good vacuum but not boosting. Will need to do more testing, it may have a bad main diaphragm. I know the rear brakes work, as they were the ONLY working brakes when I got the car (front caliper pistons were seized).

And the speedo stopped working this week too. I hope I can fix things faster than they break.

[BDA]

The fronts should lock up a bit before the rears. If the rears lock first, the car will try to swap ends. There may also be an issue with the brake adjustment in the rear. That's not to say your rear booster is working properly. Rebuild kits are available for the boosters, but if it is the booster, check it to make sure it's in good enough shape to rebuild. The aluminum body can get pitted from corrosion. White Post Restorations (http://whitepost.com/) says they can rebuild anything. If it needs it and you're not up to rebuilding it, they would be a good option.

As for the speedo problem, check that the cable isn't broken. That's a pretty common occurrence. It could also be that the speedo gears in the tranny are stripped, but I think that's much less likely since the shards from that would probably interfere with the operation of the tranny (I was left with 3rd and 4th gear when that happened to me).

Take heart! I'm sure you'll catch up with your car! These cars are simple enough that there aren't that many things to break!

[EuropaTC]

I hope I can fix things faster than they break.

    now that's a tough call, this is a Lotus y'know ?  Lots Of Trouble, Usually Serious....

But back on topic, like BDA said the speedo cable is quite long and is known to fail because if it's not lubricated well or the outer has sharp bends, then it must have quite a bit of stress on it. I think the Europa is the only car I've ever had to replace cables, and looking back I've done it twice !

On the brakes, the front/rear brake balance is a topic that's been discussed quite a bit, and without meaning to upset you  it could be that your car is fine but the driver needs adjustment....   (big smile here). 

Europas are light at the front and braking sharply it's all too easy to lock the fronts.  It's been discussed a lot on the Yahoo group and in the group files section there are brake calculators which show the rear brakes only contribute something like 25% in the overall scheme.  Hence the reason there are rear disc conversions around to increase this to 30-35%.

But some guys (Jay Mitchell ? apologies if it's the wrong guy) pointed out that driver technique can make the stock brakes work fine.  The trick I find is to apply the brakes lightly for the first touch until you can feel the weight transfer coming in to load the front wheels, then go heavier.  Easy to do driving normally, not so much in a panic stop.

If it's any consolation I have wider, modern tyres all round, no servo and  rear discs but I can still lock up the fronts if I stab on the pedal. 

Brian

[4129R]

If it's any consolation I have wider, modern tyres all round,

Do you have any problems with the wider tyres hitting the back of the wheel arches on the front when turning?

Alex in Norfolk.

[EuropaTC]

Do you have any problems with the wider tyres hitting the back of the wheel arches on the front when turning?
Alex in Norfolk.

Hi Alex,

Nope, or rather not that I've seen and I do use full lock to get in and out of the garage. Likewise I've not seen any marks in the arches after driving but then again the suspension doesn't move a lot these days ! 

I know that on the S2 with the same size wheels/tyres there is a slight rub on full lock because Richard told me about his,  but  I think the TC has a different footwell arrangement ?  I suppose it depends on the wheel offset/inset and could be calculated but I'm afraid I just bolted them on and then looked for rubbing marks....

Brian

[4129R]

With 6" x 13" Minilites I had to use thin spacers to stop the inside of the wheel hitting the suspension wishbones, aluminium hitting steel and making horrible grinding noises. Now I have black rubber on fibreglass instead.

I will see if thinner spacers stop both things happening.

Alex in Norfolk

[analogmike]

Thanks for the replies!

You don't know me, but I'm a 2 time SCCA National champion (1st was 30 years ago!) and built and set up my winning 911S myself (even lighter in the front), and also won an IMSA race in 2011 in GTC class in a 911 GT3 cup with TRG, so I have a very good feel for car setup. The rear brakes are definitely not getting any boost. I just need to do more testing to figure out what's wrong. Both of my boosters are fairly new, so should be able to get the rear working again.

When I get them working I will get some decent tires, I think the Toyo 185/60 and 205/60 should fit the stock 5.5 rims and are about the only good choice available. A British race engineer I work with told me about Avon CR6ZZ competition tires which come in the stock sizes but a lot more $, I wonder if anyone has tried these? They would look more original and be more fun to slide

http://www.avonmotorsport.com/historic/historic/cr6zz

Thanks again, getting it sorted little by little while enjoying it!!!

[BDA]

I'm running 195/50-15s on the front and 205/50-15s on the rear and I don't get any scraping. Unfortunately, I don't remember what wheel width I have or what their offset is (I suspect they're 6 1/2" or 7" wide and I tried to preserve the same proportional offset as the original alloys). I did get a little scraping early on but that could have been before I changed the offset of the front wheels. I think Brian is right that offset matters. However, I did get some scraping in the front under some circumstances with the stock alloys and tires with one of the Europas I've owned. That was a long time ago and that's all I remember about it. It could have been that I had a rear wheel on the front - but that doesn't answer why I'm not getting any scraping now. I think there might have been a QC issue but I have no idea how tolerances would stack to allow that.

[BDA]

Hi analogmike!

That's quite a record! 

Let us know what you find out.

[jbcollier]

Swap brake feed and supply lines on the boosters.  If only one booster is bad, it should show up.  Finally, bypass the boosters and see what that does.

[4129R]

A British race engineer I work with told me about Avon CR6ZZ competition tires which come in the stock sizes but a lot more $, I wonder if anyone has tried these?

I have the Avon CRZZZ 295/15s on my other toy. I haven't lost traction in the dry, but I have swapped ends easily in the damp.

Alex in Norfolk

[EuropaTC]

You don't know me, but I'm a 2 time SCCA National champion (1st was 30 years ago!) and built and set up my winning 911S myself (even lighter in the front), and also won an IMSA race in 2011 in GTC class in a 911 GT3 cup with TRG, so I have a very good feel for car setup.

   and here's me trying to tell you how to brake......      apologies for trying to "teach granny to suck eggs"  Mike. 

For no logical reason at all other than the reference to Audi I'd just assumed you'd moved from a modern car to one of these old things and were having the usual driver-adjusting problems, which is clearly not the case.

From the posts so far it sounds as if the servo's are now sorted,  the rear drums rebuilt with new cylinders and so the only other areas I can think of for poor rear performance are the rear lines (trapped, bent/kinked),  the short flexible to the rear suspension arm and the feed from the master cylinder itself. Bleeding the system would have highlighted poor fluid supply from kinked lines, so unless either the flexibles or tandem m/cylinder compartment are failing under pressure, I'm struggling.

There might be an "expectations" issue involved especially if you're comparing with Porsche, who probably put a touch more engineering into their cars....

Brian

[analogmike]

Thanks for the feedback on the Avons, Alex. I don't usually drive my toys if there will be rain, so I'm not concerned about wet performance. Just have to decide if I want the Avons in stock size or Toyos in 60 series and wider...

Brian, I think there is certainly validity in what you said about the rears being weak, but they were certainly TOO weak and now I think I know why.

Today I popped the plastic tops off the boosters, got the car running then turned it off, with vacuum being held in both boosters. I pushed on the brake pedal with a long stick and sure enough the poppet valves popped up nicely, the rear first. So that was not the problem.... my poppet repairs worked fine.

I pulled off the brake drums and remembered that I had driven with the parking brake on quite a distance last fall, and the drums got very hot. The shoes did not look too bad, but I think they were glazed. So I sanded down the shoes and drum with some rough sandpaper and cleaned them with brakeleen. Then I drove around gently and started using the brakes. They felt better... after several brakings I stopped and felt the brakes, the rears are getting nice and hot now, both sides working! So I think the booster is working fine now and I have better friction to stop the car. I didn't drive much after that short drive, but washed the car (first time it's been wet since I bought it) and will try to bring it to Caffeine and Carburetors in New Canaan, CT tomorrow morning, that should be enough  driving to see if they are ok.

I noticed the pads are pretty new, DELPHI brand. I remember my last car with drum brakes was a 240Z about 30 years ago, and the rears were weak too, I put on some "green stuff" shoes and that helped a lot. If I think the rears still need more after breaking them in right, I may look for a more aggressive pad.

Thanks again!!!