MC1234 Posted June 18, 2023 Report Share Posted June 18, 2023 Hello, I have a 1973 CR TR6 which I've owned for a few months. It's in good condition and has been well maintained. Yesterday I took it on the motorway for the first time and after cruising at 60-65 mph for around 15 miles I started to notice I was losing power and could smell burning. Within a few minutes I had to pull on to the hard shoulder. When I came to a stop the engine revved fine so there was no loss of engine power. When I got out both front wheels were smoking heavily and did so for 10 mins or more. After a few mins liquid grease started running from the hub of one of the front wheels. I'm guessing that the brake callipers (and/or the brake disc) had swelled in the heat and the brakes were effectively locked on? And the heat of it all liquified the grease in the bearings? Does this sound the likeliest explanation? This morning I took one of the front wheels off and all looked OK apart from a burning smell (see photo). I did notice that when I turn the brake disc the calipers are touching against it. Is that normal or should there be more clearance? Any thoughts, solutions appreciated. Matt Quote Link to post Share on other sites
PodOne Posted June 18, 2023 Report Share Posted June 18, 2023 Hi Matt The calliper bodies should not be touching the discs any where only the pads should contact the discs in use and have a gap between pad and disc when not in use. Something is binding are the pads sticking or worn out? Some pics as to where they are touching might help others give some more help. Andy Quote Link to post Share on other sites
Peter Cobbold Posted June 18, 2023 Report Share Posted June 18, 2023 Since both wheels were affected the cause is most likely to be found in the servo or brake master cylinder. The brakes are in effect being applied while you drive and the heat has melted the wheel bearing grease. You will need to repack the bearings. This thread might help find the problem; Peter Quote Link to post Share on other sites
MC1234 Posted June 18, 2023 Author Report Share Posted June 18, 2023 Thanks Peter and Andy. When I said the calipers were touching the disc I meant to say the pads. There is light contact on the disc but I suspect that is fairly normal? Yes, it does seem as though something expanded with the heat of cruising at 60mph+ and caused both brakes to lock on. Lots to think about, thanks for your comments. Matt Quote Link to post Share on other sites
Mike C Posted June 18, 2023 Report Share Posted June 18, 2023 It's normal to have light contact between the pads and disc. As both of your brakes locked up together I suspect you have a hydraulic problem. If you used disc brake grade grease in your front wheel bearings and it melted your front brakes have been subjected to really extreme temperatures-I'd check all the disc brake rubber components when I replaced the grease. Quote Link to post Share on other sites
Waldi Posted June 19, 2023 Report Share Posted June 19, 2023 Matt, Most likely the MC is the cause as Peter says. While driving, the brakes warm up and the brake fluid expands. That’s normal. The increased volume can flow back to the reservoir. If it cannot flow back to the reservoir the hydraulic pressure increases and you are “braking”. A swollen rubber hose can give the same effect, but only on one side. The MC may be defective or partly closed due to lack of clearance between servo and MC. Since the system got so hot, I recommend to inspect all components, and likely recondition the calipers. Waldi Quote Link to post Share on other sites
stuart Posted June 19, 2023 Report Share Posted June 19, 2023 What brake fluid are you using? Stuart. Quote Link to post Share on other sites
MC1234 Posted June 19, 2023 Author Report Share Posted June 19, 2023 (edited) thanks for the further comments. I think my first job is to replace the front wheel bearings. I then need to read up on the brake system and perhaps try adjusting the pushrod. Stuart, unfortunately I don't what brake fluid I'm using as it was in the car when I bought it earlier this year. Matt Edited June 19, 2023 by MC1234 Quote Link to post Share on other sites
Mike C Posted June 19, 2023 Report Share Posted June 19, 2023 2 hours ago, MC1234 said: thanks for the further comments. I think my first job is to replace the front wheel bearings. I then need to read up on the brake system and perhaps try adjusting the pushrod. Stuart, unfortunately I don't what brake fluid I'm using as it was in the car when I bought it earlier this year. Matt "Yesterday I took it on the motorway for the first time"- you don't know if anything was done to the brake system just before you bought it? You could have a new but dodgy master cylinder or booster. Quote Link to post Share on other sites
FatJon Posted June 20, 2023 Report Share Posted June 20, 2023 Started losing power after some time, front brakes really hot. Both are classic symptoms of too little clearance between the brake servo rod and the master cylinder. If it also had a super hard brake pedal when it got hot then that about seals the deal. Been there! It will have had either the cylinder or the servo replaced by someone who didn't know that adjustment is necessary. It all works fine for the first few miles, usually at lower speeds then the brakes slowly lock on over a few miles until you grind to a halt thinking the engine has lost power, which it hasn't. Quote Link to post Share on other sites
Dave McDonald Posted June 21, 2023 Report Share Posted June 21, 2023 23 hours ago, FatJon said: …symptoms of too little clearance between the brake servo rod and the master cylinder. It will have had either the cylinder or the servo replaced by someone who didn't know that adjustment is necessary. What adjustment is available/possible between servo and master cylinder? Just fitted new m/c to my TR5 restoration and I wasn’t aware of any need to adjust or more importantly how to adjust. Please advise. Dave McD Quote Link to post Share on other sites
ntc Posted June 21, 2023 Report Share Posted June 21, 2023 1 hour ago, Dave McDonald said: What adjustment is available/possible between servo and master cylinder? Just fitted new m/c to my TR5 restoration and I wasn’t aware of any need to adjust or more importantly how to adjust. Please advise. Dave McD Clearance from the pushrod to the master Dave Quote Link to post Share on other sites
Dave McDonald Posted June 21, 2023 Report Share Posted June 21, 2023 But how do you 1. Measure it and then 2.adjust clearance. Surely the servo rod just engages in the dished back end of the m/c piston? No mention of adjustment in Brown Book repair manual. I’ve never adjusted anything in past when fitting a new m/c and never had brake binding problem. Perhaps I’ve just been lucky. Puzzled of Retford Quote Link to post Share on other sites
ntc Posted June 21, 2023 Report Share Posted June 21, 2023 5 minutes ago, Dave McDonald said: But how do you 1. Measure it and then 2.adjust clearance. Surely the servo rod just engages in the dished back end of the m/c piston? No mention of adjustment in Brown Book repair manual. I’ve never adjusted anything in past when fitting a new m/c and never had brake binding problem. Perhaps I’ve just been lucky. Puzzled of Retford The end of the rod is adjustable ie threaded use a straight edge across the face and adjust to the correct clearance Quote Link to post Share on other sites
Dave McDonald Posted June 21, 2023 Report Share Posted June 21, 2023 2 minutes ago, ntc said: The end of the rod is adjustable ie threaded use a straight edge across the face and adjust to the correct clearance Ok, I’ll have to look into it. Fortunately I’ve not filled with brake fluid yet so not a big problem to remove m/c. Dave McD aka Puzzled of Retford. Quote Link to post Share on other sites
FatJon Posted June 21, 2023 Report Share Posted June 21, 2023 no need to drain fluid to adjust. Undo the two nuts holding MC to servo and shuffle it off the studs then you can see the rod the adjust length if necessary. The quick test if you have the symptoms described is just remove the MC from the servo, then slip a washer over each stud and refit the MC. If the problem is gone you find it. Remove the washers, tweek the rod, refit and your all finished. Quote Link to post Share on other sites
Mk2 Chopper Posted June 21, 2023 Report Share Posted June 21, 2023 I had this, luckily at slow speed straight away after replacing the MC. The standard adjustment in the book didn't work for this combination. I did exactly the same and loosened the MC to servo bolts and the brakes came off. Then I dabbed some paint on the pushrod after adjusting it and when it made a feint impression on the MC I knew I had the 'air gap' I needed. Gareth. Quote Link to post Share on other sites
Tom B Posted June 22, 2023 Report Share Posted June 22, 2023 The setting of the pushrod is done by putting a straight edge across the top of the servo and measuring the distance between the edge and the push rod (with feeler gauges). On mine, the push rod was adjusted on a thread with a locking nut. I put a small amount of loctite on the locking nut for good measure. Just be aware that it is good to measure the master cylinder as well to make sure that there is at least the gap stated when assembled. The previous poster in this thread may have suffered from this. If the clearance between the push rod and the master cylinder is too large then the "bite" point on the brake will be low. If it is too small then there is the risk of the brakes binding as you may have noticed. It is not a difficult job but a bit of care with the measurements is important. Good luck. Quote Link to post Share on other sites
ntc Posted June 22, 2023 Report Share Posted June 22, 2023 On 6/21/2023 at 12:29 PM, Dave McDonald said: Ok, I’ll have to look into it. Fortunately I’ve not filled with brake fluid yet so not a big problem to remove m/c. Dave McD aka Puzzled of Retford. Hopefully you are not confused now Dave Quote Link to post Share on other sites
Dave McDonald Posted June 22, 2023 Report Share Posted June 22, 2023 All reasonably clear now. I’ll check it soon Dave McD Quote Link to post Share on other sites
petertrs Posted June 23, 2023 Report Share Posted June 23, 2023 I have also suffered from this problem, twice over the last three years or so! It started after I replaced the master cylinder and then servo when addressing a variable braking issue that developed about 8yrs after a total rebuild of the car. The first longish journey after replacing the servo resulted in me grinding to a halt on a motorway. Letting things cool down and then slighly loosening the m/c from the servo got me home. In short I hadn't checked the adjustment of the servo pin and it was protruding too much. The Haynes Manual gives a measurement as does 'Buck Eyed Triumph'. Getting a good pedal bite whilst not preloading the hydraulics is a delicate balance.Talking to some UK TR companies their approach varied but one sensible approach is to take off the m/c reservoir and measure when the tipping valve actuates. I set mine up on the bench with depth guage and monitoring the tippng valve. All was well for about a year and then the same happened. The position of the piston in different master cylinders does vary in dimension. Having rechecked everything and also monitoring the servo for 'creep' for about an hour with the engine running I couldn't find the issue. After a few enquiries the best I came up with is that there was a period when TRW master cylinders were supplied with dodgy valves. ( I also discovered that TRW and Lucas Cylinders all come off the same production line.) I rebuilt the M/C with all new inards and 18 months down the road all appears well (so far). Interestingly an article inTR Action a couple of issues ago detailed a similar issue with a TR6 during a holiday to France - attributed to the fauly batch of master cylinders. Quote Link to post Share on other sites
reginald Posted June 23, 2023 Report Share Posted June 23, 2023 There can be an issue with the master cylinder piston sitting further in than with original master cylinder, so the clearance can still be to big when measuring across with a straight edge. I had to adjust the rod further out to compensate, I used the original master cylinder to check this. Richard Quote Link to post Share on other sites
Mk2 Chopper Posted June 23, 2023 Report Share Posted June 23, 2023 14 minutes ago, reginald said: There can be an issue with the master cylinder piston sitting further in than with original master cylinder, so the clearance can still be to big when measuring across with a straight edge. I had to adjust the rod further out to compensate, I used the original master cylinder to check this. Richard I concur. Gareth Quote Link to post Share on other sites
MC1234 Posted June 25, 2023 Author Report Share Posted June 25, 2023 (edited) Many thanks for the further comments and suggestions. I finally had some spare time to work on my TR6 today. I thought I'd start by changing the wheel bearings and once they're done will start to investigate the brakes. All went fine with the wheel bearings but I had real trouble re-attaching the brake calipers as the gap between the brake pads was almost too narrow to fit over the brake disk. It took a lot of fiddling and eventually I managed to get them over the disks and re-attached. The disk just about spins but certainly doesn't spin freely. Is that normal or is this the cause of my brake overheating problems? I have no experience of working on brakes unfortunately so I just don't know how 'tight' the caliper/pads should be when you fit them over the disk. But to my untrained eye there seems very little clearance between pad and disk so any expansion in heat will presumably lead to the brakes binding? Matt Edited June 25, 2023 by MC1234 Quote Link to post Share on other sites
BlueTR3A-5EKT Posted June 25, 2023 Report Share Posted June 25, 2023 You need one of these Girling tools. . Insert between the pads or pistons, turn it to push the pistons back onto the callipers The calliper will just slip on then as the pads and pistons are retracted. Quote Link to post Share on other sites
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