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MKI / MKII S type 240 340 & Daimler 1955 - 1967

Rebuild brake servo, or get a new one?

 
  #1  
Old 11-18-2018, 07:39 PM
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Default Rebuild brake servo, or get a new one?

Hello all

For those wanting to get to the point / question - Is it a better idea to try rebuild an original brake booster / servo from a 1965 Mk2, or just buy the available replacement (LR18230). The servo will be going into a '61 Mk2, the rebuild kit costs about $100 less than the new unit, and the new unit does not seem like it will fit in exactly the same way. That said, the new unit is..well....brand new, and will be a lot less work, may even perform better than the OEM unit ever did. I don't care about "originality" in particular case - safety first.

For those that like the story....

In examining my recent acquisition, ('61 Mk2) I noted the brakes were weird, like something was wrong with the vacuum booster / servo. A little flashlight action under the hood explained the issue.....there is no vacuum booster / servo. The vacuum reserve tank was also removed and a little more investigation identified what looks like appropriate-sized vacuum hoses, blocked off. The brakes have been reported as "gone through and replaced front and back" and while I believe the current owner is sincere as far as what he was told, I'm less convinced the owner before him actually did the brakes to the extent suggested - the really rusty brake lines as a first clue, then a missing vacuum servo. So, I think I'll go through the brakes again, just to sure.

I went home and rummaged through my parts bin, and I found the original booster / servo from my '65 Mk2. For the '65, I went with a new replacement unit because the new "not original" servo and mounting solution is the least of the "not original" items under the hood. I have no idea if the old original servo works, because the car was not running prior to the change, but it appears sound and looks to be in good condition. For the '61, I could go either way - the new unit would certainly be less work, costs just a little more, and the entire thing is new - BUT - based on the design of the new unit, I find it hard to believe it will just drop in and fit. Rebuilding the OEM unit from the '65 probably makes install easier, but the unit is still old and will require a bit of work to rebuild. In addition, because the servo is missing from the '61, I don't actually know how it is supposed to mount up - could be I'm missing parts too.

So - rebuild or buy new?



 
  #2  
Old 11-19-2018, 12:52 AM
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Personally I would rebuild for originality and ease of fit.

The fluid side of the Servo is contained in the rebuild kit, but as far as I am aware the air side parts are not available. The air side does not usually pose any problems, but before you go any further check that the 2 air side diaphragms are in good condition. if they are then go ahead with the rebuild.

The mounting is fairly simple, there is a bracket at the rear (bulkhead side) that consists of an aluminium saddle and steel strap that fits around the slave cylinder on the servo and bolts to the inner wing panel and 3 bolts on the front that attach to the cowl inside the wing.

Then it's a straight forward job, just be systematic, and make sure you don't lose any of the small parts on the piston and seals or get them in the wrong order. I have some pictures on my thread which shows some info and have plenty of other pictures that are not on there if you need them.
 
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Old 11-19-2018, 05:21 AM
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SNG Barratt does a refurbishment service on exchange. Send them your old one for which you get a credit if it can be rebuilt & they will send you a truly superb refurbished unit from their in-house workshops. Their refurbished units look brand new right down to perfect plating. Originality was important to me & that was something I could tick off the list without touching it. They will send you a refurbished one off the shelf so there is no delay. You will get your credit for the old unit in arrears.

Then as TJ says mounting is easy. Pipe lengths & fittings will all be correct etc.. Rebuilding Servos is a PIA.
 

Last edited by Glyn M Ruck; 11-20-2018 at 01:19 AM.
  #4  
Old 11-20-2018, 02:10 AM
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Originally Posted by Glyn M Ruck View Post
Rebuilding Servos is a PIA.
I got that feeling, just looking at the components.
 
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Old 11-20-2018, 08:49 AM
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Originally Posted by Treozen View Post
I got that feeling, just looking at the components.
I got sick & tired of rebuilding twin Lockheed Bonaldi Servos on Alfa's in my youth. I'd rather pay someone to do it.
 
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Old 11-20-2018, 11:11 AM
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I rebuilt one of these servos in the mid-eighties using a repair kit. There are two aspects to rebuilding these servos on a DIY basis. Firstly the big and small diameter hydraulic seals bear on the bores of the iron casting. It's important to make sure these bores are clean and clear of all corrosion. Use of hones of the right diameter may be necessary to get a good surface. The second aspect is that the rebuid process gives some measurements for fitting the push rod and this requires a depth gauge. A caliper gauge normally includes such a thing, and that is what I used. I had no trouble at all with the servo after the rebuild.

I also fitted a new Reservac tank and valve. These latter can cause a load of trouble due to rusting through of the tank destroying any vacuum capability, and also the little valve corroding away to dust.

Looking on the SNG Barratt web pages for the Mark 2 brake servo, there are two non-original but more modern replacements that are a lot cheaper than the rebuilt originals they offer. If originality is not desired, (and the servo is buried out of sight in the wing, anyway), I'd be strongly tempted to fit a more modern servo.
 

Last edited by Fraser Mitchell; 11-20-2018 at 11:24 AM.
  #7  
Old 11-20-2018, 12:08 PM
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Yes indeed. if you want to save some bucks & understand that both require varying degrees of modification to fit.

More modern is a bit of a misnomer. Nothing of consequence has really changed in servo design. More choice in boost ratios yes. The same increase in boost can be achieved by fitting the later S Type servo. Early S types used the same servo as the MK2. Mounting remains the same.

If I was not going to go the SNG Barratt route I would still send the unit in for refurb but have the cylinder bore stainless steel lined to standard spec so standard rebuild seals etc can be used as I have done with both my master cylinders, clutch slave, and all calipers (both caliper bores & pistons in SS). Then things are highly durable & worry free especially on single circuit brakes & all looks original.

Stainless sleeving & pistons is pretty much standard procedure with classic rebuilds in SA. Great with the hygroscopic nature of brake fluid & cars that don't see daily use.
 

Last edited by Glyn M Ruck; 11-20-2018 at 07:51 PM.
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Old 11-20-2018, 01:22 PM
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From memory servo designs have changed over the years, IIRC my original ‘S’ servo was a sliding piston design whereas the later VH44 is a rolling diaphragm.
I’ll try to find some illustrations shortly.
 
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Old 11-20-2018, 02:11 PM
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Originally Posted by Fraser Mitchell View Post

Looking on the SNG Barratt web pages for the Mark 2 brake servo, there are two non-original but more modern replacements that are a lot cheaper than the rebuilt originals they offer. If originality is not desired, (and the servo is buried out of sight in the wing, anyway), I'd be strongly tempted to fit a more modern servo.
For this car, I'm trying to stay true to the original in general terms, but I won't be upset one bit using a new servo nobody will ever really see - seems like the best solution really, I'm not building a car to win points for originality, and I'd sooner trust a new servo to my amateur rebuild attempt.
 
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Old 11-20-2018, 06:16 PM
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Originally Posted by Treozen View Post
For this car, I'm trying to stay true to the original in general terms, but I won't be upset one bit using a new servo nobody will ever really see - seems like the best solution really, I'm not building a car to win points for originality, and I'd sooner trust a new servo to my amateur rebuild attempt.
So would I ~ it's not something I do every day! I could hardly claim proficiency. My job on my resto was sourcing the right parts & researching originality & being fussy about standards & what I wanted. I did very little of the grunt work myself. I don't enjoy it like I used to with heads under hoods/bonnets every weekend. I now enjoy driving the result. Cleaning & polishing inside & out & underbonnet. Making toolkits pretty & messing with detail issues like flocking etc.

Early & late S Type boosters for interest.





 

Last edited by Glyn M Ruck; 11-20-2018 at 07:11 PM.
  #11  
Old 11-20-2018, 07:58 PM
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Originally Posted by Glyn M Ruck View Post

Early & late S Type boosters for interest.

Yikes.... as a general rule, if a life-safety device schematic has more than 16 parts, I outsource or buy new, lol.




 
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Old 11-21-2018, 01:48 PM
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Treozen, you may want to contact White Post Restorations with regard to gtting your original servo rebuilt. I have used them in the past for sleeving/rebuilding brake components; their work is excellent and comes with a lifetime warranty.

Their website for brake rebuilding is:

https://whitepost.com/brake-sleeving...ding-services/

This firm is located in Virginia; I note that you are in Washington State, so there would be no issues with shipping, customs, etc., when using White Post.
 
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  #13  
Old 11-21-2018, 07:01 PM
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I'll check them out - thanks.
 
 
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