MG TD Brake System Rebuild Notes July 11, 2006

Transcription

1 MG TD Brake System Rebuild Ntes July 11, 2006 Larry Sher General References MG Factry Wrkshp Manual Nte in particular page M12 Sectin "Replacement f the Wheel Cylinder". Hrst Schach, MG TD Restratin Bk Parts blwups frm MG TD Parts List MG TD-TF Internet Bulletin Bard Miscellaneus Ntes Threads n bleeder and pipe fitting are 3/8 x 20 BSF. Grease fitting can be fabricated frm a 10 mm grease fitting, rethreaded fr 3/8 x 20 BSF. Disassembly During disassembly it was discvered that the frnt left brake drum had a chip in the uter lip. This was likely frm a wheel puller with arms having been used n the drum at sme time in the past. In tracking dwn a replacement brake drum it was fund that the size f the frnt drums was larger than the rear drums by apprximately 1 inch. The frnt drums are apparently frm an MGA The ther cmpnents that appear t be MGA running gear include the rund backing plate and the shes. Frnt drums had the fllwing numbers cast in them: MOWOG BC ATB 4165 These shuld be apprximately 11 ¾ diameter drums. A replacement MGA drum was purchased frm British Wire Wheels t replace the chipped ne. An article in the TSO (Feb 1976, page 22) suggests ther differences, t. In an MGA, the banj fittings and brake pipes are Unified thread. Further, the brake pipe cnnecting the tw banj fittings is lnger t span the greater distance assciated with the larger drums. The brake hses have Unified fittings instead f Whitwrth and the hse length may be different. (The TSO article als described mdificatins t the tie rd ends that will need t be made s that te-in may be set prperly fr the TD. This will all need t be srted ut t figure ut what parts are required t rebuild the brakes.) The brake pipe set I purchased was designed fr TD/TF. This must mean the frnt brake cylinders are TD/TF cylinders, as the thread size was crrect. These pipes fit fine. There was an bvius hmemade plate t adapt what I believe t be TD/TF frnt brake cylinders t the MGA backing plate. I cnclude that the nly MGA parts are the frnt drums, shes, and backing plate. Rear drums are MG TD/TF These are apprximately 10 ¾ diameter I believe these shuld carry the number: ATB 4126 They are actually stamped with the smewhat hard t read numbers: A2394 and 12

2 Wheel Disassembly/Reassembly Remve knck-ff (ne nly) Lsen castellated nut Castellated nuts (nly) n axle stub must be remved, in rder t remve the brake drum. Remve the ctter pin, which may be extracted thrugh the hle in splined sleeve f the brake drum. Stainless steel ctter pins were used during reassembly. A breaker bar was used with the scket driver t lsen the nut. (This was an apprximately three ft black irn pipe frm a pipe clamp.) The castellated nuts will be remved cmpletely after the wire wheels are remved. Castellated nuts are threaded as fllws: Left frnt: Left-hand thread, 1 1/4 SAE Right frnt: Right-hand thread, 1 1/4 SAE Left rear: Right-hand thread, 1 1/8 SAE Right rear: Right-hand thread, 1 1/8 SAE Put n knck-ff. Repeat abve fr all fur wheels. Put car n jack stands Remve fur knck-ffs Remve fur rad wheels. Remve fur castellated nuts The large washer behind castellated nut has beveled edge ut. Brake Drums Back ff fully the brake adjusters befre remving wheel. These are accessed thrugh a hle in the drum. There is ne adjuster n each rear wheel and tw adjusters n each frnt wheel. During reassembly the rear brake adjusters may be replaced with adjusters that have a shim welded n the bttm t take up sme f the gap. Nte: The castellated axle nut must be remved befre ding this step. On sme wheels the brake drum easily slid ff the axle stub. If the brake drum is nt easily remved a wheel puller will be required. It is best nt t use the kind f wheel puller that has three r fur arms which g arund the utside f the brake drum. The drum is made f cast irn and the wheel puller arm can break ff a piece f the drum. An alternative wheel puller was made by drilling a hle in the center f an ld knck-ff. A large nut was welded n the inside f the knck-ff. A matching 5 blt with hex head will be used with this wheel puller. (Nte that tw mdified knck-ffs are required, ne fr the wheels n the left side f the car and ne fr the wheels n the right side, as the threads are ppsite). Spin the knck-ff puller fully n. Tighten the blt thrugh the knck-ff until it cntacts the axle. Tighten the blt with a scket wrench and the drum will slide ff the axle. Lcking tabs n the brake drum nuts d nt need t be remved. After remving drum and cleaning the end f the axle, a line was scribed n the axle end t shw the alignment f the ctter pin. This will make it easier t determine hw far t tighten the castellated nut n reassembly. Remve shes by prying apart ne she frm the ther, then mving ne she utbard s it can be passed by the inbard she. Fr frnt wheels it is t difficult t separate the shes by hand. Use tw pieces f 2x3 apprximately 2 ½ lng and ne piece f 2x3 apprximately 6 lng. These frm a scissrs that can be used t pry apart the brake shes r align them fr reassembly Brake Cylinders Remve the brake cylinders It may be difficult t remve the pistn frm the brake cylinder. This can be dne easily by screwing a 3/8 x 20 Whitwrth grease fitting int the brake cylinder,

3 then pumping grease int the cylinder. Hydraulic pressure will squeeze the pistn ut f the brake cylinder. Cleaning Metal parts were placed in an ultrasnic cleaner filled with Simple Green. Any remaining paint r hardened grease was remved with a tthbrush and Simple Green. Finally, parts were saked fr several hurs in Metal Ready t prepare them fr eventual painting r reinstallatin withut further treatment. Metal Ready shuld prvide sme level f rust preventin fr these parts. Brass (banj fittings, etc.) and parts that had machined surfaces that fit tgether t make a leak-free seal were nt placed in Metal Ready. Cylinders Rear brake cylinders (tw) replaced with reprductin brake cylinders (Mss). Frnt brake cylinders (fur) resleeved in stainless steel by Mark Frappier. Master cylinder resleeved in stainless steel by Mark Frappier. Split steel washers used t attach cylinders t the car were replaced with split stainless steel washers. Mark Frappier 82 Muntainview Street Agawam, MA Resleeve wheel cylinder in stainless steel: $45 per cylinder Resleeve master cylinder in stainless steel: $65 Return shipping and insurance: $10.36 C.H.Tpping & C. 520 Esther Street Lng Beach, CA (562) Reline fur brake shes (tw pair): $30 fr fur shes Return shipping: $12.80

4 Reassembly Use Silicne Dt 5 brake fluid Silicne grease (same as silicne dielectric grease) was used during different pints in the reassembly. When rebuild kits were installed in cylinders, a very thin smear f silicne grease was used t lubricate all internal rubber parts. Master Cylinder Disassembly Brake master cylinder culd nt be pened. After circlip was remved thick steel washer culd nt be withdrawn. This end f the master cylinder was placed in Simple Green in an ultrasnic cleaner t n effect. A micrtrch was used t heat the washer and a very thin stainless steel lab spatula was slid under the washer and the washer carefully pried up. Disassembly fllwed. Rebuild Use silicne grease (thin smear) t aid assembly Silicne grease helps t pull the dnut cup ver the internal pistn. Make sure this cup is fully seated. When inserting tiny rubber cup, press rubber cup sides, which bulge thrugh the metal cup hles, back int the interir using a blunt tl. T insert last cup int the master cylinder use a tiny curved spatula t wrk arund the sides and gently press cup int the master cylinder at the same time. Gasila was used n sme pipe fittings, Installatin Rubber bt small pening ges ver wide shulder n mst rearward nut. Silicne assembly grease aids what is a very difficult jb. Push pening ver blind side by pressing n bt frm the rear f the car. Then hld bt in the crrect psitin by hlding with fingers frm the frnt. Next, wrk ne s way arund the bt frm the rear, pushing it ver the nut and nt the shulder. Brake Cylinder (Rear) Mss repr rear brake cylinder needed t be filed at ne end s that cylinder wuld fit thrugh cutut in cylinder backing plate. Rund edges after filing s rubber bt desn t tear n cylinder. T insert, cylinder pistn needs t be remved during cylinder fitting thrugh backing plate, then reinserted after cylinder is in place. Rubber bt is a very snug fit ver cylinder. T install the bt ver the pipe fitting at the tp, turn the bt inside ut at this tp prtin, then push the pening in the bt ver the pipe fitting, finally allwing the bt t spring int its crrect psitin. Plastic caps were left in place ver the pipe penings in the cylinders, s dirt r dust wuld nt get int the cylinders. Flex Lines Screw frnt flex lines t brake cylinders first, then t bracket n chassis. Screw rear flex line t three-way fitting first, then t bracket n chassis. Make sure flex lines are nt twisted during installatin. There are reference lines n the flex lines that can be sighted t make sure twisting has nt ccurred. Other Parts Replace all rubber parts, including using rebuild kits fr wheel and master cylinders and new rubber bts. Replace all cpper washers. I sanded the washers using very fine grit sandpaper n a glass plate t insure flatness. Even new cpper washers shuld be annealed. Heat all cpper washers t red ht, then allw t cl t rm temperature befre installing.

5 Sme peple use Gasila t prevent leaks at banj and pipe fittings. I used Gasila n pipe fittings, specifically in the master cylinder, but did nt use Gasila n banj fittings. During reassembly castellated nuts were trqued t the minimum values, then turned further t align the scribed line n the axle stub with slt in the castellated nut. Trque Specificatins Frnt castellated nuts: ft punds. Rear castellated nuts: ft punds. Trque (Actual) Actual trque values were as fllws: Left frnt: 70 ft punds Right frnt: 40 ft punds Left rear: 80 ft punds Right rear: 105 ft punds If it is nt pssible t btain the described trque values, washers may be swapped frm ne side f the car t the ther t see if this allws the nuts t be tightened t the desired trque values. If the crrect trque value range still cannt be btained, the washer may be filed dwn t remve sme thickness. This can be dne by mving the washer back and frth by hand ver a steel file. The left frnt washer was filed dwn frm t and the right frnt washer was filed dwn frm t Bleeding Try very hard nt t create bubbles when transferring silicn fluid (pur and transfer slwly). Fill each cylinder with fluid befre installing. I did nt have much success ding this. Master cylinder shuld never g empty during bleeding Order fr bleeding: RR then LR then RF then LF (farthest frm master cylinder t nearest) Operate brake pedal slwly t avid bubbles in brake fluid. D this many times t bleed. Have ne persn perate the brake pedal while the ther persn perates the bleeder valve at the wheel. Sequence f steps: Open bleeder Press brake pedal slwly. Clse bleeder Release brake pedal slwly Repeat Rebleed the next day t remve any remaining air. Brake switch arc suppressin device Parts 1. Tw 0.22 micrfarad capacitrs (Radi Shack) (r ne 0.47 micrfarad capacitr) 2. Plarid camera picture cat brush tube (plastic), cut dwn 3. Slice frm rubber stpper, with tw small hles fr wires, t be inserted in tube 4. Silicne caulk Assembly/Installatin 1. Slder capacitrs, wired in parallel, then put wires thrugh rubber slice 2. Fill tube with silicne caulk, then press in capacitrs and rubber slice 3. Wire capacitrs in parallel with brake switch. Make sure wires nt stressed and that wires can t shrt against chassis. Use heat shrink tubing as necessary. (see article abut Brake Light Relay by Dave DuBis r cntact Dave fr mre suggestins).

6 Rubber fume excluder ver pedals in cckpit 1. Check that hles in rubber bt line up with hles in metal tp plate, thrugh which screws will g. If nt, punch new hles. 2. Remve hrizntal pedal extensin (if installed) 3. Put electrical tape ver sharp tp edges f vertical pedal psts 4. Smear silicne grease inside bt and n vertical pedal psts 5. Carefully stretch rubber bt ver psts 6. Secure metal plate with screws n tp f bt 7. I repsitined pedal extender n ne pedal and did nt install extender n anther pedal t give my feet mre rm t wrk the pedals Wheels and Tires Five new Vredestein steel belted radial tires (165SR15, $68.99 each), als radial inner tubes ($8.07 each), frm Tires Unlimited ( Tire pressure f 30 punds appears ptimal. Tires were munted by Huse f Wheels/Wheel Repair Service, Auburn, MA ( Wire wheels were tuned and balanced. See invice fr details abut each wheel. Each wheel marked with a punch. Punches Placement 1 Spare 2 Left frnt 3 Right frnt 4 Right rear 5 Left rear